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A stunning amount of energy is unleashed when a star goes nova.
A nova is a sudden, short-lived explosion from a compact star not much larger than Earth. The outburst comes from a collapsed star known as a white dwarf, which circles so close to a normal star that a stream of gas flows between them. This gas piles up into a layer on the white dwarf's surface until it reaches a flash point and detonates in a runaway thermonuclear explosion. Astronomers estimate that between 20 and 50 novae occur each year in our galaxy, but despite their power most go undiscovered. NASA’s Fermi Gamma-ray Space Telescope has observed several nearby novae and found that each blast produces gamma rays, the most energetic form of light. Scientists think the gamma rays result from collisions among multiple shock waves that race from the site of the explosion in a rapidly expanding shell of debris. Watch the video to see an animation of a nova eruption. | 0.802477 | 3.30474 |
On Friday, the New Horizons mission released the highest resolution images yet of the Kuiper Belt object Ultima Thule, which the probe flew by on January 1st: Spot On! New Horizons Spacecraft Returns Its Sharpest Views of Ultima Thule
The mission team called it a “stretch goal” – just before closest approach, precisely point the cameras on NASA’s New Horizons spacecraft to snap the sharpest possible pics of the Kuiper Belt object nicknamed Ultima Thule, its New Year’s flyby target and the farthest object ever explored.
Now that New Horizons has sent those stored flyby images back to Earth, the team can enthusiastically confirm that its ambitious goal was met.
These new images of Ultima Thule – obtained by the telephoto Long-Range Reconnaissance Imager (LORRI) just 6½ minutes before New Horizons’ closest approach to the object (officially named 2014 MU69) at 12:33 a.m. EST on Jan. 1 – offer a resolution of about 110 feet (33 meters) per pixel. Their combination of high spatial resolution and a favorable viewing angle gives the team an unprecedented opportunity to investigate the surface, as well as the origin and evolution, of Ultima Thule – thought to be the most primitive object ever encountered by a spacecraft.
“Bullseye!” said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute (SwRI). “Getting these images required us to know precisely where both tiny Ultima and New Horizons were — moment by moment – as they passed one another at over 32,000 miles per hour in the dim light of the Kuiper Belt, a billion miles beyond Pluto. This was a much tougher observation than anything we had attempted in our 2015 Pluto flyby.
And here is a clip of the fly-by:
New Horizons scientists created this movie from 14 different images taken by the New Horizons Long Range Reconnaissance Imager (LORRI) shortly before the spacecraft flew past the Kuiper Belt object nicknamed Ultima Thule (officially named 2014 MU69) on Jan. 1, 2019. The central frame of this sequence was taken on Jan. 1 at 5:26:54 UT (12:26 a.m. EST), when New Horizons was 4,117 miles (6,640 kilometers) from Ultima Thule, some 4.1 billion miles (6.6 billion kilometers) from Earth. Ultima Thule nearly completely fills the LORRI image and is perfectly captured in the frames, an astounding technical feat given the uncertain location of Ultima Thule and the New Horizons spacecraft flying past it at over 32,000 miles per hour.
(Note: To loop the video, right button click on it and select “Loop” from the list of options shown.)
Here are the two parts of the documentary, New Horizons – Summiting the Solar System, about the New Horizons fly-by of Ultima Thule:
Summiting the Solar System is a story of exploration at its most ambitious and extreme. On January 1, 2019, NASA’s New Horizons spacecraft flies by a small Kuiper Belt Object known scientifically as 2014 MU69, but nicknamed “Ultima Thule.” Ultima is four billion miles from Earth, and will be the most ancient and most distant world ever explored close up. It is expected to offer discoveries about the origin and evolution of our solar system. Chosen by the team and the public, the nickname honors the mythical land beyond the edges of the known world. But “Summiting” is much more than the story of a sophisticated, plutonium-fueled robotic spacecraft exploring far from the Sun. The New Horizons mission is powered as much by the passions of a small team of humans—men and women, scientists and engineers—for whom pushing the frontiers of the known, climbing the very peaks of the possible, has been the dream of many decades.
“Summiting” goes behind the scenes of the most ambitious occultation campaigns ever mounted, as scientists deployed telescopes to Senegal and Colombia in 2018, and Argentina, South Africa and New Zealand in 2017, to glimpse Ultima as it passed in front of a star, and gathered data on the object’s size and orbit that has been essential to planning the flyby. Mission scientists recall the astonishing scientific success of flying through the Pluto system in 2015, and use comparative planetology to show how Earth and Pluto are both amazingly different and—with glaciers, tall mountains, volcanoes and blue skies—awesomely similar. Appealing to space junkies and adrenaline junkies alike, “Summiting” brings viewers along for the ride of a lifetime as New Horizons pushes past Pluto and braves an even more hazardous unknown. | 0.815063 | 3.207107 |
An object previously identified as a free-floating, large Jupiter analog turns out to be two objects — each with the mass of a few Jupiters. This system is the lowest-mass binary we’ve ever discovered.
Tracking Down Ages
Brown dwarfs represent the bottom end of the stellar mass spectrum, with masses too low to fuse hydrogen (typically below ~75-80 Jupiter masses). Observing these objects provides us a unique opportunity to learn about stellar evolution and atmospheric models — but to properly understand these observations, we need to determine the dwarfs’ masses and ages.
This is surprisingly difficult, however. Brown dwarfs cool continuously as they age, which creates an observational degeneracy: dwarfs of different masses and ages can have the same luminosity, making it difficult to infer their physical properties from observations.
We can solve this problem with an independent measurement of the dwarfs’ masses. One approach is to find brown dwarfs that are members of nearby stellar associations called “moving groups”. The stars within the association share the same approximate age, so a brown dwarf’s age can be estimated based on the easier-to-identify ages of other stars in the group.
An Unusual Binary
Recently, a team of scientists led by William Best (Institute for Astronomy, University of Hawaii) were following up on such an object: the extremely red, low-gravity L7 dwarf 2MASS J11193254–1137466, possibly a member of the TW Hydrae Association. With the help of the powerful adaptive optics on the Keck II telescope in Hawaii, however, the team discovered that this Jupiter-like object was hiding something: it’s actually two objects of equal flux orbiting each other.
To learn more about this unusual binary, Best and collaborators began by using observed properties like sky position, proper motion, and radial velocity to estimate the likelihood that 2MASS J11193254–1137466AB is, indeed, a member of the TW Hydrae Association of stars. They found roughly an 80% chance that it belongs to this group.
Under this assumption, the authors then used the distance to the group — around 160 light-years — to estimate that the binary’s separation is ~3.9 AU. The assumed membership in the TW Hydrae Association also provides binary’s age: roughly 10 million years. This allowed Best and collaborators to estimate the masses and effective temperatures of the components from luminosities and evolutionary models.
The team found that each component is a mere ~3.7 Jupiter masses, placing them in the fuzzy region between planets and stars. While the International Astronomical Union considers objects below the minimum mass to fuse deuterium (around 13 Jupiter masses) to be planets, other definitions vary, depending on factors such as composition, temperature, and formation. The authors describe the binary as consisting of two planetary-mass objects.
Regardless of its definition, 2MASS J11193254–1137466AB qualifies as the lowest-mass binary discovered to date. The individual masses of the components also place them among the lowest-mass free-floating brown dwarfs known. This system will therefore be a crucial benchmark for tests of evolutionary and atmospheric models for low-mass stars in the future.
William M. J. Best et al 2017 ApJL 843 L4. doi:10.3847/2041-8213/aa76df
Related Journal Articles
This post originally appeared on AAS Nova, which features research highlights from the journals of the American Astronomical Society. | 0.840335 | 4.048478 |
Late last week scientists from many countries gathered at the foot of the Andes to inaugurate the Pierre Auger Observatory in Malargüe, Argentina.
This event marked the completion of a vast complex of cosmic-ray detectors — 1,600 of them, spread across some 1,200 square miles (3,000 square kilometers) — designed to detect the collision of ultrahigh-energy particles with Earth's atmosphere and to deduce their origin. The most potent cosmic rays, which are atomic nuclei traveling at relativistic speeds, can carry up to 10 million times more kinetic energy than those created in particle accelerators on Earth.
When a potent cosmic ray strikes Earth, it slams into the nucleus of a gas molecule high in the atmosphere. This collision triggers a chain reaction of secondary particles (termed an air shower) that cascade down to lower levels. Cosmic rays strike our planet constantly, but the most powerful ones — packing 10 million trillion electron volts — are extremely rare. On average, only one of these arrives over each square kilometer of ground per year.
The Pierre Auger Observatory, named a pioneering French cosmic-ray researcher, employs two independent methods to detect and study high-energy cosmic rays. One technique senses the light emitted when secondary particles interact with water one or more of the 1,600 tanks. The other method records ultraviolet light emitted high in the atmosphere during each air shower. (You can learn more about the air showers and their detection here.)
I'll bet the celebration in Argentina had the feel of a new company that made its first big sale a year before the official grand opening. Construction of Pierre Auger Observatory began in 2000, and it went online in 2004 with only about half of its detectors in place. By late last year its researchers had deduced that the most powerful cosmic rays come appear to emanate from active galactic nuclei (AGNs), ultrabright objects powered by supermassive black holes.
So far, the $53 million Pierre Auger Observatory has involved more than 350 physicists from 70 institutions in 17 countries. However, there's more work to be done. A second field of detectors will also be built in southeastern Colorado, providing sky coverage on both sides of the equator. | 0.823255 | 3.71899 |
Three major stratospheric science balloon flight campaigns—Austral 2017, EUSO Balloon and FIREBALL—in preparation at CNES are set to make this year an exceptional one for astrophysics ballooning.
Austral 2017 has just got underway in the southern hemisphere. Teams from CNES and the IRAP astrophysics and planetology research are putting the finishing touches to the PILOT (Polarized Instrument for LOng wavelengTh) science gondola in Alice Springs, Australia. The science goal is to measure the polarized emission of interstellar dust grains in order to map the direction of our galaxy’s magnetic field, thus paving the way for future cosmology missions. After a first successful campaign in the northern hemisphere in 2015, PILOT is ready to launch again as soon as weather conditions are right.
EUSO Balloon, a second innovative exploratory mission, has also started in Wanaka, New Zealand. EUSO (Extreme Universe Space Observatory) is designed to validate a technique for detecting ultra-high-energy cosmic rays penetrating Earth’s atmosphere. The aim is to test the prototype of an ultra-sensitive, ultra-fast optical instrument, to measure background ultraviolet radiation and to attempt to detect air showers for the first time. The first EUSO flight was accomplished in August 2014 from Timmins in Canada with a 400,000-m3 CNES stratospheric balloon to an altitude of 40 kilometres. For this second flight, EUSO will be carried aloft by a 532,000-m3 U.S. superpressure balloon (SPB) for an expected 100 days.
Lastly, the FIREBALL mission (Faint Intergalactic Redshifted Emission Balloon) to study the warm-hot intergalactic medium (WHIM) is set to fly from Fort Sumner in New Mexico this September. The intergalactic medium is the source of gas from which galaxies are born and grow. The energy released by this hot gas, thought to account for 50% of ordinary matter in the cosmos, is extremely tenuous and can therefore only be measured by highly innovative instruments. The FIREBALL project is being led by Caltech and the LAM astrophysics laboratory in Marseille, which has extensive expertise in UV balloon astronomy and is supplying the complete spectrograph. The CNES balloon team is supplying the gondola and NASA will be conducting the flight with a 830,000-m3 balloon. | 0.84326 | 3.324549 |
Pretty darn big, I’d say.
The illustration above shows the relative scale of the comet that ESA’s Rosetta and Philae spacecraft will explore “up-close and personal” later this year. And while it’s one thing to say that the nucleus of Comet 67P/Churyumov-Gerasimenko is about three by five kilometers in diameter, it’s quite another to see it in context with more familiar objects. Think about it — a comet as tall as Mt Fuji!
At the time of this writing Rosetta is 35 days out on approach to Comet 67P/C-G, at a distance of about 51,000 km (31,700 miles) and closing. Three “big burn” maneuvers have already been performed between May 7 and June 4 to adjust the spacecraft’s course toward the incoming comet, and after smaller ones on June 18 and July 2 there are a total of five more to go. See details of Rosetta’s burn maneuvers here.
As incredibly sensitive as they are, Rosetta’s instruments — which were able to detect the water vapor coming from Comet 67P/C-G from a distance of over 360,000 km — have even sniffed the hydrazine exhaust from its own thruster burns.
Luckily the remaining burns are relatively small compared to the first three, with the final being very brief, so any data contamination by Rosetta’s own exhaust shouldn’t become an issue once the spacecraft has established orbit in August.
Launched in March 2004, ESA’s Rosetta mission will be the first to orbit and land a probe on a comet, observing its composition and behavior as it makes its close approach to the Sun in 2015. Click here to see where Rosetta is right now.
Source: ESA’s Rosetta blog
Note: While 3-5 km seems pretty big (especially when stood on end) comet nuclei can be much larger, 10 to 20 km in diameter up to the enormous 40+ km size of Hale-Bopp. As comets go, 67P/C-G is fairly average. (Except that, come August, it will be the only comet with an Earthly spacecraft in tow!) | 0.822252 | 3.505929 |
This story is part of BBC Earth's "Best of 2016" list, our greatest hits of the year. Browse the full list.
On 30 June 1908, an explosion ripped through the air above a remote forest in Siberia, near the Podkamennaya Tunguska river.
The fireball is believed to have been 50-100m wide. It depleted 2,000 sq km of the taiga forest in the area, flattening about 80 million trees.
The earth trembled. Windows smashed in the nearest town over 35 miles (60km) away. Residents there even felt heat from the blast, and some were blown off their feet.
The crash was followed by a noise like stones falling from the sky, or of guns firing
Fortunately, the area in which this massive explosion occurred was sparsely inhabited. There were no official reports of human casualties, though one local deer herder reportedly died after he was thrust into a tree from the blast. Hundreds of reindeer were also reduced to charred carcasses.
One eyewitness account said that "the sky was split in two, and high above the forest the whole northern part of the sky appeared covered with fire…
"At that moment there was a bang in the sky and a mighty crash… The crash was followed by a noise like stones falling from the sky, or of guns firing."
This "Tunguska event" remains the most powerful of its kind recorded in history – it produced about 185 times more energy than the Hiroshima atomic bomb (with some estimates coming in even higher). Seismic rumbles were even observed as far away as the UK.
And yet, over a hundred years later researchers are still asking questions about what exactly took place on that fateful day. Many are convinced that it was an asteroid or a comet that was responsible for the blast. But very few traces of this large extraterrestrial object have ever been found, opening the way for more outlandish explanations for the explosion.
The Tunguska region of Siberia is a remote place, with a dramatic climate. It has a long hostile winter and a very short summer, when the ground changes into a muddy uninhabitable swamp. This makes the area extremely hard to get to.
When the explosion happened, nobody ventured to the site to investigate. This was partly because the Russian authorities had more pressing concerns than sating scientific curiosity, says Natalia Artemieva of the Planetary Science Institute in Tucson, Arizona.
He found a large area of flattened trees, spreading out about 50km wide
Political strife in the country was growing – World War One and the Russian Revolution were just a few years away. "There were only some publications in local papers, not even in St Petersburg or Moscow," she says.
It was only a few decades later, in 1927, that a Russian team led by Leonid Kulik finally made a trip to the area. He had stumbled across a description of the event six years earlier and convinced Russian authorities that a trip would be worthwhile. When he got there, the damage was still immediately apparent, almost 20 years after the blast.
He found a large area of flattened trees, spreading out about 31 miles (50km) wide in a strange butterfly shape. He proposed that an extraterrestrial meteor had exploded in the atmosphere.
It puzzled him that there was no impact crater, or in fact, any meteoric remnants at all. To explain this, he suggested that the swampy ground was too soft to preserve whatever hit it and that any debris from the collision had been buried.
Kulik still hoped that he could uncover the remains, as he wrote in his 1938 conclusions. "We should expect to encounter, at a depth of hardly less than 25 metres, crushed masses of this nickeliferous iron, individual pieces of which may have a weight of one or two hundred metric tons."
Some suggested the Tunguska event could have been the result of matter and antimatter colliding
Russian researchers later said that it was a comet, not a meteor that caused the damage. Comets are largely made up of ice – not rock, like meteorites – so the absence of alien rock fragments would make more sense this way. The ice would have started to evaporate as it entered Earth's atmosphere, and continue to do so as it hit the ground.
But that was not the end of the debate. Because the exact identity of the explosion was unclear, strange alternative theories soon started to appear.
Some suggested the Tunguska event could have been the result of matter and antimatter colliding. When this happens, the particles annihilate and emit intense bursts of energy.
Another proposal was that a nuclear explosion caused the blast. An even more outlandish suggestion was that an alien spaceship crashed at the site on its search for the fresh water of Lake Baikal.
As you might expect, none of these theories stuck. Then, in a 1958 expedition to the site, researchers discovered tiny remnants of silicate and magnetite in the soil.
Further analysis showed they were high in nickel, a known characteristic of meteoric rock. The meteor explanation looked correct after all – and K. Florensky, author of a 1963 report on the event, was keen to put the more fantastical theories to rest:
They were more concerned with bigger asteroids that might cause global extinctions
"While I am aware of the advantages of sensational publicity in drawing public attention to a problem, it should be stressed that unhealthy interest aroused as a result of distorted facts and misinformation should never be used as a basis for the furtherance of scientific knowledge."
But that did not stop others coming up with even more imaginative ideas. In 1973 a paper was published in the reputable journal Nature, suggesting that a black hole collided into Earth to cause the explosion. This was quickly disputed by others.
Artemieva says ideas like this are simply a by-product of human psychology. "People who like secrets and 'theories' usually do not listen to scientists," she says. A huge explosion, coupled with a lack of cosmic remnants, is ripe for these kinds of speculations.
But she also says scientists must shoulder some responsibility, because they took so long to analyse the explosion site. They were more concerned with bigger asteroids that might cause global extinctions, just as the Chicxulub asteroid did. It wiped out most of the dinosaurs 66 million years ago.
In 2013 one team put a stop to much of the speculation of the earlier decades. Led by Victor Kvasnytsya of the National Academy of Sciences of Ukraine, the researchers analysed microscopic samples of rocks collected from the explosion site in 1978. The rocks had a meteoric origin. Crucially, the fragments they analysed were recovered from a layer of peat dating back to 1908.
Various gravitational interactions can make [asteroids] change their orbit more dramatically
The remnants had traces of a carbon mineral called lonsdaleite, which has a crystal structure almost like diamond. This particular mineral is known to form when a graphite-containing structure, such as a meteor, crashes into Earth.
"Our study of samples from Tunguska, as well as research of many other authors reveals meteorite origin of Tunguska event," says Kvasnytsya. "We believe that nothing paranormal happened at Tunguska."
The main problem, he says, is that researchers had spent too much time looking for large pieces of rock. "What was necessary was to look for very small particles," such as the ones his team studied.
But it is not a definitive conclusion. Meteor showers occur often. Many small ones might therefore sprinkle their remnants onto Earth unnoticed. Samples with meteoric origin could presumably come from one of these. Some researchers also cast doubt that the peat collected dates from 1908.
Even Artemieva says she needs to revise her models to understand the total absence of meteorites at Tunguska.
Still, in line with Leonid Kulik's early observations, today the broad consensus remains that the Tunguska event was caused by a large cosmic body, like an asteroid or comet, colliding with Earth's atmosphere.
Most asteroids have quite stable orbits, many of which are found in the asteroid belt between Mars and Jupiter. However, "various gravitational interactions can make them change their orbit more dramatically," says Gareth Collins of Imperial College London, UK.
Occasionally these rocky bodies can cross over into Earth's orbit which can put them onto a collision course with us. At the point one enters into our atmosphere and begins to fragment, it is known as a meteor.
What made the Tunguska event so dramatic was that it was an extremely rare case of what researchers call a "megaton" event – as the energy emitted was about 10-15 megatons of TNT, though even higher estimates have also been proposed.
This is also why the Tunguska event has been difficult to make full sense of. It is the only event of that magnitude that has happened in recent history. "That limits our understanding," says Collins.
Artemieva now says there are clear stages that took place, which she has outlined in a review to be published in the Annual Review of Earth and Planetary Sciences in the second half of 2016.
Most people think they come whaling in from outer space and leave a crater
First, the cosmic body entered our atmosphere at 9-19 miles per second (15-30km/s).
Fortunately, our atmosphere is good at protecting us. "It will break apart a rock smaller than a football field across," explains NASA researcher Bill Cooke, who leads NASA's Meteoroid Environment Office. "Most people think they come whaling in from outer space and leave a crater, and there's a big smoking piece of rock on the ground. The truth is kind of the opposite."
The atmosphere will generally break rocks up a few kilometres above the Earth's surface, producing an occasional shower of smaller rocks that, by the time they hit the ground, will be cold.
In the case of Tunguska, the incoming meteor must have been extremely fragile, or the explosion so intense, it obliterated all its remnants 8-10km above Earth.
This process explains the event's second stage. The atmosphere vaporised the object into tiny pieces, while at the same time intense kinetic energy also transformed them into heat.
"The process is similar to a chemical explosion. In conventional explosions, chemical or nuclear energy is transformed into heat," says Artemieva.
The intense heat resulted in shockwaves that were felt for hundreds of kilometres
In other words, any remnants from whatever entered Earth's atmosphere were turned into cosmic dust in the process.
If events unfolded this way, it explains the lack of large chunks of cosmic material at the site. "It is very difficult to find a millimetre-size grain in a big area. It is necessary to search in the peat," says Kvasnytsya.
As the object entered our atmosphere and broke apart, the intense heat resulted in shockwaves that were felt for hundreds of kilometres. When this airburst then hit the ground it flattened all the trees in the vicinity.
Artemieva suggests an enormous plume resulted from the updraught, which was then followed by a cloud, "thousands of kilometres in diameter".
But Tunguska's story is not over. Even now, some other researchers have proposed that we have been missing an obvious clue to explain the event.
In 2007 an Italian team suggested that a lake 5 miles (8km) north-north-west of the explosion's epicentre could be an impact crater. Lake Cheko, they say, did not feature on any maps before the event.
Luca Gasperini of the University of Bologna in Italy, travelled to the lake in the late 1990s, and says it is difficult to explain the origin of the lake in any other way. "Now we are sure it was formed after the impact, not from the main Tunguska body but of a fragment of the asteroid that was preserved by the explosion."
Any 'enigmatic' objects at the bottom of this lake could be easily recovered with minimal efforts
Gasperini firmly believes that a large piece of asteroid lies 33ft (10m) below the bottom of the lake, buried in sediment. "It would be very easy for Russians to get there and drill," he says. Despite heavy criticism of the theory, he still hopes someone will scour the lake for remnants of meteoric origin.
That Lake Cheko is an impact crater is not a popular idea. It is just another "quasi-theory" says Artemieva. "Any 'enigmatic' objects at the bottom of this lake could be easily recovered with minimal efforts – the lake is not deep," she says. Collins also disagrees with Gasperini's idea.
In 2008, he and colleagues published a rebuttal to the theory, stating that "unaffected mature trees" were close to the lake, which would have been obliterated if a large piece of rock had fallen close by.
Regardless of the details, the influence of the Tunguska event is still felt. Research papers on the subject continue to be published.
Today, astronomers also peer into the skies with powerful telescopes to look for signs that rocks with the potential to cause a similar event are heading our way, and to assess the risk that they pose.
When a Tunguska type event happens again, the overwhelming probability is that it will happen nowhere near human population
In 2013 in Chelyabinsk, Russia, a relatively small meteor around 62ft (19m) wide created visible disruption. This surprised researchers like Collins. His models had predicted it would not cause as much damage as it did.
"What's challenging is that this process of the asteroid disrupting in the atmosphere, decelerating, evaporating and transferring its energy to the air, is a very complicated process. We would like to understand it more, to better predict consequences of these events in future."
Chelyabinsk-sized meteors were previously believed to occur roughly every 100 years, while Tunguska-sized events had been predicted to occur once a millennium. This figure has since been revised. Chelyabinsk-sized meteors could be happening 10 times more frequently, says Collins, while Tunguska style impacts could occur as often as once every 100-200 years.
Unfortunately, we are and will remain defenceless against similar events, says Kvasnytsya. If another explosion like the Tunguska event took place above a populated city, it would cause thousands if not millions of casualties, depending where it hit.
But it is not all bad news. The probability of that happening is extremely small, says Collins, especially given the huge surface area of Earth that is covered in water. "When a Tunguska-type event happens again, the overwhelming probability is that it will happen nowhere near human population."
We may never find out whether the Tunguska event was caused by a meteor or comet, but in a way that does not matter. Either could have resulted in the intense cosmic disruption, which we are still talking about over a century later.
Melissa Hogenboom is BBC Earth's feature writer. She is @melissasuzanneh on Twitter.
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If you liked this story, sign up for the weekly bbc.com features newsletter called "If You Only Read 6 Things This Week". A handpicked selection of stories from BBC Future, Earth, Culture, Capital, Travel and Autos, delivered to your inbox every Friday. | 0.896249 | 3.077791 |
Hubble Hones In on a Hypergiant’s Home
Image credit: ESA/Hubble & NASA Text credit: European Space Agency
This beautiful Hubble image reveals a young super star cluster known as Westerlund 1, only 15,000 light-years away in our Milky Way neighborhood, yet home to one of the largest stars ever discovered.
Stars are classified according to their spectral type, surface temperature, and luminosity. While studying and classifying the cluster’s constituent stars, astronomers discovered that Westerlund 1 is home to an enormous star. Originally named Westerlund 1-26, this monster star is a red supergiant (although sometimes classified as a hypergiant) with a radius over 1,500 times that of our sun. If Westerlund 1-26 were placed where our sun is in our solar system, it would extend out beyond the orbit of Jupiter.
Most of Westerlund 1’s stars are thought to have formed in the same burst of activity, meaning that they have similar ages and compositions. The cluster is relatively young in astronomical terms —at around three million years old it is a baby compared to our own sun, which is some 4.6 billion years old. | 0.805757 | 3.085681 |
Amateur Astronomers See Comet ISON
Sept. 24, 2013: Anticipation is building as Comet ISON approaches the sun for a close encounter on Thanksgiving Day (Nov. 28). No one knows if the blast of solar heating ISON receives will turn it into one of the finest comets in years--or destroy the icy visitor from the outer solar system.
Astronomer Carey Lisse, the head of NASA's Comet ISON Observing Campaign, hopes that "every telescope on Earth will be trained on the comet in October and November." He may get his wish. As September comes to an end, amateur astronomers around the world are already monitoring the comet.
"Comet ISON is approaching Mars in the pre-dawn sky," explains Lisse. "It is invisible to the naked eye, but within reach of backyard telescopes."
"I photographed Comet ISON on Sept. 15th using my 4-inch refractor," reports astrophotographer Pete Lawrence of Selsey UK. "The comet's tail is nicely on view even through this relatively small instrument." image
In Aquadilla, Puerto Rico, astronomer Efrain Morales Rivera saw the comet on Sept. 14th "rising above the canopy of the rain forest just minutes before sunrise. I used a 12-inch telescope," he says. image
In mid-September, the approaching comet was glowing like a star of 14th magnitude. That's dimmer than some forecasters expected.
"Certainly we would love it to be a couple of magnitudes brighter right now," says researcher Karl Battams of the Naval Research Lab in Washington, D.C.,"but it's doing just fine. I'd say it's still on course to become a very eye-catching object."
Battams is especially optimistic about NASA's twin STEREO probes and the NASA/ESA Solar and Heliospheric Observatory. Those three spacecraft are equipped with coronagraphs--devices which cover the blinding disk of the sun to produce an artificial eclipse. The coronagraphs will be able to see ISON at its brightest when it is making its closest approach to the sun on Thanksgiving.
If ISON survives its brush with solar fire, sky watchers on Earth might get an eye-full as well.
Based on the latest images, internationally known comet expert John Bortle says "ISON appears likely to survive the in-bound leg of its journey all the way to the Sun. It will probably brighten more slowly than all the early hype led the public to believe. Nevertheless, Comet ISON should very briefly become exceptionally bright, at least rivaling the planet Venus in the hours preceding its closest approach to the sun."
After Thanksgiving (Nov 28th), Comet ISON will emerge from the sun's glare well-positioned for observers in the northern hemisphere. The comet's tail will likely be visible to the naked-eye in both the morning and evening sky throughout December 2013.
A useful point of comparison is Comet Lovejoy, which put on a grand show after it brushed the sun in 2011. People in the southern hemisphere still remember the comet's tail stretching halfway across the night sky. Judging from the brightness of Comet ISON, Matthew Knight of the Lowell Observatory believes that “ISON is likely a few times bigger than Lovejoy was, so I am optimistic that Comet ISON will become an impressive sungrazer."
Because this is Comet ISON's first visit to the inner solar system, no one can say for sure what will happen. Comets are unpredictable, capable of fizzling at the last minute even after months of promising activity.
Battams, who has been "burned" before by sungrazing comets, cautions that "at no point in the next couple of months are we going to know if Comet ISON will survive or not until we actually observe it with our own eyes."
"Observations from amateur astronomers are really valuable pieces of the puzzle for us," adds Battams. "They help us to see how the comet is evolving."
The NASA Comet ISON Observing Campaign aims to get as many eyes on ISON as possible. To learn how you can help, visit http://isoncampaign.org. | 0.837244 | 3.286421 |
Every so often in the vast cosmos something exciting happens in one of the relatively few places that humans happen to watch closely. Like a rare bird touching down for a bath in the Trevi Fountain, such serendipitously placed exotica produces a wealth of witnesses and plenty of photographic documentation.
So it was with a recent supernova in the spiral galaxy M51—better known to casual stargazers as the Whirlpool Galaxy, a photogenic swirl some 25 million light-years away. Shortly after the light from an exploding star there reached Earth at the end of May 2011, amateur reports of the cataclysm began pouring in to the Central Bureau for Astronomical Telegrams, a clearinghouse for new telescope data. Soon the explosion was assigned the official designation supernova 2011dh.
The Whirlpool Galaxy has plenty of admirers, so a brand-new bright spot on the edge of the spiral was sure to catch the attention of many observers. “It’s really one of the nearest galaxies, and it’s a galaxy that’s beautiful and very famous,” says astronomer Schuyler Van Dyk of the California Institute of Technology.
Even better, the well-documented supernova in the Whirlpool Galaxy turned out to be a rare variety known as a type IIb supernova. Those explosions result from the collapse of a massive star that has been stripped of most of its outlying hydrogen shell, possibly by the pull of a binary stellar companion. Of all the stars that end their lives in a catastrophic collapse—just one of two ways to produce a supernova—only about one in 10 produces a type IIb.
Astronomers have some general explanations for type IIb explosions, but uncovering the exact chain of events leading up to a supernova is a difficult task. Because astronomers never know that a star is about to go supernova until it has already exploded, it is usually impossible to determine which star, exactly, met its violent end. Only in rare cases can astronomers turn up sufficiently detailed pre-explosion images of the region in question to identify the culprit. In 2011, however, the famousness of the Whirlpool Galaxy once again came in handy. “Within days of discovery of the supernova we went to the Hubble Space Telescope data archive, and it turned out that one of the former directors of the HST had orchestrated this beautiful mosaic of M51—this glorious picture in various colors,” Van Dyk says. In the Hubble images, at the very spot where the supernova appeared without warning in 2011, there had been in 2005 an unremarkable yellow supergiant star.
But many researchers found that the profile of the explosion did not fit what would be expected from the collapse of a supergiant. Instead their data for 2011dh pointed to the explosion of a more shrunken star—perhaps a binary companion of the yellow supergiant that had been stripped down, nearly to its core, by the gravitational pull of its neighbor. “We thought initially that the progenitor was essentially this very stripped star, very blue, and so it was unseen” in the Hubble images, Van Dyk says. “The yellow star was hiding the bluer star that actually exploded—that was our conjecture.”
A competing team, however, had arrived at a different conclusion. An early analysis by Justyn Maund, now of Queen's University Belfast, and his colleagues found that the giant star that Hubble had spotted at the site of the explosion had indeed been the progenitor. “They said that the yellow star was the star that exploded,” Van Dyk says. “They had other data that was more consistent with a more extended progenitor. So there we were.”
By this March, nearly two years after the supernova first appeared in the Whirlpool Galaxy, Van Dyk and his colleagues commandeered Hubble once more to take another look. To their surprise, the yellow supergiant star, which they had presumed to be a mere bystander to the explosion, had vanished. Another team, using telescopes on the ground, saw the same thing. “We just wanted to see what the evolution of the supernova was,” Van Dyk says. “We fully expected the yellow supergiant to still be there in these images this year.”
The supergiant’s disappearance implicated the star as the source of the supernova after all. Van Dyk and his colleagues published their findings, which validated the conclusions of their competitors, in the August 1 issue of The Astrophysical Journal Letters. “The other team was actually correct, and we were fully contrite in that way,” Van Dyk says.
But the saga of supernova 2011dh will not end there. As the bright blemish of the supernova remnant continues to fade, the Whirlpool will return to its pre-2011 appearance—minus one supergiant star. Toward the end of the year, as early as mid-November, the supernova’s glow will have faded so much that the yellow supergiant’s surviving partner should come into view—if indeed the star was locked in a binary pairing as has been invoked to explain the rare type IIb event. “You should actually be able to see the companion star in the binary system,” Van Dyk says, noting that multiple teams have secured time on the Hubble telescope to follow the evolution of supernova 2011dh. “If they see the binary companion, then that lends a lot of credence to this binary pathway to this type of supernova,” he adds. “And that would be really important.” | 0.83165 | 3.938827 |
At a meeting sponsored by the American Academy, the Royal Society, and the Carnegie Institution for Science, Wendy Freedman (Crawford H. Greenewalt Chair and Director of Carnegie Observatories at the Carnegie Institution for Science) and Martin Rees (Fellow of Trinity College; Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge; Astronomer Royal; and Visiting Professor at Imperial College London and at Leicester University) discussed what we know and do not know about the universe. Richard A. Meserve (President of the Carnegie Institution for Science) moderated the discussion. The meeting took place on April 29, 2014, at the Carnegie Institution for Science. An edited version of the presentations follows.
Richard A. Meserve
Richard A. Meserve is President of the Carnegie Institution for Science. He was elected a Fellow of the American Academy of Arts and Sciences in 1994, and serves on the Academy’s Council and Trust. He is also a member of the advisory committee to the Academy’s Global Nuclear Future Initiative and to the Academy’s Science and Technology policy study group.
One of the defining characteristics of science is the reality that the more you know, the more you realize you don’t know. And there is perhaps no field today in which that is more evident than in astronomy. Over the last two decades, we have learned that we fundamentally do not understand the stuff that comprises 95 percent of the universe: dark energy and dark matter. In one sense, in this time of scientific achievement, our ignorance is a little embarrassing. But in another sense, this is a time of enormous excitement. There are deep mysteries to be solved, presenting a great challenge to the researchers of our time.
We first learned about dark energy about fifteen years ago. Cosmologists had long expected that the force of gravity produced by the matter in the universe would cause the universe’s expansion to slow down, and perhaps eventually to reverse course. But contrary to everyone’s expectations, observations of Type Ia supernovae by the High-Z Supernova Search Team in 1998 and by the Supernova Cosmology Project one year later suggested that the expansion of the universe is actually accelerating. Thus, we were presented with a great mystery: why is the universe’s expansion accelerating, and what could possibly be fueling it? To answer these questions, cosmologists rethought the known contents of the universe, determining that about 70 percent of its matter/energy inventory is embodied in dark energy, a substance we have not yet begun to understand.
But even before the discovery of evidence for dark energy, we had already found evidence of dark matter. In fact, Vera Rubin, a Carnegie astronomer, was responsible for the verification of the existence of dark matter. Rubin helped prove dark matter’s existence through her measurements of its influence on the movement of stars within galaxies. The trajectories she observed simply did not fit Newton’s laws of gravity; there had to be matter that we cannot observe. Once we accommodate it, we find that dark matter constitutes about 25 percent of the matter/energy inventory of the universe.
So, the stars and galaxies and the conventional matter we observe all around us really only compose 5 percent of what constitutes our universe. Our research has revealed to us deep mysteries about the remaining 95 percent, inspiring the title of tonight’s discussion, “The Universe Is Stranger Than We Thought.”
Wendy Freedman is Crawford H. Greenewalt Chair and Director of Carnegie Observatories at the Carnegie Institution for Science. She was elected a Fellow of the American Academy of Arts and Sciences in 2000.
A century ago, we astronomers understood the universe to be both dominated by stars and unchanging with time. We observed the diurnal motions of stars, but they were, to us, fixed; the universe was neither expanding nor contracting. A century later, we have learned that ours is a dynamic universe: it is evolving, it is changing with time, it is filled not only with stars but with galaxies composed of stars and exotic objects like black holes, and it is overwhelmingly filled with dark energy and with matter that bears little resemblance to the matter that we know about. These findings were part of a century of far-reaching cosmological discovery. Today, I will concentrate on three discoveries in particular: the discovery of the expanding universe, the discovery of evidence supporting the presence of dark matter in the universe, and the discovery of the acceleration of the expansion of the universe.
I will begin with the discovery of the universe’s expansion, for which we are indebted to Edwin Hubble, after whom the Hubble Space Telescope is named. The history of Hubble’s discovery – and of cosmology in the twentieth century generally – is inextricably intertwined with the history of the Carnegie Institution of Science itself. Andrew Carnegie had a vision: if you hired exceptional scientists, and if you gave them resources, a laboratory, and the apparatus to do science, then interesting discoveries would follow. Likewise, George Ellery Hale, the first director of the observatories of the Carnegie Institution, had a vision of his own: if you built large telescopes with reflecting mirrors, then you would make discoveries in astronomy. Hale was fond of saying, “Make no little plans. They have no magic to stir men’s blood,” a quotation from the American architect Daniel Burnham. And Hale certainly made no little plans, arriving in Pasadena in 1903, where he identified Mount Wilson as a site for his observatory of large reflecting telescopes.
At Mount Wilson, Hale first built a solar telescope (he was a solar astronomer and, in fact, was the astronomer who discovered that there were magnetic fields on the Sun) and then began construction of a 60-inch mirror telescope. This 60-inch telescope is what then Carnegie astronomer Harlow Shapley used to discover that our Sun is not the center of the universe, where it had been presumed to reside ever since Copernicus had in 1543 shown that the Earth was not the center of the universe. Shapley showed that the Sun is actually located about two-thirds of the way out in a disk, a plane, of what we now know as our Milky Way galaxy. That was an extraordinary early discovery to come out of the first telescopes at Hale’s observatory. But it was the 100-inch Mount Wilson telescope, whose construction began before the 60-inch telescope was even complete, that enabled Hubble to make his discoveries about the expanding universe.
Edwin Hubble used the 100-inch telescope to study a class of objects known as “nebulae.” In the early twentieth century, nebula was the classification given to any number of diffuse objects, including interstellar clouds of dust and gas that we now know act as stellar nurseries, star clusters and galaxies beyond the Milky Way. Figure 1 features a photograph of Hubble examining a glass photographic plate, as well as an image of the nearby Andromeda nebula shown on a plate Hubble took. Glass photographic plates were the detectors in use when the 100-inch Mount Wilson telescope became operational. The black fuzzy mass centered on the glass plate is what Hubble identified as a nebula. These objects had been catalogued by astronomers for a couple hundred years. The question was, were these nebulae objects swirling around regions of gas and dust, collecting under gravity to form new stars in the Milky Way? Or were they perhaps galaxies like the Milky Way, at far greater distances? In the box in the upper right corner of the photographic plate in Figure 1, which is a negative image, you can see where Hubble marked “VAR!” “VAR” stands for variable, and the new variable Hubble had found was a class of star called a Cepheid: a star whose luminosity and pulsation period allow astronomers to measure distances to extragalactic objects.
Left: Astronomer Edwin Hubble examining plate, c. 1952
Right: Hubble’s discovery plate of a Cepheid in Andromeda
Using Cepheids, Hubble was able to show that Andromeda was well beyond the confines of our own galaxy – we now know it is about two million light years away from us. Hubble went on to make these measurements for many different galaxies and, as illustrated by Figure 2, he was able to show that when he plotted the velocity (km/s; erroneously labeled just “km” on Hubble’s graph) of the galaxy on one axis and the distance (millions of parsecs or Megaparsecs, where 1 parsec = 3.26 light years) on the other, there was a correlation between how fast the galaxy was moving and the distances he measured. That is, the farther away the galaxy is, the faster it is moving away from us.
These were two spectacular discoveries: 1) what followed is that we now know that there are about one hundred billion such galaxies in our observable universe in addition to our own, and that within galaxies like our Milky Way, there are about one hundred billion stars; and 2) that the universe is expanding and that the galaxies are participating in this overall expansion of the universe.
Hubble Diagram (1929)
We think Hubble did not actually believe that the universe was expanding, despite the evidence his empirical results provided. It was the integration of Einstein’s General Theory of Relativity that described, based on Hubble’s observational results about the linear relationship between velocity and distance, that the universe must have had a beginning. If the universe is expanding now, there must have been a time when it was compressed, hot, and dense. Einstein’s theory and Hubble’s observations led to our picture of a universe developed from the Big Bang: a furiously hot and dense explosion about 14 billion years ago. This extrapolation of Hubble’s observations has since been confirmed by more exact measurements of the Cepheid variables recently taken with the Hubble Space Telescope and its sister satellite, the Spitzer Space Telescope (which operates in the medium infrared, very long wavelengths) – which have charted out the distance scale of the universe based on many galaxies. Further, using the Hubble Space Telescope, we have estimated the age of the universe to be about 13.7 billion years, a number that has been corroborated by numerous independent findings.
The second discovery I want to talk about is the existence of dark matter in the universe. That story begins with the observations of Fritz Zwicky at Caltech in the 1930s, and the observations by Carnegie astronomer Horace Babcock, who in 1939 made the first measurements of the velocity of stars in the Andromeda galaxy (the same galaxy in which Hubble discovered Cepheids). Zwicky found that the velocities of galaxies in the nearby Coma cluster were so high that the galaxies could not have been bound to the cluster; they should have escaped long ago. Babcock learned that the velocity of stars and gas in the Andromeda galaxy increases and then stays constant as you move away from the center of the galaxy toward the outer regions. The expectation was that in the same manner that we observe the orbital velocities of planets in our solar system reduce proportionally to the distance from the Sun, the velocities of stars and gases in galaxies should fall off in the outer regions. For decades, these data were largely ignored because they were not expected and simply could not be explained. Then in the 1970s, Vera Rubin, of Carnegie’s Department of Terrestrial Magnetism in Washington, D.C., made her own observations. Once again, the velocities of outer stars and gases in every galaxy that Rubin and her collaborator Kent Ford measured either increased or remained flat. Other astronomers measured the velocities of hydrogen clouds within galaxies. None of these velocities decreased with distance as they did in the solar system.
Rubin’s findings signaled that there was additional matter in the outer regions of these galaxies whose gravitational influence bound these high-velocity stars to the structure. Without additional matter, there simply would not be enough mass to prevent the stars, moving at such great speeds, from escaping the galaxy. There were alternative explanations, but the evidence for what would become known as dark matter kept increasing. The measurements of velocities of other galaxies in clusters confirmed Fritz Zwicky’s measurements in the Coma cluster. Additionally, with new advancements in X-ray astronomy, astronomers were able to discover gas as hot as 100 million degrees Celsius residing in these galaxy clusters. But without additional mass to bind this gas to the cluster, it should have, at those temperatures, evaporated. Finally, Einstein’s General Relativity predicted that space would bend in the vicinity of a massive object, and light would bend around it. This phenomenon, known as gravitational lensing, reveals to us the strength of the gravitational influence of the object that is changing the light’s course. But the arcs we observe suggest that there is far more mass acting upon the light than is accounted for by the luminous matter in galaxies alone.
Ultimately, only about 4 percent of the total composition of mass and energy in the universe is ordinary visible matter. The vast majority of the matter in the universe is dark. We cannot see it and it does not emit visible light or any kind of electromagnetic radiation. So what could this dark matter be? Could it be rocks, planets, remnants of old stars that no longer shine? Could it be gas, massive compact objects, space dust, or black holes? In the 1980s, many groups embarked on searches for dark matter in such forms that we already understood, and all failed. The only option left standing was an undiscovered particle, one formed soon after the Big Bang.
The current best hypothesis is that dark matter is a relic from the early universe that interacts with ordinary matter only through gravity. That is, dark matter does not interact via electromagnetic or other known forces. Researchers are currently looking for dark matter in underground laboratories, shielded by lead from other noise sources, using detectors made of elements like germanium and silicon to look for this very faint signal from what could be these weakly interacting massive particles. The Fermi gamma-ray satellite, as well as the Large Hadron Collider – a particle accelerator between France and Switzerland that accelerates particles to very high velocities and smashes them – are also looking for evidence of dark matter candidates. Physicists and astronomers hope that these elusive particles will be discovered in the next decade – a Nobel Prize for this discovery awaits.
The third discovery I would like to discuss is the acceleration of the expansion of the universe, a discovery made in 1998 and 1999 by two independent groups studying Type Ia supernovae. Type Ia supernovae are thought to occur in a binary star system in which one of the stars is a white dwarf (a star that has completed its normal life cycle and has ceased nuclear fusion). If the white dwarf accretes enough mass from its companion star and exceeds a certain mass, that white dwarf explodes in so bright a display that you can actually see it over most of the observable universe. Another possibility is that the explosion occurs when two white dwarf stars merge. Whatever the mechanism, the supernovae themselves can be as bright as an entire galaxy. Using these supernovae, we have found that as we look back further in time (farther in space), the expansion rate has increased over time – the expansion of the universe is accelerating.
The reason for this acceleration is not well understood at this time. We do not know the nature of the dark energy that is causing the acceleration of the expansion, but it makes up most of the composition of the universe. To give you some sense of what we think we know about dark energy, the density of dark energy is tiny – about 10-30 grams per cubic centimeter (for a relative comparison, the density of water is about 1 gram per cubic centimeter). It appears that there is energy in the vacuum of space, and although the density is so slight, the sheer volume of space establishes the energy’s dominance in our universe. Although astronomers have now measured the effects of dark energy and dark matter in several independent ways, we do not yet understand the fundamental nature of what is causing the universe to be stretched apart; nor do we know at this time what composes 95 percent of the universe.
To conclude, I quickly want to say a few words about what is on the horizon, because this is a very exciting time in astronomy. The successor to the Hubble Space Telescope, the James Webb Space Telescope – which features a mirror 6.5 meters (250 inches) in diameter – is due to be launched in 2018. Unlike the Hubble, which orbits the Earth about 350 miles above our heads (for comparison, the Earth-Moon distance is about 250,000 miles), the James Webb Space Telescope will reside about one million miles from the Earth, and will let us study some of the earliest moments in the universe, including the so-called Dark Ages about 400,000 years after the Big Bang, about which we know virtually nothing.
Back on the ground, I have had the pleasure of leading an international consortium planning the Giant Magellan Telescope (GMT), now poised to enter its construction phase. The GMT is a joint effort by the Carnegie Institution, the Smithsonian Institution, Harvard University, the Universities of Arizona, Chicago, Texas at Austin, and Texas A&M, as well as Australia and South Korea. The GMT is a 25-meter (1000-inch) telescope that will use seven mirrors, each over 27 feet in diameter, to capture images ten times the resolution of the Hubble Space Telescope. These mirrors are being manufactured underneath the football stadium at the University of Arizona – not what the football stadium was designed to do, but it really is a good use of the empty space in the facility! We will ship these mirrors and assemble this telescope at Carnegie’s Las Campanas Observatory in the Andes Mountains in Chile, home to our current 6.5-meter Magellan Telescopes. We hope to begin taking data with the GMT in 2021.
In summary, our universe has revealed itself to be quite extraordinary. It is stranger than we think, it is vast, it is expanding and that expansion is accelerating, it is filled with exotic objects and new kinds of matter and energy. And I would venture that it is very unlikely to be through surprising us.
Martin Rees is a Fellow of Trinity College and Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge. He holds the title of Astronomer Royal and is a Visiting Professor at Imperial College London and at Leicester University. He was elected a Foreign Honorary Member of the American Academy of Arts and Sciences in 1975.
Charles Darwin’s On the Origin of Species closes with these famous words: “Whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”
But the young Earth – Darwin’s “simple beginning” – was in fact already very complicated, chemically and geologically. Astronomers aim to probe back farther than this beginning; to set our Earth in its vast cosmic context and address basic questions like: How did planets such as ours form? How did stars originate? Where did the atoms that make up planets and stars come from? Over the past few decades there has been a crescendo of progress and discovery, owed primarily to advancing instrumentation: more powerful telescopes, computers, and space technology.
Unmanned probes to other planets have beamed back pictures of varied and distinctive worlds: Venus, rendered torrid and uninhabitable by the greenhouse effect that has poisoned its atmosphere; and Mars, with its intricate geology, now being explored by the Curiosity rover. Farther afield, we have fascinating close-ups of Jupiter’s moons: icy Europa and sulphurous Io. The European probe Huygens has landed on Saturn’s giant moon Titan, revealing flowing rivers of liquid ethane at -170 degrees Celsius.
Astronomers aim not only to understand the solar system in which we live, but to trace back farther in our history – to understand how stars and planets form, and from where their constituent atoms came. We have made huge progress in delineating a process of cosmic emergence, which we can trace back to a mysterious, hot, and dense beginning 13.8 billion years ago.
But let’s start our cosmic exploration closer to home. And this leads to one of the great unknowns, which certainly would have fascinated Darwin: what creatures might be out there in space already?
Prospects for life look bleak in our solar system – even on Mars or under the ice of Saturn’s moon Enceladus. But prospects brighten if we widen our horizons to other stars – far beyond the reach of any probe we can now envisage. Indeed, a hot current topic in astronomy is the realization that many other stars – perhaps even most of them – are orbited by retinues of planets, like the Sun is.
These planets are not detected directly but inferred by precise measurement of their parent star. One technique is very simple. From our vantage point, a star dims slightly when a planet is “in transit” in front of it. An Earth-like planet transiting a Sun-like star causes a fractional dimming, recurring once per orbit, of one part in ten thousand.
NASA’s Kepler spacecraft spent three years monitoring the brightness of over one hundred and fifty thousand stars, at least twice every hour, with this precision. It has determined the orbits of more than two thousand planets, and allowed us to infer their sizes from the depth of the dip during transit. We are especially interested in possible “twins” of our Earth: planets the same size as ours, on orbits with temperatures such that water neither boils nor stays frozen. The best such candidate so far is one of five planets orbiting a star half the mass of the Sun (and much fainter). The outermost planet has 1.2 times the Earth’s radius, and it orbits at a distance from the parent star such that liquid water might just exist. There may be better candidates still to be retrieved from the Kepler data. Moreover, Kepler has only looked at a thousandth of the area of the sky; so we would expect, after scanning it all, to find a candidate planet that is ten times closer and one hundred times less faint than this one.
The real goal, of course, is to see Earth-like planets directly – not just their shadows. But that is hard. To realize just how hard, suppose an alien astronomer with a powerful telescope was viewing the Earth from thirty light years away – the distance of a nearby star. Our planet would seem to be, in Carl Sagan’s phrase, a “pale blue dot,” very close to a star (our Sun) that outshines it: like a firefly next to a searchlight. But if the aliens could detect this dot, there is a lot they could infer. The shade of blue would be slightly different, depending on whether the Pacific Ocean or the Eurasian land mass was facing them (of course, also depending on the global pattern of cloud cover). So the alien astronomers could infer the length of our “day,” the length of our seasons, the gross topography, and the climate. By analyzing the faint light, they could infer that the Earth had a biosphere. In the 2020s, telescopes like the Giant Magellan Telescope and its European counterpart, the Extremely Large Telescope (with a mirror 39 meters across), will be drawing such inferences about planets the size of our Earth that orbit other Sun-like stars.
Could there be life on these planets? Here we are still in the realm of speculation. Even if simple life is common, it is a separate question whether it is likely to evolve into anything we might recognize as intelligent or complex – whether Darwin’s writ runs through the wider cosmos. Perhaps the cosmos teems with life; on the other hand, our Earth could be unique among the billions of planets that surely exist.
What has surprised people about these planetary systems is their great variety: Jupiter-mass planets very near their stars; planets on extremely eccentric orbits; and planets orbiting double-star systems, a relationship that produces two “suns” in the planet’s sky. But the existence of these planets was not surprising given what we have learned about how stars form via the contraction of clouds of dusty gas. If a proto-stellar cloud has any angular momentum, it will spin faster as it contracts and spin off a dusty disc around the protostar, in which gas condenses and dust agglomerates into rocks and planets. We believe this to be a generic process in all protostars.
Flashback to Newton, who famously explained why planets move in ellipses, but did not understand why they were orbiting on roughly the same plane: the ecliptic. Newton believed it was providence, but we now understand it as a natural outcome of formation from a dusty proto-stellar disc. We have pushed back the causal chain farther than Newton could. Indeed, as Wendy Freedman has adumbrated, we have pushed it right back to the cosmos’s hot, dense beginning. We can trace cosmic history back to one second after the Big Bang, when the temperature was 1 MeV and helium and deuterium formed via nuclear fusion. Indeed we can probably be confident back to a nanosecond after the Big Bang, when each particle had about 50 GeV of energy – as much as can be achieved in the Large Hadron Collider accelerator in Geneva.
Our complex cosmos today manifests a huge range of temperature and density – from blazingly hot stars to the dark night sky. People sometimes worry about how this intricate complexity emerged from an amorphous fireball. It might seem to violate a hallowed physical principle – the second law of thermodynamics – which describes an inexorable tendency for patterns and structure to decay or disperse. The answer to this seeming paradox lies in the force of gravity. Gravitating structures have a negative specific heat. As they lose energy, they get hotter. If the nuclear reactions that generate its power were switched off, the Sun would gradually contract, but in the process its center would get hotter: higher pressure would be needed to balance gravity as the Sun shrunk.
In the expanding universe, gravity enhances, density contrasts. Any patch of the universe that starts off slightly denser than average would decelerate more because it feels extra gravity; its expansion lags farther and farther behind, until it eventually stops expanding and separates out. Computer simulations of part of a “virtual universe” clearly show incipient structures unfolding and evolving. Within the resulting galaxy-scale clumps, gravity enhances the contrasts still further: gas is pulled in and compressed into stars. Simulations of this kind, displayed as movies, portray how galaxies emerged sixteen powers of ten times faster than it actually happened! Each galaxy is an arena within which stars, planets, and perhaps life can emerge.
And there is one important point: the initial irregularities fed into the computer models are not arbitrary; they are inferred from the observed fluctuations in the temperature of the cosmic microwave background. The amplitude is only one part in one hundred thousand, but computing forward, the fluctuations are amplified by gravity into the conspicuous structures – galaxies, galaxy clusters – in the present universe. This vindicates the claim that structure emerges by clustering of the gravitationally dominant dark matter during cosmic expansion.
As I said, we can trace cosmic history back to a nanosecond after the Big Bang, when the entire visible universe was squeezed to the size of our solar system. But questions like “where did the fluctuations come from?” and “why did the early universe contain the actual mix we observe of protons, photons, and dark matter?” take us back to an even younger universe, where matter was hugely more compressed still.
The physics at that era are of course still conjectural. But an astonishingly bold theory called “inflation” suggests that the fluctuations could have been generated by microscopic quantum fluctuations that are stretched by the subsequent expansion right up to the scales of galaxies, and beyond. The generic idea of inflation has achieved success in predicting two features of the fluctuations: that they are Gaussian, and that their amplitude depends on scale in a distinctive way. As well as generating the density fluctuations that evolve into galaxies, quantum effects could generate a second kind of fluctuation: gravitational waves that generate transverse motions, without changing the density.
Recent claims to have detected the latter would, if confirmed, offer further support for “inflation”; their strength is an important discriminant among different models.
Now for another basic question: How much space is there altogether? How large is physical reality? We can only see a finite volume, a finite number of galaxies. That is essentially because there is a horizon, a shell around us delineating the distance light could have travelled since the Big Bang. But that shell has no more physical significance than the circle that delineates your horizon if you are in the middle of the ocean. There is no perceptible gradient across the visible universe, which suggests that, if finite and bounded, it stretches thousands of times farther. But that is just a minimum. If it stretched far enough, then all combinatorial possibilities would be repeated. Far beyond the horizon, we could all have avatars. Even conservative astronomers are confident that the volume of space-time within range of our telescopes – what astronomers have traditionally called “the universe” – is only a tiny fraction of the aftermath of our Big Bang.
But that is not all. Plausible models for 1016 GeV physics lead to so-called eternal inflation. “Our” Big Bang could be just one island of space-time in a vast cosmic archipelago. This is speculative physics – it is perplexing today, just as the shape of the Solar System was to Newton and the “Big Bang” was until fifty years ago. But it is physics, not metaphysics; we can hope to push the casual chain back farther still.
So a challenge for twenty-first-century physics is to address two fundamental questions. First, are there many big bangs rather than just one? Second, if there are many, are they all governed by the same physics or not? Many string theorists do not think so. They think there could be a huge number of different vacuum states – arenas for different microphysics. If they are right, what we call “laws of nature” may in this grander perspective be local bylaws governing our cosmic patch. Many patches could be still-born or sterile: the laws prevailing in them might not allow any kind of complexity. We therefore would not expect to find ourselves in a typical universe; rather, we would be a typical member of the subset where an observer could evolve. This is sometimes called anthropic selection.
Such conjectures motivate us to explore what range of parameters would allow complexity to emerge. Those who are allergic to multiverses can regard this just as an exercise in counterfactual history (rather as historians speculate on what might have happened to America if the British had fought more competently in 1776, and biologists conjecture how our biosphere might have evolved if the dinosaurs had not been wiped out).
Anthropic arguments are irrelevant if the constants are unique. Otherwise, they are the best explanation we will ever have. It is reminiscent of planetary science four hundred years ago, even before Newton. At that time, Kepler thought that the Earth was unique, its orbit related to the other planets by beautiful mathematical ratios. We now realize that even within our own galaxy there are billions of stars, each with planetary systems. Earth’s orbit is special only insofar as it is in the range of radii and eccentricities compatible with life. Maybe we are due for an analogous conceptual shift on a far grander scale. Our Big Bang may not be unique any more than planetary systems are. Its parameters may be “environmental accidents,” like the details of the Earth’s orbit. The hope for neat explanations in cosmology may be as vain as Kepler’s numerological quest.
Mention of a multiverse often triggers the response that unobservable domains are not part of science. I want to contest this by way of aversion therapy, the psychological process of increased exposure whereby you are, for example, at first presented with a spider a long way away, but end up at ease even with tarantulas crawling over you. I mentioned that there are galaxies beyond our horizon: in a decelerating universe, their existence is untroublesome, since as the universe’s expansion slows, they will eventually be observable. However, as Wendy Freedman explained, we realize now that these galaxies are accelerating away from us, which means that they will never in principle be observable. But does that make them any less “real”? They are the aftermath of “our” Big Bang. But since they will never be observable, why is their reality more acceptable than that of galaxies in the aftermaths of other big bangs (if there are other big bangs, which we, of course, do not know)? We will only take other big bangs seriously if they are a prediction of a unified theory that gains credibility by being “battle tested” in other ways.
If there is a multiverse, it will take our Copernican demotion one stage further: our Big Bang may be one among billions. It may disappoint some physicists if some of the key numbers they are trying to explain turn out to be mere environmental contingencies. But in compensation, we would realize space and time were richly textured, but on a scale so vast that astronomers are not directly aware of it – not any more than a plankton whose “universe” was a spoonful of water would be aware of the world’s topography and biosphere.
The bedrock nature of space and time and the unification of cosmos and quantum are surely among science’s great “open frontiers.” But calling this the quest for a “theory of everything” is hubristic and misleading. It is irrelevant to 99 percent of scientists. Problems in biology and in environmental and human sciences remain unsolved because it is hard to elucidate the complexities of Darwin’s “forms most wonderful,” not because we do not understand subatomic physics well enough.
Now let’s focus back on the Earth. I have lived my life among astronomers, and I can assure you that their awareness of vast expanses of space and time does not make them more serene in everyday life. But there is one special perspective that astronomers can offer: an awareness of a vast future. The stupendous time spans of the evolutionary past are now part of common culture. But most people still somehow think that humans are the culmination of the evolutionary tree. That hardly seems credible to astronomers.
Our Sun formed 4.5 billion years ago and has 6 billion more years before its fuel runs out. It will then flare up, engulfing the inner planets. The expanding universe will continue – perhaps forever – destined to become ever colder, ever emptier. Any creatures witnessing the Sun’s demise 6 billion years hence won’t be human – they will be as different from us as we are from a bug. Posthuman evolution – here on Earth and far beyond – could be as prolonged as the Darwinian evolution that has led to us, and could be even more wonderful. And, of course, the evolution is even faster now: machines may take over.
However, even in this concertinaed timeline – extending billions of years into the future, as well as into the past – this century may be a defining moment, for good or for ill. It is the first century when complex entities – technologically empowered humans – have mapped the cosmos and have begun to understand how they emerged. But it is also the first century where one species – ours – holds the Earth’s future in its hands, and could jeopardize life’s immense potential here and far beyond.
This pale blue dot in the cosmos is a special place. It may be a unique place. And we are its stewards at a crucial era. That is a message for us all, whether we are interested in astronomy or not.
© 2014 by Richard A. Meserve, Wendy Freedman, and Martin Rees, respectivelyTo view or listen to the presentations, visit https://www.amacad.org/universe. | 0.890944 | 3.830082 |
Earth isn’t alone: The Red Planet shakes, too.
For the first time, a tremor has been detected on Mars by NASA’s InSight lander. The seismic waves, recorded on April 6, are pretty puny, equating to a magnitude 2 or 2.5 quake here on Earth, and don’t reveal much about Mars’ interior. But even the tiniest quivers on the Red Planet are big news: They suggest that Mars, like Earth, is seismically active—and here on our home planet, scientists are already eager for an encore.
“We've been waiting months for a signal like this,” InSight team member Philippe Lognonné said in a statement. “It's so exciting to finally have proof that Mars is still seismically active.”
InSight, which launched last May, first deployed its ultra-sensitive seismometer back in December. Its monitoring phase officially began several weeks ago, shortly after the lander placed a protective dome over the instrument to shield it from buffeting winds and extreme temperature fluctuations.
Before this month, the seismometer had registered a smattering of other unrelated events, like strong winds and the movements of the lander’s robotic arm. But this bout of shaking could finally be the real deal: an actual quake generated from the Red Planet’s interior.
NASA scientists are still in the midst of sussing out the exact cause of the rumbling. Here on Earth, quakes happen when tectonic plates grind up against one another. But trembles on Mars, which lacks tectonic plates, seem to have a different origin: The planet is still gradually cooling down—and temperature changes cause its rocky crust to contract and crack, resulting in occasional quivers. Quakes can also be triggered by meteors impacting Mars’ surfaces, though, and that possibility hasn’t been ruled out.
By studying Mars’ subtle shaking, researchers hope to better understand the planet’s structure and composition. Depending on the materials they pass through, seismic waves behave differently—and gathering this kind of data could help scientists figure out how Mars and other rocky bodies in our Solar System formed.
Already, the April 6 quake has stirred a bit of intrigue. It seems the tremor occurred relatively close to the lander, and lasted for more than 10 minutes—a long time for shaking that would have been pretty much imperceptible on our own planet. Protracted rumbling could indicate that the ground beneath InSight holds little water, which muffles seismic waves, or that the makeup of its soil differs vastly from what’s here on Earth.
That’s about all researchers know so far. Unfortunately, this quake wasn’t quite strong enough reveal anything deep beneath the Red Planet’s surface. But the fact that it happened at all is encouraging—simply because it’s unlikely to be a one-off event.
Plus, there are already hints of a repeat. InSight tuned into three other sets of seismic signals on March 14, April 10, and April 11. But these other potential marsquakes, which are still unconfirmed, were even smaller and more ambiguous in origin than the April 6 tremor.
The hope is that a dozen more marsquakes will occur before the lander reaches the end of its tenure. InSight is scheduled to operate for two more (Earth) years. If its solar-powered instruments continue to behave, though, that period could lengthen. “It’s a waiting game...we just have to wait until the planet cooperates,” NASA planetary scientist Amy Weber told Julia Rosen at the Los Angeles Times.
There’s no telling what’s to come—but on this foreign, distant world, every bit of information makes a difference. “[InSight is] helping paint the picture that Mars is still an active place,” Tanya Harrison, a Mars scientist at Arizona State University, told Maya Wei-Haas and Michael Greshko at National Geographic. “We’ve just been building incrementally onto this story.” | 0.800104 | 3.792492 |
MAUNA KEA, Hawaii (April 11th, 2002) Two independent teams of astronomers are presenting the discovery of new features in an edge-on disk around the nearby star Beta Pictoris at the Gillett Symposium on “Debris Disks and the Formation of Planets” in Tucson, Arizona.
Infrared images from the W. M. Keck Observatory reveal an important clue in the configuration of dust confined to a solar-system sized region close to the star: the dust orbits in a plane that is offset by approximately 14 degrees from that of the outer disk. Moreover, the offset is in the opposite direction from that of a larger scale warp detected previously by Hubble Space Telescope. This double warp is believed to be due to the presence of one or more unseen planets and constitutes one of the strongest pieces of evidence yet which links observations of circumstellar disks to the actual formation of planets.
At the Keck II telescope at Mauna Kea, Hawaii, Prof. David Koerner and graduate student Zahed Wahhaj of the University of Pennsylvania led a team of astronomers from NASA’s Jet Propulsion Laboratory (JPL), Franklin and Marshall College, and Caltech in observations of Beta Pic with MIRLIN, a mid-infrared camera from JPL (http://cougar.jpl.nasa.gov/mirlin.html). Alycia Weinberger, now at the Carnegie Institution of Washington, and Eric Becklin and Ben Zuckerman from UCLA carried out observations with the Long Wavelength Spectrometer at Keck I (LWS) (http://www2.keck.hawaii.edu:3636/realpublic/inst/lws/lws.html). Both telescopes have 10-meter (400-inch) apertures. Both MIRLIN and LWS work at wavelengths between 8 and 20 microns.
Prof. Koerner reported, “We’ve seen disk features before that could be due to planets—inner holes, narrow rings, and variations in azimuthal brightness. To date, however, most of these were discovered far outside the region where planets reside in our own solar system, and plausible non-planetary explanations have been found for some of them. In contrast, the distorted disk plane in Keck images occurs at Jovian-planet distances from the star (from 5 to 30 Astronomical Units or AU; 1 AU is the average distance between the Earth and the Sun). Moreover, no obvious explanation exists for its origin other than the gravitational influence of planets. The different inclinations of dust grain orbits around Beta Pic bear a resemblance to those of planetary orbits in our own solar system. Pluto’s orbit is inclined by 17 degrees compared to Earth’s, and Mercury’s differs by 7 degrees, for example. The new Keck images may be interpreted as circumstantial evidence for a similarly organized planetary system.”
Dr. Weinberger added, “The images show the power of large ground-based telescopes, like Keck, to reveal disk details in the hot inner portions of disks.” In addition to imaging, Weinberger and colleagues obtained spectra at different locations along the disk using the same Keck instrument (LWS). Spectroscopy spreads the disk radiation into component wavelengths, much the same way that a prism divides up visible light. The result enables astronomers to study composition as well as geometry. Weinberger’s group found that, at the position of the newly discovered warp, the disk is composed of small silicate particles that are hotter than expected. Weinberger says, “It may be that as a planet warps the disk, it also causes more collisions of rocks in its neighborhood.” The very small grains produced in collisions would tend to be hotter, at the same distance from the star, than larger dust grains. Outside the warp, in the outer part of the disk, the disk light appears to come either from larger grains or from dust that is composed of something other than silicates.
To ensure that the observed offset was not the product of optical distortion in either the atmosphere or telescope, Zahed Wahhaj carried out computer modeling of the Keck image using a disk model and images of a nearby star that were taken at the same time. His analysis provides an estimate of the uncertainty in the measured value of the offset. “We generated millions of different computer models of disks and used them to simulate images of Beta Pic as observed with the Keck telescope. Computational comparisons of the models with the images showed that the inner disk is offset from the outer disk by an angle somewhere between 10 and 18 degrees. This is in good agreement with a value between 11 and 15 degrees, as determined by the other team.”
Beta Pictoris is a young star about 20 million years old that is located 63 light years away in the constellation Pictor (the painter’s easel). The star is located too far south to be visible from the continental United States, but it can be seen in winter from Hawaii where it rises just 20 degrees above the horizon. In 1983, astronomers discovered dust radiation, first from Vega, and later from Beta Pictoris using the Infrared Astronomical Satellite (IRAS).
The Gillett Symposium commemorates Fred Gillett’s role in the discovery of the first IRAS disk detection around Vega and is being held in his memory one year after his death. Subsequent telescope observations of Beta Pic yielded the first image of a protoplanetary disk. Like all observations carried out at visible wavelengths, it required a coronagraph to block out the glare from the central star. As a consequence, the region of the disk corresponding to our solar system was not discernible for study. The human eye is insensitive to the infrared light collected in the new Keck observations of Beta Pic. The contrast between star and disk radiation is more favorable, however, so the Jovian planet region was discernible for the first time.
The W. M. Keck Observatory provides astronomers from associated institutions access to two 10-meter telescopes, the world’s largest. Each telescope features a revolutionary primary mirror composed of 36 hexagonal segments that work in concert as a single piece of reflective glass to provide unprecedented power and precision. Each telescope stands eight stories tall and weighs 300 tons, yet operates with nanometer precision. The observatory is operated by the California Association for Research in Astronomy, a partnership of the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration (NASA), which joined the partnership in October 1996. For more information, visit the W. M. Keck Observatory Web site at www.keckobservatory.org or send e-mail to: [email protected]. | 0.883921 | 3.942821 |
Radiocarbon dating — a key tool used for determining the age of prehistoric samples — is about to get a major update. For the first time in seven years, the technique is due to be recalibrated using a slew of new data from around the world. The result could have implications for the estimated ages of many finds — such as Siberia’s oldest modern human fossils, which according to the latest calibrations are 1,000 years younger than previously thought.
The work combines thousands of data points from tree rings, lake and ocean sediments, corals and stalagmites, among other features, and extends the time frame for radiocarbon dating back to 55,000 years ago — 5,000 years further than the last calibration update in 2013.
Archaeologists are downright giddy. “Maybe I’ve been in lockdown too long,” tweeted Nicholas Sutton, an archaeologist at the University of Otago in New Zealand, “but … I’m really excited about it!”
Although the recalibration mostly results in subtle changes, even tiny tweaks can make a huge difference for archaeologists and paleo-ecologists aiming to pin events to a small window of time. A new calibration curve “is of key importance” for understanding prehistory, says Tom Higham, archaeological chronologist and director of the Oxford Radiocarbon Accelerator Unit, UK.
The basis of radiocarbon dating is simple: all living things absorb carbon from the atmosphere and food sources around them, including a certain amount of natural, radioactive carbon-14. When the plant or animal dies, they stop absorbing, but the radioactive carbon that they’ve accumulated continues to decay. Measuring the amount left over gives an estimate as to how long something has been dead.
But this basic calculation assumes that the amount of carbon-14 in the environment has been constant in time and space — which it hasn’t. In recent decades, the burning of fossil fuel and tests of nuclear bombs have radically altered the amount of carbon-14 in the air, and there are non-anthropogenic wobbles going much further back. During planetary magnetic-field reversals, for example, more solar radiation enters the atmosphere, producing more carbon-14. The oceans also suck up carbon — a little more so in the Southern Hemisphere, where there is more ocean — and circulate it for centuries, further complicating things.
As a result, conversion tables are needed that match up calendar dates with radiocarbon dates in different regions. Scientists are releasing new curves for the Northern Hemisphere (IntCal20), Southern Hemisphere (SHCal20), and marine samples (MarineCal20). They will be published in the journal Radiocarbon in the next few months.
Since the 1960s, researchers have mainly done this recalibration with trees, counting annual rings to get calendar dates and matching those with measured radiocarbon dates. The oldest single tree for which this has been done, a bristlecone pine from California, was about 5,000 years old. By matching up the relative widths of rings from one tree to another, including from bogs and historic buildings, the tree record has now been pushed back to 13,910 years ago.
Since 1998 there have been four official IntCal calibrations, adding in data from laminated lake and marine sediments, cave stalagmites and corals (which can be both radiocarbon dated and independently assessed using techniques such as radioactive thorium/uranium dating). In 2018, some stalagmites in Hulu Cave in China provided a datable record stretching back 54,000 years1.
IntCal20 is based on 12,904 data points, nearly double the size of 2013’s data set. The results are far more satisfying, says Paula Reimer, who heads the IntCal working group and leads the radiocarbon-dating Chrono Centre at Queen’s University Belfast, UK. For a known, brief magnetic field reversal 40,000 years ago, for example, the 2013 curve’s carbon-14 peak was too low and too old by 500 years — an annoyance fixed by the new curve.
Higham says the recalibration is fundamental for understanding the chronology of hominins living 40,000 years ago. “I am really excited about calibrating our latest data using this curve,” he says.
Recalibrate and reassess
IntCal20 revises the date for a Homo sapiens jawbone found in Romania called Oase 1, potentially making it hundreds of years older than previously thought2. Genetic analyses of Oase 1 have revealed that it had a Neanderthal ancestor just four to six generations back, says Higham, so the older the Oase 1 date, the further back Neanderthals were living in Europe. Meanwhile, the oldest H. sapiens fossil found in Eurasia — Ust’-Ishim, unearthed in Siberia — is almost 1,000 years younger according to the new conversion curves. “It changes the earliest date we can place on modern humans in central Siberia,” says Higham. He cautions, however, that there are more sources of error in such measurements than just radiocarbon calibration: “Contamination is the biggest influence for dating really old bones like these.”
Others will use the recalibration to assess environmental events. For example, researchers have been arguing for decades over the timing of the Minoan eruption at the Greek island of Santorini. Until now, radiocarbon results typically gave a best date in the low 1600s BC, about 100 years older than given by most archaeological assessments. IntCal20 improves the accuracy of dating but makes the debate more complicated: overall, it bumps the calendar dates for the radiocarbon result about 5–15 years younger, but — because the calibration curve wiggles around a lot — it also provides six potential time windows for the eruption, most likely in the low 1600s BC, but maybe in the high 1500s BC2.
So the two groups still disagree, says Reimer, but less so, and with more complications. “Some of them are still arguing,” says Reimer. “There’s no hard answer.”
Nevertheless, anyone looking at practically anything relating to human history from the past 50,000 years will be enthusiastic about the new calibration, says Higham: “This is a particularly exciting time to be working on the past.” | 0.821852 | 3.281974 |
Owls may be scarce near your favourite viewing spot, but the Northern Hemisphere spring sky contains one celestial owl that you can track down in small telescopes – Messier 97 (NGC 3587). Commonly called the Owl Nebula, M97 is a planetary nebula discovered by Pierre Méchain in 1781 that is currently ideally placed for observation almost overhead at nightfall in the constellation of Ursa Major, the Great Bear.
Possibly as large as The Shard in London, Apollo asteroid 2017 VR12 passes just 3¾ lunar distances from Earth at 7:53am GMT on 7 March. For a few nights, this magnitude +12 space rock is a viable target for small backyard telescopes as it gallops through Coma Berenices and Virgo, passing just 0.8 degrees from Spica on the UK night of 7–8 March.
Five hundred-metre-wide asteroid 2017 CS passes just 1.9 million miles, or 7.9 lunar distances, from Earth on the afternoon of Monday 29 May 2017. For a few nights around this date, Northern Hemisphere observers with 6-inch and larger ‘scopes can see the asteroid gallop through the constellations of Canes Venatici, Boötes and Hercules at up to 14 degrees/day.
A peanut-shaped asteroid almost a mile long known as 2014 JO25 passes within 5 lunar distances of Earth on 19 April — the closest any known space rock of this size has approached our planet since September 2004. We show you how to find this fast-moving potentially hazardous asteroid in small telescopes during the UK night of 19-20 April.
The elegant simplicity of NGC 4111, seen here in this image from the NASA/ESA Hubble Space Telescope, hides a more violent history than you might think. NGC 4111 is a lenticular, or lens-shaped, galaxy, lying about 50 million light-years from us in the constellation of Canes Venatici (The Hunting Dogs).
Having brushed by bright star Arcturus on 1 January, Comet Catalina (C/2013 US10) continues its trek through the constellations of the far north. Now a circumpolar object for the British Isles, in the early hours of 17 January it lies between famous double star Mizar (ζ Ursae Majoris) and the Pinwheel Galaxy (M101), virtually overhead in the UK.
This NASA/ESA Hubble Space Telescope image shows the galaxy Messier 94, which lies in the small northern constellation of Canes Venatici (the Hunting Dogs), about 16 million light-years away. Within the bright ring or starburst ring around Messier 94, new stars are forming at a high rate and many young, bright stars are present within it.
Galactic arms, sunflowers and whirlpools are only a few examples of nature’s apparent preference for spirals. A beautiful example is Messier 63, nicknamed the Sunflower Galaxy, its winding arms shining bright due to the presence of recently formed, blue–white giant stars and clusters, readily seen in this NASA/ESA Hubble Space Telescope image. | 0.923897 | 3.533878 |
Scientists were stunned after viewing the latest images from NASA’s New Horizons spacecraft. Not only is the surface of Pluto covered in large icy mountains, low-lying hazes, and streams of frozen nitrogen – it also looks eerily like the arctic.
The photo below was taken just 15 minutes after New Horizons made its closest approach to Pluto on July 14, 2015. The spacecraft looked back toward the sun and caught this backlit panorama of Pluto’s rugged mountains and flat icy plains. The backlighting highlights over a dozen layers of haze in Pluto’s atmosphere. Trippy! 🌒
This new view offers a unique look at Pluto’s varied terrains and atmosphere. It was taken by New Horizons’ wide-angle Ralph/Multispectral Visual Imaging Camera (MVIC) on July 14 and downlinked to Earth on Sept. 13. Below is a close up of Pluto’s majestic icy mountains and flat glassy plains. It was taken at a distance of 11,000 miles.
“This image really makes you feel you are there, at Pluto, surveying the landscape for yourself,” said New Horizons Principal Investigator Alan Stern, of the Southwest Research Institute, Boulder, Colorado. “But this image is also a scientific bonanza, revealing new details about Pluto’s atmosphere, mountains, glaciers and plains.”
Let me quickly break down the geography of Pluto’s ‘heart.’ Sputnik Planum is the name of the smooth region on the left of the heart. The white upland region on the right may be coated in nitrogen ice that evaporated from the surface of Sputnik. The box shows the location of the glacier detail image below.
It’s official – the world has Pluto fever! NASA’s New Horizons spacecraft just completed its nearly decade long mission to fly by the dwarf planet Pluto. Christmas has come early for the scientific community as the exciting discoveries keep rolling in! What they’ve learned over the past week will blow your mind. 🌖🚀
Each of the Apollo missions that touched down on the Moon planted an American flag in the soil. What if, instead of planting a flag that represented our country, we planted a flag that represented our WORLD? 🌎
Oskar Pernefeldt of the Beckmans College of Design in Stockholm, Sweden, has proposed one simple blue flag to represent all of planet Earth as part of his graduation project.
Here is the symbolic explanation, according to Pernefeldt: “Centered in the flag, seven rings form a flower – a symbol of the life on Earth. The rings are linked to each other, which represents how everything on our planet, directly or indirectly, are linked. The blue field represents water which is essential for life – also as the oceans cover most of our planet’s surface. The flower’s outer rings form a circle which could be seen as a symbol of Earth as a planet and the blue surface could represent the universe.”
Pernefeldt’s flag is designed to represent planet Earth and help remind people that we all share this planet, regardless of national boundaries. I’m in love with this idea! It is part of the reason I love following the International Space Station. The ISS is one of those magical places where multiple nationalities come together to work towards a common goal, no matter what country they call home.
These photos provide a glimpse into the future if Pernefeldt’s vision ever became a reality.
Click the video below for a more detailed explanation of how the International Flag of Planet Earth was constructed.
Construction video of The International Flag of Planet Earth.
The video is a part of the graduation project by Oskar Pernefeldt, 2015. | 0.801924 | 3.03084 |
Stardome educator, Josh Kirkley, dives into the exciting topic of our search for life outside of Earth.
Earth has always been the stand out planet in our Solar System. Not only are we the only known planet with life, but we are also the only known planet to hold bodies of liquid water on the surface.…and that’s important. All living things require water. We do not know any type of life that can go without it, so it makes sense that we look for water when searching for life outside of Earth.
So far, all the other planets have shown no signs of life at all, or even large bodies of liquid water like Earth. Venus is too hot, and Mercury’s proximity to the Sun sterilises the planet with high doses of radiation. The gas giants have no solid surface, let alone any water, so it’s highly unlikely they harbour any type of life. Billions of years ago, Mars did have oceans and possibly even life, but not anymore. Today it’s a cold desert that lost its oceans when they evaporated into space. We only see tiny quantities of flowing water down the side of craters during the summer months, but it’s still very little. It holds some water at its poles and in frozen quantities underground, but it’s unlikely that any significant kind of life could thrive in this hostile environment today.
These factors make Earth look like the only planet in our Solar System that has life. But planets are not the only places we look for life anymore. Within the last few decades, scientists have been turning their eyes to some even more fascinating worlds than the planets; their moons.
Europa – Water world of our Solar System.
Europa, an icy moon of Jupiter, was first observed by Galileo Galilei in 1610. We knew nothing about this moon until the Pioneer missions in the 70’s provided us with our first grainy images of the surface. The Voyager missions followed in the 80’s, sending us our first clear images of Europa’s surface and leading scientists to speculate that an ocean could be hidden beneath the icy shell.
In the 90’s, NASA followed up on this speculation, sending the Galileo mission to Jupiter. The spacecraft made several close fly-bys of Europa and gave us much of the information we know about the moon today. It heralded some amazing results by scanning the surface in incredible detail and revealing a moon that is covered in a criss-cross of lines and cracks. Much to our surprise, we also discovered that Europa is almost completely crater-free with the smoothest surface of anybody in our SolarSystem.
The discovery revealed that Europa has a young surface, indicating that something geological was occurring beneath the surface. NASA observed Europa in 2012 with the Hubble telescope and it captured what appeared to be jets of water spraying out into space from the poles. Further observations in 2016 confirmed this discovery, and we now know that Europa does indeed hold a huge ocean of water beneath its surface. So much so, it is believed that Europa holds twice as much liquid water as Earth!
Alien life – What could be down there?
So, if Europa does have an ocean, does it have life? A question scientists have been asking for years. This far-out world may very well be the first place we discover alien life. It is hard to think of what life on Europa may look like but we can get some ideas by looking at Earth life. In the depths of Earth’s ocean trenches, we find some of the strangest beings on our planet. Fish that glow, squid with huge eyes, and aquatic beings that seem to be the stuff of science fiction. As scary as deep ocean life on Earth appears, they are a good indication of what life on Europa may look like.
Light does not penetrate very far down into our oceans and the majority of Earth’s seafloor is pitch black. Creatures have learnt to live in this hostile environment, adapting to their surroundings over millennia through evolution. Some have learnt the trick of bioluminescence, creating their own artificial light to draw in potential prey for a meal without the help of sunlight. Europa’s oceans are likely to be very dark too. It’s unlikely that sunlight is able to pass through the icy crust.
If life does exist on Europa, it is plausible that they may resemble deep sea creatures here on Earth. Maybe we will find squid-like creatures that have also learnt how to harness bioluminescence in their favour. We won’t really know until we go there. Both NASA and ESA are developing plans to explore Europa in the 2020s and into the 2030s. Some of these missions may even carry a lander that could drill down into the surface and dive into the ocean beneath. It’s a tantalising thought wondering what these future missions may hold, but until then, we wait. | 0.871433 | 3.364081 |
eso1147 — Naučno saopštenje
VLT Finds Fastest Rotating Star
5. decembar 2011.
ESO's Very Large Telescope has picked up the fastest rotating star found so far. This massive bright young star lies in our neighbouring galaxy, the Large Magellanic Cloud, about 160 000 light-years from Earth. Astronomers think that it may have had a violent past and has been ejected from a double star system by its exploding companion.
An international team of astronomers has been using ESO’s Very Large Telescope at the Paranal Observatory in Chile, to make a survey of the heaviest and brightest stars in the Tarantula Nebula (eso1117), in the Large Magellanic Cloud. Among the many brilliant stars in this stellar nursery the team has spotted one, called VFTS 102 , that is rotating at more than two million kilometres per hour — more than three hundred times faster than the Sun and very close to the point at which it would be torn apart due to centrifugal forces. VFTS 102 is the fastest rotating star known to date .
The astronomers also found that the star, which is around 25 times the mass of the Sun and about one hundred thousand times brighter, was moving through space at a significantly different speed from its neighbours .
“The remarkable rotation speed and the unusual motion compared to the surrounding stars led us to wonder if this star had had an unusual early life. We were suspicious.” explains Philip Dufton (Queen’s University Belfast, Northern Ireland, UK), lead author of the paper presenting the results.
This difference in speed could imply that VFTS 102 is a runaway star — a star that has been ejected from a double star system after its companion exploded as a supernova. This idea is supported by two further clues: a pulsar and an associated supernova remnant in its vicinity .
The team has developed a possible back story for this very unusual star. It could have started life as one component of a binary star system. If the two stars were close, gas from the companion could have streamed over and in the process the star would have spun faster and faster. This would explain one unusual fact — why it is rotating so fast. After a short lifetime of about ten million years, the massive companion would have exploded as a supernova — which could explain the characteristic gas cloud known as a supernova remnant found nearby. The explosion would also have led to the ejection of the star and could explain the third anomaly — the difference between its speed and that of other stars in the region. As it collapsed, the massive companion would have turned into the pulsar that is observed today, and which completes the solution to the puzzle.
Although the astronomers cannot yet be sure that this is exactly what happened, Dufton concludes “This is a compelling story because it explains each of the unusual features that we’ve seen. This star is certainly showing us unexpected sides of the short, but dramatic lives of the heaviest stars.”
Some stars end their lives as compact objects such as pulsars (see note ), which may spin much more rapidly than VFTS 102, but they are also very much smaller and denser and do not shine by thermonuclear reactions like normal stars.
Pulsars are the result of supernovae. The core of the star collapses to a very small size creating a neutron star which spins very rapidly and emits powerful jets of radiation. These jets create a regular “pulse” as seen from Earth as the star rotates around its axis. The associated supernova remnant is a characteristic cloud of gas blown away by the shock wave resulting from the collapse of the star into a neutron star.
This research was presented in a paper in the Astrophysical Journal Letters, “The VLT-FLAMES Tarantula Survey: The fastest rotating O-type star and shortest period LMC pulsar — remnants of a supernova disrupted binary?”, by Philip L. Dufton et al.
The team is composed of P.L. Dufton (Astrophysics Research Centre, Queen’s University Belfast (ARC/QUB), UK), P.R. Dunstall (ARC/QUB, UK), C.J. Evans (UK Astronomy Technology Centre, Royal Observatory Edinburgh (ROE), UK), I. Brott (University of Vienna, Department of Astronomy, Austria), M. Cantiello (Argelander Institut fur Astronomie der Universitat Bonn, Germany, Kavli Institute for Theoretical Physics, University of California, USA), A. de Koter (Astronomical Institute ‘Anton Pannekoek’, University of Amsterdam, The Netherlands), S.E. de Mink (Space Telescope Science Institute, USA), M. Fraser (ARC/QUB, UK), V. Henault-Brunet (Scottish Universities Physics Alliance (SUPA), Institute for Astronomy, University of Edinburgh, ROE, UK), I.D. Howarth (Department of Physics & Astronomy, University College London, UK), N. Langer (Argelander Institut fur Astronomie der Universitat Bonn, Germany), D.J. Lennon (ESA, Space Telescope Science Institute, USA), N. Markova (Institute of Astronomy with NAO, Bulgaria), H. Sana (Astronomical Institute ‘Anton Pannekoek’, University of Amsterdam, The Netherlands), W.D. Taylor (SUPA, Institute for Astronomy, University of Edinburgh, ROE, UK).
ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 40-metre-class European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Queen's University of Belfast
Tel.: +44 028 9097 3552
ESO, La Silla, Paranal, E-ELT & Survey Telescopes Press Officer
Garching bei München, Germany
Tel.: +49 89 3200 6655
Mob.: +49 151 1537 3591 | 0.86294 | 3.843673 |
Europa is the best bet for finding alien life in the solar system. Mounds of visual evidence suggest that Jupiter's fourth-largest moon has a subterranean ocean with at least twice the amount of liquid water as Earth's oceans. Likely geysers have been spotted spouting from the surface of the moon. What's more, Europa—along with Saturn's moon Enceladus—is thought to have a rocky core, creating an ocean floor for the subsurface water that could provide minerals and salty compounds critical to life. Hydrothermal vents, like those in the deepest parts of Earth's oceans, could provide sustenance and warmth for alien microbes, and possibly even tube worms, crabs or fish.
All this makes Europa an obvious target for exploration, and you better believe we're going. A flyby mission is already in the works, targeting a launch in the early 2020s, and topographic data from that mission will be used to pick a landing site—a landing site for the spacecraft NASA just detailed in a preliminary study called a Science Definition Team (SDT) report.
From the SDT report:
Europa may hold the clues to one of NASA's long standing goals – to determine whether or not we are alone in the universe. The highest-level science goal of the mission presented here is to search for evidence of life on Europa.
The mission, as outlined in the report, has two primary goals in addition to searching for life on Europa. The first is to analyze the surface composition, and the second is to characterize both the surface and subsurface conditions to determine the viability of a future mission to tunnel into the subterranean ocean and explore it directly.
Because Europa has no atmosphere, a heat shield would not be required for the lander, but that also means a parachute would do no good in slowing the craft for a soft landing. The SDT report suggests using retrorockets on a sky crane tethered to the lander to place the probe on the surface, similar to the method used to land Curiosity on Mars. The probe would then function for 20+ days on battery power, taking at least five samples to be analyzed by its science instruments during that time. The lander's mothership would enter orbit around Europa after depositing the probe and serve as a communication relay to transmit data back to Earth.
The report outlines three primary science instruments to search for life in samples taken from the surface of Europa. The first is an Organic Compositional Analyzer (OCA) with a Gas Chromatograph-Mass Spectrometer (GC-MS) that would analyze the electromagnetic spectrum of sample material to identify organic compounds. The second is a Microscope for Life Detection (MLD) "capable of distinguishing microbial cells as small as 0.2 microns in diameter, and as dilute as 100 cells per cubic centimeter (cc, or equivalently 1 mL) of ice." The third is a Vibrational Spectrometer (VS) that uses UV light to distinguish between organic and inorganic compounds "down to a level of parts per thousand by mass."
The spacecraft would also use a number of mechanical components to acquire the samples for analysis. A robotic arm, sample excavation tool, sample collection device, and sample transfer mechanisms deposit the material to the primary science instruments, which are housed within the spacecraft for radiation shielding.
NASA has scheduled two town hall meetings, on March 19 and April 23, to receive feedback on the SDT report from the science community at large. The team reports that the Europa lander mission "could be launched as early as 2024," but that seems optimistic considering the mission depends on data from the Europa flyby spacecraft that has yet to be launched, and the lander team plans to use NASA's SLS rocket, also still in development.
Such an ambitious target launch date is nevertheless encouraging, suggesting that the research team feels confident the necessary technology for the mission is already available—it's just a matter of signing off on the bill and pulling all the components together. Considering it was a congressional directive that spurred NASA to fund this report in the first place, it seems likely that Washington will be open to funding a Europa lander, and funding it sooner rather than later.
If there is alien life in this solar system, we are going to find it. | 0.860743 | 3.700006 |
Barreling in from space at 13,000 mph before stopping a mere 25 feet above the ground would make anyone want to catch their breath, and NASA’s Curiosity rover is no exception. Now that the “Seven Minutes of Terror” is over, the compact-car-sized biochemistry lab is spending its first two weeks doing the same thing you might do after stepping off a hair-raising roller coaster: making sure its parts are where they’re supposed to be and functioning correctly.
That means daily surprises, as technicians at the Jet Propulsion Laboratory in La Canada Flintridge, Calif., raise antennas, activate cameras, and gradually bring systems on line. Among the early treats: 297 black-and-white thumbnail pictures, which NASA processed into a low-quality video showing the final two-and-a-half minutes of Curiosity’s stomach-churning plunge through the Martian atmosphere. The thumbnails, though grainy, show the protective heat shield dropping away, the bumps from the rover’s parachute descent, and dust kicking up as cables lowered the rover to the Martian surface. Scientists expect to have a full-resolution video from Curiosity’s descent imager in a few days.
The rover also sent a new postcard: the first full-color landscape image of Curiosity’s Gale Crater home, taken as part of a focus test to check one of the cameras mounted on the rover’s mast. Until this week the camera, called the Mars Hand Lens Imager (MAHLI), hadn’t moved its focal components since July 2011—four months before Curiosity launched. Even now, with the mast still tucked horizontally atop the rover’s front left shoulder, the camera’s initial focus test offers a tempting glimpse of the north wall of the rim at Gale Crater.
But that’s just a small taste of what this particular camera, one of 17 aboard Curiosity, will provide once the mast is lifted and extended, especially once the camera’s clear dust covers lift away. “It’s so awesome because we can put this camera anywhere,” says Ken Edgett of Malin Space Science Systems in San Diego, which operates the camera. “Up, down, within an inch of the soil, underneath the rover, anywhere. It’ll extend up above the mast to give us the giraffe’s-eye view, or give us the oblique, dog’s-eye view across the Martian surface. This camera can look wherever we want.”
Many of this week’s most captivating images haven’t come from Curiosity but a high-resolution camera aboard the Mars Reconnaissance Orbiter, another player on NASA’s robotic exploration team. One day after capturing a stunning shot of Curiosity parachuting towards Martian surface, the Orbiter executed an unusual 41-degree roll to deliver a fascinating “crime scene” image taken by a high-resolution camera aboard the Mars Reconnaissance Orbiter some 186 miles above the surface. The view offers a look at the pimple-sized rover in relation to the locations where Curiosity’s heat shield, parachute, back shell, and ballyhooed sky crane crash-landed after dropping away from the rover during its descent.
(Cover Story: Live From Mars)
Simply put, they’re all in the same Gale Crater neighborhood. The heat shield is farthest from Curiosity, about three-quarters of a mile away. Both the back shell and sky crane wound up about four-tenths of a mile from the rover. Of particular visual interest is a jagged pattern in the Martian soil to one side of the downed sky crane. “Those dark areas downrange are the disturbed dust,” says Sarah Milkovich, a JPL scientist. “It’s the same pattern we see when we have meteorites forming impact craters on the surface of a planetary body.” Since the impacts from the spacecraft’s components kicked up plenty of dust as well, Milkovich says future images should have even greater resolution. The Orbiter will again aim its cameras at Gale Crater in a few days, possibly for color photos.
All of this is just prep work, however. In the coming two weeks, JPL engineers will conduct numerous systems checks while the science team decides where, if anywhere, they want to go. “It’s designed as a go-to mission, but the place where we landed looks really interesting,” says project scientist John Grotzinger. “We have millions of years of Mars history to sample, and it starts where we landed, so we don’t really want to roll out of there.” One reason scientists chose to land at Gale Crater is the fact it’s surface soil is part of what geologists call an alluvial fan, meaning it’s the site where ancient water shed debris from the crater’s rim and nearby Mount Sharp. “It could be a jackpot,” Grotzinger says. “We studied Mount Sharp first, but now that we’re starting in on the ellipse we’re realizing this place is awesome.”
But even interplanetary rovers in awesome locations have to tackle mundane chores, and Curiosity’s turn begins this weekend when the rover waits for a software upgrade. Much like we change operating systems on a home PC, Curiosity will spend parts of four days upgrading its dual computers. There are no Lions or Windows on Mars, however. Curiosity is switching from the blandly named R9 operating system to, yes, the R10. The upgrade removes much of the computer’s entry, descent and landing functions, which are no longer needed, and replaces them with software for controlling the robotic arm and sample analysis. “Once we get on that new OS we can start flexing our arm and checking the surface,” says mission manager Michael Watkins. No connection speed issues for Curiosity’s upgrade; the rover already downloaded the new software while en route to Mars.
Curiosity may also begin rolling next week, but not far. “We’ll probably do a ‘test bump’ with some wheel rotation,” Watkins says. The wheels won’t move much—maybe one full rotation, which amounts to no more than three feet of movement. It’s all part of the “slow and go” mantra that scientists say is a luxury they’ve never had during a Mars mission. “It’s a learning experience for us too,” says Watkins. “In the meetings we’re always thinking we need to go fast because with the other rovers we had tasks we tried to get to right away. But this time we’re saying from the start, ‘we’ve got two years, let’s use that rover to our full capability.'”
Or as Edgett says, “it’s going to go on, and on, and on.” He means it as a joke, but there’s at least a chance that he’s right, and that Curiosity will continue throwing treats our way for years to come. | 0.862424 | 3.310163 |
|Discovered by||Galileo Galilei|
|Discovery date||8 January 1610|
|Pronunciation||// or as Greco-Latin Īō (approximated as //)|
|Periapsis||420000 km (0.002807 AU)|
|Apoapsis||423400 km (0.002830 AU)|
Mean orbit radius
|421700 km (0.002819 AU)|
|1.769137786 d (152853.5047 s, 42.45930686 h)|
Average orbital speed
|Inclination||0.05° (to Jupiter's equator)|
2.213° (to the ecliptic)
|Dimensions||3,660.0 × 3,637.4 × 3,630.6 km|
|1821.6±0.5 km (0.286 Earths)|
|41910000 km2 (0.082 Earths)|
|Volume||2.53×1010 km3 (0.023 Earths)|
|Mass||(8.931938±0.000018)×1022 kg (0.015 Earths)|
|1.796 m/s2 (0.183 g)|
Equatorial rotation velocity
|5 to 40 nbar|
|Composition by volume||90% sulfur dioxide|
Io //, or Jupiter I, is the innermost and third-largest of the four Galilean moons of the planet Jupiter. It is the fourth-largest moon in the solar system, has the highest density of all of them, and has the lowest amount of water (by atomic ratio) of any known astronomical object in the Solar System. It was discovered in 1610 by Galileo Galilei and was named after the mythological character Io, a priestess of Hera who became one of Zeus's lovers.
With over 400 active volcanoes, Io is the most geologically active object in the Solar System. This extreme geologic activity is the result of tidal heating from friction generated within Io's interior as it is pulled between Jupiter and the other Galilean satellites—Europa, Ganymede and Callisto. Several volcanoes produce plumes of sulfur and sulfur dioxide that climb as high as 500 km (300 mi) above the surface. Io's surface is also dotted with more than 100 mountains that have been uplifted by extensive compression at the base of Io's silicate crust. Some of these peaks are taller than Mount Everest, the highest point on Earth's surface. Unlike most satellites in the outer Solar System, which are mostly composed of water ice, Io is primarily composed of silicate rock surrounding a molten iron or iron sulfide core. Most of Io's surface is composed of extensive plains coated with sulfur and sulfur dioxide frost.
Io's volcanism is responsible for many of its unique features. Its volcanic plumes and lava flows produce large surface changes and paint the surface in various subtle shades of yellow, red, white, black, and green, largely due to allotropes and compounds of sulfur. Numerous extensive lava flows, several more than 500 km (300 mi) in length, also mark the surface. The materials produced by this volcanism make up Io's thin, patchy atmosphere and Jupiter's extensive magnetosphere. Io's volcanic ejecta also produce a large plasma torus around Jupiter.
Io played a significant role in the development of astronomy in the 17th and 18th centuries. It was discovered in January 1610 by Galileo Galilei, along with the other Galilean satellites. This discovery furthered the adoption of the Copernican model of the Solar System, the development of Kepler's laws of motion, and the first measurement of the speed of light. From Earth, Io remained just a point of light until the late 19th and early 20th centuries, when it became possible to resolve its large-scale surface features, such as the dark red polar and bright equatorial regions. In 1979, the two Voyager spacecraft revealed Io to be a geologically active world, with numerous volcanic features, large mountains, and a young surface with no obvious impact craters. The Galileo spacecraft performed several close flybys in the 1990s and early 2000s, obtaining data about Io's interior structure and surface composition. These spacecraft also revealed the relationship between Io and Jupiter's magnetosphere and the existence of a belt of high-energy radiation centered on Io's orbit. Io receives about 3,600 rem (36 Sv) of ionizing radiation per day.
Although Simon Marius is not credited with the sole discovery of the Galilean satellites, his names for the moons were adopted. In his 1614 publication Mundus Iovialis anno M.DC.IX Detectus Ope Perspicilli Belgici, he proposed several alternative names for the innermost of the large moons of Jupiter, including "The Mercury of Jupiter" and "The First of the Jovian Planets". Based on a suggestion from Johannes Kepler in October 1613, he also devised a naming scheme whereby each moon was named for a lover of the Greek mythological Zeus or his Roman equivalent, Jupiter. He named the innermost large moon of Jupiter after the Greek mythological figure Io. Marius's names were not widely adopted until centuries later (mid-20th century). In much of the earlier astronomical literature, Io was generally referred to by its Roman numeral designation (a system introduced by Galileo) as "Jupiter I", or as "the first satellite of Jupiter".
The customary English pronunciation of the name is //, though sometimes people attempt a more 'authenic' pronunciation, //. The name has two competing stems in Latin: Īō and (rarely) Īōn. The latter is the basis of the English adjectival form, Ionian.
Features on Io are named after characters and places from the Io myth, as well as deities of fire, volcanoes, the Sun, and thunder from various myths, and characters and places from Dante's Inferno: names appropriate to the volcanic nature of the surface. Since the surface was first seen up close by Voyager 1, the International Astronomical Union has approved 225 names for Io's volcanoes, mountains, plateaus, and large albedo features. The approved feature categories used for Io for different types of volcanic features include patera ("saucer"; volcanic depression), fluctus ("flow"; lava flow), vallis ("valley"; lava channel), and active eruptive center (location where plume activity was the first sign of volcanic activity at a particular volcano). Named mountains, plateaus, layered terrain, and shield volcanoes include the terms mons, mensa ("table"), planum, and tholus ("rotunda"), respectively. Named, bright albedo regions use the term regio. Examples of named features are Prometheus, Pan Mensa, Tvashtar Paterae, and Tsũi Goab Fluctus.
The first reported observation of Io was made by Galileo Galilei on 7 January 1610 using a 20x-power, refracting telescope at the University of Padua. However, in that observation, Galileo could not separate Io and Europa due to the low power of his telescope, so the two were recorded as a single point of light. Io and Europa were seen for the first time as separate bodies during Galileo's observations of the Jovian system the following day, 8 January 1610 (used as the discovery date for Io by the IAU). The discovery of Io and the other Galilean satellites of Jupiter was published in Galileo's Sidereus Nuncius in March 1610. In his Mundus Jovialis, published in 1614, Simon Marius claimed to have discovered Io and the other moons of Jupiter in 1609, one week before Galileo's discovery. Galileo doubted this claim and dismissed the work of Marius as plagiarism. Regardless, Marius's first recorded observation came from 29 December 1609 in the Julian calendar, which equates to 8 January 1610 in the Gregorian calendar, which Galileo used. Given that Galileo published his work before Marius, Galileo is credited with the discovery.
For the next two and a half centuries, Io remained an unresolved, 5th-magnitude point of light in astronomers' telescopes. During the 17th century, Io and the other Galilean satellites served a variety of purposes, including early methods to determine longitude, validating Kepler's third law of planetary motion, and determining the time required for light to travel between Jupiter and Earth. Based on ephemerides produced by astronomer Giovanni Cassini and others, Pierre-Simon Laplace created a mathematical theory to explain the resonant orbits of Io, Europa, and Ganymede. This resonance was later found to have a profound effect on the geologies of the three moons.
Improved telescope technology in the late 19th and 20th centuries allowed astronomers to resolve (that is, see as distinct objects) large-scale surface features on Io. In the 1890s, Edward E. Barnard was the first to observe variations in Io's brightness between its equatorial and polar regions, correctly determining that this was due to differences in color and albedo between the two regions and not due to Io being egg-shaped, as proposed at the time by fellow astronomer William Pickering, or two separate objects, as initially proposed by Barnard. Later telescopic observations confirmed Io's distinct reddish-brown polar regions and yellow-white equatorial band.
Telescopic observations in the mid-20th century began to hint at Io's unusual nature. Spectroscopic observations suggested that Io's surface was devoid of water ice (a substance found to be plentiful on the other Galilean satellites). The same observations suggested a surface dominated by evaporates composed of sodium salts and sulfur. Radiotelescopic observations revealed Io's influence on the Jovian magnetosphere, as demonstrated by decametric wavelength bursts tied to the orbital period of Io.
The first spacecraft to pass by Io were the Pioneer 10 and 11 probes on 3 December 1973 and 2 December 1974, respectively. Radio tracking provided an improved estimate of Io's mass, which, along with the best available information of its size, suggested it had the highest density of the Galilean satellites, and was composed primarily of silicate rock rather than water ice. The Pioneers also revealed the presence of a thin atmosphere and intense radiation belts near the orbit of Io. The camera on board Pioneer 11 took the only good image of the moon obtained by either spacecraft, showing its north polar region. Close-up images were planned during Pioneer 10's encounter, but those were lost because of the high-radiation environment.
When the twin probes Voyager 1 and Voyager 2 passed by Io in 1979, their more advanced imaging system allowed for far more detailed images. Voyager 1 flew past Io on 5 March 1979 from a distance of 20,600 km (12,800 mi). The images returned during the approach revealed a strange, multi-colored landscape devoid of impact craters. The highest-resolution images showed a relatively young surface punctuated by oddly shaped pits, mountains taller than Mount Everest, and features resembling volcanic lava flows.
Shortly after the encounter, Voyager navigation engineer Linda A. Morabito noticed a plume emanating from the surface in one of the images. Analysis of other Voyager 1 images showed nine such plumes scattered across the surface, proving that Io was volcanically active. This conclusion was predicted in a paper published shortly before the Voyager 1 encounter by Stan Peale, Patrick Cassen, and R. T. Reynolds. The authors calculated that Io's interior must experience significant tidal heating caused by its orbital resonance with Europa and Ganymede (see the "Tidal heating" section for a more detailed explanation of the process). Data from this flyby showed that the surface of Io is dominated by sulfur and sulfur dioxide frosts. These compounds also dominate its thin atmosphere and the torus of plasma centered on Io's orbit (also discovered by Voyager).
Voyager 2 passed Io on 9 July 1979 at a distance of 1,130,000 km (700,000 mi). Though it did not approach nearly as close as Voyager 1, comparisons between images taken by the two spacecraft showed several surface changes that had occurred in the four months between the encounters. In addition, observations of Io as a crescent as Voyager 2 departed the Jovian system revealed that seven of the nine plumes observed in March were still active in July 1979, with only the volcano Pele shutting down between flybys.
The Galileo spacecraft arrived at Jupiter in 1995 after a six-year journey from Earth to follow up on the discoveries of the two Voyager probes and ground-based observations taken in the intervening years. Io's location within one of Jupiter's most intense radiation belts precluded a prolonged close flyby, but Galileo did pass close by shortly before entering orbit for its two-year, primary mission studying the Jovian system. Although no images were taken during the close flyby on 7 December 1995, the encounter did yield significant results, such as the discovery of a large iron core, similar to that found in the rocky planets of the inner Solar System.
Despite the lack of close-up imaging and mechanical problems that greatly restricted the amount of data returned, several significant discoveries were made during Galileo's primary mission. Galileo observed the effects of a major eruption at Pillan Patera and confirmed that volcanic eruptions are composed of silicate magmas with magnesium-rich mafic and ultramafic compositions. Distant imaging of Io was acquired for almost every orbit during the primary mission, revealing large numbers of active volcanoes (both thermal emission from cooling magma on the surface and volcanic plumes), numerous mountains with widely varying morphologies, and several surface changes that had taken place both between the Voyager and Galileo eras and between Galileo orbits.
The Galileo mission was twice extended, in 1997 and 2000. During these extended missions, the probe flew by Io three times in late 1999 and early 2000 and three times in late 2001 and early 2002. Observations during these encounters revealed the geologic processes occurring at Io's volcanoes and mountains, excluded the presence of a magnetic field, and demonstrated the extent of volcanic activity. In December 2000, the Cassini spacecraft had a distant and brief encounter with the Jovian system en route to Saturn, allowing for joint observations with Galileo. These observations revealed a new plume at Tvashtar Paterae and provided insights into Io's aurorae.
Following Galileo's planned destruction in Jupiter's atmosphere in September 2003, new observations of Io's volcanism came from Earth-based telescopes. In particular, adaptive optics imaging from the Keck telescope in Hawaii and imaging from the Hubble telescope have allowed astronomers to monitor Io's active volcanoes. This imaging has allowed scientists to monitor volcanic activity on Io, even without a spacecraft in the Jovian system.
The New Horizons spacecraft, en route to Pluto and the Kuiper belt, flew by the Jovian system and Io on 28 February 2007. During the encounter, numerous distant observations of Io were obtained. These included images of a large plume at Tvashtar, providing the first detailed observations of the largest class of Ionian volcanic plume since observations of Pele's plume in 1979. New Horizons also captured images of a volcano near Girru Patera in the early stages of an eruption, and several volcanic eruptions that have occurred since Galileo.
The Juno spacecraft was launched in 2011 and entered orbit around Jupiter on July 5, 2016. Juno's mission is primarily focused on improving our understanding of planet's interior, magnetic field, aurorae, and polar atmosphere. Juno's orbit is highly inclined and highly eccentric in order to better characterize Jupiter's polar regions and to limit its exposure to the planet's harsh inner radiation belts. This orbit also keeps Juno out of the orbital planes of Io and the other major moons of Jupiter. Juno's closest approach to Io occurs during Perijove 25 on February 17, 2020, at a distance of 195,000 kilometers. During several orbits, Juno has observed Io from a distance using JunoCAM, a wide-angle, visible-light camera, to look for volcanic plumes and JIRAM, a near-infrared spectrometer and imager, to monitor thermal emission from Io's volcanoes.
There are two forthcoming missions planned for the Jovian system. The Jupiter Icy Moon Explorer (JUICE) is a planned European Space Agency mission to the Jovian system that is intended to end up in Ganymede orbit. JUICE has a launch scheduled for 2022, with arrival at Jupiter planned for October 2029. JUICE will not fly by Io, but it will use its instruments, such as a narrow-angle camera, to monitor Io's volcanic activity and measure its surface composition during the two-year Jupiter-tour phase of the mission prior to Ganymede orbit insertion. Europa Clipper is a planned NASA mission to the Jovian system focused on Jupiter's moon Europa. Like JUICE, Europa Clipper will not perform any flybys of Io, but distant volcano monitoring is likely. Europa Clipper has a planned launch in 2025 with an arrival at Jupiter in the late 2020s or early 2030s, depending on launch vehicle.
The Io Volcano Observer (IVO) is a proposal to NASA, currently in Phase A, for a low-cost, Discovery-class mission that would launch in 2026 or 2028. It would perform ten flybys of Io while in orbit around Jupiter beginning in the early 2030s.
Orbit and rotation
Io orbits Jupiter at a distance of 421,700 km (262,000 mi) from Jupiter's center and 350,000 km (217,000 mi) from its cloudtops. It is the innermost of the Galilean satellites of Jupiter, its orbit lying between those of Thebe and Europa. Including Jupiter's inner satellites, Io is the fifth moon out from Jupiter. It takes Io about 42.5 hours to complete one orbit around Jupiter (fast enough for its motion to be observed over a single night of observation). Io is in a 2:1 mean-motion orbital resonance with Europa and a 4:1 mean-motion orbital resonance with Ganymede, completing two orbits of Jupiter for every one orbit completed by Europa, and four orbits for every one completed by Ganymede. This resonance helps maintain Io's orbital eccentricity (0.0041), which in turn provides the primary heating source for its geologic activity. Without this forced eccentricity, Io's orbit would circularize through tidal dissipation, leading to a geologically less active world.
Like the other Galilean satellites and the Moon, Io rotates synchronously with its orbital period, keeping one face nearly pointed toward Jupiter. This synchrony provides the definition for Io's longitude system. Io's prime meridian intersects the equator at the sub-Jovian point. The side of Io that always faces Jupiter is known as the subjovian hemisphere, whereas the side that always faces away is known as the antijovian hemisphere. The side of Io that always faces in the direction that Io travels in its orbit is known as the leading hemisphere, whereas the side that always faces in the opposite direction is known as the trailing hemisphere.
From the surface of Io, Jupiter would subtend an arc of 19.5°, making Jupiter appear 39 times the apparent diameter of Earth's Moon.
Interaction with Jupiter's magnetosphere
Io plays a significant role in shaping Jupiter's magnetic field, acting as an electric generator that can develop 400,000 volts across itself and create an electric current of 3 million amperes, releasing ions that give Jupiter a magnetic field inflated to more than twice the size it would otherwise have. The magnetosphere of Jupiter sweeps up gases and dust from Io's thin atmosphere at a rate of 1 tonne per second. This material is mostly composed of ionized and atomic sulfur, oxygen and chlorine; atomic sodium and potassium; molecular sulfur dioxide and sulfur; and sodium chloride dust. These materials originate from Io's volcanic activity, but the material that escapes to Jupiter's magnetic field and into interplanetary space comes directly from Io's atmosphere. These materials, depending on their ionized state and composition, end up in various neutral (non-ionized) clouds and radiation belts in Jupiter's magnetosphere and, in some cases, are eventually ejected from the Jovian system.
Surrounding Io (at a distance of up to six Io radii from its surface) is a cloud of neutral sulfur, oxygen, sodium, and potassium atoms. These particles originate in Io's upper atmosphere and are excited by collisions with ions in the plasma torus (discussed below) and by other processes into filling Io's Hill sphere, which is the region where Io's gravity is dominant over Jupiter's. Some of this material escapes Io's gravitational pull and goes into orbit around Jupiter. Over a 20-hour period, these particles spread out from Io to form a banana-shaped, neutral cloud that can reach as far as six Jovian radii from Io, either inside Io's orbit and ahead of it or outside Io's orbit and behind it. The collision process that excites these particles also occasionally provides sodium ions in the plasma torus with an electron, removing those new "fast" neutrals from the torus. These particles retain their velocity (70 km/s, compared to the 17 km/s orbital velocity at Io), and are thus ejected in jets leading away from Io.
Io orbits within a belt of intense radiation known as the Io plasma torus. The plasma in this doughnut-shaped ring of ionized sulfur, oxygen, sodium, and chlorine originates when neutral atoms in the "cloud" surrounding Io are ionized and carried along by the Jovian magnetosphere. Unlike the particles in the neutral cloud, these particles co-rotate with Jupiter's magnetosphere, revolving around Jupiter at 74 km/s. Like the rest of Jupiter's magnetic field, the plasma torus is tilted with respect to Jupiter's equator (and Io's orbital plane), so that Io is at times below and at other times above the core of the plasma torus. As noted above, these ions' higher velocity and energy levels are partly responsible for the removal of neutral atoms and molecules from Io's atmosphere and more extended neutral cloud. The torus is composed of three sections: an outer, "warm" torus that resides just outside Io's orbit; a vertically extended region known as the "ribbon", composed of the neutral source region and cooling plasma, located at around Io's distance from Jupiter; and an inner, "cold" torus, composed of particles that are slowly spiraling in toward Jupiter. After residing an average of 40 days in the torus, particles in the "warm" torus escape and are partially responsible for Jupiter's unusually large magnetosphere, their outward pressure inflating it from within. Particles from Io, detected as variations in magnetospheric plasma, have been detected far into the long magnetotail by New Horizons. To study similar variations within the plasma torus, researchers measure the ultraviolet light it emits. Although such variations have not been definitively linked to variations in Io's volcanic activity (the ultimate source for material in the plasma torus), this link has been established in the neutral sodium cloud.
During an encounter with Jupiter in 1992, the Ulysses spacecraft detected a stream of dust-sized particles being ejected from the Jovian system. The dust in these discrete streams travels away from Jupiter at speeds upwards of several hundred kilometres per second, has an average particle size of 10 μm, and consists primarily of sodium chloride. Dust measurements by Galileo showed that these dust streams originate from Io, but exactly how these form, whether from Io's volcanic activity or material removed from the surface, is unknown.
Jupiter's magnetic field, which Io crosses, couples Io's atmosphere and neutral cloud to Jupiter's polar upper atmosphere by generating an electric current known as the Io flux tube. This current produces an auroral glow in Jupiter's polar regions known as the Io footprint, as well as aurorae in Io's atmosphere. Particles from this auroral interaction darken the Jovian polar regions at visible wavelengths. The location of Io and its auroral footprint with respect to Earth and Jupiter has a strong influence on Jovian radio emissions from our vantage point: when Io is visible, radio signals from Jupiter increase considerably. The Juno mission, currently in orbit around Jupiter, should help to shed light on these processes. The Jovian magnetic field lines that do get past Io's ionosphere also induce an electric current, which in turn creates an induced magnetic field within Io's interior. Io's induced magnetic field is thought to be generated within a partially molten, silicate magma ocean 50 kilometers beneath Io's surface. Similar induced fields were found at the other Galilean satellites by Galileo, generated within liquid water oceans in the interiors of those moons.
Io is slightly larger than Earth's Moon. It has a mean radius of 1,821.3 km (1,131.7 mi) (about 5% greater than the Moon's) and a mass of 8.9319×1022 kg (about 21% greater than the Moon's). It is a slight ellipsoid in shape, with its longest axis directed toward Jupiter. Among the Galilean satellites, in both mass and volume, Io ranks behind Ganymede and Callisto but ahead of Europa.
Composed primarily of silicate rock and iron, Io is closer in bulk composition to the terrestrial planets than to other satellites in the outer Solar System, which are mostly composed of a mix of water ice and silicates. Io has a density of 3.5275 g/cm3, the highest of any moon in the Solar System; significantly higher than the other Galilean satellites (Ganymede and Callisto in particular, whose densities are around 1.9 g/cm3) and slightly higher (~5.5%) than the Moon's 3.344 g/cm3. Models based on the Voyager and Galileo measurements of Io's mass, radius, and quadrupole gravitational coefficients (numerical values related to how mass is distributed within an object) suggest that its interior is differentiated between a silicate-rich crust and mantle and an iron- or iron-sulfide-rich core. Io's metallic core makes up approximately 20% of its mass. Depending on the amount of sulfur in the core, the core has a radius between 350 and 650 km (220–400 mi) if it is composed almost entirely of iron, or between 550 and 900 km (340–560 mi) for a core consisting of a mix of iron and sulfur. Galileo's magnetometer failed to detect an internal, intrinsic magnetic field at Io, suggesting that the core is not convecting.
Modeling of Io's interior composition suggests that the mantle is composed of at least 75% of the magnesium-rich mineral forsterite, and has a bulk composition similar to that of L-chondrite and LL-chondrite meteorites, with higher iron content (compared to silicon) than the Moon or Earth, but lower than Mars. To support the heat flow observed on Io, 10–20% of Io's mantle may be molten, though regions where high-temperature volcanism has been observed may have higher melt fractions. However, re-analysis of Galileo magnetometer data in 2009 revealed the presence of an induced magnetic field at Io, requiring a magma ocean 50 km (31 mi) below the surface. Further analysis published in 2011 provided direct evidence of such an ocean. This layer is estimated to be 50 km thick and to make up about 10% of Io's mantle. It is estimated that the temperature in the magma ocean reaches 1,200 °C. It is not known if the 10–20% partial melting percentage for Io's mantle is consistent with the requirement for a significant amount of molten silicates in this possible magma ocean. The lithosphere of Io, composed of basalt and sulfur deposited by Io's extensive volcanism, is at least 12 km (7.5 mi) thick, and likely less than 40 km (25 mi) thick.
Unlike Earth and the Moon, Io's main source of internal heat comes from tidal dissipation rather than radioactive isotope decay, the result of Io's orbital resonance with Europa and Ganymede. Such heating is dependent on Io's distance from Jupiter, its orbital eccentricity, the composition of its interior, and its physical state. Its Laplace resonance with Europa and Ganymede maintains Io's eccentricity and prevents tidal dissipation within Io from circularizing its orbit. The resonant orbit also helps to maintain Io's distance from Jupiter; otherwise tides raised on Jupiter would cause Io to slowly spiral outward from its parent planet. The tidal forces experienced by Io are about 20,000 times stronger than the tidal forces Earth experience due to the moon, and the vertical differences in its tidal bulge, between the times Io is at periapsis and apoapsis in its orbit, could be as much as 100 m (330 ft). The friction or tidal dissipation produced in Io's interior due to this varying tidal pull, which, without the resonant orbit, would have gone into circularizing Io's orbit instead, creates significant tidal heating within Io's interior, melting a significant amount of Io's mantle and core. The amount of energy produced is up to 200 times greater than that produced solely from radioactive decay. This heat is released in the form of volcanic activity, generating its observed high heat flow (global total: 0.6 to 1.6×1014 W). Models of its orbit suggest that the amount of tidal heating within Io changes with time; however, the current amount of tidal dissipation is consistent with the observed heat flow. Models of tidal heating and convection have not found consistent planetary viscosity profiles that simultaneously match tidal energy dissipation and mantle convection of heat to the surface.
Although there is general agreement that the origin of the heat as manifested in Io's many volcanoes is tidal heating from the pull of gravity from Jupiter and its moon Europa, the volcanoes are not in the positions predicted with tidal heating. They are shifted 30 to 60 degrees to the east. A study published by Tyler et al. (2015) suggests that this eastern shift may be caused by an ocean of molten rock under the surface. The movement of this magma would generate extra heat through friction due to its viscosity. The study's authors believe that this subsurface ocean is a mixture of molten and solid rock.
Other moons in the Solar System are also tidally heated, and they too may generate additional heat through the friction of subsurface magma or water oceans. This ability to generate heat in a subsurface ocean increases the chance of life on bodies like Europa and Enceladus.
Based on their experience with the ancient surfaces of the Moon, Mars, and Mercury, scientists expected to see numerous impact craters in Voyager 1's first images of Io. The density of impact craters across Io's surface would have given clues to Io's age. However, they were surprised to discover that the surface was almost completely lacking in impact craters, but was instead covered in smooth plains dotted with tall mountains, pits of various shapes and sizes, and volcanic lava flows. Compared to most worlds observed to that point, Io's surface was covered in a variety of colorful materials (leading Io to be compared to a rotten orange or to pizza) from various sulfurous compounds. The lack of impact craters indicated that Io's surface is geologically young, like the terrestrial surface; volcanic materials continuously bury craters as they are produced. This result was spectacularly confirmed as at least nine active volcanoes were observed by Voyager 1.
Io's colorful appearance is the result of materials deposited by its extensive volcanism, including silicates (such as orthopyroxene), sulfur, and sulfur dioxide. Sulfur dioxide frost is ubiquitous across the surface of Io, forming large regions covered in white or grey materials. Sulfur is also seen in many places across Io, forming yellow to yellow-green regions. Sulfur deposited in the mid-latitude and polar regions is often damaged by radiation, breaking up the normally stable cyclic 8-chain sulfur. This radiation damage produces Io's red-brown polar regions.
Explosive volcanism, often taking the form of umbrella-shaped plumes, paints the surface with sulfurous and silicate materials. Plume deposits on Io are often colored red or white depending on the amount of sulfur and sulfur dioxide in the plume. Generally, plumes formed at volcanic vents from degassing lava contain a greater amount of S
2, producing a red "fan" deposit, or in extreme cases, large (often reaching beyond 450 km or 280 mi from the central vent) red rings. A prominent example of a red-ring plume deposit is located at Pele. These red deposits consist primarily of sulfur (generally 3- and 4-chain molecular sulfur), sulfur dioxide, and perhaps sulfuryl chloride. Plumes formed at the margins of silicate lava flows (through the interaction of lava and pre-existing deposits of sulfur and sulfur dioxide) produce white or gray deposits.
Compositional mapping and Io's high density suggest that Io contains little to no water, though small pockets of water ice or hydrated minerals have been tentatively identified, most notably on the northwest flank of the mountain Gish Bar Mons. Io has the least amount of water of any known body in the Solar System. This lack of water is likely due to Jupiter being hot enough early in the evolution of the Solar System to drive off volatile materials like water in the vicinity of Io, but not hot enough to do so farther out.
The tidal heating produced by Io's forced orbital eccentricity has made it the most volcanically active world in the Solar System, with hundreds of volcanic centres and extensive lava flows. During a major eruption, lava flows tens or even hundreds of kilometres long can be produced, consisting mostly of basalt silicate lavas with either mafic or ultramafic (magnesium-rich) compositions. As a by-product of this activity, sulfur, sulfur dioxide gas and silicate pyroclastic material (like ash) are blown up to 200 km (120 mi) into space, producing large, umbrella-shaped plumes, painting the surrounding terrain in red, black, and white, and providing material for Io's patchy atmosphere and Jupiter's extensive magnetosphere.
Io's surface is dotted with volcanic depressions known as paterae which generally have flat floors bounded by steep walls. These features resemble terrestrial calderas, but it is unknown if they are produced through collapse over an emptied lava chamber like their terrestrial cousins. One hypothesis suggests that these features are produced through the exhumation of volcanic sills, and the overlying material is either blasted out or integrated into the sill. Examples of paterae in various stages of exhumation have been mapped using Galileo images of the Chaac-Camaxtli region. Unlike similar features on Earth and Mars, these depressions generally do not lie at the peak of shield volcanoes and are normally larger, with an average diameter of 41 km (25 mi), the largest being Loki Patera at 202 km (126 mi). Loki is also consistently the strongest volcano on Io, contributing on average 25% of Io's global heat output. Whatever the formation mechanism, the morphology and distribution of many paterae suggest that these features are structurally controlled, with at least half bounded by faults or mountains. These features are often the site of volcanic eruptions, either from lava flows spreading across the floors of the paterae, as at an eruption at Gish Bar Patera in 2001, or in the form of a lava lake. Lava lakes on Io either have a continuously overturning lava crust, such as at Pele, or an episodically overturning crust, such as at Loki.
Lava flows represent another major volcanic terrain on Io. Magma erupts onto the surface from vents on the floor of paterae or on the plains from fissures, producing inflated, compound lava flows similar to those seen at Kilauea in Hawaii. Images from the Galileo spacecraft revealed that many of Io's major lava flows, like those at Prometheus and Amirani, are produced by the build-up of small breakouts of lava flows on top of older flows. Larger outbreaks of lava have also been observed on Io. For example, the leading edge of the Prometheus flow moved 75 to 95 km (47 to 59 mi) between Voyager in 1979 and the first Galileo observations in 1996. A major eruption in 1997 produced more than 3,500 km2 (1,400 sq mi) of fresh lava and flooded the floor of the adjacent Pillan Patera.
Analysis of the Voyager images led scientists to believe that these flows were composed mostly of various compounds of molten sulfur. However, subsequent Earth-based infrared studies and measurements from the Galileo spacecraft indicate that these flows are composed of basaltic lava with mafic to ultramafic compositions. This hypothesis is based on temperature measurements of Io's "hotspots", or thermal-emission locations, which suggest temperatures of at least 1,300 K and some as high as 1,600 K. Initial estimates suggesting eruption temperatures approaching 2,000 K have since proven to be overestimates because the wrong thermal models were used to model the temperatures.
The discovery of plumes at the volcanoes Pele and Loki were the first sign that Io is geologically active. Generally, these plumes are formed when volatiles like sulfur and sulfur dioxide are ejected skyward from Io's volcanoes at speeds reaching 1 km/s (0.62 mi/s), creating umbrella-shaped clouds of gas and dust. Additional material that might be found in these volcanic plumes include sodium, potassium, and chlorine. These plumes appear to be formed in one of two ways. Io's largest plumes, such as those emitted by Pele, are created when dissolved sulfur and sulfur dioxide gas are released from erupting magma at volcanic vents or lava lakes, often dragging silicate pyroclastic material with them. These plumes form red (from the short-chain sulfur) and black (from the silicate pyroclastics) deposits on the surface. Plumes formed in this manner are among the largest observed at Io, forming red rings more than 1,000 km (620 mi) in diameter. Examples of this plume type include Pele, Tvashtar, and Dazhbog. Another type of plume is produced when encroaching lava flows vaporize underlying sulfur dioxide frost, sending the sulfur skyward. This type of plume often forms bright circular deposits consisting of sulfur dioxide. These plumes are often less than 100 km (62 mi) tall, and are among the most long-lived plumes on Io. Examples include Prometheus, Amirani, and Masubi. The erupted sulfurous compounds are concentrated in the upper crust from a decrease in sulfur solubility at greater depths in Io's lithosphere and can be a determinant for the eruption style of a hot spot.
Io has 100 to 150 mountains. These structures average 6 km (3.7 mi) in height and reach a maximum of 17.5 ± 1.5 km (10.9 ± 0.9 mi) at South Boösaule Montes. Mountains often appear as large (the average mountain is 157 km or 98 mi long), isolated structures with no apparent global tectonic patterns outlined, in contrast to the case on Earth. To support the tremendous topography observed at these mountains requires compositions consisting mostly of silicate rock, as opposed to sulfur.
Despite the extensive volcanism that gives Io its distinctive appearance, nearly all its mountains are tectonic structures, and are not produced by volcanoes. Instead, most Ionian mountains form as the result of compressive stresses on the base of the lithosphere, which uplift and often tilt chunks of Io's crust through thrust faulting. The compressive stresses leading to mountain formation are the result of subsidence from the continuous burial of volcanic materials. The global distribution of mountains appears to be opposite that of volcanic structures; mountains dominate areas with fewer volcanoes and vice versa. This suggests large-scale regions in Io's lithosphere where compression (supportive of mountain formation) and extension (supportive of patera formation) dominate. Locally, however, mountains and paterae often abut one another, suggesting that magma often exploits faults formed during mountain formation to reach the surface.
Mountains on Io (generally, structures rising above the surrounding plains) have a variety of morphologies. Plateaus are most common. These structures resemble large, flat-topped mesas with rugged surfaces. Other mountains appear to be tilted crustal blocks, with a shallow slope from the formerly flat surface and a steep slope consisting of formerly sub-surface materials uplifted by compressive stresses. Both types of mountains often have steep scarps along one or more margins. Only a handful of mountains on Io appear to have a volcanic origin. These mountains resemble small shield volcanoes, with steep slopes (6–7°) near a small, central caldera and shallow slopes along their margins. These volcanic mountains are often smaller than the average mountain on Io, averaging only 1 to 2 km (0.6 to 1.2 mi) in height and 40 to 60 km (25 to 37 mi) wide. Other shield volcanoes with much shallower slopes are inferred from the morphology of several of Io's volcanoes, where thin flows radiate out from a central patera, such as at Ra Patera.
Nearly all mountains appear to be in some stage of degradation. Large landslide deposits are common at the base of Ionian mountains, suggesting that mass wasting is the primary form of degradation. Scalloped margins are common among Io's mesas and plateaus, the result of sulfur dioxide sapping from Io's crust, producing zones of weakness along mountain margins.
Io has an extremely thin atmosphere consisting mainly of sulfur dioxide (SO
2), with minor constituents including sulfur monoxide (SO), sodium chloride (NaCl), and atomic sulfur and oxygen. The atmosphere has significant variations in density and temperature with time of day, latitude, volcanic activity, and surface frost abundance. The maximum atmospheric pressure on Io ranges from 3.3 × 10−5 to 3 × 10−4 pascals (Pa) or 0.3 to 3 nbar, spatially seen on Io's anti-Jupiter hemisphere and along the equator, and temporally in the early afternoon when the temperature of surface frost peaks. Localized peaks at volcanic plumes have also been seen, with pressures of 5 × 10−4 to 40 × 10−4 Pa (5 to 40 nbar). Io's atmospheric pressure is lowest on Io's night side, where the pressure dips to 0.1 × 10−7 to 1 × 10−7 Pa (0.0001 to 0.001 nbar). Io's atmospheric temperature ranges from the temperature of the surface at low altitudes, where sulfur dioxide is in vapor pressure equilibrium with frost on the surface, to 1,800 K at higher altitudes where the lower atmospheric density permits heating from plasma in the Io plasma torus and from Joule heating from the Io flux tube. The low pressure limits the atmosphere's effect on the surface, except for temporarily redistributing sulfur dioxide from frost-rich to frost-poor areas, and to expand the size of plume deposit rings when plume material re-enters the thicker dayside atmosphere. The thin Ionian atmosphere also means any future landing probes sent to investigate Io will not need to be encased in an aeroshell-style heatshield, but instead require retrothrusters for a soft landing. The thin atmosphere also necessitates a rugged lander capable of enduring the strong Jovian radiation, which a thicker atmosphere would attenuate.
Gas in Io's atmosphere is stripped by Jupiter's magnetosphere, escaping to either the neutral cloud that surrounds Io, or the Io plasma torus, a ring of ionized particles that shares Io's orbit but co-rotates with the magnetosphere of Jupiter. Approximately one ton of material is removed from the atmosphere every second through this process so that it must be constantly replenished. The most dramatic source of SO
2 are volcanic plumes, which pump 104 kg of sulfur dioxide per second into Io's atmosphere on average, though most of this condenses back onto the surface. Much of the sulfur dioxide in Io's atmosphere is sustained by sunlight-driven sublimation of SO
2 frozen on the surface. The day-side atmosphere is largely confined to within 40° of the equator, where the surface is warmest and most active volcanic plumes reside. A sublimation-driven atmosphere is also consistent with observations that Io's atmosphere is densest over the anti-Jupiter hemisphere, where SO
2 frost is most abundant, and is densest when Io is closer to the Sun. However, some contributions from volcanic plumes are required as the highest observed densities have been seen near volcanic vents. Because the density of sulfur dioxide in the atmosphere is tied directly to surface temperature, Io's atmosphere partially collapses at night, or when Io is in the shadow of Jupiter (with an ~80% drop in column density). The collapse during eclipse is limited somewhat by the formation of a diffusion layer of sulfur monoxide in the lowest portion of the atmosphere, but the atmosphere pressure of Io's nightside atmosphere is two to four orders of magnitude less than at its peak just past noon. The minor constituents of Io's atmosphere, such as NaCl, SO, O, and S derive either from: direct volcanic outgassing; photodissociation, or chemical breakdown caused by solar ultraviolet radiation, from SO
2; or the sputtering of surface deposits by charged particles from Jupiter's magnetosphere.
Various researchers have proposed that the atmosphere of Io freezes onto the surface when it passes into the shadow of Jupiter. Evidence for this is a "post-eclipse brightening", where the moon sometimes appears a bit brighter as if covered with frost immediately after eclipse. After about 15 minutes the brightness returns to normal, presumably because the frost has disappeared through sublimation. Besides being seen through ground-based telescopes, post-eclipse brightening was found in near-infrared wavelengths using an instrument aboard the Cassini spacecraft. Further support for this idea came in 2013 when the Gemini Observatory was used to directly measure the collapse of Io's SO
2 atmosphere during, and its reformation after, eclipse with Jupiter.
High-resolution images of Io acquired when Io is experiencing an eclipse reveal an aurora-like glow. As on Earth, this is due to particle radiation hitting the atmosphere, though in this case the charged particles come from Jupiter's magnetic field rather than the solar wind. Aurorae usually occur near the magnetic poles of planets, but Io's are brightest near its equator. Io lacks an intrinsic magnetic field of its own; therefore, electrons traveling along Jupiter's magnetic field near Io directly impact Io's atmosphere. More electrons collide with its atmosphere, producing the brightest aurora, where the field lines are tangent to Io (i.e. near the equator), because the column of gas they pass through is longest there. Aurorae associated with these tangent points on Io are observed to rock with the changing orientation of Jupiter's tilted magnetic dipole. Fainter aurora from oxygen atoms along the limb of Io (the red glows in the image at right), and sodium atoms on Io's night-side (the green glows in the same image) have also been observed.
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Media related to Io at Wikimedia Commons
- Io profile at NASA's Solar System Exploration site
- Bill Arnett's Io webpage from The Nine Planets website
- Io overview from the University of Michigan's Windows to the Universe
- Calvin Hamilton's Io page from the Views of the Solar System website
- Paul Schenk's 3D images and flyover videos of Io and other outer solar system satellites
- High resolution video simulation of rotating Io by Seán Doran
- Catalog of NASA images of Io
- Galileo images of Io
- New Horizons images of Io
- Io through Different New Horizons Imagers
- Io global basemaps at the USGS Astrogeology Science Center based on Galileo and Voyager images
- Io nomenclature and map with feature names from the USGS planetary nomenclature page
- Interactive map of Io by Google Maps | 0.922699 | 3.751811 |
Infrared observatory measures expansion of universe
(Phys.org)—Astronomers using NASA's Spitzer Space Telescope have announced the most precise measurement yet of the Hubble constant, or the rate at which our universe is stretching apart.
The Hubble constant is named after the astronomer Edwin P. Hubble, who astonished the world in the 1920s by confirming our universe has been expanding since it exploded into being 13.7 billion years ago. In the late 1990s, astronomers discovered the expansion is accelerating, or speeding up over time. Determining the expansion rate is critical for understanding the age and size of the universe.
Unlike NASA's Hubble Space Telescope, which views the cosmos in visible light, Spitzer took advantage of long-wavelength infrared light to make its new measurement. It improves by a factor of 3 on a similar, seminal study from the Hubble telescope and brings the uncertainty down to 3 percent, a giant leap in accuracy for cosmological measurements. The newly refined value for the Hubble constant is 74.3 plus or minus 2.1 kilometers per second per megaparsec. A megaparsec is roughly 3 million light-years.
"Spitzer is yet again doing science beyond what it was designed to do," said project scientist Michael Werner at NASA's Jet Propulsion Laboratory in Pasadena, Calif. Werner has worked on the mission since its early concept phase more than 30 years ago. "First, Spitzer surprised us with its pioneering ability to study exoplanet atmospheres," said Werner, "and now, in the mission's later years, it has become a valuable cosmology tool."
In addition, the findings were combined with published data from NASA's Wilkinson Microwave Anisotropy Probe to obtain an independent measurement of dark energy, one of the greatest mysteries of our cosmos. Dark energy is thought to be winning a battle against gravity, pulling the fabric of the universe apart. Research based on this acceleration garnered researchers the 2011 Nobel Prize in physics.
"This is a huge puzzle," said the lead author of the new study, Wendy Freedman of the Observatories of the Carnegie Institution for Science in Pasadena. "It's exciting that we were able to use Spitzer to tackle fundamental problems in cosmology: the precise rate at which the universe is expanding at the current time, as well as measuring the amount of dark energy in the universe from another angle." Freedman led the groundbreaking Hubble Space Telescope study that earlier had measured the Hubble constant.
Glenn Wahlgren, Spitzer program scientist at NASA Headquarters in Washington, said infrared vision, which sees through dust to provide better views of variable stars called cepheids, enabled Spitzer to improve on past measurements of the Hubble constant.
"These pulsating stars are vital rungs in what astronomers call the cosmic distance ladder: a set of objects with known distances that, when combined with the speeds at which the objects are moving away from us, reveal the expansion rate of the universe," said Wahlgren.
Cepheids are crucial to the calculations because their distances from Earth can be measured readily. In 1908, Henrietta Leavitt discovered these stars pulse at a rate directly related to their intrinsic brightness.
To visualize why this is important, imagine someone walking away from you while carrying a candle. The farther the candle traveled, the more it would dim. Its apparent brightness would reveal the distance. The same principle applies to cepheids, standard candles in our cosmos. By measuring how bright they appear on the sky, and comparing this to their known brightness as if they were close up, astronomers can calculate their distance from Earth.
Spitzer observed 10 cepheids in our own Milky Way galaxy and 80 in a nearby neighboring galaxy called the Large Magellanic Cloud. Without the cosmic dust blocking their view, the Spitzer research team was able to obtain more precise measurements of the stars' apparent brightness, and thus their distances. These data opened the way for a new and improved estimate of our universe's expansion rate.
"Just over a decade ago, using the words 'precision' and 'cosmology' in the same sentence was not possible, and the size and age of the universe was not known to better than a factor of two," said Freedman. "Now we are talking about accuracies of a few percent. It is quite extraordinary."
The study appears in the Astrophysical Journal. | 0.852018 | 3.839541 |
If an asteroid were headed for Earth, it wouldn't make for an exciting movie
Astronomers have discovered more than 600,000 rocks of various sizes and shapes circling the sun. The majority of these dwell in the vast space between the orbits of the planets Mars and Jupiter and are called asteroids. These asteroids are millions of miles away and so small that you need a telescope just to spot them. But every once in a while, an asteroid (also known as a meteoroid), will fly by or strike Earth and ignite our attention.
Large asteroids have hit Earth dozens of times in the distant past. The surface of our planet bears the scars of these massive impacts such as evidenced in the craters in Russia, the United States and the ocean floor. 214 million years ago, one impacting meteoroid left a hole in the ground over 60 miles wide in Quebec, Canada. From outer space, astronauts can still see the crater, which water has partially filled to form the expansive Lake Manicouagan.
Meteor Crater in Arizona is perhaps the best-known example of an impact site. 50,000 years ago, an asteroid entered Earth’s atmosphere, streaked across the sky (where it becomes defined as a meteor) and then slammed into the desert floor about 40 miles east of present-day Flagstaff, Arizona. The violence of the impact vaporized most of the meteor as it excavated a crater nearly one mile across and more than 500 feet deep. Meteorites, the physical remnants of this impactor, were strewn across the plain. Known as Canyon Diablo meteorites, these rocks from space are collectors' items valued all around the world.
NEAs and PHAs
Astronomers vigilantly scan the skies for an asteroid that may cross paths with Earth. They investigate NEAs (Near Earth Asteroids) – objects that come closer to the sun and our planet.
Out of those NEAs, astronomers then determine if they are PHAs (Potentially Hazardous Asteroids). PHAs are any space rocks larger than about 400 feet in diameter that may someday come within 5 million miles of Earth. These are the asteroids to keep a close eye on. If they were to impact the planet, they would cause regional to global devastation. Luckily, none of the PHAs are known to be on a collision course with Earth.
How to save the Earth
If future astronomers ever see an asteroid heading for Earth, time is critical. Despite what some movies portray, blowing up an asteroid is probably the worst idea. An explosion of an asteroid would create many smaller, hazardous asteroids that could strike anywhere on the globe.
The best method for saving Earth from an approaching asteroid is to get to it early. Fly a very heavy spacecraft next to the asteroid and let the force of gravity do its work. The spacecraft’s bulk will tug ever so lightly on the asteroid. With enough time, astronomers can nudge an asteroid without ever touching it and guide it to a new course that will safely fly past Earth.
This gravity method would not make for a very exciting movie because it would take months or years to take effect. However, astronomers are continually scanning the skies in search of Earth-crossing asteroids. The sooner we detect them, the better.
The Hubble Space Telescope captured some grinning galaxies while searching for newborn stars.
When you head outside to stargaze this fall and you see a shooting star, don’t fear. Not one person has been killed by a meteor in more than 100 years. Instead, sit back, relax, marvel at the heavens and appreciate all the empty space between the cosmos and you.
Dean Regas is the Outreach Astronomer at the Cincinnati Observatory, co-host of PBS’ Star Gazers, and author of the book 100 Things to See in the Night Sky. He can be reached at [email protected]
If you go: Meet a Meteorite
What: See, touch and buy hundreds of meteorites from around the solar system – including pieces of the moon and Mars. Plus viewing of the stars through the telescope (weather permitting)
When: Saturday, Nov. 17, from 7-9 p.m.
Where: Cincinnati Observatory, 3489 Observatory Place, Mount Lookout.
Admission: $10/adult, $5/student, free for Veterans and Observatory Members
Info: Great for all ages. No reservations needed. www.cincinnatiobservatory.org
When Asteroid 2018 EB flew by Earth in early October, scientists noticed it was a unique double asteroid. | 0.839511 | 3.797725 |
One of the most exciting developments in astronomy in recent years has been the explosion in the discovery of exoplanets. Finding planets outside of our solar system was once a relatively rare occurrence, but starting in 2014 the numbers began to increase exponentially.
It hasn't been solid growth year-to-year, but in 2017 there were over 1,400 discovered. That's out of 3,767 total discovered. What's to explain the sudden growth? Real Engineering takes a look at how technology has changed the way we discover planets, and how math helps us turn small observations into a lot of data.
Using the recently discovered TRAPPIST-1 star system as an example, Real Engineering looks at TRAPPIST–South, a robotic telescope based in Chile that is operated out of Belgium. There are a number of ways to hunt for exoplanets but TRAPPIST-South shows the basic underlying principles.
A lightweight 1.9 foot telescope, TRAPPIST (a forced acronym meant to honor the Trappist beers of Belgium) debuted in 2010. Watching a dwarf star, the scientists in Belgium found a dimming of its light. That's a strong sign that there's a planet in orbit blocking the light. From here, it's largely a matter of math.
There's so much space out there that even large objects like planets take a long time to find. And while current technology is helpful, scientists are eager for what the just launched Transiting Exoplanet Survey Satellite will find. In the hunt for exoplanets, the best may be yet to come.
Source: Real Engineering | 0.869108 | 3.305037 |
On October 19th, 2017, the Panoramic Survey Telescope and Rapid Response System-1 (Pan-STARRS-1) in Hawaii announced the first-ever detection of an interstellar asteroid, named 1I/2017 U1 (aka. ‘Oumuamua).
In the months that followed, multiple additional observations were conducted that allowed astronomers to get a better idea of its size and shape, revealing it to be strangely cigar-shaped, roughly 400 metres (1312 ft) in length and approximately 40-50 metres (130-162.5 ft) in height and width, tumbling through space. These observations also showed it may be composed of dense metal-rich rock, and that it had the characteristics of both a comet and an asteroid.
However, the report on ‘Oumuamua (roughly translated as “scout”, ou being Hawaiian for “reach out for” and mua meaning “first, in advance of” – which is repeated for emphasis) that captured public imagination is the idea that the object may have been an interstellar probe.
At the heart of this idea is the fact that ‘Oumuamua accelerated away from the Sun faster than would have been the case of it receiving a “gravity assist” in swinging around our star. Initially, it was suggested that the additional acceleration was the result of the off-gassing of volatiles – frozen water, etc., that had been heated during ‘Oumuamua’s close swing around the Sun. However, no such off-gassing had been observed when the object was closer to the Sun, which would have been expected.
In June 2018, an alternative explanation for the acceleration was posited: that it was the result of solar pressure being exerted on the object.
However, at the end of October 2018, Shmuel Bialy, a post-doctoral researcher at the CfA’s Institute for Theory and Computation (ITC) and Prof. Abraham Loeb, the Frank B. Baird Jr. Professor of Science at Harvard University, went one stage further. They proposed that while ‘Oumuamua might well be natural in origin – it could also be the object is in fact an alien probe, intentionally sent to our solar system and which uses a light sail (or what we’d call a solar sail were it to be used with a probe sent from Earth to explore out solar system) for propulsion.
Currently there is an unexplained phenomena, namely, the excess acceleration of ‘Oumuamua, which we show may be explained by the force of radiation pressure from the Sun. We explain the excess acceleration of `Oumuamua away from the Sun as the result of the force that the Sunlight exerts on its surface. For this force to explain measured excess acceleration, the object needs to be extremely thin, of order a fraction of a millimetre in thickness but tens of meters in size. This makes the object lightweight for its surface area and allows it to act as a light-sail. Its origin could be either natural (in the interstellar medium or proto-planetary disks) or artificial (as a probe sent for a reconnaissance mission into the inner region of the Solar System).
– E-mail from Baily and Loeb on their paper concerning ‘Oumuamua
Their views were circulated to various news outlets via e-mail and cause something of a stir in the first week or so of November.
Loeb has actually been an advocate of ‘Oumuamua being of intelligent origin since it was first discovered. He was one of the first to call for radio telescopes to listen to it across a range of frequencies for any signs of transmissions from it. When the SETI Institute‘s Allen Telescope Array did so without success, he pushed for the Green Bank Telescope in West Virginia to listen for radio emissions – which it did for a 6-day period December 2017, again without success
As no signals were found to be emanating from the object, rather than drop the idea of it being artificial, Loeb has put forward the ideas that it has either malfunctioned, or it is active, and we simply can’t detect the fact that it is. He’s even suggested that given Pan-STARS only managed to spot the object after it has passed perihelion, could mean that it is only “one of many” such probes sent our way, and we’ve missed the others.
Bialy has been a little more cautious with things, pointing out the paper is “high speculative”. But the fact is, the paper does come across more of an attempt to substantiate a belief (that ‘Oumuamua is of artificial origin) than anything else, and in doing so, it does ignore certain data and makes some sweeping assumptions.
For example, the paper tends to dismiss the idea that ‘Oumuamua’s unexpected acceleration was consistent with a push from solar radiation pressure. However, Michele Bannister, a planetary astronomer from New Zealand and one of many to push back against the “ET probe” idea via Twitter, used a graphic that shows the acceleration exhibited by ‘Oumuamua’s is entirely in keeping with similar non-gravitational accelerations seen with comets within the solar system.
Other astronomers have also been sceptical of Loeb’s and Bialy’s idea that ‘Oumuamua is of intelligent design. Their views can be pretty much summed up by the response given by Alan Fitzsimmons, an astrophysicist at Queens University, Belfast:
Like most scientists, I would love there to be convincing evidence of alien life, but this isn’t it. [Data] has already shown that its observed characteristics are consistent with a comet-like body ejected from another star system. And some of the arguments in this study are based on numbers with large uncertainties.
At present, ‘Oumuamua is beyond the orbit of Jupiter and will pass beyond Saturn in 2019 – although it will be another 20,000 years before it leaves the solar system and re-enters interstellar space. Trajectory data further suggests that ‘Oumuamua came to us from the vicinity of Vega (although it may not have originated from there). Taking its velocity into account, astronomers believe the journey from Vega probably took around 600,000 years – although some suggest its likely point of origin could be the Carina nebula, 8,000 light years away, in which case, ‘Oumuamua may have been travelling through the galaxy for 45 million years.
The fact is, we’ll probably never know where it originated, just as the idea that it is of artificial design can never be ruled out for certain. But, when weighing the chances of ‘Oumuamua being some kind of alien probe, zipping through our inner solar system like the vessel from Arthur C. Clarke’s Rendezvous With Rama, against it being a piece of natural interstellar debris, Occam’s Razor does tend to point to the latter rather than the former.
SpaceX To Move Forward with Preliminary BFR Testing
In September, I covered the SpaceX announcement that the company plans to use its upcoming massive Big Falcon Rocket (BFR) and Big Falcon Ship (BFS) to fly a group of private citizens around the Moon. As a part of that announcement SpaceX CEO, Elon Musk gave an updated on the state of development for BFR / BFS and outline a rough roadmap on development.
In particular, the BFS shown at the time was a major departure from earlier iterations of the design. In particular, it now sports three large fins at its rear end. All three are intended to be landing legs – the BFS being designed to land vertically – with two of them actuated to move up and down as flight control surfaces during atmospheric decent. These are matched by two forward actuated canards, also designed to provide aerodynamic control during a descent through an atmosphere.
That announcement left a lot of people in the space community keeping an eye on SpaceX for further updates, and in a tweet in November 7th, 2018, Musk revealed the next step along the road to developing the BFR / BFS will be to fly a “mini BFS” atop a Falcon 9 or possibly a Falcon Heavy launch vehicle.
When pressed for a time frame for the first flight, Musk indicated the company will be aiming for around June 2019, and the flights will be launched from the SpaceX test facilities near Brownsville, Texas. Such an aggressive time frame suggests the “mini-BFS” will not be an actual scale model of the Big Falcon Spacecraft, but a close facsimile, possibly using a modified upper stage of the Falcon 9.
The focus of the tests will be to place the upgraded Falcon upper stage into orbit, and then using it to test an ultra light” heat shield through re-entry and also test aerodynamic control surfaces of the type proposed of BFS through high Mach speeds. However, as the Falcon 9’s upper stage motor is optimised for operating in a vacuum, the test flights will not include any attempt to try to land the test vehicle propulsively. However, this does not necessarily mean the test article will be lost.
In April 2018, Musk suggested the company were developing a novel means to recover the Falcon 9’s upper stage, which if serious, could provide a means to recover the “mini BFS”:
This is gonna sound crazy, but…
SpaceX will try to bring a rocket upper stage back from orbital velocity using a giant party balloon.
And then land on a bouncy house.
– Elon Musk tweeting in April 2018.
China Unveils Space Station Replica
China has unveiled a full-scale replica of the core module of its new space station, Tiangong-3 at the Biennial Airshow in the southern coastal city of Zhuhai, which is also the country’s main aerospace industry exhibition.
Called Tianhe-1 (“Harmony of the Heavens”) the core of module is some 18 metres in length – making it somewhat smaller than the core elements of the International Space Station (ISS). Tianhe-1 is scheduled for launch in 2020, and includes a multi-axis docking port. Once in orbit, it will be joined by two living / science modules attached to the multi-axis port system, with the entire 60-tonne station due to be declared operational in 2022, and remain so for around 10 years.
In addition, China has reaffirmed the station will be open “all countries” to conduct science experiments, and national and international research institutes, universities, and public and private companies have been invited to propose projects to fly on the station.
According to Chinese state media covering the unveiling of the module replica, some 40 plans from 27 countries and regions have been received, according to state media. One organisations that has replied is the European Space Agency, which has already sent members of the European Astronaut Corps to China to receive training (including language training) in order to participate in missions to the completed Tiangong-3.
One country unlikely to participate in the programme will be the United States, where the hope is commercial operators will take up the challenge of operating and providing orbital facilities as the US ends it support for the International Space Station. | 0.93112 | 3.991539 |
Cataclysm is as essential to reality as emergence. The destructions, degradations and disasters of the universe are part of the story of its life, a movement from a complex to a simple state that allows for the emergence of newness.
Imagine a star twenty times the size of our sun. The force of gravity would reduce it to a cinder were it not for the opposing energy sent forth from its heart, created by the fusing of hydrogen nuclei into helium nuclei. This activity allows it to maintain, in Swimme’s words, “a seething equilibrium” for some ten million years.
But when the hydrogen has all been transformed into helium that fusion process ends. Gravity causes the star to collapse into a smaller space until its core heats up to the temperature required to fuse helium into carbon. The cycle repeats as carbon fuses into oxygen, then oxygen into silicon and on and on until only iron remains. Iron releases no energy when it fuses; nothing is left to push out from the star’s centre to oppose the force of gravity.
The star can only implode upon itself and in seconds a multi-million year process is over; a massive star becomes a mere speck.
Cygnus Loop Nebula: a small portion of the nebula which is actually the expanding blastwave from a stellar cataclysm — a supernova explosion — which occurred about 15,000 years ago. The supernova remnant lies 2,500 light years away in the constellation Cygnus the Swan.
But the energy of the implosion has crushed the constituent electrons and protons together to form neutrons, releasing more elementary particles called neutrinos.
This reverses the imploding movement to blast the star apart in a firework display more brilliant than a galaxy of shining stars. As it expands a nucleosynthesis takes place, creating the nuclei of all the elements of the universe. In this supernova explosion are birthed the elements that will form our planet and our bodies.
(For a fuller explication of this process, see Chapter 3: “The Emanating Brilliance of Stars” in Journey of the Universe co-authored by Brian Swimme & Mary Evelyn Tucker, Yale University Press, New Haven & London, 2011)
The life story of a star is an astounding example of cataclysm giving birth to new life. But the power of cataclysm is seen in many aspects of life in the universe.
Two hundred and fifty million years ago (when our earth was already ancient of days at age four billion and a bit…) a cataclysm occurred that eliminated 96% of marine species and 70% of land species. Swimme says that huge die-offs occur roughly every one hundred million years, and we are right in the middle of one now.
Whatever our capacities for conscious denial, Swimme believes our hearts and our bodies feel this awareness in a rising sense of frustration, of regret, of failure. I would add to that a profound sense of grief. I recall watching a power-point that singer/songwriter Carolyn McDade prepared to illustrate the species in my own bio-region under threat of extinction. As I watched the unique, startling beauty of each form of life, the soulful eyes of owls, reptiles, birds, otters, small mammals gazing back at me from the screen, I was shaken by a grief so sudden and wrenching that I wept. All the while, Carolyn’s voice sang a prayer of pleading:
“ let them continue on….”
Later that summer I saw in the river near my home an otter with a mate and young, and felt a deep joy…
Concurrent with this extinction of species we have the desertification of land, the shrinking rain forests, the dying rivers and lakes as though engaged in a death dance between nature and man-made structures. We see the waning into near-extinction of many of the religious, political, economic, education, health and societal systems in which we had once placed our trust.
Is there a graced way to live into a period of cataclysm? Swimme suggests that we might identify with the power that is destroying us by consciously surrendering aspects of ourselves, our society, our way of being in the world, that no longer serve us, thus enabling the universe to pulverize those aspects…
We can try to see the destruction of consumer culture as part of the earth’s work of cataclysm, seeking to free us, to free our lives.
When cataclysm strikes an area of the planet through flood or fire, earthquake, tornado or tsunami, haven’t we heard voices raised that dared to bless the disaster for revealing what is really worth valuing in life?
Do we not experience this re-assessment of what really matters in our present COVID 19 crisis?
The twentieth century mystic Etty Hillesum, shortly before her death in Auschwitz in 1943, at the age of twenty nine, wrote words that may be a light for us in this time:
I shall try to help you, God, to stop my strength ebbing away, though I cannot vouch for it in advance. But one thing is becoming increasingly clear to me: that you cannot help us, that we must help you to help ourselves. And that is all we can manage these days, also all that really matters: that we safeguard that little piece of you, God, in ourselves. And in others as well.
Alas, there doesn’t seem to be much you yourself can do about our circumstances, about our lives. Neither do I hold you responsible.
You cannot help us but we must help you and defend your dwelling place inside us to the end.
This is our moment, Brian Swimme believes: our star exploding, ready to create emeralds and giraffes, ready to release us into a new earth community.
For the next level of growth, of deepening, something has to wake us up, shake us up. It may take a tornado to blow us all the way to Oz where the greatest gifts await us.
Jean Houston says that the call of this time of Cataclysm is to “radical reinvention” in order to speciate, to become a deepening spirit of the earth for her new emergence.
Never before in history have so many devoted themselves to develop fully, to regard problems as opportunities in work clothes.
Encouraging us that we have just the right gifts on just the right planet to bring this new earth community to life, Jean adds,
“You are blessed to be alive at this time.” | 0.820628 | 3.846868 |
Track the Tide
The Harbormaster is a precision East Coast tide clock. It makes it easy to track the tide at your favorite coastal location, regardless of where you are.
Time is a Precious Commodity
The Meridian helps you keep track of time in a classic, elegant display that can stand alone or as part of a complete weather station.
Digital Time and East Coast Tide Clock
The Cronus gives you both functions in a single digital time and tide clock. It can be enjoyed on its own or as a complement to our other digital weather instruments.
How Does a Time and Tide Clock Work?
It has been known for centuries along the east coast, tides occur approximately 50 minutes later each day than they did the day before. The primary reason for this daily lag can be traced to the moon. It takes the earth 24 hours to make one complete rotation around the sun. This rotation is called a “solar day”. It takes the moon 24 hours and 50 minutes to make one complete rotation around the earth. This rotation is called a “lunar day”. It is the moon’s close proximity to us and the relatively strong gravitational effect it has on the earth that causes the tides to follow the moon’s lunar schedule of 24 hours and 50 minutes per cycle.
The Forces Behind Time and Tide Clock Readings
While the lunar cycle is the primary force behind the workings of the tide, it is not the only force. On a daily basis, the average tidal cycle of 24 hours and 50 minutes can be affected by such cosmic variables as the relative position of the earth to the sun and the specific elliptical pattern of the moon around the earth. Localized variables affecting daily tides also exist. These include strong winds, changes in atmospheric pressure, distant storms and an infinite number of other atmospheric conditions. The total effect of all these different factors causes tides to vary from their average of 24 hours and 50 minutes. These variations can cause the reading of a tide clock to be either fast or slow in relation to actual tides, by as much as one hour or more on any given day. However, the rhythmic 24 hour and 50 minute cycle will prevail over any given 28-day lunar period.
This means that on any given day a tide clock may read fast or slow, but over a 28-day period, it will average itself out to be correct. For most purposes, high and/or low tide is not a point in time, but a condition that exists over a period of time. If for some reason you require exact tide information you should always refer to a current tide table. The purpose of a tide clock is not to be exact, but to tell us the best approximate time to go swimming, fishing, boating, etc.
Do you have questions about how to select a time and tide clock? Reach out to us today and we’d be happy to assist you. | 0.819195 | 3.159792 |
A lot of human scientific and technological progress over the span of recorded history has been related to discerning patterns. People noticed that the Sun and Moon both had regular periodicity to their movements, leading to models that ultimately changed our view of our place in the Universe. The apparently wandering trails swept out by the planets were later regularised by the work of Johannes Kepler and Tycho Brahe; an outstanding example of a simple idea explaining more complex observations.
In general Mathematics has provided a framework for understanding the world around us; perhaps most elegantly (at least in work that is generally accessible to the non-professional) in Newton’s Laws of Motion (which explained why Kepler and Brahe’s models for planetary movement worked). The simple formulae employed by Newton seemed to offer a precise set of rules governing everything from the trajectory of an arrow to the orbits of the planets and indeed galaxies; a triumph for the application of Mathematics to the natural world and surely one of humankind’s greatest achievements.
For centuries it appeared that natural phenomena seemed to have simple principles underlying them, which were susceptible to description in the language of Mathematics. Sometimes (actually much more often than you might think) the Mathematics became complicated and precision was dropped in favour of – generally more than good enough – estimation; but philosophically Mathematics and the nature of things appeared to be inextricably interlinked. The Physicist and Nobel Laureate E.P. Wigner put this rather more eloquently:
The miracle of the appropriateness of the language of mathematics for the formulation of the laws of physics is a wonderful gift which we neither understand nor deserve.
In my youth I studied Group Theory, a branch of mathematics concerned with patterns and symmetry. The historical roots (no pun intended) of Group Theory are in the solvability of polynomial equations, but the relation with symmetry emerged over time; revealing an important linkage between geometry and algebra. While Group Theory is a part of Pure Mathematics (supposedly studied for its own intrinsic worth, rather than any real-world applications), its applications are actually manifold. Just one example is that groups lie (again no pun intended) at the heart of the Standard Model of Particle Physics.
However, two major challenges to this happy symbiosis between Mathematics and the Natural Sciences arose. One was an abrupt earthquake caused by Kurt Gödel in 1931. The other was more of a slowly rising flood, beginning in the 1880s with Henri Poincaré and (arguably) culminating with Ruelle, May and Yorke in 1977 (though with many other notables contributing both before and after 1977). The linkage between Mathematics and Science persists, but maybe some of the chains that form it have been weakened.
Potentially fallacious patterns
However, rather than this article becoming a dissertation on incompleteness theorems or (the rather misleadingly named) chaos theory, I wanted to return to something more visceral that probably underpins at least the beginnings of the long association of Mathematics and Science. Here I refer to people’s general view that things tend to behave the same way as they have in the past. As mentioned at the beginning of this article, the sun comes up each morning, the moon waxes and wanes each month, summer becomes autumn (fall) becomes winter becomes spring and so on. When you knock your coffee cup over it reliably falls to the ground and the contents spill everywhere. These observations about genuine patterns have served us well over the centuries.
It seems a very common human trait to look for patterns. Given the ubiquity of this, it is likely to have had some evolutionary benefit. Indeed patterns are often there and are often useful – there is indeed normally more traffic on the roads at 5pm on Fridays than on other days of the week. Government spending does (with the possible exception of current circumstances) generally go up in advance of an election. However such patterns may be less useful in other areas. While winter is generally colder than summer (in the Northern hemisphere), the average temperature and average rainfall in any given month varies a lot year-on-year. Nevertheless, even within this variability, we try to discern patterns to changes that occur in the weather.
We may come to the conclusion that winters are less severe than when we were younger and thus impute a trend in gradually moderating winters; perhaps punctuated by some years that don’t fit what we assume is an underlying curve. We may take rolling averages to try to iron out local “noise” in various phenomena such as stock prices. This technique relies on the assumption that things change gradually. If the average July temperature has increased by 2°C in the last 100 years, then it maybe makes sense to assume that it will increase by the same 2°C ±0.2°C in the next 100 years. Some of the work I described earlier has rigorously proved that a lot of these human precepts are untrue in many important fields, not least weather prediction. The phrase long-term forecast has been 100% shown to be an oxymoron. Many systems – even the simplest, even those which are apparently stable – can change rapidly and unpredictably and weather is one of them.
For the avoidance of doubt I am not leaping into the general Climate Change debate here – except in the most general sense. Instead I am highlighting the often erroneous human tendency to believe that when things change they do so smoothly and predictably. That when a pattern shifts, it does so to something quite like the previous pattern. While this assumed smoothness is at the foundation of many of our most powerful models and techniques (for example the grand edifice of The Calculus), in many circumstances it is not a good fit for the choppiness seen in nature.
Obligatory topical section on volcanoes
The above observations about the occasionally illusory nature of patterns lead us to more current matters. I was recently reading an article about the Eyjafjallajokull eruption in The Economist. This is suffused with a search for patterns in the history of volcanic eruptions. Here are just a few examples:
- Last time Eyjafjallajokull erupted, from late 1821 to early 1823, it also had quite viscous lava. But that does not mean it produced fine ash continuously all the time. The activity settled into a pattern of flaring up every now and then before dying back down to a grumble. If this eruption continues for a similar length of time, it would seem fair to expect something similar.
- Previous eruptions of Eyjafjallajokull seem to have acted as harbingers of a subsequent Katla [a nearby volcano] eruptions.
- [However] Only two or three […] of the 23 eruptions of Katla over historical times (which in Iceland means the past 1,200 years or so) have been preceded by eruptions of Eyjafjallajokull.
- Katla does seem to erupt on a semi-regular basis, with typical periods between eruptions of between 30 and 80 years. The last eruption was in 1918, which makes the next overdue.
To be fair, The Economist did lace their piece with various caveats, for example the above-quoted “it would seem fair to expect”, but not all publications are so scrupulous. There is perhaps something comforting in all this numerology, maybe it gives us the illusion that we can make meaningful predictions about what a volcano will do next. Modern geologists have used a number of techniques to warn of imminent eruptions and these approaches have been successful and saved lives. However this is not the same thing as predicting that an eruption is likely in the next ten years solely because they normally occur every century and it is 90 years since the last one. Long-term forecasts of volcanic activity are as chimerical as long-term weather forecasts.
A little light analysis
Looking at another famous volcano, Vesuvius, I have put together the following simple chart.
The average period between eruptions is just shy of 14 years, but the pattern is anything but regular. If we expand our range a bit, we might ask how many eruptions occurred between 10 and 20 years after the previous one. The answer is just 9 of the 26, or about 35%. Even if we expand our range to periods of calm lasting between 5 and 25 years (so 10 years of leeway on either side), we only capture 77% of eruptions. The standard deviation of the periods between recorded eruptions is a whopping 12.5; eruptions of Vesuvius are not regular events.
One aspect of truly random distributions at first seems counterfactual, this is their lumpiness. It might seem reasonable to assume that a random set of events would lead to a nicely spaced out distribution; maybe not a set of evenly-spaced points, but a close approximation to one. In fact the opposite is generally true; random distributions will have clusters of events close to each other and large gaps between them.
The above exhibit (a non-wrapped version of which may be viewed by clicking on it) illustrates this point. It compares a set of pseudo-random numbers (the upper points) with a set of truly random numbers (the lower points). There are some gaps in the upper distribution, but none are large and the spread is pretty even. By contrast in the lower set there are many large gaps (some of the more major ones being tagged a, … ,h) and significant clumping. Which of these two distributions more closely matches the eruptions of Vesuvius? What does this tell us about the predictability of its eruptions?
The predictive analytics angle
As always in closing I will bring these discussions back to a business focus. The above observations should give people involved in applying statistical techniques to make predictions about the future some pause for thought. Here I am not targeting the professional statistician; I assume such people will be more than aware of potential pitfalls and possess much greater depth of knowledge than myself about how to avoid them. However many users of numbers will not have this background and we are all genetically programmed to seek patterns, even where none may exist. Predictive analytics is a very useful tool when applied correctly and when its findings are presented as a potential range of outcomes, complete with associated probabilities. Unfortunately this is not always the case.
It is worth noting that many business events can be just as unpredictable as volcanic eruptions. Trying to foresee the future with too much precision is going to lead to disappointment; to say nothing of being engulfed by lava flows.
|||The solvability of polynomials is of course equivalent to whether or not roots of them exist.|
|||Lie groups lie at the heart of quantum field theory – a interesting lexicographical symmetry in itself|
|||Indeed it has been argued that non-linear systems are more robust in response to external stimuli than classical ones. The latter tend to respond to “jolts” in a smooth manner leading to a change in state. The former often will revert to their previous strange attractor. It has been postulated that evolution has taken advantage of this fact in demonstrably chaotic systems such as the human heart.|
|||Here I include the – to date – 66 years since Vesuvius’ last eruption in 1944 and exclude the eruption in 1631 as there is no record of the preceding one.|
|||For anyone interested, the upper set of numbers were generated using Excel’s RAND() function and the lower are successive triplets of the decimal expansion of pi, e.g. 141, 592, 653 etc.|
|||Again for those interested the average gap in the upper set is 10.1 with a standard deviation of 4.3; the figures for the lower set are 9.7 and 9.6 respectively.| | 0.803056 | 3.424679 |
Duration: 45 minutes
First broadcast: Thursday 03 March 2011
Melvyn Bragg and his guests discuss the age of the Universe.
Since the 18th century, when scientists first realised that the Universe had existed for more than a few thousand years, cosmologists have debated its likely age. The discovery that the Universe was expanding allowed the first informed estimates of its age to be made by the great astronomer Edwin Hubble in the early decades of the twentieth century. Hubble’s estimate of the rate at which the Universe is expanding, the so-called Hubble Constant, has been progressively improved.
Today cosmologists have a variety of other methods for ageing the Universe, most recently the detailed measurements of cosmic microwave background radiation – the afterglow of the Big Bang – made in the last decade. And all these methods seem to agree on one thing: the Universe has existed for around 13.75 billion years.
Astronomer Royal and Emeritus Professor of Cosmology and Astrophysics at the University of Cambridge
Member of the Institute of Astronomy and Fellow of Emmanuel College at the University of Cambridge
Director of the Institute for Computational Cosmology at the University of Durham. | 0.817673 | 3.035722 |
The dynamics are complex. The changes affect the 'insolation' (sunlight falling on parts of the Earth). This leads to cycles of climate on Earth, at about 21,000, 41,000 years, 100,000 and 400,000 years. This whole field is still under active research.
Similar astronomical theories had been advanced in the 19th century by Joseph Adhemar, James Croll and others. However, there was at first no reliable dated evidence. The issue was not settled until deep-ocean cores were taken and a paper published in Science in 1976.
Orbital shape (eccentricity)Edit
Earth's orbit is an ellipse. The eccentricity is a measure of the departure of this ellipse from circularity. The shape of the Earth's orbit varies in time between nearly circular and mildly elliptical.
Axial tilt (obliquity)Edit
The angle of the Earth's axial tilt varies with respect to the ecliptic plane, because perturbations from other planets shift the Earth's orbit.
When the obliquity increases, the summers in both hemispheres receive more heat and light from the Sun, and winters less. Conversely, when the obliquity decreases, summers receive less sunshine and winters more. These slow 2.4° obliquity variations are roughly periodic. They take about 41,000 years to shift between a tilt of 22.1° and 24.5° and back again.
Precession is the wobble of the Earth's axis. This gyroscopic motion is due to the tidal forces exerted by the sun and the moon on the solid Earth, which has the shape of an oblate spheroid rather than a sphere. The sun and moon contribute roughly equally to this effect. Its period is about 26,000 years.
When the axis points toward the Sun, one polar hemisphere has a greater difference between the seasons while the other has milder seasons. The hemisphere that is in summer at perihelion receives much of the corresponding increase in solar radiation, but that same hemisphere in winter at aphelion has a colder winter. The other hemisphere will have a relatively warmer winter and cooler summer.
Planets orbiting the Sun follow elliptical (oval) orbits that rotate gradually over time (apsidal precession).
In addition, the orbital ellipse itself precesses in space, primarily as a result of interactions with Jupiter and Saturn. This shortens the period of the precession of the equinoxes from 25,771.5 to ~21,636 years.
The inclination of Earth's orbit drifts up and down relative to its present orbit with a cycle having a period of about 70,000 years. Milankovitch did not study this three-dimensional movement. This movement is known as 'precession of the ecliptic' or 'planetary precession'.
Researchers noted this drift, and also that the orbit moves relative to the orbits of the other planets. The invariable plane, the plane that represents the angular momentum of the Solar System, is approximately the orbital plane of Jupiter. The inclination of the Earth's orbit has a 100,000 year cycle relative to the invariable plane. This is very similar to the 100,000 year eccentricity period. This 100,000-year cycle closely matches the 100,000-year pattern of ice ages.
It has been proposed that a disk of dust and other debris exists in the plane, which affects the Earth's climate. The Earth moves through this plane around January 9 and July 9, when there is an increase in radar-detected meteors and meteor-related noctilucent clouds.
A study of the Antarctic ice core, using oxygen-nitrogen ratios in air bubbles trapped in the ice, concluded that the climatic response documented in the ice cores was driven by Northern hemisphere insolation as proposed by the Milankovitch hypothesis. This is an additional validation of the Milankovitch hypothesis by a relatively new method. It is not consistent with the "inclination" theory of the 100,000-year cycle.
- Milankovitch, Milutin (1998) . Canon of insolation and the Ice Age problem. Belgrade: Zavod za Udz̆benike i Nastavna Sredstva. ISBN 8617066199.; see also "Astronomical theory of climate change".
- Hays J.D; Imbrie J. & Shackleto, N.J. 1976. Variations in the Earth's orbit: pacemaker of the ice ages. Science 194 (4270): 1121–1132.
- Richard A Muller & Gordon J MacDonald (1997). "Glacial cycles and astronomical forcing". Science. 277 (1997/07/11): 215–8. doi:10.1126/science.277.5323.215.
- Richard A Muller. "Origin of the 100 kyr Glacial Cycle: eccentricity or orbital inclination?". Retrieved March 2, 2005.
- Kawamura et al. 2007. Nature. 448, p912-917 | 0.843787 | 4.02283 |
In science, it is important to distinguish between an observation and an interpretation. Observations are things we measure; while interpretations are the conclusions we derive from those observations. In well-designed experiments the resulting interpretations are the only possible explanations for the observations—but this is a rare occurrence. More often, alternate interpretations are possible.
Unfortunately, it is often the interpretation that gets reported in the review papers, the press, and the textbooks, while the observations may only be reported in the primary source. In cases where alternate interpretations are possible—or worse, where the observations do not actually support the vaunted interpretation—it may be necessary to examine the primary source (perhaps, even, the raw data) to determine which conclusions are justified and which are not.
To illustrate this point, let me examine an example from my own research.1 Most consider the existence of dark matter and dark energy to be scientific facts—but, in reality, this conclusion is just one of several possible interpretations based upon observations.
Do Dark Matter and Dark Energy Exist?
We have never directly observed dark matter; its existence is inferred from astronomical observation. Using the Doppler shift of light, we can very accurately measure the speed at which stars and gas clouds orbit their galactic centers. When we compare the measured velocity to the velocity calculated on the basis of the gravitational force provided by all visible mass (see here), we find that the measured velocity does not fall off rapidly with distance as predicted by our theory of gravity. Rather it remains flat at a high value out to great distances from the center of the galaxy. The accepted interpretation for this observation is that, in order to increase the gravitational force enough to keep the stars and gas in orbit around the galaxy, there must be dark matter providing additional mass that we cannot see.
However, dark matter is not the only interpretation that can explain why galaxies have flat rotation curves. It could be that our understanding of gravity is incomplete. By slightly modifying the gravitational force equation, Modified Newtonian Dynamics (MoND) can fit the galactic rotation curves without the need for dark matter. But MoND is an empirical law, not a theory—it does not explain galactic rotation curves unless there is a theory of gravity from which the MoND equation can be derived. (Similarly, Kepler’s laws fit planetary motion, but the basis for them was not understood until Isaac Newton came up with the theory of universal gravitation.)
Several such theories have been proposed, but my favorite postulates the existence of gravitational dipoles that modify gravity with gravitational vacuum polarization.2 This is my favorite theory, not only because I have proposed3 research (still unfunded) to test the underlying assumption behind this theory (specifically, that antimatter and matter repel each other gravitationally), but also because it would solve two other big mysteries in physics: missing antimatter in the universe and Type Ia supernova data.4 (It could solve the latter mystery without the need for a cosmological constant or dark energy.5)
Adjusting Arguments and Beliefs
Scientists like to think that their beliefs are entirely empirical, based only upon observation. To a certain extent, this is true. For example, before the Type Ia supernova data were published, almost all physicists and astronomers believed that the cosmological constant Λ must be exactly 0 since the universe is expanding and the natural value for Λ is enormous (10120 larger than the observed value). However, after seeing the new observations, researchers now believe Λ must be non-zero, though tiny. If confronted with a verified measurement that matter and antimatter repel each other gravitationally, most of these same scientists would change their beliefs yet again.
On a personal note, and to provide additional insight into scientists’ research, RTB scholar and UCLA researcher Jeff Zweerink is working on an experiment that is attempting to observe dark matter interactions. One might think that Jeff and I would consider ourselves rivals since I’m proposing an experiment that could show that dark matter need not exist. On the contrary, we consider ourselves colleagues. Essentially, we are both trying to explain the same observation; we are just approaching the problem in different ways. Either of us would be delighted if the other succeeded because then we would know the explanation and would gain additional insight into how God created the universe. Even if we have to forfeit apologetics arguments based upon whichever explanation proves incorrect, apologetics arguments founded on the other explanation would be strengthened as a result of the new observation.
The main point here for apologists is the importance of recognizing that when a new scientific result appears to conflict with our Christian worldview, the result reported is usually one interpretation of the data. And while this particular interpretation may clash with our worldview, it is likely that there are other possible interpretations of the relevant observations that will not cause conflict.
If you are a regular reader of Today’s New Reason to Believe, you will recognize that many of the articles address the question of how to interpret a new scientific result in light of the Christian worldview. The facts are the observations (when properly measured), and observations generally can be interpreted in a number of different ways. When a scientific result seems to contradict the Christian worldview, ask what observations form the basis for this result, and what alternate interpretations are possible.(TP,RTB)
*** Will Myers, Intelligent Design And Biblical Scripture | 0.891165 | 4.078074 |
When it comes to the elements in the periodic table found throughout the Universe, it's only the first two that originated from the Big Bang: hydrogen and helium. Everything else was formed from stars, whether:
- fused in their cores, from lighter elements into heavier ones,
- built in supernovae, where the tremendous energy-and-particle release created elements as far up the periodic table as we know how to go,
- created from mergers of collapsed objects, like two neutrons stars, which gives rise to the heaviest of elements,
- or created afterwards from the nebulous remnants of stars, either by radioactive decay or by those atoms being blasted apart by high-energy cosmic radiation.
In all cases, this enriched matter then gets incorporated (along with the leftover hydrogen and helium) into future generations of everything that forms next, including nebulae, stars and planets. This includes our own Solar System and everything in it, including the Sun and planet Earth. It's literally a fact that well over 90% (by mass) of everything on our world was at one point a part of a star, ejected back into interstellar space, often multiple times, before winding up as part of our thriving, biologically active world.
But when we look at the full gamut of elements in the periodic table, there's one missing that you might have expected to be there: the 43rd one, Technetium, a shiny, gray metal as dense as lead with a melting point of over 3,000 °F, that simply doesn't occur naturally on our world.
The reason it doesn't occur is because all of its isotopes are radioactive, with the longest-lived ones having a half-life of just a few million years. Even if the Earth was created with significant amounts of it, the odds are minuscule that there's even one atom of it left by now, after more than four billion years have passed. In fact, it's only from the decay of materials like Uranium ore (below) that Technetium is naturally produced, with each gram of Uranium giving rise to approximately one picogram (10^-12 g) of Technetium.
Sure, we can produce it from nuclear fission, where we've made tons of it, or from particle accelerators. We can even put one of its isotopes to good use for medicinal purposes, which we continue to do today. But even though this element doesn't occur naturally on Earth, it does occur in stars, and not through any of the processes we listed above. When stars produce Technetium, they do it through a process that's much more subtle than simply fusing elements together or creating them in the catastrophic environments of a supernova or neutron star merger.
It's the giant stars that make free neutrons while they burn helium, from the fusion of either carbon-13 or neon-22. Our Sun will someday become one, swelling to more than 100 times its present size as it does. When this occurs, and free neutrons are copiously produced, they get added to the heavy elements inside the star, one-at-a-time, allowing the elements to work their way, slowly, up the periodic table. You might think it's a long way to get up to Technetium, but stars live for hundreds of millions of years in this giant phase. There's a whole class of stars known as Technetium stars that showcase this element as part of their spectrum, with one of the brightest almost visible to the naked eye.
In reality, this capturing of slow neutrons allows us to build all the elements heavier than iron all the way up to lead and bismuth, but technetium is special because it's only naturally found in these giant stars. In fact, it's only visible after a specific stage in the life cycle of these stars: after the s-process elements produced in the core are dredged up and brought to the star's outer layers. Technetium was made in the laboratory back in the 1930s, but was first discovered in these giant stars in 1952, the only naturally occurring place in the Universe where it's been discovered in any sort of large abundance.
This is incredibly interesting, because it means that the Technetium must have been formed incredibly recently, because it would all be gone after just a few million years. As these giant stars reach the end of their lives, they'll eventually blow off their outer layers into planetary nebulae, further enriching the interstellar medium with material ripe to form the next generation of stars and planets.
But by time this occurs, there's already no Technetium left; it's a signature we've never found in a single planetary nebula. The brief timespan between when this short-lived element is brought to the surface and when the outer layers are blown off is long enough -- even at just a few million years -- that by time the material for the next generation of stars is available, there are no traces of this element left.
If you have enough energy, resources and time, you can construct Technetium artificially. But if you want to find it in nature? You've only got two options: either wait billions of years for the right radioactive decay to occur, or head towards the last stages of a red giant star's life, and bask in the presence of this short-lived metallic wonder. | 0.905079 | 3.869652 |
August 25, 2015 – The closest-yet views of Ceres, delivered by NASA’s Dawn spacecraft, show the small world’s features in unprecedented detail, including Ceres’ tall, conical mountain; crater formation features and narrow, braided fractures.
“Dawn is performing flawlessly in this new orbit as it conducts its ambitious exploration. The spacecraft’s view is now three times as sharp as in its previous mapping orbit, revealing exciting new details of this intriguing dwarf planet,” said Marc Rayman, Dawn’s chief engineer and mission director, based at NASA’s Jet Propulsion Laboratory, Pasadena, California.
At its current orbital altitude of 915 miles (1,470 kilometers), Dawn takes 11 days to capture and return images of Ceres’ whole surface. Each 11-day cycle consists of 14 orbits. Over the next two months, the spacecraft will map the entirety of Ceres six times.
The spacecraft is using its framing camera to extensively map the surface, enabling 3-D modeling. Every image from this orbit has a resolution of 450 feet (140 meters) per pixel, and covers less than 1 percent of the surface of Ceres.
At the same time, Dawn’s visible and infrared mapping spectrometer is collecting data that will give scientists a better understanding of the minerals found on Ceres’ surface.
Engineers and scientists will also refine their measurements of Ceres’ gravity field, which will help mission planners in designing Dawn’s next orbit — its lowest — as well as the journey to get there. In late October, Dawn will begin spiraling toward this final orbit, which will be at an altitude of 230 miles (375 kilometers).
Dawn is the first mission to visit a dwarf planet, and the first to orbit two distinct solar system targets. It orbited protoplanet Vesta for 14 months in 2011 and 2012, and arrived at Ceres on March 6, 2015.
Dawn’s mission is managed by JPL for NASA’s Science Mission Directorate in Washington. Dawn is a project of the directorate’s Discovery Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama. UCLA is responsible for overall Dawn mission science. Orbital ATK Inc., in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team. | 0.813578 | 3.114238 |
The NASA - Voyager 1 Spacecraft took this Narrow-Angle Camera image on March, 5, 1979 from a distance of about 69.000 Km (such as approx. 42.849 miles) from the Jovian, Volcanic moon Io. The Surface Feature shown here is an Unnamed Volcanic Caldera which may be actively spewing (--- ejecting at a very high velocity) Material into the Space around Io (look at the very dark brown-reddish "fuzz" located near the upper-right (Dx) side of the Caldera Rim).
In addition, a large amount of very dark Lava has flowed out of the Fissure (as a matter of fact, we, as IPF, believe that there are at least three Active Fissures located near the Edge of the Caldera) and spread on (---> covered part of) the Floor of the Caldera. The pinkish color of the Surface surrounding the Caldera is, most likely, due to the presence of extremely large quantities of Sulphur-based Particles which, being too light and slow, did not escape from the Gravity Field of Io and, some time after they were expelled from the Caldera (or - maybe - from other active Volcanoes located nearby), fell back down on the moon, like a "dusty rain".
This image (which is an Original Mars Odyssey Orbiter b/w and NON Map-Projected frame published on the NASA - Planetary Photojournal with the ID n. PIA 02288) has been additionally processed, extra-magnified to aid the visibility of the details, contrast enhanced and sharpened, Gamma corrected and then colorized (according to an educated guess - or, if you prefer, an informed speculation - carried out by Dr Paolo C. Fienga/LXTT/IPF) in Absolute Natural Colors (such as the colors that a normal human eye would actually perceive if someone were onboard the NASA - Voyager 1 Spacecraft and then looked ahead, towards the Jovian Volcanic moon Io), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team. | 0.841729 | 3.569324 |
A little reading and effort is recommended and the Wikipedia page is straight forward enough, if you're not completely math-phobic.
But if you want an answer, Rob Jeffries 9,500 km is right, however, that's center point to center point. Surface to surface, that would only be less than 2,000 km, which would be crazy close. That close the Moon would take up about (guessing) close to 50% of the sky, maybe 70 degrees or so, when directly overhead. But that 2000 km number doesn't take into account tidal stretching or rotation, as the Moon would almost certainly be tidally locked and rotating in sync with it's orbit like it does now and the Earth would be similarly tidally locked and have a tidal and gravitational bulge in the direction of the Moon.
Taking into account rotation, that pushes it out to the cube root of 3, not 2 or about 14% further, but that's center to center. The surface to surface distance would be increased to about 3,000 KM. Still insanely close. Any orbital eccentricity would increase instability though, so for a safe distance, Earth to Moon where the Moon wouldn't break apart at all, but it would still stretch measurably, I wouldn't want it any closer than about 5,000 or 6,000 km from the Earth's surface. That's a ballpark guess with tidal forces, tidal locking, solar perturbations and orbital eccentricity all in mind and even there, some loose moon dust and rocks might regularly blow off and shower onto the Earth. 6,000 KM (surface to surface) is less than twice the Moon's diameter, so it would still be enormous in the sky, but I think that's about the distance where the Moon would hold together in orbit. The math says even closer, but that doesn't take into effect various issues like eccentricity, rigidity, etc. It gets rather hard to calculate with rock solid accuracy taking into account all the details. But, point is, the Moon would need to be stupid/gonzo/cray close before it begins to break apart. Some 50-60 times closer (surface to surface) than it is now.
Now as far as escape, the math of the Hill Sphere or Sphere of Influence is pretty straight forward, but the long-term stable zone is about 1/2 to 1/3rd of the Hill Sphere calculation, some 500,000 to 750,000 km. Somewhere in there or perhaps just beyond that range the Moon probably becomes unstable and escapes the Earth's orbit becoming a very large and potentially very dangerous near earth object. That doesn't mean that the Moon would just fly away past 750,000 km. It would remain in orbit for multiple orbits, hundreds, maybe thousands even past that distance, but past the stable region it would probably destabilize over time and escape eventually.
The Moon is perhaps as much as 70% of the way towards where it could eventually escape the Earth, but that final 30% is a LOT. The moon isn't going anywhere anytime soon. It's still comfortably inside the long-term stable region and should remain orbiting the Earth for billions of years.
Hope that helps. | 0.837529 | 3.574269 |
I don’t know if the number of space enthusiasts working in the entertainment industry has increased or if people in general have started to like space more, but there has been a marked increase in the popularity of space-related media in the last decade. And thanks to movies like Star Trek, The Black Hole, Interstellar etc., black holes have been repeatedly featured on the big screen.
Black holes are quite an interesting ‘entity’, if one may call them that. They show some seriously mind-boggling features and since they are not ‘visible’, per se, can prove to be quite difficult to spot. Therefore, if you were to embark on a space journey in a hypothetical spacecraft that never runs out of fuel and can withstand any amount of damage, how often would you find black holes?
Before we answer that, it’s important to understand a few things…
What’s a ‘Black hole’?
The most basic way of defining a black hole would be to say that it’s a region of space-time that has such a strong gravitational field that nothing, not even light, can escape it. Since light does not escape them, black holes appear completely dark, or in effect, don’t appear at all, hence the name ‘black’ holes.
Why can’t light escape black holes?
Light travels very fast; clocking a speed of 300,000 kilometers per second (186,000 miles per second), which is no casual feat. Given that immense speed, it seems impossible to imagine something that could stop something as fast as light from escaping its grip.
Consider this: if you threw a ball hard enough to make it move at 12 kilometers per second, two things would happen: 1. the ball shall shoot into space, overcoming Earth’s gravity (because it would overcome Earth’s escape velocity of 11.2 km/s; 2. you would no longer be considered a normal human being. Likewise, the escape velocity of black holes is much greater than the speed of light, so light has a hard time leaving them.
When a massive star dies, it explodes as a supernova, leaving its core as either a neutron star or a black hole. However, these are not the only black holes. The observations of ground-based instruments and the Hubble Space Telescope have revealed the presence of unimaginably enormous supermassive black holes in the centers of galaxies that hold millions of solar-masses worth of material.
Furthermore, with our increasing information on other galaxies, scientists have also come to recognize the presence of extragalactic black holes. Furthermore, it’s believed that ‘seed’ black holes existed even before galaxies and stars were formed.
Chandra X-ray Observatory
The inception of the Chandra Observatory was a big step towards identifying and learning more about black holes. Previously referred to as the Advanced X-ray Astrophysics Facility (AXAF), it’s a space observatory that was launched by NASA in 1999. It is 100 times more sensitive to X-ray sources than anything that had previously been used, and it is one of the “Great Observatories”, which include legends like the Hubble Space Telescope, the Spitzer Space Telescope and the Compton Gamma Ray Observatory.
In 2001, it detected the first X-ray emission from a supermassive black hole called Sagittarius A, which is located in the center of our galaxy. It also confirmed the abundance of supermassive black holes in two ‘deep fields’, and indicated that these black holes had been more active in the past. It also discovered a new type of black hole in galaxy M82. The latest discovery of the observatory came in February 2016, when it recorded a jet from a very distant black hole named called B3 0727+409 that was being illuminated by the leftover glow from the Big Bang.
For more information about the Chandra Observatory and its latest findings, check out their website.
Black holes are quite common, at least more common than we thought a century ago. They may be even greater in number, but we need far more advanced space technology to get a proper ‘glimpse’ of these mysterious phenomena of our universe. | 0.874771 | 3.64256 |
October 23, 2019 report
Stardust machine shows presence of carbon nanograins, molecular compounds but few aromatics
A team of researchers affiliated with several institutions in Spain and one in France has built what they call their Stardust machine—a device that mimics the activity around a red giant where real stardust forms. In their paper published in the journal Nature Astronomy, the group describes their new machine and what it showed them about the means by which stardust forms naturally. Michael Gatchell, with Stockholm University, has published a News & Views piece discussing the work in the same journal issue.
Red giants are very large stars that are believed to be in a late stage of development in which their hydrogen has been depleted, leaving no fuel for fusion reactions. Scientists study them because they are believed to provide the building blocks for planets and other objects in the universe. Astronomers also believe that they are the source of stardust that exists in the interstellar medium. Stardust is believed to originate in the envelope that surrounds a red giant and has a complex composition—in addition to the interstellar molecule, scientists have identified over 200 unique molecular species. But because of the hostile environment in which stardust originates, it has been difficult for scientists to figure out how it forms.
Most experiments to mimic the process involve burning chemicals or plasma decomposition—but they have not yielded the answers researchers have been looking for. In this new effort, the researchers have taken another approach—building a machine to mimic the conditions in a red giant envelope. The researchers call it simply Stardust. With the ultra-high vacuum machine, researchers carry out bottom-up stardust formation experiments. Such experiments involve combining atomic gas aggregates with in situ characterizations.
The researchers report that experiments using Stardust have revealed that carbonaceous dust particles similar to those believed to be created near red giants could lead to the creation of randomly shaped carbon materials. They also found that aromatic species and fullerenes were not created under such conditions, which went against current theories regarding stardust formation. They suggest their findings are likely going to force a revision in circumstellar envelope theory.
© 2019 Science X Network | 0.803668 | 3.21275 |
NASA to launch Parker Solar Probe to touch the Sun
Parker Solar Probe will explore the corona, a region of the Sun only seen from Earth when the Moon blocks out the Sun's bright face during total solar eclipses.
The US space agency NASA on July 20, 2018 announced to launch the Parker Solar Probe, a robotic car-size spacecraft, to study the Sun and reveal multiple mysteries behind the star.
The spacecraft will be launched in August 2018 on the United Launch Alliance Delta IV Heavy from Cape Canaveral in Florida.
This planned seven-year mission will fly into the Sun's corona within 3.8 million miles (6.1 million km) from the solar surface, seven times closer than any other spacecraft.
Parker Solar Probe
• Parker Solar Probe is part of NASA’s Living with a Star Program to explore aspects of the Sun-Earth system that directly affect life and society.
• The spacecraft has been designed to endure wicked heat while zooming through the solar corona to study the outermost part of the stellar atmosphere that gives rise to the solar wind.
• Parker Solar Probe will fly down within 4 million miles of the sun's surface, facing heat and radiation like no spacecraft before it.
• It will provide new data on solar activity and will help scientists in forecasting major space-weather events that impact life on Earth.
What made this mission a reality?
Technology like the heat shield, solar array cooling system and fault management system has made such a mission a reality.
The heat shield called the Thermal Protection System (TPS) is a sandwich of carbon-carbon composite surrounding four and half inches of carbon foam.
The solar array cooling system allows the solar arrays to produce power under the intense thermal load from the Sun and the fault management system protects the spacecraft during the long periods of time when the spacecraft can’t communicate with the Earth.
The probe holds the answers of scientists' outstanding questions
• Parker Solar Probe will explore the corona, a region of the Sun only seen from Earth when the Moon blocks out the Sun's bright face during total solar eclipses.
• The corona holds the answers of scientists' outstanding questions about the Sun's activity and processes. Scientists hope to learn the secret of the corona's enormously high temperatures.
• The spacecraft is also expected to reveal the mechanisms at work behind the acceleration of solar energetic particles, which can reach speeds more than half as fast as the speed of light as they rocket away from the Sun.
Parker Solar Probe uses four suites of instruments
The spacecraft carries several instruments to study the Sun remotely or directly. Together, the data from these instruments will help scientists answer three foundational questions about the Sun.
• FIELDS suite: Led by the University of California, Berkeley, the FIELDS suite measures the electric and magnetic fields around the spacecraft. FIELDS captures waves and turbulence in the inner heliosphere with high time resolution.
• WISPR instrument: The Wide-Field Imager for Parker Solar Probe (WISPR) instrument is the only imaging instrument aboard the spacecraft.
• SWEAP suite: The SWEAP (Solar Wind Electrons Alphas and Protons Investigation) suite uses two complementary instruments to gather data. It measures properties as velocity, density, and temperature to improve our understanding of the solar wind and coronal plasma.
• ISʘIS suite: The ISOIS suite (Integrated Science Investigation of the Sun) measures particles across a wide range of energies. The symbol ‘ʘ’ stands for the Sun. | 0.810096 | 3.331342 |
WASHINGTON — When two extremely dense neutron stars crashed together in a distant galaxy, astronomers struck scientific gold, confirming previously unproven theories, including some from Albert Einstein.
Scientists announced Monday that after picking up two faint signals in mid-August, they were able to find the location of the long-ago crash and see the end of it play out. Measurements of the light and other energy that the crash produced helped them answer some cosmic questions.
Scientists, starting with Einstein, figured that when two neutron stars collide they would produce a gravitational wave, a ripple in the universe-wide fabric of space-time. Four other times that these waves were detected they were the result of merging black holes. This is the first time scientists observed one caused by a neutron star crash.
WHERE GOLD COMES FROM
The Big Bang created light elements like hydrogen and helium. Supernovas created medium elements, up to iron. But what about the heavier ones like gold, platinum and uranium? Astronomers thought they came from two neutron stars colliding, and when they saw this crash they confirmed it. One astronomer described as a “giant train wreck that creates gold.” They estimate that this one event generated an amount of gold and platinum that outweighs the entire Earth by a factor of 10.
Gamma ray bursts are some of the most energetic and deadly pulses of radiation in the universe. Astronomers weren’t quite sure where short gamma ray bursts came from, but figured that a crash of neutron stars was a good bet. Watching this event confirmed the theory.
Astronomers know the universe is expanding, and they use a figure called the Hubble Constant to describe how fast. Two different ways scientists have of measuring this speed of expansion yields two numbers that are somewhat close to each other, but not quite the same. By measuring how far the gravitational wave had to travel, astronomers came up with another estimate that was between the earlier two, but it also comes with a large margin of error.
HOW FAST DO RAYS AND WAVES GO?
The crash showed that gravitational waves and gamma rays travel at nearly the speed of light — which is what Einstein’s General Relativity theory says. NASA astrophysicist Julie McEnery said: “Yet again, Einstein passes another test.” | 0.833694 | 3.625869 |
India Leapfrogs to Moon Club
Doing what no one has ever done before requires steely determination and ginormous aptitude. Scientists at the Indian Space Research Organisation possess both in ample quantities and then some more. Over 1000 scientists worked relentlessly over the past several years on the ambitious Chandrayaan 2, a mission that promises to once again stamp India as a dominant player in space exploration. On 22nd July, a shimmering golden spacecraft roared skyward on a pillar of flame at2:43 p.m. . commonly called as Chandrayaan-2, the Bahubali spacecraft is now on its way to the moon’s south polar region, and if all goes well, its lander will touch down there in early September.
With this mission, India is aiming to become the first country ever to achieve a soft, controlled landing so close to the moon’s south pole, and just the fourth country ever to land softly on the lunar surface, joining Russia, the United States, and China.
Its scientific instruments will shed light on the moon’s mysterious interior and thin exosphere, and they will provide key details about the chemistry of the moon’s south polar region, which no superpower has attempted before.
What is Chandrayaan-2, and why is it significant?
The Chandrayaan-2 mission is the latest lunar spacecraft sent to the moon by India’s national space agency, the Indian Space Research Organization, or ISRO. The mission aims to follow up on 2008’s Chandrayaan-1 orbiter, India’s first lunar spacecraft. Though the orbiter died prematurely—10 months into a two-year-mission—its data proved crucial in detecting frozen water on the moon’s surface. It also gave huge motivation to the scientists involved in that mission and also the courage to attempt the unthinkable till now.
Sriram Bhairavarasu, a postdoctoral fellow at the Lunar and Planetary Institute and a former member of the Chandrayaan-2 radar team said while talking to nationalgeographic “Chandrayaan-1 in the last decade inspired so many levels within the country, and I am one of them; I started my Ph.D. in 2009 after the mission was launched, and I was an ISRO research fellow for the next seven years. It’s a big part of me.”
Chandrayaan-2’s safe descent would add to a remarkable string of successes for ISRO’s planetary science program. When the Mangalyaan Mars Orbiter(MOM) was safely landed at Mars in 2014, it made India the first country ever to successfully visit the red planet on its first attempt. ISRO’s science missions are also notable for their relatively low prices. Complex missions to other worlds regularly cost billions to build—but with a reported budget of $144 million, Chandrayaan-2 costed much lower than the science fiction film Interstellar.
The new moon mission is setting another milestone, as the first in ISRO’s history where women were at the helm of the project. Muthayya Vanitha, the mission’s project director, previously worked on Mangalyaan, and Ritu Karidhal, Chandrayaan-2’s mission director, played a major role in ensuring MOM’s successful arrival at the red planet. With an association of over three decades with ISRO, there could not have been a better choice for Project Director of Chandrayaan 2 than Vanitha Muthayya.
Vanitha has a degree in electronics and communication and a number of media reports suggest that despite all her experience, she was initially reluctant to be the Project Director of Chandrayaan 2 but was eventually persuaded. After all, her experience as a systems engineer made her the right candidate.
Karidhal has played a massive role in Chandrayaan 2’s successful launch and has had to shoulder massive responsibility to deliver on the plans. She has been quoted in previous media reports as saying that she and the entire team – irrespective of gender – have had to work extremely long hours on the Chandrayaan 2 mission over the past several years.
Karidhal is an alumnus of IISC in Bengaluru from where she completed her M.Tech. This after an M.Sc. in Physics from Lucknow University. She would join ISRO in 1997 and soon proved herself through sheer hard work.
Where and how will Chandrayaan-2 be landing?
As per a report in national geographic three previous missions, including Chandrayaan-1, sent probes careening into the lunar south pole to throw up debris clouds on impact that overhead orbiters could chemically analyze. And in 2009, operators of the Japanese orbiter Kaguya (SELENE) guided the aging spacecraft into the ground near the southern Gill crater. But Chandrayaan-2 is designed to descend in a controlled manner and operate on the surface. Unlike Chandrayaan-1, which consisted only of an orbiter, Chandrayaan-2 includes an orbiter, a lander, and a rover.
The report says that to help ensure a soft landing, Chandrayaan-2 isn’t making a straight shot at the moon. It will start its trek by orbiting Earth, and its onboard thrusters will progressively take the spacecraft farther away over several orbits, until it sets course for the moon. Once near the moon, Chandrayaan-2 will fire its thrusters to enter a circular lunar orbit about 62 miles above its surface.
The orbiter will then separate from its precious cargo: the 3,243-pound Vikram lander. Vikram—named after physicist Vikram Sarabhai, ISRO’s first chairman—will then autonomously brake and scan the lunar surface to detect craters and possible obstacles.
If all goes well, Vikram will touch down on the moon on September 6, alighting onto either of the landing sites between the crater Manzinus C and Simpelius N, at a latitude of about 70 degrees south. Strictly speaking, Vikram won’t be landing on the lunar south pole, but it’s by far the southernmost controlled landing ever attempted on the moon.
Soon after landing, Vikram will unfold a ramp, and Pragyaan will pop out. This 60-pound rover, named after the Sanskrit word for “wisdom,” is designed to cover a distance of 1,640 feet, powered by a 50-watt solar panel. Vikram and Pragyaan are designed to last an entire lunar day, or about two Earth weeks. Though it’s unclear whether they will survive the frigid lunar night, their orbiter companion will last for another year.
What the mission will attempt
Chandrayaan-2 is carrying 13 scientific patyloads: eight on its orbiter, three on the Vikram lander, and two on the Pragyaan rover.
The orbiter, essentially an upgraded version of Chandrayaan-1, carries a camera that can map the moon’s surface with 16-foot resolution. It also can map the surface occurrence of certain elements such as magnesium, and it will be able to detect the composition of the moon’s whisper-thin exosphere. One particular camera will provide Vikram and Pragyaan with high-resolution images of their landing site. And its radar system will be able to peer into areas of perpetual shadow within the poles’ craters. If “dirty ice” mixed with lunar soil is hiding there, Chandrayaan-2 will be able to see it.
Vikram’s payload includes a seismometer designed to detect moonquakes, and it will carry a probe to measure the density of electrons and other charged particles near the moon’s surface. The Pragyaan rover also packs a scientific punch: It will be lugging around a block of radioactive curium-244 that will spit out x-rays and high-energy particles. As this glow washes over nearby rocks, the elements within them will fluoresce, letting Pragyaan see their chemical makeup.
The mission’s overall goal is to better understand the distribution of water ice and other compounds preserved near the lunar poles, as well as the structure of the moon’s interior. Such research will help our scientistsnot only to better understanding of the origins of the moon and the solar system,but, also will help future astronauts better map potential sources of water. | 0.809158 | 3.091662 |
Hubble celebrates its 29th birthday with unrivaled view of the Southern Crab Nebula [heic1907]
18 April 2019This incredible image of the hourglass-shaped Southern Crab Nebula was taken to mark the NASA/ESA Hubble Space Telescope's 29th anniversary in space. The nebula, created by a binary star system, is one of the many objects that Hubble has demystified throughout its productive life. This new image adds to our understanding of the nebula and demonstrates the telescope's continued capabilities.
|The Crab of the Southern Sky. Credit: NASA, ESA, and STScI, CC BY 4.0|
On 24 April 1990, the NASA/ESA Hubble Space Telescope was launched on the space shuttle Discovery. It has since revolutionised how astronomers and the general public see the Universe. The images it provides are spectacular from both a scientific and a purely aesthetic point of view.
Each year the telescope dedicates a small portion of its precious observing time to take a special anniversary image, focused on capturing particularly beautiful and meaningful objects. This year's image is the Southern Crab Nebula, and it is no exception .
This peculiar nebula, which exhibits nested hourglass-shaped structures, has been created by the interaction between a pair of stars at its centre. The unequal pair consists of a red giant and a white dwarf. The red giant is shedding its outer layers in the last phase of its life before it too lives out its final years as a white dwarf. Some of the red giant's ejected material is attracted by the gravity of its companion.
When enough of this cast-off material is pulled onto the white dwarf, it too ejects the material outwards in an eruption, creating the structures we see in the nebula. Eventually, the red giant will finish throwing off its outer layers, and stop feeding its white dwarf companion. Prior to this, there may also be more eruptions, creating even more intricate structures.
Astronomers did not always know this, however. The object was first written about in 1967, but was assumed to be an ordinary star until 1989, when it was observed using telescopes at the European Southern Observatory's La Silla Observatory. The resulting image showed a roughly crab-shaped extended nebula, formed by symmetrical bubbles of gas and dust.
These observations only showed the outer hourglass emanating from a bright central region that could not be resolved. It was not until Hubble observed the Southern Crab in 1999 that the entire structure came into view. This image revealed the inner nested structures, suggesting that the phenomenon that created the outer bubbles had occurred twice in the (astronomically) recent past.
It is fitting that Hubble has returned to this object twenty years after its first observation. This new image adds to the story of an active and evolving object and contributes to the story of Hubble's role in our evolving understanding of the Universe.
The Southern Crab Nebula is so named to distinguish it from the better-known Crab Nebula, a supernova remnant visible in the constellation of Taurus.
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
ESA/Hubble, Public Information Officer | 0.854 | 3.750545 |
Only a small fraction of the isotopes are known to be stable indefinitely. All the others disintegrate spontaneously with the release of energy by processes broadly designated as radioactive decay. For full treatment, see isotope:
|Radioactive Sources; Isotopes and Uranium Ore||Natural[ edit ] On Earth, naturally occurring radionuclides fall into three categories: Radionuclides are produced in stellar nucleosynthesis and supernova explosions along with stable nuclides.|
|Radioisotopes in Medicine | Nuclear Medicine - World Nuclear Association||Except orders going to Canada, which are shipped FedEx Economy. Call or email for pricing.|
|What are the medicinal uses of radioactive isotopes||Sealed radioactive sources are used in industrial radiography, gauging applications, and mineral analysis. The attributes of naturally decaying atoms, known as radioisotopes, give rise to their multiple applications across many aspects of modern day life see also information paper on The Many Uses of Nuclear Technology.|
The letter m is sometimes appended after the mass number to indicate a nuclear isomera metastable or energetically-excited nuclear state as opposed to the lowest-energy ground statefor example m 73Ta The common pronunciation of the AZE notation is different from how it is written: For example, 14 C is a radioactive form of carbon, whereas 12 C and 13 C are stable isotopes.
Primordial nuclides include 32 nuclides with very long half-lives over million years and that are formally considered as " stable nuclides ", because they have not been observed to decay.
In most cases, for obvious reasons, if an element has stable isotopes, those isotopes predominate in the elemental abundance found on Earth and in the Solar System. However, in the cases of three elements tellurium, indium, and rhenium the most abundant isotope found in nature is actually one or two extremely long-lived radioisotope s of the element, despite these elements having one or more stable isotopes.
Of the nuclides never observed to decay, only 90 of these all from the first 40 elements are theoretically stable to all known forms of decay. Element 41 niobium is theoretically unstable via spontaneous fissionbut this has never been detected. Many other stable nuclides are in theory energetically susceptible to other known forms of decay, such as alpha decay or double beta decay, but no decay products have yet been observed, and so these isotopes are said to be "observationally stable".
The predicted half-lives for these nuclides often greatly exceed the estimated age of the universe, and in fact there are also 27 known radionuclides see primordial nuclide with half-lives longer than the age of the universe.
Adding in the radioactive nuclides that have been created artificially, there are 3, currently known nuclides. See list of nuclides for details.
Radioactive isotopes[ edit ] The existence of isotopes was first suggested in by the radiochemist Frederick Soddybased on studies of radioactive decay chains that indicated about 40 different species referred to as radioelements i.
Soddy proposed that several types of atoms differing in radioactive properties could occupy the same place in the table. Richards found variations between the atomic weight of lead from different mineral sources, attributable to variations in isotopic composition due to different radioactive origins.
Thomson in as part of his exploration into the composition of canal rays positive ions. Each stream created a glowing patch on the plate at the point it struck. Thomson observed two separate patches of light on the photographic plate see imagewhich suggested two different parabolas of deflection.
Thomson eventually concluded that some of the atoms in the neon gas were of higher mass than the rest. Aston subsequently discovered multiple stable isotopes for numerous elements using a mass spectrograph. In Aston studied neon with sufficient resolution to show that the two isotopic masses are very close to the integers 20 and 22, and that neither is equal to the known molar mass Aston similarly showed[ when?
Thus different isotopes of a given element all have the same number of electrons and share a similar electronic structure. Because the chemical behavior of an atom is largely determined by its electronic structure, different isotopes exhibit nearly identical chemical behavior.
The main exception to this is the kinetic isotope effect: This is most pronounced by far for protium 1 H.The objective of the challenge is for the group to retrieve a bucket containing deadly radioactive isotope and tip the contents into a second bucket in a defined safety zone.
The team only have a rope to complete the challenge and they cannot enter the marked off area. Stable isotopes do not undergo radioactive decay.
WHAT IS A STABLE ISOTOPE? A "stable isotope" is any of two or more forms of an element whos nuclei contains the same number of protons and electrons, but a different number of neutrons. Diagnostic techniques in nuclear medicine use radioactive tracers which emit gamma rays from .
Medical Use of Radioisotopes Medical Imaging Thanks to radioactive isotopes, images can be obtained via gamma camera or a PET scan in nuclear diagnostics.
Radioactive isotope, also called radioisotope, radionuclide, or radioactive nuclide, any of several species of the same chemical element with different masses whose nuclei are unstable and dissipate excess energy by spontaneously emitting radiation in the form of alpha, beta, and gamma rays.
Other significant applications include the use of radioactive isotopes as compact sources of electrical power—e.g., plutonium in spacecraft.
In such cases, the heat produced in the decay of the radioactive isotope is converted into electricity by means of thermoelectric junction circuits or related devices. The objective of the challenge is for the group to retrieve a bucket containing deadly radioactive isotope and tip the contents into a second bucket in a defined safety zone.
The team only have a rope to complete the challenge and they cannot enter the marked off area. | 0.886564 | 3.466312 |
Jet Propulsion Laboratory News Release
2013 July 25
PASADENA, Calf. -- The true identity of centaurs, the small celestial bodies orbiting the sun between Jupiter and Neptune, is one of the enduring mysteries of astrophysics. Are they asteroids or comets? A new study of observations from NASA's Wide-field Infrared Survey Explorer (WISE) finds most centaurs are comets.
Until now, astronomers were not certain whether centaurs are asteroids flung out from the inner solar system or comets traveling in toward the sun from afar. Because of their dual nature, they take their name from the creature in Greek mythology whose head and torso are human and legs are those of a horse.
"Just like the mythical creatures, the centaur objects seem to have a double life," said James Bauer of NASA's Jet Propulsion Laboratory in Pasadena, Calif. Bauer is lead author of a paper published online July 22 in the Astrophysical Journal. "Our data point to a cometary origin for most of the objects, suggesting they are coming from deeper out in the solar system."
"Cometary origin" means an object likely is made from the same material as a comet, may have been an active comet in the past, and may be active again in the future.
The findings come from the largest infrared survey to date of centaurs and their more distant cousins, called scattered disk objects. NEOWISE, the asteroid-hunting portion of the WISE mission, gathered infrared images of 52 centaurs and scattered disk objects. Fifteen of the 52 are new discoveries. Centaurs and scattered disk objects orbit in an unstable belt. Ultimately, gravity from the giant planets will fling them either closer to the sun or farther away from their current locations.
Although astronomers previously observed some centaurs with dusty halos, a common feature of outgassing comets, and NASA's Spitzer Space Telescope also found some evidence for comets in the group, they had not been able to estimate the numbers of comets and asteroids.
Infrared data from NEOWISE provided information on the objects' albedos, or reflectivity, to help astronomers sort the population. NEOWISE can tell whether a centaur has a matte and dark surface or a shiny one that reflects more light. The puzzle pieces fell into place when astronomers combined the albedo information with what was already known about the colors of the objects. Visible-light observations have shown centaurs generally to be either blue-gray or reddish in hue. A blue-gray object could be an asteroid or comet. NEOWISE showed that most of the blue-gray objects are dark, a telltale sign of comets. A reddish object is more likely to be an asteroid.
"Comets have a dark, soot-like coating on their icy surfaces, making them darker than most asteroids," said the study's co-author, Tommy Grav of the Planetary Science Institute in Tucson, Ariz. "Comet surfaces tend to be more like charcoal, while asteroids are usually shinier like the moon."
The results indicate that roughly two-thirds of the centaur population are comets, which come from the frigid outer reaches of our solar system. It is not clear whether the rest are asteroids. The centaur bodies have not lost their mystique entirely, but future research from NEOWISE may reveal their secrets further.
The paper is available online at: http://iopscience.iop.org/0004-637X/773/1/22/ .
JPL, managed by the California Institute of Technology in Pasadena, managed and operated WISE for NASA's Science Mission Directorate. The NEOWISE portion of the project was funded by NASA's Near Earth Object Observation Program. WISE completed its key mission objective, two scans of the entire sky, in 2011 and has been hibernating in space since then.
For more information about the WISE mission, visit: http://www.nasa.gov/wise .
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Neutron star smashup 'transforms' our understanding of Universe
PARIS, France – For the first time, scientists have witnessed the cataclysmic crash of two ultra-dense neutron stars in a galaxy far away, and concluded that such impacts forged at least half the gold in the Universe.
Shockwaves and light flashes from the collision travelled some 130 million light-years to be captured by Earthly detectors on August 17, excited teams revealed at press conferences held around the globe on Monday as a dozen related science papers were published in top academic journals.
"We witnessed history unfolding in front of our eyes: two neutron stars drawing closer, closer... turning faster and faster around each other, then colliding and scattering debris all over the place," co-discoverer Benoit Mours of France's CNRS research institute told Agence France-Presse.
The groundbreaking observation solved a number of physics riddles and sent ripples of excitement through the scientific community.
Most jaw-dropping for many, the data finally revealed where much of the gold, platinum, uranium, mercury and other heavy elements in the Universe came from.
Telescopes saw evidence of newly-forged material in the fallout, the teams said – a source long suspected, now confirmed.
"It makes it quite clear that a significant fraction, maybe half, maybe more, of the heavy elements in the Universe are actually produced by this kind of collision," said physicist Patrick Sutton, a member of the US-based Laser Interferometer Gravitational-Wave Observatory (LIGO) which contributed to the find.
Neutron stars are the condensed, burnt-out cores that remain when massive stars run out of fuel, blow up, and die.
Typically about 20 kilometers (12 miles) in diameter, but with more mass than the Sun, they are highly radioactive and ultra-dense – a handful of material from one weighs as much as Mount Everest.
It had been theorized that mergers of two such exotic bodies would create ripples in the fabric of space-time known as gravitational waves, as well as bright flashes of high-energy radiation called gamma ray bursts.
On August 17, detectors witnessed both phenomena, 1.7 seconds apart, coming from the same spot in the constellation of Hydra.
"It was clear to us within minutes that we had a binary neutron star detection," said David Shoemaker, another member of LIGO, which has detectors in Livingston, Louisiana and Hanford, Washington.
"The signals were much too beautiful to be anything but that," he told Agence France-Presse.
The observation was the fruit of years of labor by thousands of scientists at more than 70 ground- and space-based observatories on all continents.
Along with LIGO, they include teams from Europe's Virgo gravitational wave detector in Italy, and a number of ground- and space-based telescopes including NASA's Hubble.
"This event marks a turning point in observational astronomy and will lead to a treasure trove of scientific results," said Bangalore Sathyaprakash from Cardiff University's School of Physics and Astronomy, recalling "the most exciting of my scientific life."
"It is tremendously exciting to experience a rare event that transforms our understanding of the workings of the Universe," added France Cordova, director of the National Science Foundation which funds LIGO.
The detection is another feather in the cap for German physicist Albert Einstein, who first predicted gravitational waves more than 100 years ago.
Three LIGO pioneers, Barry Barish, Kip Thorne and Rainer Weiss, were awarded the Nobel Physics Prize this month for the observation of gravitational waves, without which the latest discovery would not have been possible.
The ripples have been observed four times before now – the first time by LIGO in September 2015. All four were from mergers of black holes, which are even more violent than neutron star crashes, but emit no light.
The fifth and latest detection was accompanied by a gamma ray burst which scientists said came from nearer in the Universe and was less bright than expected.
"What this event is telling us is that there may be many more of these short gamma ray bursts going off nearby in the Universe than we expected," Sutton said – an exciting prospect for scientists hoping to uncover further secrets of the Universe.
Among other things, it is hoped that data from neutron star collisions will allow the definitive calculation of the rate at which the cosmos is expanding, which in turn will tell us how old it is and how much matter it contains.
"With these observations we are not just learning what happens when neutron stars collide, we're also learning something fundamental about the nature of the Universe," said Julie McEnery of the Fermi gamma ray space telescope project. – Rappler.com | 0.844359 | 3.769561 |
In 1930 a 20-year-old Indian student named Subrahmanyan Chandrasekhar was sailing from Madras to England to pursue his studies in astrophysics. During the voyage he toyed with equations describing the stability of stars. And from a few lines of this mathematics, a momentous discovery emerged.
Astronomers of the day had only a sketchy understanding of what makes stars tick. They knew that a star is a ball of hot gas engaging in a cosmic balancing act. The gas tries to expand out into the vacuum of the surrounding space but gravity holds it back. In stars like the sun, an equilibrium is achieved, but only as long as the gas burns fuel to generate heat, which we now know is produced by nuclear reactions in the core.
However, uncertainty surrounded the question of what happens when the fuel runs out. It seemed that gravity would inevitably gain the upper hand, causing the star to contract, and the smaller the radius, the fiercer the gravitational force would become at the surface. Astronomers had long been familiar with tiny stars known as white dwarfs, which contain a mass comparable to the sun but squashed into a volume roughly the size of the Earth. These burned-out stellar remnants are so dense that their atoms are pressed cheek by jowl. Further compression would mean the atoms themselves would be crushed, which was initially assumed to be impossible due to the laws of quantum physics.
From his nautical calculations Chandrasekhar discovered otherwise. The equations suggested that if a star has a big enough mass, the crushing effect of its immense gravity would cause the atomic electrons to approach the speed of light, rendering the stellar material more squishy and heralding the further gravitational collapse of the star. In the absence of any other factor, the ball of matter would implode totally and vanish down its own gravitational well, forming an object that today we call a black hole. But in the early 1930s such an object was considered too outlandish to take seriously.
Chandrasekhar was able to calculate the critical mass above which this gravitational instability would set in. The answer he obtained was 1.44 solar masses, now known as the Chandrasekhar limit. On reaching England, he announced his result, only to find it was ignored or dismissed as nonsense from a young upstart. The most distinguished astronomer of the day, Sir Arthur Eddington, publicly ridiculed Chandrasekhar in an infamous encounter at the Royal Astronomical Society in 1935, declaring that there should be a law of nature “to prevent a star from behaving in this absurd way!”
Yet history proved Eddington wrong. If a burned-out star has a mass exceeding Chandrasekhar’s limit, it does indeed collapse. One possible fate is to form a so-called neutron star, in which the atoms are crushed into neutrons and the object stabilises at a radius about the size of Sydney. Neutron stars were discovered in the 1960s and today form an important branch of astronomy. Most of them have masses not far from the Chandrasekhar limit. More massive stars end their days by totally collapsing. When they shrink to a few kilometres across, their gravity is so great that even light cannot escape, and a black hole results.
Although it took decades for the concept of a black hole to be fully understood and accepted, the basic idea was hiding in plain sight since just after Albert Einstein first published his general theory of relativity in 1915. Chandrasekhar acknowledged this in his 1983 Nobel Prize address, where he wrote: “This important result is implicit in a fundamental paper by Karl Schwarzschild published in 1916”. Although the theoretical possibility of a black hole was inherent all along in Einstein’s theory, it took the youthful genius of Chandrasekhar to prove that such an object could result from the transformation of a dying star.
By the time of the Prize, the existence of black holes had become firmly established, and Subrahmanyan Chandrasekhar’s calculations fully vindicated. Yet he was so stung by Eddington’s derision, he decided to leave the UK in 1937 and settle in the US, where he followed a distinguished career until his death in 1995.
Chandrasekhar died leaving open a fascinating question. Might there exist an intermediate state between a neutron star and a black hole? This would be an object above 1.44 solar masses, too heavy to form a neutron star, but prevented from total collapse by an exotic form of ultra-dense matter such as a soup of quarks – the constituents of protons and neutrons. To date nobody has discovered a quark star, but the notion remains a theoretical possibility, perhaps awaiting the attention of another student genius with the insight to settle the matter.
Paul Davies is Regents' Professor and Director of the Beyond Centre for Fundamental Concepts in Science at Arizona State University. He is also a prolific author, and Cosmos columnist.
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There’s never been a more important time to explain the facts, cherish evidence-based knowledge and to showcase the latest scientific, technological and engineering breakthroughs. Cosmos is published by The Royal Institution of Australia, a charity dedicated to connecting people with the world of science. Financial contributions, however big or small, help us provide access to trusted science information at a time when the world needs it most. Please support us by making a donation or purchasing a subscription today. | 0.848628 | 4.069283 |
Live 60Fe has recently been reported in a deep-ocean ferromanganese crust. Analysis of the isotopic ratios in the sample suggests that the measured 60Fe abundance exceeds the levels generated by terrestrial and cosmogenic sources, and it has been proposed that the excess of 60Fe is a signature of a supernova that exploded near the earth several Myr ago. In this paper, we consider the possible background sources, and confirm that the measured 60Fe is significantly higher than all known backgrounds, in contrast with the reported abundance of live 53Mn in the same sample. We discuss scenarios in which the data are consistent with a supernova event at a distance D∼30 pc and an epoch tSN∼5 Myr ago. We propose tests that could confirm or refute the interpretation of the 60Fe discovery, including searches for 10Be, 129I and 146Sm. Such a nearby supernova event might have had some impact on the earth's biosphere, principally by enhancing the cosmic-ray flux. This might have damaged the earth's ozone layer, enhancing the penetration of solar ultraviolet radiation. In this connection, we comment on the Middle Miocene and Pliocene mini-extinction events. We also speculate on the possibility of a supernova-induced "cosmic-ray winter", if cosmic rays play a significant role in seeding cloud formation. | 0.82643 | 3.084287 |
Sunday, May 20, 2012
Oerter contra the principle of causality
The Scholastic principle of causality states that any potential, if actualized, must be actualized by something already actual. (It is also sometimes formulated as the thesis that whatever is moved is moved by another or whatever is changed is changed by another. But the more technical way of stating it is less potentially misleading for readers unacquainted with Scholastic thinking, who are bound to read things into terms like “motion” or “change” that Scholastic writers do not intend.)
In an earlier post I responded to an objection to the principle raised by physicist Robert Oerter, who has, at his blog, been writing up a series of critical posts on my book The Last Superstition. Oerter has now posted two further installments in his series, which develop and defend his criticism of the principle of causality. Let’s take a look.
Quantum mechanics and causality
Recall that in an earlier post Oerter claimed that quantum mechanics casts doubt on the principle of causality insofar as it describes “systems that change from one state to another without any apparent physical ‘trigger.’” Recall also that I pointed out that it is simply a fallacy to infer from the premise that QM describes such-and-such a state without describing its cause to the conclusion that QM shows that such-and-such a state has no cause.
In the first of the two further installments he’s posted since my response, Oerter replies to this sort of objection as follows:
This is a valid point. Just because quantum mechanics… is the most amazingly well-tested, most accurate, most far-reaching description of the universe that we have ever produced, we can't just conclude that it's the end of the story. Maybe quantum mechanics is incomplete - maybe there is some further, more precise, theory that will tell us about the causes of electron transitions and radioactive decay…
This very point was raised in a famous paper by Einstein, Podolsky, and Rosen, who argued in 1935 that quantum mechanics must be incomplete… An [sic] major advance came in 1964, when John Bell showed that (under a very general set of assumptions) any attempt to “complete” quantum mechanics would end up making predictions that differed from those of QM. This led to a series of experiments designed to look for such differences. The upshot: quantum mechanics has come out the winner in every test to date…
[A]ny additional “causes” added to quantum mechanics will result in violations of quantum mechanical predictions.
Let's suppose that there is some physical property - something not included in the quantum mechanical description - that determines for each atom exactly when the electron will decay. Call it property A. Since property A is a physical property, it must have some physical effect. If it has some physical effect, then it must be possible to separate out systems with one value of property A from systems with some other value. That is, we can use property A as a filter…
Applying this filter, we separate out a subset from our original set of identically prepared atoms. This subset, having a physical difference from the original set, will have a measurably different set of physical properties… Thus, this subset will violate the rules of quantum mechanics.
Now, I put it to you that the 100-year history of successful predictions of quantum mechanics strongly suggests that there are no such additional physical properties…
End quote. Now, to see what is wrong with this, recall the analogy I drew in my previous post with Kepler’s laws of planetary motion. I noted that it would be fallacious to argue from the premise that Kepler’s laws describe the orbits of the planets without making reference to any cause of those orbits to the conclusion that Kepler’s laws show that the orbits of the planets have no cause. And it would remain fallacious whatever you think about Kepler’s laws and whether or not you think the orbits of the planets have a cause. For the point has nothing to do with the truth or falsity of either the premise or the conclusion. It has to do instead with the logical relationship between the premise and conclusion. The premise doesn’t entail the conclusion, and it doesn’t even make the conclusion more probable. It is evidentially irrelevant to the conclusion.
Hence, suppose someone who insisted that Kepler’s laws do show that the planetary orbits have no cause responded to criticism of this fallacious inference by saying: “That’s a valid point. Even though Kepler’s laws have had tremendous predictive success, they may not be the end of the story. Maybe some future theory will posit some heretofore unknown massive bodies additional to the ones we already know about (the sun, planets, asteroids, etc.), which make the planets orbit the sun in just the way they do. But the problem is that if there were such further bodies, they would influence the ones we do know about in such a way that their behavior would not match Kepler’s predictions. So the success of Kepler’s laws strongly suggests that there are no such additional bodies. So Kepler’s laws really do give us reason to doubt that the orbits of the planets have any cause.”
Such a response would, of course, completely miss the point. For the point has nothing at all to do with the empirical question of whether there exist some heretofore unknown bodies additional to the sun, planets, asteroids, etc. which exert a causal influence on the rest of the solar system. The point is much simpler (though also much deeper) than that sort of issue. It is not a point about the existence of causes of this or that particular kind, but a point about causality as such. And the point is that Kepler’s laws, which merely describe the behavior of the planets, tell you nothing one way or the other about why the planets behave that way. They are not even addressing that question. Hence they cannot answer that question. Nor (we might note for those who eschew metaphysics) can they tell you whether the question is a good question, whether it has any answer in the first place, etc. To the issue at hand, they are simply irrelevant.
Now the same thing is true of the relationship between QM and the principle of causality. To point out that it is fallacious to infer from the premise that QM describes such-and-such a state without describing its cause to the conclusion that QM shows that such-and-such a state has no cause, is not to say that for all we know there may be some heretofore undiscovered physical property which exerts an influence on the energy level of the electron (or whatever). The point is much simpler (though also much deeper) than that sort of issue. It is that QM, which merely describes the behavior of a system, tells you nothing one way or the other about why the system behaves that way. It also tells you nothing one way or the other about whether the question of why it behaves that way is a good question, whether it has any answer in the first place, etc. To the issue at hand, QM is simply irrelevant.
This naturally brings us to another objection to his position that Oerter considers in his recent post, to the effect that the principle of causality is “a metaphysical premise that can't be contradicted by any possible set of observations.” Oerter’s reply is that to insist, on metaphysical grounds, that the actualization of a potential must always have a cause is either to beg the question against him, or to rest one’s position on definitions of the key terms (“actuality,” “potentiality,” “change,” etc.) without giving any reason to think that the terms so defined really capture anything in the real world.
To see what is wrong with this response, consider once again the fallacious inference from the premise that Kepler’s laws describe the orbits of the planets without making reference to any cause of those orbits to the conclusion that Kepler’s laws show that the orbits of the planets have no cause. Suppose that when you pointed out the fallaciousness of this inference to someone who made it, he replied: “Your position either begs the question against me or rests on arbitrary definitions!” Obviously this too would simply miss the point, since the criticism of the inference in question was not: “The orbits of the planets do have a cause, here’s my theory about what that cause is, here are the technical terms my theory makes use of, etc.” The criticism was rather: “Whether or not the orbits of the planets really do have a cause, the inference you are making is fallacious, because Kepler’s laws by themselves aren’t even relevant to that particular question.” Similarly, the inference from the premise that QM describes such-and-such a state without describing its cause to the conclusion that QM shows that such-and-such a state has no cause is fallacious, and it remains fallacious whether or not the principle of causality is true, whether or not the definitions of its key terms have any application to reality, etc. Even if the Aristotelian position turned out to be false, quantum mechanics wouldn’t be what falsifies it.
Oerter also addresses another potential objection to his position, to the effect that “the laws of quantum mechanics are the cause of the change [i.e. the change described in examples of the sort Oerter appeals to].” The first part of Oerter’s response is as follows:
This objection can be dismissed easily. The question is what causes the change to happen at the particular time it happens. QM is silent on this question.
Further, in most philosophical views of physical laws, the laws have no causal efficacy. For instance, we might think of laws as just descriptions of the way things actually behave. But a description of how something happens is not a cause of it happening. So, the moon's orbit around the earth isn't caused by the law of gravity. It's caused by the actual gravity of the actual earth.
Now as it happens I more or less agree with what Oerter says here. Indeed, it is ironic that he should say it, because it actually supports my position rather than his. Oerter writes that “we might think of laws as just descriptions of the way things actually behave.” Exactly. Laws -- including the laws enshrined in QM -- are descriptive. They tell you what happens, but they do not tell you why it happens that way. They may, of course, make reference to particular sorts of causal factors -- gravitation, mass, charge, etc. -- but the explication of these factors itself simply amounts to a further description of what these causes do, not why they do it. Indeed, the causality as such of gravitation, mass, etc. is, strictly speaking, irrelevant to the laws. That A and B will behave in such-and-such a way is all the law qua law commits you to; that A is the cause of B drops out as irrelevant. That is why Newton’s law of universal gravitation was so useful even when we had no clear idea of what gravity was or how it worked. And that is why positivists could hold that causality was a pre-scientific holdover which could be dispensed with. They were wrong to hold this, but the point is that they could hold it with a straight face in the first place only because the status of causality as such -- its nature and even its existence -- is something about which the laws of physics themselves (including the laws of QM) are silent.
But the status of causality as such is precisely what the principle of causality is about. And that is why QM has nothing to tell us about the principle of causality. They are simply not addressing the same question. Given that you have already determined on independent grounds whether or not the principle of causality is true, QM may raise questions about how it is to be understood in contexts like that of the hydrogen atom (to allude to Oerter’s example). But there is nothing special about QM in that regard. One billiard ball knocking into another, melting and freezing, electromagnetism, gravitational attraction, plant and animal growth, volitional behavior, divine creation, all involve very different sorts of efficient causality. There are also distinctions to be drawn between essentially ordered and accidentally ordered causes, between causes that contain what is in their effects formally and those that contain what is in their effects only virtually, between total causes and partial causes, between the causality of substances and that of accidents, and so forth. If you think that all efficient causality reduces to some crude, deterministic billiard-ball model, then QM might seem to be a challenge to the very notion of causality. (“Look, there’s no little billiard ball deterministically pushing the electron into a higher energy level! Causality itself crumbles!”) But no Aristotelian or Scholastic would buy this simplistic conception of efficient causality in the first place. (Naturalist critics of Aristotelian-Scholastic arguments rarely beg one question at a time. They beg whole books full of questions.)
The principle of causality itself does not make any claim about how exactly efficient causes operate in all of these diverse cases. It just tells us that whatever the details turn out to be, any potential will only be actualized by something already actual. How does this work out in the case of QM? This brings us to the second part of Oerter’s response to the claim that the laws of QM are the cause of change. He writes:
Finally, even if we think of physical laws as having some sort of actual existence and causal efficacy, well, the laws of QM exist right at the moment the electron is excited, so by this view the electron should immediately decay. In Aristotelian terms, we are looking for the efficient cause: the thing that brings about the change at the instant it occurs. The laws of physics apply equally to all times; they can't be the reason something happens at some particular time.
(It seems to me that the laws of physics could be considered the formal cause in Aristotelian language. But Feser says that modern philosophers have abandoned formal (as well as final) causes. Does anyone know if laws can, or cannot, be considered formal causes?)
The answer to this latter question is: No, laws are not formal causes. Nor do laws have any sort of independent existence or efficacy as efficient causes. The correct thing to say from an Aristotelian point of view is rather something like this: Natural substances have essences or substantial forms that ground their characteristic patterns of operation. For instance, it is in virtue of the substantial form of a tree that it tends to sink roots and grow branches; it is in virtue of the substantial form of water that it tends to freeze at one temperature and boil at another temperature; it is in virtue of something common to the substantial forms of material objects in general that they exert a gravitational pull on each other; and so forth. Now a “law of nature” is a description of these patterns, a description of how things will tend to operate given their natures, essences, or substantial forms. The existence and operation of laws of nature thus presupposes the existence and operation of concrete natural substances. Indeed, strictly speaking it is not the laws that exist and operate; “laws” are mere abstractions from the concrete substances. What exist and operate are the concrete substances themselves. The laws are not even formal causes but rather mere descriptions of how things operate given their formal causes, i.e. their substantial forms. (See chapter 6 of David Oderberg’s Real Essentialism for an important recent treatment of laws of nature from an Aristotelian-Thomistic point of view.)
[This is, by the way, why “laws of nature” don’t really explain anything, at least not ultimately. The very idea is a holdover from a time when Descartes, Newton, and Co. wanted to chuck out the Aristotelian framework, and replaced the idea that things operate according to intrinsic natures or substantial forms with the idea of operation according to externally imposed divine commands or “laws.” Stripped of this theological context, the notion of a “law” must either be cashed out in Aristotelian terms of the kind suggested above, or in other metaphysical terms equally unwelcome to the naturalist, or -- as Nancy Cartwright has pointed out -- collapse into incoherence. It is ironic that atheists so unreflectively help themselves to an inherently theological idea, albeit an idea derived from modernist rather than Scholastic theology.]
In the case of the hydrogen atom (once again to appeal to Oerter’s example), what we have is a concrete system that behaves in the way described by QM. Now as I have noted before, whether to give QM a realist (as opposed to an instrumentalist) interpretation in the first place is itself a vexed metaphysical question. And since it is a metaphysical question, it is precisely the sort of question to which we can legitimately bring to bear considerations like the principle of causality. So even if there were some conflict between that principle and QM (which, as I have argued, there is not) it wouldn’t follow that we’d have to give up either. If (as I would claim) we have independent reason to affirm the principle of causality, what would follow from such a conflict is that we should take an instrumentalist rather than realist view of QM -- a position some philosophers and scientists with no Aristotelian ax to grind would adopt in any case.
An interpretation of QM that is both Aristotelian and realist will, naturally, insist that it is not the laws of QM themselves that cause anything, since they are mere abstractions from concrete systems operating in accordance with their substantial forms. Hence it is in virtue of the substantial form of a hydrogen atom that it will behave in the manner described by QM, just as it is by virtue of the substantial forms of material things in general that they will exert a gravitational attraction on one another. Now for the Aristotelian, the substantial form of an inanimate substance is not the efficient cause of its natural operations; rather, those operations flow “spontaneously” from it, precisely because it is in the nature of the substance to operate in those ways. (See James Weisheipl’s Nature and Motion in the Middle Ages for an important treatment of the subject.) Hence that a planet exerts a gravitational pull is just something it does by virtue of its nature or substantial form; it does not need a continuously operating efficient cause to make it exert such a pull. That does not mean that there is in no sense an efficient cause of a thing’s natural operations, but that efficient cause is just that which gave the substance in question its substantial form in the first place, i.e. that which generated the substance or brought it into being. It is not something that needs continuously to operate after the thing is brought into being. Hence the efficient cause of a planet’s exerting a gravitational pull on other objects is just whatever natural processes brought that planet into existence millions of years ago, thereby giving it the nature or substantial form it has. Its exerting that pull is now something it just does “spontaneously,” by virtue of its nature. (Mind you, that does not mean that it can exist or operate even for a moment without a divine sustaining cause; it cannot do so, for reasons I spell out in my ACPQ article “Existential Inertia and the Five Ways.” But that is a separate issue. What I am talking about here is whether there needs to be some efficient cause alongside it within the natural order that causes it to exert a gravitational pull.)
Now, along the same lines, we might say that the hydrogen atom also behaves as it does “spontaneously,” simply by virtue of having the substantial form it does. Why do the electron transitions occur in just the pattern they do? Because that’s the sort of thing that happens in anything having the substantial form of a hydrogen atom, just as gravitational attraction is the sort of thing that naturally happens in anything having a substantial form of the sort typical of material objects. What is the efficient cause of this pattern? The efficient cause is whatever brought a particular hydrogen atom into existence, just as the efficient cause of gravitational attraction is whatever brought a particular material object into existence. That is one way, anyway, of giving an Aristotelian interpretation of QM phenomena of the sort cited by Oerter, and it is intended only as a sketch made for purposes of illustration rather than a completely worked out account. But it shows how QM can be naturally fitted into the Aristotelian framework using concepts that already exist within the latter.
Of course, critics of Aristotelianism will reject this way of interpreting what is going on. Fine and dandy. (Though please don’t waste everyone’s time with sophomoric Molière-style “dormitive virtue” objections to substantial forms. I have explained why this objection is no good in The Last Superstition and Aquinas.) The point is that QM itself gives one no reason whatsoever to reject it. If the critics of the Aristotelian position are to find rational grounds for rejecting it, they must look elsewhere.
Newton and local motion
In the second of the two installments he’s posted since my initial response to him, Oerter raises the hoary objection from Newton’s law of inertia against the principle that whatever is moved is moved by another. Now, as I have already noted, the less misleading way of stating the principle is as the thesis that any potential, if actualized, must be actualized by something already actual. And when it is put that way, it is less obvious that there is any conflict with Newton’s law. After all, Newton’s law tells us that every body continues in its state of rest or of uniform motion in a straight line, unless it is compelled to change that state by forces impressed upon it. And how, exactly, does this contradict the thesis that any potential, if actualized, must be actualized by something already actual?
The answer is that there is no conflict at all, because (once again) the principle of causality and the laws of physics are not even addressing the same question. Now I discussed this issue briefly in The Last Superstition, and it is to what I said there that Oerter is responding. But I addressed the issue at greater length in Aquinas (at pp. 76-79), which it seems Oerter has not read. And I address it at much greater length still in my paper “The medieval principle of motion and the modern principle of inertia,” which is forthcoming in the Proceedings of the Society for Medieval Logic and Metaphysics (and which, when it appears, should be available online as well as in print).
I’m not going to repeat everything I’ve said in Aquinas or preempt what I say in the forthcoming paper, but some general remarks should suffice for present purposes. There are five general reasons why the purported conflict between Newton’s law and the principle of causality is illusory (reasons I develop at length in the paper). First, there would be no formal contradiction between the two even if they were using “motion” in the same sense. For like Kepler’s laws and the laws of QM, Newton’s law is descriptive. It tells us how a body behaves, but not why it behaves that way. Thus the law does not rule out the thesis that the reason a body so behaves is because of a “mover” which actualizes its potencies for motion. (To be sure, the law does rule out any scenario where a body continues at rest or uniform rectilinear motion while acted upon by physical forces impressed upon it. But -- to appeal once again to the analogy with Kepler’s laws -- the principle of causality no more requires that what actualizes a potency is, specifically, a physical force of this sort than to affirm a cause of the orbits of the planets requires positing a special kind of massive body additional to the sun, planets, asteroids, etc.)
Second, Newton’s law and the principle of causality are not in fact using “motion” in precisely the same sense in the first place. Newton’s law pertains to local motion specifically, i.e. change with respect to place. The principle of causality applies to change of any kind, which includes not only local motion but change with respect to quantity, change with respect to quality, and change from one substance to another. Now some might object that these other sorts of change can all be reduced to local motion. I think that is quite false, but that is neither here nor there for present purposes. For the deeper point is that when the principle of causality speaks of motion (local or otherwise) what it is talking about is the actualization of potentials. And Newton’s law simply has nothing whatsoever to say about that. In particular, when Newton’s law says that a body in motion will tend to stay in motion, it is not asserting that a potential which is being actualized will continue being actualized. Even if it were suggested that Newton’s law entails this, the point is that that isn’t what the principle of inertia itself, as understood within physics, is saying. Indeed, the whole aim of early modern physics of the sort practiced by Newton was to provide a description of nature that sidestepped the whole Aristotelian-Scholastic apparatus of actuality and potentiality, substantial forms, and the like. Modern physics didn’t offer different answers to the questions the Scholastics were asking. It simply changed the subject.
A third point is that Newtonian inertial motion is often characterized as a “state” -- that is, as the absence of any real change. Now if such motion really is a state, then there is no conflict with the principle of causality, for if inertial motion involves no real change, than it involves no actualization of potential -- in which case, obviously, it involves no actualization of a potential without a cause. Indeed, since Newton’s law says that a genuine change in an object’s local motion can occur only if a force acts upon it, the law implicitly affirms the principle of causality! Hence if inertial motion really is a “state,” then what Newton and his Aristotelian predecessors disagreed about was not whether genuine change requires a cause, but only about whether local motion of a uniform rectilinear sort counts as genuine change.
A fourth point is that those who assert a conflict between Newton and Aristotle often direct their attacks at a straw man. In particular, it is sometimes thought that Aristotle and Aquinas maintained that no object can persist in any local motion unless some mover is continuously conjoined to it as an efficient cause. But in fact they denied this; their view was that an object will tend to move toward its “natural place” simply by virtue of its substantial form, and will do so even in the absence of that which imparted this form, and thus in the absence of that which is the efficient cause of their local motion. (This is related to the point made earlier about the operations that a substance will carry out “spontaneously” given its substantial form. And here too, Weisheipl’s book is the place to look for a detailed treatment of the subject.) To be sure, the idea of “natural place” is a piece of Aristotelian physics (as opposed to metaphysics) that is obsolete; and the violent (as opposed to natural) motions of objects were thought to require some conjoined mover. But all of that is beside the point. For the point is that Aristotle’s and Aquinas’s principle of causality in fact did not presuppose that local motion as such requires a continuously conjoined physical cause.
Finally, and as all of this indicates, there can be no conflict between Newton’s law and the principle of causality because the former is a thesis of natural science and the latter a thesis of metaphysics -- or more precisely, of that branch of metaphysics known as the philosophy of nature. As Bertrand Russell and others with no Aristotelian or theological ax to grind have emphasized, what physics gives us is really only the abstract mathematical structure of the material world. It does not tell us what fills out that structure, does not tell us the intrinsic nature of the material world. But that is what metaphysics, and in particular the philosophy of nature, are concerned with. Moreover, the philosophy of nature, as modern Scholastics have understood it, tells us what the natural world must be like whatever the specific laws of physics, chemistry, etc. turn out to be. And the Scholastic position is that the distinction between actuality and potentiality, the principle of causality, and other fundamental elements of the Aristotelian conception of nature are among the preconditions of any possible material world susceptible of scientific study.
That is why no findings of empirical science can undermine the claims of metaphysics and the philosophy of nature. It is also why no findings of empirical science can undermine the Aristotelian-Thomistic arguments for the existence of God, for these are grounded in premises drawn, not from natural science, but from metaphysics and the philosophy of nature. Now that does not mean that these arguments of natural theology are not susceptible of rational evaluation and criticism. What it means is that such evaluation and criticism will have to be philosophical and metaphysical, rather than empirical, in nature. Nor is natural theology in this regard at all different from atheism. Atheists who think they are arguing from “purely scientific” premises never really are. They are, without exception, arguing from metaphysical assumptions -- and usually unexamined ones at that -- that are first read into empirical science and then read back out, like the rabbit the magician can pull out of the hat only because he’s first hidden it there.
Readers who disagree with these claims are cordially invited to refute them -- without either begging the question or smuggling in metaphysical assumptions of precisely the sort they deny making. Good luck with that. | 0.812746 | 3.039351 |
A dusty disk around a distant star has faded surprisingly fast, leaving scientists few clues to how it disappeared.
Only a few years ago, the space around the star TYC 8241 2652 1 was filled with dust and gas, but recent observations show the region — an ideal spot for alien planets to form — has all but vanished.
"It's like the classic magician's trick: Now you see it, now you don't," principal investigator Carl Melis of the University of California, San Diego said in a statement. "Only in this case, we're talking about enough dust to fill an inner solar system, and it really is gone!"
The star is 450 light-years away, in the constellation Centaurus. At 10 million years old, it is a younger version of our 4.5-billion-year-old sun.
A quick exit
Tiny specks of dust orbiting a star absorb its energy and shine in infrared light. As the glow brightens and dims, astronomers can estimate how much material surrounds the star.
The disk around the star TYC 8241 2652 1 was discovered in 1983 and remained relatively constant for 2 1/2 decades. Scientists estimated that 1,000 trillion grains of dust — the equivalent of all the sand on the beaches of Earth — circled this younger version of our sun.
But in 2009, things changed.
Observations by the Gemini South telescope in Chile and several other instruments found that the infrared light emitted by the dust had dropped by more than half. In subsequent studies, the amount of dust around the star had all but vanished, dropping by a factor of nearly 30 in two years.
Such a dramatic change is astonishingly fast when compared to the million-year time scale of most astronomical events, researchers said. [Top 10 Star Mysteries]
"The dust disappearance at TYC 8241 2652 1 was so bizarre and so quick, initially I figured that our observations must simply be in error in some strange way," said study co-author Ben Zuckerman of the University of California, Los Angles.
The quickly vanishing disk may help scientists better understand how planets formed in early solar systems, including our own, researchers said.
The case of the disappearing disk
The amount of dust around a star rises and falls over time. After a star forms, young planets are created from the leftover debris, known as a protoplanetary disk.
But the early life of a solar system is typically a time of violent collisions, so while much of the dust is initially swept up in the creation process, the disk is repopulated as large chunks of rock crash into one other. The disk around the 10-million-year-old star was thought to be in this second stage, with rocky objects constantly smashing together.
Where did the dust disappear to so quickly? Two different theories have been advanced to explain what caused the sudden loss.
The first model suggests that the dust fell into the star, while the second proposes that the explosive impacts could have blown much of the dust completely out of the system.
The second theory, known as the collisional cascade model, would likely require time scales longer than two years to clear the dust from the system, researchers said.
But there's still a nagging mystery. Neither of the two theories clearly fits the evidence obtained by observations of TYC 8241 2652 1.
"A perplexing thing about this discovery is that we don't have a really satisfactory explanation to address what happened around this star," Melis said.
The findings were published online today (July 4) in the journal Nature. | 0.821143 | 4.014453 |
If inverse square laws are larger particles comprised of infinitesimal particles, adjacent tidal axii subject to two relative speeds will or would most likely explain day lengths.
On these adjacent inner planet a quarter of an orbit advanced beyond a transit diagrams, planetary speed magnitudes come tidal axii speed magnitudes are relative to each other. With respect of the motion of the sun, the diagrams are all timeless and the push vectors instantaneous forces
You do sort of need a spatial picture of the structure of an inverse square law field in your head first for all this. If you live in lieu of one, next week Euclid or Sir Isaac may be able to help out in that department.
Apart from a transit being an alignment of two planets with the sun, the things to note from the rotation rate table are the inner two planets are like the moon. Have rotation periods of the order of their orbital periods. And outer adjacent planets are pairs with similar rotation periods. Thus the rotation aspect you can see on this table.
If you can note that and can consider the rotation aspect to be a possible/probable ingredient of our solar system, it's all pretty interesting. The same face of the moon always being towards the earth is a pretty good clue to the moon being turned by the tidal quadrant of its gravity field. The inexactness of the elements of the rotation aspect for the planets, well the rotations are going to be 'orbital' period conflict rotations of inverse square laws between planets. Not just a locked synchronisation with one other planet.
The facts we have are Venus turns backwards on its axis once whilst this fixed sun professor planet does 2/3's of its solar cycle. And, every 584 earth days, the same face of Venus is almost precisely towards the earth when Venus passes between the earth and the sun. There are a few other little rotational/cyclical near exact ratios between the inner three planets as well. For instance, a Venus sunrise occurs every 117. something earth days. Meaning there is almost precisely 5 Venus sunrises to each Venus transit of the earth. And Mercury rotates twice on its axis every 117.3 days.
The Venus - Mercury relationship is really a quite compelling suggestion of the idea of gravity field turn rates being the clue to planetary rotation rates. Hard to see why the Martians even doubt themselves on this. The Venus 'orbital' direction and the Venus rotation direction are opposite. As Venus advances around the sun, the face of Venus directed towards the sun changes. This face change is synchronised to the Mercury rotation period while the actually Venus rotation period is synchronised to the earth year.
That almost says it all. The lingering doubts of the Martians must be that it all means that the earth's lunar tides are really earth solar tides that are getting moved around the earth by the moon.
Anyway, if the tides of a planet get to be seen as factors of the equal and opposite quadrant nature of an inverse square law, in time we should see that, minus a moon or moons, the solar low tide axis of a planet becomes a circle around the motion of the sun at a planet's distance from the sun.
Then, if the earth - moon high tides run through the Venus inverse square law during a transit, the low tide axis of the earth - sun system gets marginally shifted out of this circle toward the 'orbits' of Venus and Mars as this earth planet moves forward.
At the same time the Venus inverse square law and the earth inverse square law are being turned backwards as Venus and the earth move forward.
If you get some spare time, you could do worse than having a go at it.
As mentioned, it appears that the earth's lunar tides are really solar tides but are getting moved around the earth by the moon.
To have some fun, the various ellipses could be whacked on. The interesting thing is the tangent from an inner planet is directed in the region of the next planet out a quarter cycle beyond the transit of the inner planet. As well the Venus - earth situation is very close to a right angle. And the Venus orbit of a fixed sun is very close to a perfect circle.
The way the planets are always tending towards a complete alignment suggests the inverse square laws of the planets are a tension within the motion of the sun's inverse square law.
On one hand the planets have the relative speed that the motion of the sun's inverse square law supplies at a planet's distance from the sun. (Kepler's third law)
On the other, adjacent planetary inverse square laws are tidally pushing on each other with their various relative speeds within the motion of the sun's inverse square law and inspiring mutual relative speeds for each other.
These mutual inspirations appear as the rotation rates of the planets and the ellipses (Kepler's second law). Maybe anyway. Future moving inverse square law professors will work it out. Pluto's inverse square law seems to be marginally outside the tension. Not sure. Not really the Bode perspective, but the distances of the planets from the sun looks like being to do with each other. Then there are the questions of what turns the sun's inverse square law? Is a planet's inverse square law its axis of rotation? Do the planetary cores turn with their inverse square law quadrants? Does the speed of the sun control day lengths. etc, etc.
If you are part of an up and coming generation of young people or whoever, have a think. After the journey to discern it, declaring that rotation rate table to be coincidence without certainty of such would be against your and your descendants best interests. In a hundred years time your descendants could be getting life on earth tuned in with the galactic journey they are on. Which should have more good than harm in it.
When personally bringing the table into focus, it is quickly realised finding a way of pointing the tidal flaw in mutual gravitation to fixed inverse square law ears is the more important chore at hand. But there is something going on between the rotations of the planets. Uranus seems to be tidally jammed between Neptune and Saturn. If it is on the right track, the 24 hours in our day would be a consequence of the uniqueness of the solar system. The more you involve your self with the table, the more magical our existence seems to be.
The way Kepler presented his great work is probably where the trouble is. Time squared in the third law means nothing. Likewise the fact that a planet sweeps out equal areas in equal times in his second law.
1/ The first law says the paths of the planets around the sun are elliptical when the sun is fixed and with the sun being at one foci of the ellipse.
2/ The second law says the speed of an individual planet relative to the sun varies with the inverse of its distance from the sun.
3/ The third law says the average speed of any planet relative to the sun varies with the inverse square of distance from the sun.
(link)Did Newton answer Halley's question.
The Galilean problem of the planets ascending and descending at the same time aside, the answer to Halley's question was a circle. Not an ellipse. Somehow Sir Isaac has attributed the equal areas in equal times to the inverse square law. All the equal areas in equal times means is as specified in 2/ above. Plus the striking conflict with the third law. | 0.897097 | 3.684974 |
Bode’s Law or more correctly Titius-Bode’s Law is named after two German astronomers, Johann Daniel Titius and
Johann Elert Bode, who proposed in the 18th century that there was a mathematical relationship between the then six known planets and their distance from the sun, with each one roughly twice the distance as the previous planet. Although the idea was conceived by Titius, it was Bode who gave it greater prominence, when he used it to predict the existence of Uranus and later Ceres in the Asteroid Belt. At that point it was accepted as a ‘law’.
The subject has been debated throughout the 20th century. I.J. Good, a British mathematician who worked with Alan Turing during the war at Bletchley Park, offered a paper in support of Titius-Bode in 1968(b). Bradley Efron, an American statistician, proposed an opposing view(c). Both papers are best suited to the mathematically advanced.
The late Timo Niroma has offered some interesting observations(j) on the mechanics behind Titius-Bode and developed a cosmology based upon atomic weights, noting that “What happens in small scale seems to obey the same laws on a much grander scale.”
Georgi Gladyshev, a Russian scientist, has proposed a explanation for Titius-Bode based on the work of Raphael Liesegang(g) who proposed the concept of ‘periodic precipitation’. Gladyshev applied Liesegang’s theory to the early stages of the formation of our Solar System(h)(i). Hopefully, this may bring us closer to the physics behind the distribution of the planets!
It has also been proposed that a Titius-Bode-Type ‘rule’ seems to be applicable to planetary satellite systems(d) and there appears to be evidence(a) that Titius-Bode is also applicable to exoplanetary systems!
The Titius-Bode Law has also been linked with the Fibonacci Series(e) as well as the Golden Mean(f).
Velikovskian catastrophism proposes[0037.152] that Atlantis was destroyed as a result of the periodic close encounters of our planet with Venus and/or Mars during the 2nd millennium BC.
For my own part, I have always felt that Bode’s Law was a highly convincing concept, but unfortunately I do not have the mathematical or astronomical ability required to objectively verify its reality, nor the proposed Fibonnaci Sequence and the Golden Mean relationship with it. It would appear that acceptance of Bode would create difficulties not just for the Saturn Theory but also for Velikovsky’s idea that Venus was just a large piece of ejecta from Jupiter that had catastrophic close encounters with Earth and Mars, within human experience, just a few thousand years ago. Such an idea would mean that prior to the Saturnian rearrangement of the planets or the Velikovskian creation of Venus, the positional relationship of the planets probably did not conform to any known mathematical model but after this/these calamitous events everything ‘coincidentally’ settled into orbits that are now claimed to conform to Bode, Fibonacci and the Golden Mean! Can we believe that after careening around the solar system including a number of close encounters with Earth that all the planets adopted new orbits that conformed with Bode’s Law. Surely, this is a coincidence too far?
*Although the ‘Law’ has been generally abandoned by mainstream scientists, there is still interest in some quarters. One of those was the British astronomer, the late Michael Ovenden (1926-1987) who produced a modified version of the original formula (k). Another version involvesan interpretation of quantum mechanics, called pilot wave theory (l).* | 0.897312 | 3.699834 |
Coronal Mass Ejections
Coronal Mass Ejections (CMEs) are a direct result of magnetic instabilities (i.e. solar flares) on the surface of the Sun erupting and expelling millions of tons of solar plasma into interplanetary space. CMEs are strongly influenced by the interplanetary magnetic field (IMF).
A hazard to settlers?
On Earth, we are protected from dangerous high energy particles emitted by the Sun. The Earth's magnetic field acts as an umbrella, deflecting incoming ions and electrons, channeling them to the Earth's poles. This generates magnificent displays of light in polar regions, the Aurora Borialis (over the North Pole) and Aurora Australis (over the South Pole). The light is emitted in the upper polar atmosphere, in the various layers of the ionosphere. Mars does not have the luxury of a protective magnetic field, and does not experience aurorae in polar regions.
In addition, the Earth's atmosphere is over 100 times thicker than Mars'. This greatly increases the insulation of the planet from solar energetic particles, magnifying the intensity of aurorae. The Earth's atmosphere has the protective thickness equivalent to 10.3 meters of water, or approximately 3.4 meters of regolith (very important when considering settlement design). The protective thickness of Mars' atmosphere is equal to only about a 27 cm thickness of water.
Settlement designers must therefore assume that Mars' atmosphere will not protect settlers from high energy, ionizing particles emitted from the Sun.
Detecting damaging CME ions
Warning Mars settlers about the onset of damaging ions is therefore a high priority. Even on Earth, predicting CMEs and dangerous ions is very important as a massive current of global scale is applied during solar storms. This effect can damage delicate satellite circuits, thermally expand the upper atmosphere (thickening the atmosphere in low Earth orbit, slowing down satellites and decreasing their orbital altitudes) and even cause damage to power grids on the ground (auroral electrojets can have the effect of overloading country-wide electricity grids). Methods of predicting and detecting Coronal Mass Ejections are constantly being developed, but the most effective way of detecting the onset of an Earth-bound CME is to have a probe between the Earth and Sun.
A contingency for Mars
Currently, Mars has no probe or observatory in the line of sight (LOS) of the Sun, leaving an unpatrolled expanse of interplanetary space for dangerous solar ions to pass unchecked. A possible solution (akin to the Earth's SoHO or ACE observatories) could be to establish a simple and inexpensive solar observatory at the first Lagrangian Point (L1) in the Mars-Sun system. This is a gravitationally stable point in direct LOS with the Sun where a probe can be inserted to orbit around the Sun at the same rate as Mars. This proposed system would provide some warning for Mars settlers of the propagation of solar ions toward the Red Planet. See also: Early warning system. If no such sensors were positioned between the Sun and Mars, interplanetary spacecraft or Mars habitats might be designed to include a sensor that can detect the x-ray burst that preceeds a solar proton event. However, this system would probably only provide a 20-minute advance warning.
- See discussion section.
- Geomagnetic Storms Can Threaten Electric Power Grid - American Geophysical Union article.
- The Solar and Heliospheric Observatory (SoHO) acting as an early warning device.
- SoHO mission page.
- ACE mission page.
- Lagrangian Point on Wikipedia.
- Rapp D. (2006). Radiation Effects and Shielding Requirements in Human Missions to the Moon and Mars. Mars 2:46-71. https://doi.org/10.1555/mars.2006.0004
|Concepts:||Greenhouse · Settlements · Locations · General|
|Hazards:||Space Weather · Climate · General|
|Technology:||Hi-Tech · Lo-Tech · Energy · Spaceflight science · Communication · General|
|Human Considerations:||Economics · Health · Governance · Trade · Law · Social| | 0.826231 | 4.081864 |
NASA's Dawn spacecraft shut down its ion propulsion system today as scheduled. The spacecraft is now gliding toward a Mars flyby in February of next year.
"Dawn has completed the thrusting it needs to use Mars for a gravity assist to help get us to Vesta," said Marc Rayman, Dawn's chief engineer, of NASA's Jet Propulsion Laboratory, Pasadena, Calif. "Dawn will now coast in its orbit around the sun for the next half a year before we again fire up the ion propulsion system to continue our journey to the asteroid belt."
Dawn's ion engines may get a short workout next January to provide any final orbital adjustments prior to its encounter with the Red Planet. Ions are also scheduled to fly out of the propulsion system during some systems testing in spring. But mostly, Dawn's three ion engines will remain silent until June, when they will again speed Dawn toward its first appointment, with asteroid Vesta.
Dawn's ion engines are vital to the success of the misson's 8-year, 4.9-billion-kilometer (3-billion-mile) journey to asteroid Vesta and dwarf planet Ceres. One of these extremely frugal powerhouses can generate more than 24 hours of thrusting while consuming about .26 kilograms (about 9 ounces) of the spacecraft's xenon fuel supply -- less than the contents of a can of soda. Over their lifetime, Dawn's three ion propulsion engines will fire cumulatively for about 50,000 hours (over five years) -- a record for spacecraft.
Dawn will begin its exploration of asteroid Vesta in 2011 and the dwarf planet Ceres in 2015. These two icons of the asteroid belt have been witness to so much of our solar system's history. By utilizing the same set of instruments at two separate destinations, scientists can more accurately formulate comparisons and contrasts. Dawn's science instrument suite will measure shape, surface topography, tectonic history, elemental and mineral composition, and will seek out water-bearing minerals. In addition, the Dawn spacecraft itself and how it orbits both Vesta and Ceres will be used to measure the celestial bodies' masses and gravity fields.
The Dawn mission to asteroid Vesta and dwarf planet Ceres is managed and operated by JPL for NASA's Science Mission Directorate, Washington, D.C. The University of California, Los Angeles, is responsible for overall Dawn mission science. Other scientific partners include: Max Planck Institute for Solar System Research, Katlenburg, Germany; DLR Institute for Planetary Research, Berlin, Germany; Italian National Institute for Astrophysics, Rome; and the Italian Space Agency. Orbital Sciences Corporation of Dulles, Virginia, designed and built the Dawn spacecraft.
Dude! Check out the 17 Nov. Overtime Replay on "RealTime with Bill Maher" website in which Ashton Kutcher says we should, as a first pass at govt. budget cuts, "Stop sending stuff to Mars". "Surprisingly", the repug congresswoman jumps on the bandwagon, with a very Palinesque comment, and so does Maher. "Surprisingly", the same congresswoman is mute on whether churches should be taxed Check it out! It would be good to see a post on this too! | 0.878751 | 3.525716 |
Many galaxies far more active than the Milky Way have enormous twin jets of radio waves extending far into intergalactic space. Normally these go in opposite directions, coming from a massive black hole at the centre of the galaxy. However, a few are more complicated and appear to have four jets forming an ‘X’ on the sky.
Several possible explanations have been proposed to understand this phenomenon. These include changes in the direction of spin of the black hole at the centre of the galaxy, and associated jets, over millions of years; two black holes each associated with a pair of jets; and material falling back into the galaxy being deflected into different directions forming the other two arms of the ‘X’.
Exquisite new MeerKAT observations of one such galaxy, PKS 2014-55, strongly favour the latter explanation as they show material “turning the corner” as it flows back towards the host galaxy; the results have just been accepted for publication in the journal Monthly Notices of the Royal Astronomical Society.
This work was carried out by a team from the South African Radio Astronomy Observatory (SARAO), the (US) National Radio Astronomy Observatory (NRAO), the University of Pretoria, and Rhodes University.
Previous studies of these unusual galaxies lacked the high quality imaging provided by the recently completed MeerKAT telescope. This telescope array consists of 64 radio dishes located in the Karoo semi-desert in the Northern Cape province of South Africa. Computers combined the data from these antennas into a telescope 8 km in diameter, and provided images in the radio band of unprecedented quality for PKS 2014-55 which enabled solving the mystery of its shape.
Bernie Fanaroff, former director of the SKA South Africa project that built MeerKAT, and a co-author of the study, notes that “MeerKAT was designed to be the best of its kind in the world. It’s wonderful to see how its unique capabilities are contributing to resolving longstanding questions related to the evolution of galaxies.”
Lead author William Cotton of the NRAO says that “MeerKAT is one of a new generation of instruments whose power solves old puzzles even as it finds new ones – this galaxy shows features never seen before in this detail which are not fully understood.” Further research into these open questions is already underway.
THE SOUTH AFRICAN RADIO ASTRONOMY OBSERVATORY
The South African Radio Astronomy Observatory (SARAO), a facility of the National Research Foundation, is responsible for managing all radio astronomy initiatives and facilities in South Africa, including the MeerKAT radio telescope in the Karoo, and the geodesy and VLBI activities at the HartRAO facility. SARAO also coordinates the African Very Long Baseline Interferometry Network (AVN) for the eight SKA partner countries in Africa, as well as South Africa’s contribution to the infrastructure and engineering planning for the Square Kilometre Array radio telescope. To maximise the return on South Africa’s investment in radio astronomy, SARAO is managing programmes to create capacity in radio astronomy science and engineering research, and the technical capacity required to support site operations. | 0.814812 | 3.947467 |
The Spitzer Space Telescope is NASA's infrared observatory, the final component in NASA's collection of "Great Observatories." It trails Earth in orbit around the sun to send back detailed information about space.
Imagine observing the universe through infrared goggles. That's basically what Spitzer does. Spitzer’s infrared sensors detect heat from objects that our eyes (and optical telescopes) can’t see. This lets us look right through dense clouds of gas and dust to see regions where stars form, the centers of galaxies, newly forming planetary systems and objects like smaller stars and extra-solar planets that are too dim to see in visible light.
The Earth's atmosphere absorbs most incoming infrared radiation. So to look at the infrared light from distant stars and galaxies, Spitzer trails the Earth as it orbits the Sun. Spitzer is one of NASA’s four space-based Great Observatories. Each one examines the sky in a different wavelength: X-ray, gamma-ray, infrared or visible light.
This just in!
Scientists just discovered a system of seven planets, all Earth-sized, orbiting an ultra-cool star called TRAPPIST-1. The tiny star is "only" 40 light-years from Earth.
We call planets outside our own solar system exoplanets. It's especially exciting to discover Earth-sized exoplanets because we know that any place similar enough to our own home planet could be a good place to look more closely for signs of life. Three of TRAPPIST-1's seven planets are at just the right distance away from the star to be at the right temperature to have liquid water. We call that area around a star the habitable zone because liquid water is necessary for a planet to support life as we know it.
The TRAPPIST-1 system is named for the TRAPPIST telescope in Chile that discovered the first two planets. But the NASA Spitzer Telescope discovered the other five planets in orbit around TRAPPIST-1. Now other telescopes like the Hubble Space Telescope and the Kepler Space Observatory will go to work on gathering more details about the TRAPPIST-1 system. There couldn't be a more exciting time to get into the fields of astrophysics and planetary science. This is amazing stuff!
The Science Center's Spitzer Space Telescope
The Spitzer telescope on display in the gallery is a 1/5th-scale model provided by the Image Processing and Analysis Center at JPL-Caltech. | 0.88808 | 3.848584 |
Venus Express sees right down to the hell-hot surface
Thanks to ESA’s Venus Express data, scientists obtained the first large-area temperature maps of the southern hemisphere of the inhospitable, lead-melting surface of Venus.
The new data may help with searching and identifying ‘hot spots’ on the surface, considered to be possible signs of active volcanism on the planet. The results, presented today at the American Geophysical Union (AGU) assembly in San Francisco, USA, were obtained thanks to VIRTIS, the Visible and Infrared Thermal Imaging Spectrometer on board Venus Express.
To obtain this fundamental information about the surface temperature, VIRTIS made use of the so-called infrared spectral 'windows’ present in the Venusian atmosphere. Through these ‘windows’ thermal radiation at specific wavelengths can leak from the deepest atmospheric layers, pass through the dense cloud curtain situated at about 60 kilometres altitude, and then escape to space, where it can be detected by instruments like VIRTIS. In this way VIRTIS succeeded in looking through the thick carbon dioxide curtain surrounding Venus and detected the heat directly emitted by the hot rocks on the ground.
"We are very excited about these results, as they represent a very important item in the list of Venus Express' and VIRTIS' scientific objectives at Venus", says Giuseppe Piccioni, one of the Principal Investigators of the VIRTIS experiment, from the Istituto di Astrofisica Spaziale e Fisica Cosmica in Rome, Italy.
The measurements, made in August 2006 over the Themis and Phoebe Regions in the southern hemisphere of Venus, reveal temperature variations of 30 degrees between lowlands and mountain tops, correlating well with existing topographical radar data from previous missions. The Themis Region is a highland plateau located at 270º East longitude and at about 37º South latitude. It is a region that has experienced strong volcanic activity, at least in the geologic past.
On Venus there are no day and night variations of the surface temperature. The heat is globally 'trapped' under the carbon-dioxide atmosphere, with pressure 90 times higher than on Earth. Instead, the main temperature variation is due to topography. Just like on Earth, mountain tops are colder, whereas the lowlands are warmer. The 'only' difference is that on Venus 'cold' means 447º Celsius, while 'warm' means 477º Celsius. Such high temperatures are caused by the strongest greenhouse effect found in the Solar System.
"The VIRTIS results represent a major step forward in our attempt to identify specific surface features on the surface of Venus", said Jörn Helbert from the German Aerospace Center's (DLR) Institute of Planetary Research in Berlin, Germany, and a member of the VIRTIS team. "By 'peeling' off the atmospheric layers from the VIRTIS data, we can finally measure the surface temperature," Helbert added.
Eventually, the VIRTIS team hopes to identify 'hot spots' on the surface of Venus, possibly stemming from active volcanoes. In the Solar System, besides Earth, active volcanoes have been observed only on Io, a satellite of Jupiter, on Neptune's satellite Triton, and on Saturn's moon Enceladus (in the form of the so-called 'cryo-volcanism'). Venus is the most likely planet to host other active volcanoes.
In order to achieve this, the Venus Express scientists started comparing the maps of the Venusian topography obtained by NASA’s Magellan orbiter in the early 1990s with the data gathered by VIRTIS. The Magellan topography maps allow for a rough prediction of the surface temperature, too. Comparing these predictions with the measurements made by VIRTIS allows searching for hot spots that show even higher temperatures than the oven-hot surface, possibly indicative of active volcanism.
This direct interdependence between temperature and topography will enable scientists to derive new topography maps of the Venusian surface from temperature measurements. This will help in complementing the Magellan maps.
"Actually, when comparing our temperature map with topographical data from Magellan, we are not only obtaining quite a good agreement, but we can even fill gaps that the Magellan and Venera 15 radar data sets left open", concluded Pierre Drossart, the other Principal Investigator of the VIRTIS experiment, from the Observatoire de Paris Meudon, France. | 0.805026 | 3.986509 |
February 19th, 2016 was going to be just another day on Comet 67P — until suddenly, the icy space rock lit up in a blaze of glory, as if suddenly slapped by an angry angel.
The strange astronomical event would have gone unnoticed by the seven billion people living right down the cosmic street, except that lucky for us, we had a spacecraft in orbit around that sucker. Rosetta caught all the action, and scientists on Earth have now reconstructed a detailed sequence of events that may have been triggered by a landslide.
The analysis, led by Eberhard Grün of the Max-Planck-Institute for Nuclear Physics, has been accepted for publication in Monthly Notices of the Royal Astronomical Society.
“By happy coincidence, we were pointing the majority of instruments at the comet at this time, and having these simultaneous measurements provides us with the most complete set of data on an outburst ever collected,” ESA Rosetta project scientist Matt Taylor said in a statement.
Timeline on Comet 67P’s recent outburst, as witnessed by Rosetta’s cameras, dust collectors, gas and plasma analyzers. Image: ESA/Rosetta/MPS
The action began around 9:40 GMT, when Rosetta’s detectors noted a strong brightening in the coma, the halo of airborne water vapour and dust surrounding Comet 67P. Over the next few hours, the UV brightness of sunlight reflected off the coma increased sixfold, while the amount of sunlight scattered off dust grew by a factor of ten. Meanwhile, temperatures in the gas rose some 30 degrees Celsius.
Then, Rosetta was blasted by dust, its sensors registering almost 200 individual particles in just three hours, compared with an average of three to ten particles per day. By mid afternoon, the comet had settled back down.
Location of the Atum region, where Comet 67P’s recent outburst likely originated. Image: ESA/Rosetta/NavCam
By putting all of their data together, scientists believe they’ve identified the cause of the commotion: a steep slope on the comet’s larger lobe, in what’s known as the Atum region. The outburst started just after this region emerged from shadow, suggesting that heat from the sun’s rays may have vaporised a patch of exposed water ice and triggered a landslide. | 0.820322 | 3.581353 |
Dear Unhesidawntingly Enthusiastic Readers,
An ambitious explorer from Earth is gaining the best views ever of dwarf planet Ceres. More than two centuries after its discovery, this erstwhile planet is now being mapped in great detail by Dawn.
The spacecraft is engaged in some of the most intensive observations of its entire mission at Ceres, using its camera and other sensors to scrutinize the alien world with unprecedented clarity and completeness. At an average altitude of 915 miles (1,470 kilometers) and traveling at 400 mph (645 kilometers per hour), Dawn completes an orbit every 19 hours. The pioneer will be here for more than two months before descending to its final orbit.
The complex spiral maneuver down from the second mapping orbit at 2,700 miles (4,400 kilometers) went so well that Dawn arrived in this third mapping orbit on Aug. 13, which was slightly ahead of schedule. (Frequent progress of its descent, and reports on the ongoing work in the new orbit, are available here and on Twitter @NASA_Dawn.) It began this third mapping phase on schedule at 9:53:40 p.m. PDT on Aug. 17.
We had a detailed preview of the plans last year when Dawn was more than six thousand times farther from Ceres than it is today. (For reasons almost as old as Ceres itself, this phase is also known as the high altitude mapping orbit, or HAMO, although we have seen that it is the second lowest of the four mapping orbits.) Now let’s review what will happen, including a change mission planners have made since then.
The precious pictures and other data have just begun to arrive on Earth, and it is too soon to say anything about the latest findings, but stand by for stunning new discoveries. Actually, you could get pictures about as good as Dawn’s are now with a telescope 217 times the diameter of Hubble Space Telescope. An alternative is to build your own interplanetary spaceship, travel through the depths of space to the only dwarf planet in the inner solar system, and look out the window. Or go to the Ceres image gallery.
Dawn has already gained fabulous perspectives on this mysterious world from its first and second mapping orbits. Now at one third the altitude of the mapping campaign that completed in June, its view is three times as sharp. (Exploring the cosmos is so cool!) That also means each picture takes in a correspondingly smaller area, so more pictures are needed now to cover the entire vast and varied landscape. At this height, Dawn’s camera sees a square about 88 miles (140 kilometers) on a side, less than one percent of the more than one million square miles (nearly 2.8 million square kilometers). The orbital parameters were chosen carefully so that as Ceres rotates on its axis every nine hours (one Cerean day), Dawn will be able to photograph nearly all of the surface in a dozen orbital loops.
When Dawn explored the giant protoplanet Vesta from comparable orbits (HAMO1 in 2011 and HAMO2 in 2012), it pointed its scientific instruments at the illuminated ground whenever it was on the dayside. Every time its orbit took it over the nightside, it turned to point its main antenna at Earth to radio its findings to NASA’s Deep Space Network. As we explained last year, however, that is not the plan at Ceres, because of the failure of two of the ship’s reaction wheels. (By electrically changing the speed at which these gyroscope-like devices rotate, Dawn can turn or stabilize itself in the zero-gravity conditions of spaceflight.)
We discussed in January that the flight team has excogitated innovative methods to accomplish and even exceed the original mission objectives regardless of the condition of the wheels, even the two operable ones (which will not be used until the final mapping orbit). Dawn no longer relies on reaction wheels, although when it left Earth in 2007, they were deemed indispensable. The spacecraft’s resilience (which is a direct result of the team’s resourcefulness) is remarkable!
One of the many ingredients in the recipe for turning the potentially devastating loss of the wheels into a solid plan for success has been to rotate the spacecraft less frequently. Therefore, sometimes Dawn will wait patiently for half an orbit (almost 9.5 hours) as it flies above ground cloaked in the deep darkness of night, its instruments pointed at terrain they cannot detect. Other times, it will keep its antenna fixed on Earth without even glancing at the sunlit scenery below, because it can capture the views on other revolutions. This strategy conserves hydrazine, the conventional rocket propellant used by the small jets of the reaction control system in the absence of the wheels. It takes more time, but because Dawn is in orbit, time is not such a limited resource. It will take 12 passages over the illuminated hemisphere, each lasting nearly 9.5 hours, to bring the entirety of the landscape within view of its camera, but we will need a total of 14 full revolutions, or 11 days (29 Cerean days, for those of you using that calendar), to acquire and transmit all the data. The Dawn team calls this 11-day period “11 days,” or sometimes a “cycle.”
In quite a change from the days that there simply didn’t seem to be enough hydrazine onboard to accomplish all of the mission’s ambitious objectives, engineers and the spacecraft itself have collaborated to be so efficient with the precious molecules that they now have some to spare. Therefore, mission planners have recently decided to spend a few more in this mapping orbit. They have added extra turns to allow the robot to communicate with Earth during more of the transits over the nightside than they had previously budgeted. This means Dawn can send the contents of its computer memory to Earth more often and therefore have space to collect and store even more data than originally planned. An 11-day mapping cycle is going to be marvelously productive.
Full image and caption. Image credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
But Dawn has goals still more ambitious than taking pictures and recording infrared and visible spectra of the lands passing underneath it. It will conduct six complete mapping cycles, each one looking at a slightly different angle. This will effectively yield stereo views, which when combined will make those flat images pop into full three dimensionality.
In its first mapping cycle, which is taking place now, the explorer aims its instruments straight down. For the second, it will keep the camera pointed a little bit back and to the left, making another full map but with a different perspective. For the third, it will look a little back and to the right. The fourth map will be viewing the scenery ahead and to the left. The fifth map will be of the terrain immediately ahead, and the sixth will be farther back than the third but not as far to the right.
In addition to the stereo pictures and the many spectra (which reveal the nature of the minerals as well as the surface temperature), Dawn will use the color filters in its camera to record the sights in visible and infrared wavelengths.
As always, mission planners schedule more observations than are needed, recognizing that glitches can occur on a complex and challenging expedition in the forbidding depths of space. So even if some data are not collected, the goals can still be accomplished.
The probe also will continue to acquire spectra both of neutrons and of gamma rays. It is unlikely to detect more than a whisper of neutrons from Ceres at this height, but the radiation coming from elsewhere in space now will serve as a useful calibration when it measures stronger nuclear emanations from one quarter the altitude starting in December, allowing scientists to inventory Ceres’ atomic constituents.
Precise measurements of Dawn’s radio signal will reveal more details of the dwarf planet’s gravitational field and hence the distribution of mass within. When the spacecraft is not aiming its main antenna at Earth, it will broadcast through one of its three auxiliary antennas, and the Deep Space Network will be listening (almost) continuously throughout the 84 orbits.
As at Vesta, Dawn’s polar orbits are oriented so that the craft always keeps the sun in view, never entering Ceres’ shadow, even when it is nighttime on the ground below. But its course will take the robot out of sight from Earth occasionally, and the behemoth of rock and ice will block the radio signal. Of course, Dawn is quite accustomed to operating in radio silence. It follows timed instructions (called sequences) that cover a full mapping cycle, so it does not require constant contact. And in budgeting how much data Dawn can collect and transmit, mission planners have accounted for the amount of time Ceres will eclipse its view of Earth.
Thanks to the uniquely efficient and exceptionally gentle thrust of the ion engines, as well as the flexibility inherent in being in orbit, Dawn operations generally can be more leisurely than those with conventional chemical propulsion or missions that only fly past their targets rather than stay for as long as needed. In that spirit, controllers had allowed the time in the spacecraft’s main computer to drift off, as there was no need to keep it particularly accurate. But recently the clock was off by so much that they decided to correct it, so before the mapping began, they adjusted it by a whopping 0.983 seconds, eliminating a large (but still tolerable) offset.
Many residents of Earth’s northern hemisphere are completing their leisurely summer vacations. As we saw in February, Dawn has measured the orientation of Ceres’ spin axis and found that it is tipped about four degrees (compared with Earth’s axial tilt of 23 degrees). The sun then never moves very far from the dwarf planet’s equator, so seasonal variations are mild. Nevertheless, northern hemisphere summer (southern hemisphere winter) began on Ceres on July 24. Because Ceres takes longer to revolve around the sun than Earth, seasons last much longer. The next equinox won’t occur until Nov. 13, 2016, so there is still plenty of time to plan a summer vacation.
Meanwhile, Dawn is working tirelessly to reveal the nature of this complex, intriguing world. Now seeing the exotic sights with a sharper focus than ever, the probe’s meticulous mapping will provide a wealth of new data that scientists will turn into knowledge. And everyone who has ever seen the night sky beckon, everyone who has heard the universe’s irresistible invitation, and everyone who has felt the overpowering drive for a bold journey far from Earth shares in the experience of this remarkable interplanetary adventure.
Dawn is 905 miles (1,456 kilometers) from Ceres. It is also 2.06 AU (191 million miles, or 308 million kilometers) from Earth, or 775 times as far as the moon and 2.03 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 34 minutes to make the round trip.
Dr. Marc D. Rayman
5:00 p.m. PDT August 21, 2015
Flying on a blue-green ray of xenon ions, Dawn is gracefully descending toward dwarf planet Ceres. Even as Dawn prepares for a sumptuous new feast in its next mapping orbit, scientists are continuing to delight in the delicacies Ceres has already served. With a wonderfully rich bounty of pictures and other observations already secured, the explorer is now on its way to an even better vantage point.
Dawn takes great advantage of its unique ion propulsion system to maneuver extensively in orbit, optimizing its views of the alien world that beckoned for more than two centuries before a terrestrial ambassador arrived in March. Dawn has been in powered flight for most of its time in space, gently thrusting with its ion engine for 69 percent of the time since it embarked on its bold interplanetary adventure in 2007. Such a flight profile is entirely different from the great majority of space missions. Most spacecraft coast most of the time (just as planets do), making only brief maneuvers that may add up to just a few hours or even less over the course of a mission of many years. But most spacecraft could not accomplish Dawn’s ambitious mission. Indeed, no other spacecraft could. The only ship ever to orbit two extraterrestrial destinations, Dawn accomplishes what would be impossible with conventional technology. With the extraordinary capability of ion propulsion, it is truly an interplanetary spaceship.
In addition to using its ion engine to travel to Vesta, enter into orbit around the protoplanet in 2011, break out of orbit in 2012, travel to Ceres and enter into orbit there this year, Dawn relies on the same system to fly to different orbits around these worlds it unveils, executing complex and graceful spirals around its gravitational master. After conducting wonderfully successful observation campaigns in its preantepenultimate Ceres orbit 8,400 miles (13,600 kilometers) high in April and May and its antepenultimate orbit at 2,700 miles (4,400 kilometers) in June, Dawn commenced its spiral descent to the penultimate orbit at 915 miles (1,470 kilometers) on June 30. (We will discuss this orbital altitude in more detail below.) A glitch interrupted the maneuvering almost as soon as it began, when protective software detected a discrepancy in the probe’s orientation. But thanks to the exceptional flexibility built into the plans, the mission could easily accommodate the change in schedule that followed. It will have no effect on the outcome of the exploration of Ceres. Let’s see what happened.
Control of Dawn’s orientation in the weightless conditions of spaceflight is the responsibility of the attitude control system. (To maintain a mystique about their work, engineers use the term “attitude” instead of “orientation.” This system also happens to have a very positive attitude about its work.) Dawn (and all other objects in three-dimensional space) can turn about three mutually perpendicular axes. The axes may be called pitch, roll and yaw; left/right, front/back and up/down; x, y and z; rock, paper and scissors; chocolate, vanilla and strawberry; Peter, Paul and Mary; etc., but whatever their names, attitude control has several different means to turn or to stabilize each axis. Earlier in its journey, the spacecraft depended on devices known as reaction wheels. As we have discussed in many Dawn Journals, that method is now used only rarely, because two of the four units have failed. The remaining two are being saved for the ultimate orbit at about 230 miles (375 kilometers), which Dawn will attain at the end of this year. Instead of reaction wheels, Dawn has been using its reaction control system, shooting puffs of hydrazine, a conventional rocket propellant, through small jets. (This is entirely different from the ion propulsion system, which expels high velocity xenon ions to change and control Dawn’s path through space. The reaction control system is used only to change and control attitude.)
Whenever Dawn is firing one of its three ion engines, its attitude control system uses still another method. The ship only operates one engine at a time, and attitude control swivels the mechanical gimbal system that holds that engine, thus imparting a small torque to the spacecraft, providing the means to control two axes (pitch and yaw, for example, or chocolate and strawberry). For the third axis (roll or vanilla), it still uses the hydrazine jets of the reaction control system.
On June 30, engine #3 came to life on schedule at 10:32:19 p.m. PDT to begin nearly five weeks of maneuvers. Attitude control deftly switched from using the reaction control system for all three axes to only one, and controlling the other two axes by tipping and tilting the engine with gimbal #3. But the control was not as effective as it should have been. Software monitoring the attitude recognized the condition but wisely avoided reacting too soon, instead giving attitude control time to try to rectify it. Nevertheless, the situation did not improve. Gradually the attitude deviated more and more from what it should have been, despite attitude control’s efforts. Seventeen minutes after thrusting started, the error had grown to 10 degrees. That’s comparable to how far the hour hand of a clock moves in 20 minutes, so Dawn was rotating only a little faster than an hour hand. But even that was more than the sophisticated probe could allow, so at 10:49:27 p.m., the main computer declared one of the “safe modes,” special configurations designed to protect the ship and the mission in uncertain, unexpected or difficult circumstances.
The spacecraft smoothly entered safe mode by turning off the ion engine, reconfiguring other systems, broadcasting a continuous radio signal through one of its antennas and then patiently awaiting further instructions. The radio transmission was received on a distant planet the next day. (It may yet be received on some other planets in the future, but we shall focus here on the response by Earthlings.) One of NASA’s Deep Space Network stations in Australia picked up the signal on July 1, and the mission control team at JPL began investigating immediately.
Engineers assessed the health of the spacecraft and soon started returning it to its normal configuration. By analyzing the myriad diagnostic details reported by the robot over the next few days, they determined that the gimbal mechanism had not operated correctly, so when attitude control tried to change the angle of the ion engine, it did not achieve the desired result.
Because Dawn had already accomplished more than 96 percent of the planned ion-thrusting for the entire mission (nearly 5.5 years so far), the remaining thrusting could easily be accomplished with only one of the ion engines. (Note that the 96 percent here is different from the 69 percent of the total time since launch mentioned above, simply because Dawn has been scheduled not to thrust some of the time, including when it takes data at Vesta and Ceres.) Similarly, of the ion propulsion system’s two computer controllers, two power units and two sets of valves and other plumbing for the xenon, the mission could be completed with only one of each. So although engineers likely could restore gimbal #3’s performance, they chose to switch to another gimbal (and thus another engine) and move on. Dawn’s goal is to explore a mysterious, fascinating world that used to be known as a planet, not to perform complex (and unnecessary) interplanetary gimbal repairs.
One of the benefits of being in orbit (besides it being an incredibly cool place to be) is that Dawn can linger at Ceres, studying it in great detail rather than being constrained by a fast flight and a quick glimpse. By the same principle, there was no urgency in resuming the spiral descent. The second mapping orbit was a perfectly fine place for the spacecraft, and it could circle Ceres there every 3.1 days as long as necessary. (Dawn consumed its hydrazine propellant at a very, very low rate while in that orbit, so the extra time there had a negligible cost, even as measured by the most precious resource.)
The operations team took the time to be cautious and to ensure that they understood the nature of the faulty gimbal well enough to be confident that the ship could continue its smooth sailing. They devised a test to confirm Dawn’s readiness to resume its spiral maneuvers. After swapping to gimbal #2 (and ipso facto engine #2), Dawn thrust from July 14 to 16 and demonstrated the excellent performance the operations team has seen so often from the veteran space traveler. Having passed its test with flying colors (or perhaps even with orbiting colors), Dawn is now well on its way to its third mapping orbit.
The gradual descent from the second mapping orbit to the third will require 25 revolutions. The maneuvers will conclude in about two weeks. (As always, you can follow the progress with your correspondent’s frequent and succinct updates here.) As in each mapping orbit, following arrival, a few days will be required in order to prepare for a new round of intensive observations. That third observing campaign will begin on August 17 and last more than two months.
Although this is the second lowest of the mapping orbits, it is also known as the high altitude mapping orbit (HAMO) for mysterious historical reasons. We presented an overview of the HAMO plans last year. Next month, we will describe how the flight team has built on a number of successes since then to make the plans even better.
The view of the landscapes on this distant and exotic dwarf planet from the third mapping orbit will be fantastic. How can we be so sure? The view in the second mapping orbit was fantastic, and it will be three times sharper in the upcoming orbit. Quod erat demonstrandum! To see the sights at Ceres, go there or go here.
Part of the flexibility built into the plans was to measure Ceres’ gravity field as accurately as possible in each mapping orbit and use that knowledge to refine the design for the subsequent orbital phase. Thanks to the extensive gravity measurements in the second mapping orbit in June, navigators were able not only to plot a spiral course but also to calculate the parameters for the next orbit to provide the views needed for the complex mapping activities.
We have discussed some of the difficulty in describing the orbital altitude, including variations in the elevation of the terrain, just as a plane flying over mountains and valleys does not maintain a fixed altitude. As you might expect on a world battered by more than four billion years in the main asteroid belt and with its own internal geological forces, Ceres has its ups and downs. (The topographical map above displays them, and you can see a cool animation of Ceres showing off its topography here.) In addition to local topographical features, its overall shape is not perfectly spherical, as we discussed in May. Ongoing refinements based on Dawn’s measurements now indicate the average diameter is 584 miles (940 kilometers), but the equatorial diameter is 599 miles (964 kilometers), whereas the polar diameter is 556 miles (894 kilometers). Moreover, the orbits themselves are not perfect circles, and irregularities in the gravitational field, caused by regions of lower and higher density inside the dwarf planet, tug less or more on the craft, making it move up and down somewhat. (By using that same principle, scientists learn about the interior structure of Ceres and Vesta with very accurate measurements of the subtleties in the spacecraft’s orbital motions.) Although Dawn’s average altitude will be 915 miles (1,470 kilometers), its actual distance above the ground will vary over a range of about 25 miles (40 kilometers).
In March we summarized the four Ceres mapping orbits along with a guarantee that the dates would change. In addition to delivering exciting interplanetary adventures to thrill anyone who has ever gazed at the night sky in wonder, Dawn delivers on its promises. Therefore, we present the updated table here. With such a long and complex mission taking place in orbit around the largest previously uncharted world in the inner solar system, further changes are highly likely. (Nevertheless, we would consider the probability to be low that changes will occur for the phases in the past.)
Click on the name of each orbit for a more detailed description. As a reminder, the last column illustrates how large Ceres appears to be from Dawn’s perspective by comparing it with a view of a soccer ball. (Note that Ceres is not only 4.4 million times the diameter of a soccer ball but it is a lot more fun to play with.)
Resolute and resilient, Dawn patiently continues its graceful spirals, propelled not only by its ion engine but also by the passions of everyone who yearns for new knowledge and noble adventures. Humankind’s robotic emissary is well on its way to providing more fascinating insights for everyone who longs to know the cosmos.
Dawn is 1,500 miles (2,400 kilometers) from Ceres. It is also 1.95 AU (181 million miles, or 291 million kilometers) from Earth, or 785 times as far as the moon and 1.92 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 32 minutes to make the round trip.
Dr. Marc D. Rayman
8:00 p.m. PDT July 29, 2015
Dear Evidawnce-Based Readers,
Dawn is continuing to unveil a Ceres of mysteries at the first dwarf planet discovered. The spacecraft has been extremely productive, returning a wealth of photographs and other scientific measurements to reveal the nature of this exotic alien world of rock and ice. First glimpsed more than 200 years ago as a dot of light among the stars, Ceres is the only dwarf planet between the sun and Neptune.
Dawn has been orbiting Ceres every 3.1 days at an altitude of 2,700 miles (4,400 kilometers). As described last month, the probe aimed its powerful sensors at the strange landscape throughout each long, slow passage over the side of Ceres facing the sun. Meanwhile, Ceres turned on its axis every nine hours, presenting itself to the ambassador from Earth. On the half of each revolution when Dawn was above ground that was cloaked in the darkness of night, it pointed its main antenna to that planet far, far away and radioed its precious findings to eager Earthlings (although the results will be available for others throughout the cosmos as well). Dawn began this second mapping campaign (also known as "survey orbit") on June 5, and tomorrow it will complete its eighth and final revolution.
The spacecraft made most of its observations by looking straight down at the terrain directly beneath it. During portions of its first, second and fourth orbits, however, Dawn peered at the limb of Ceres against the endless black of space, seeing the sights from a different perspective to gain a better sense of the lay of the land.
And what marvels Dawn has beheld! How can you not be mesmerized by the luminous allure of the famous bright spots? They are not, in fact, a source of light, but for a reason that remains elusive, the ground there reflects much more sunlight than elsewhere. Still, it is easy to imagine them as radiating a light all their own, summoning space travelers from afar, beckoning the curious and the bold to venture closer in return for an attractive reward. And that is exactly what we will do, as we seek the rewards of new knowledge and new insights into the cosmos.
Although scientists have not yet determined what minerals are there, Dawn will gather much more data. As summarized in this table, our explorer will map Ceres again from much closer during the course of its orbital mission. New bright areas have shown up in other locations too, in some places as relatively small spots, in others as larger areas (as in the photo below), and all of them will come into sharper focus when Dawn descends further.
In the meantime, you can register your opinion for what the bright spots are. Join more than 100 thousand others who have voted for an explanation for this enigma. Of course, Ceres will be the ultimate arbiter, and nature rarely depends upon public opinion, but the Dawn project will consider sending the results of the poll to Ceres, courtesy of our team member on permanent assignment there.
In addition to the bright spots, Dawn's views from its present altitude have included a wide range of other intriguing sights, as one would expect on a world of more than one million square miles (nearly 2.8 million square kilometers). There are myriad craters excavated by objects falling from space, inevitable scars from inhabiting the main asteroid belt for more than four billion years, even for the largest and most massive resident there.
The craters exhibit a wide range of appearances, not only in size but also in how sharp and fresh or how soft and aged they look. Some display a peak at the center. A crater can form from such a powerful punch that the hard ground practically melts and flows away from the impact site. Then the material rebounds, almost as if it sloshes back, while already cooling and then solidifying again. The central peak is like a snapshot, preserving a violent moment in the formation of the crater. By correlating the presence or absence of central peaks with the sizes of the craters, scientists can infer properties of Ceres' crust, such as how strong it is. Rather than a peak at the center, some craters contain large pits, depressions that may be a result of gasses escaping after the impact. (Craters elsewhere in the solar system, including on Vesta and Mars, also have pits.)
Dawn also has spied many long, straight or gently curved canyons. Geologists have yet to determine how they formed, and it is likely that several different mechanisms are responsible. For example, some might turn out to be the result of the crust of Ceres shrinking as the heat and other energy accumulated upon formation gradually radiated into space. When the behemoth slowly cooled, stresses could have fractured the rocky, icy ground. Others might have been produced as part of the devastation when a space rock crashed, rupturing the terrain.
Ceres shows other signs of an active past rather than that of a static chunk of inert material passing the eons with little notice. Some areas are less densely cratered than others, suggesting that there are geological processes that erase the craters. Indeed, some regions look as if something has flowed over them, as if perhaps there was mud or slush on the surface.
In addition to evidence of aging and renewal, some powerful internal forces have uplifted mountains. One particularly striking structure is a steep cone that juts three miles (five kilometers) high in an otherwise relatively smooth area, looking to an untrained (but transfixed) eye like a volcanic cone, a familiar sight on your home planet (or, at least, on mine). No other isolated, prominent protuberance has been spotted on Ceres.
It is too soon for scientists to understand the intriguing geology of this ancient world, but the prolific adventurer is providing them with the information they will use. The bounty from this second mapping phase includes more than 1,600 pictures covering essentially all of Ceres, well over five million spectra in visible and infrared wavelengths and hundreds of hours of gravity measurements.
The spacecraft has performed its ambitious assignments quite admirably. Only a few deviations from the very elaborate plans occurred. On June 15 and 27, during the fourth and eighth flights over the dayside, the computer in the combination visible and infrared mapping spectrometer (VIR) detected an unexpected condition, and it stopped collecting data. When the spacecraft's main computer recognized the situation, it instructed VIR to close its protective cover and then power down. The unit dutifully did so. Also on June 27, about three hours before VIR's interruption, the camera's computer experienced something similar.
Most of the time that Dawn points its sensors at Ceres, it simultaneously broadcasts through one of its auxiliary radio antennas, casting a very wide but faint signal in the general direction of Earth. (As Dawn progresses in its orbit, the direction to Earth changes, but the spacecraft is equipped with three of these auxiliary antennas, each pointing in a different direction, and mission controllers program it to switch antennas as needed.) The operations team observed what had occurred in each case and recognized there was no need to take immediate action. The instruments were safe and Dawn continued to carry out all of its other tasks.
When Dawn subsequently flew to the nightside of Ceres and pointed its main antenna to Earth, it transmitted much more detailed telemetry. As engineers and scientists continue their careful investigations, they recognize that in many ways, these events appear very similar to ones that have occurred at other times in the mission.
Four years ago, VIR's computer reset when Dawn was approaching Vesta, and the most likely cause was deemed to be a cosmic ray strike. That's life in deep space! It also reset twice in the survey orbit phase at Vesta. The camera reset three times in the first three months of the low altitude mapping orbit at Vesta.
Even with the glitches in this second mapping orbit, Dawn's outstanding accomplishments represent well more than was originally envisioned or written into the mission's scientific requirements for this phase of the mission. For those of you who have not been to Ceres or aren't going soon (and even those of you who want to plan a trip there of your own), you can see what Dawn sees by going to the image gallery.
Although Dawn already has revealed far, far more about Ceres in the last six months than had been seen in the preceding two centuries of telescopic studies, the explorer is not ready to rest on its laurels. It is now preparing to undertake another complex spiral descent, using its sophisticated ion propulsion system to maneuver to a circular orbit three times as close to the dwarf planet as it is now. It will take five weeks to perform the intricate choreography needed to reach the third mapping altitude, starting tomorrow night. You can keep track of the spaceship's flight as it propels itself to a new vantage point for observing Ceres by visiting the mission status page or following it on Twitter @NASA_Dawn.
As Dawn moves closer to Ceres, Earth will be moving closer as well. Earth and Ceres travel on independent orbits around the sun, the former completing one revolution per year (indeed, that's what defines a year) and the latter completing one revolution in 4.6 years (which is one Cerean year). (We have discussed before why Earth revolves faster in its solar orbit, but in brief it is because being closer to the sun, it needs to move faster to counterbalance the stronger gravitational pull.) Of course, now that Dawn is in a permanent gravitational embrace with Ceres, where Ceres goes, so goes Dawn. And they are now and forever more so close together that the distance between Earth and Ceres is essentially equivalent to the distance between Earth and Dawn.
On July 22, Earth and Dawn will be at their closest since June 2014. As Earth laps Ceres, they will be 1.94 AU (180 million miles, or 290 million kilometers) apart. Earth will race ahead on its tight orbit around the sun, and they will be more than twice as far apart early next year.
Although Dawn communicates regularly with Earth, it left that planet behind nearly eight years ago and will keep its focus now on its new residence. With two very successful mapping campaigns complete, its next priority is to work its way down through Ceres' gravitational field to an altitude of about 900 miles (less than 1,500 kilometers). With sharper views and new kinds of observations (including stereo photography), the treasure trove obtained by this intrepid extraterrestrial prospector will only be more valuable. Everyone who longs for new understandings and new perspectives on the cosmos will grow richer as Dawn continues to pioneer at a mysterious and distant dwarf planet.
Dawn is 2,700 miles (4,400 kilometers) from Ceres. It is also 2.01 AU (187 million miles, or 301 million kilometers) from Earth, or 785 times as far as the moon and 1.98 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 33 minutes to make the round trip.
Dr. Marc D. Rayman
10:00 p.m. PDT June 29, 2015
Dear Emboldawned Readers,
A bold adventurer from Earth is gracefully soaring over an exotic world of rock and ice far, far away. Having already obtained a treasure trove from its first mapping orbit, Dawn is now seeking even greater riches at dwarf planet Ceres as it maneuvers to its second orbit.
The first intensive mapping campaign was extremely productive. As the spacecraft circled 8,400 miles (13,600 kilometers) above the alien terrain, one orbit around Ceres took 15 days. During its single revolution, the probe observed its new home on five occasions from April 24 to May 8. When Dawn was flying over the night side (still high enough that it was in sunlight even when the ground below was in darkness), it looked first at the illuminated crescent of the southern hemisphere and later at the northern hemisphere.
When Dawn traveled over the sunlit side, it watched the northern hemisphere, then the equatorial regions, and finally the southern hemisphere as Ceres rotated beneath it each time. One Cerean day, the time it takes the globe to turn once on its axis, is about nine hours, much shorter than the time needed for the spacecraft to loop around its orbit. So it was almost as if Dawn hovered in place, moving only slightly as it peered down, and its instruments could record all of the sights as they paraded by.
We described the plans in much more detail in March, and they executed beautifully, yielding a rich collection of photos in visible and near infrared wavelengths, spectra in visible and infrared, and measurements of the strength of Ceres' gravitational attraction and hence its mass.
To gain the same view Dawn had, simply build your own ion-propelled spaceship, voyage deep into the main asteroid belt between Mars and Jupiter, take up residence at the giant orb and look out the window. Or go to the image gallery here.
Either way, the sights are spectacular. And they have already gotten even better. As Dawn has been descending to its second mapping orbit, it paused ion-thrusting on May 16 and May 22 to take more pictures, helping navigators get a tight fix on its orbital location. We explained this technique of optical navigation earlier, but now it is slightly different. Dawn is so close to Ceres that the behemoth fills the camera's field of view. No longer charting Ceres' location relative to background stars, navigators now use distinctive features on Ceres itself. It was an indistinct, fuzzy little blob just a few months ago, but now the maps are becoming detailed and accurate. Mathematical analyses of the locations of specific landmarks in each picture allow navigators to determine where Dawn was when the picture was taken.
Let's see how this works. Suppose I gave you a picture I had taken in your house. (The last time I was there, I opted for the cover of darkness rather than a more visible demonstration of optical navigation, but we can still imagine.) Because you know the positions of the doors, windows, furniture, impact craters, paintings, etc., you could establish where I had been when I took the photo. Now that they have charted the positions of the features at Dawn's new home, navigators can do virtually the same thing.
In addition to aiding in celestial navigation, the photos provided still better views of the world Dawn traveled so long and so far to explore. Greater and greater detail is visible as Dawn orbits closer, and a tremendous variety of intriguing sights are coming into view. It may well be that the most interesting discoveries have not even been made yet, but for now, what captivates most people (and other readers as well) are the bright spots.
We have discussed them here and there in recent months, and their luminous power continues to dazzle us. What appeared initially as one fuzzy spot proved to be two smaller spots and now many even smaller regions as the focus has become sharper. Why the ground there reflects so much sunlight remains elusive. Dawn's finer examinations with its suite of sophisticated instruments in the second, third and then final mapping orbits will provide scientists with data they need to unravel this marvelous mystery. For now, the enigmatic lights present an irresistible cosmic invitation to go closer and to scrutinize this strange and wonderful world, and we are eager to accept. After all, we explore to learn, to know the unknown, and the uniquely powerful scientific method will reveal the nature of the bright areas and what they can tell us about the composition and geology of this complex dwarf planet.
› Full image and caption
After having been viewed as little more than a smudge in telescopes for more than two centuries since its discovery, Ceres now is seen as a detailed, three-dimensional world. As promised, measurements from Dawn have revised the size to be about 599 miles (963 kilometers) across at the equator. Like Earth and other planets, Ceres is oblate, or slightly wider at the equator than from pole to pole. The polar diameter is 554 miles (891 kilometers). These dimensions are impressively close to what astronomers had determined from telescopic observations and confirm Ceres to be the colossus we have described.
Before Dawn, scientists had estimated Ceres' mass to be 1.04 billion billion tons (947 billion billion kilograms). Now it is measured to be 1.03 billion billion tons (939 billion billion kilograms), well within the previous margin of error. It is an impressive demonstration of the success of science that astronomers had been able to determine the heft of that point of light so accurately. Nevertheless, even this small change of less than one percent is important for planning the rest of Dawn’s mission as it orbits closer and closer, feeling the gravitational tug ever more strongly.
Let's put this change in context. Dawn has now refined the mass, making a proportionally small adjustment of about 0.01 billion billion tons (eight billion billion kilograms). Although no more than a tweak on the overall value, it is still significantly greater than the combined mass of all asteroids visited by all other spacecraft. Ceres is so immense, so massive that even if all those asteroids were added to it, the difference would hardly even have been noticeable. This serves as another reminder that the dwarf planet really is quite unlike the millions of small asteroids that constitute the main asteroid belt. This behemoth contains about 30 percent of all the mass in that entire vast region of space. Vesta, the protoplanet Dawn orbited and studied in 2011-2012, is the second most massive resident there, holding about 8 percent of the asteroid belt's mass. Dawn by itself is exploring around 40 percent of the asteroid belt's mass!
Upon concluding its first mapping orbit, Dawn powered on its remarkable ion propulsion system on May 9 to fly down to a lower altitude where it will gain a better view. We examined the nature of the spiral paths between mapping orbits last year (and at Vesta in 2011-2012).
› Larger image
In its first mapping orbit, Dawn was 8,400 miles (13,600 kilometers) high, revolving once in 15.2 days at a speed of 150 mph (240 kilometers per hour). By the time it completes this descent, the probe will be at an altitude of 2,700 miles (4,400 kilometers), orbiting Ceres every 3.1 days at 254 mph (408 kilometers per hour). (All of the mapping orbits were summarized in this table.) We have discussed that lower orbits require greater velocity to counterbalance the stronger gravitational hold.
Dawn's uniquely capable ion propulsion system, with its extraordinary combination of efficiency and gentleness, propels the ship to its new orbital destination in just under four weeks. The descent requires five revolutions, each one faster than the one before. The flight profile is complicated, and sometimes Dawn even dips below the final, planned altitude and then rises to greater heights as it flies on a path that is temporarily elliptical. The overall trend, of course, is downward. As Dawn heads for its targeted circular orbit, its maneuvering is also generally reducing the orbit period, the time required to make one complete revolution around Ceres. Indeed, if Dawn stopped thrusting now, its orbit period would be about 83 hours, or 3.5 days.
Dawn will complete ion-thrusting on June 3, but it will not be ready to begin its next science observations then. Rather, as in the other new mapping orbits, the first order of business will be for navigators to measure the new orbital parameters accurately. The flight team then will install in Dawn's main computer the details of the orbit it achieved so it will always know its location.
In addition, the intensive campaign of observations is planned to begin when the robotic explorer travels from the night side to the day side over the north pole. With the three-day orbit period, that will next occur on June 5. Controllers will take advantage of the intervening time to conduct other activities, including routine maintenance of the two reaction wheels that remain operable, although they are powered off most of the time. (Two of the four failed years ago. Dawn no longer relies on these devices to control its orientation, and it is remarkable that the mission can accomplish all of its original objectives without them. But if two do function in the final mapping orbit later this year, they will help extend the spacecraft's lifetime for bonus studies.)
We have already presented the ambitious plans for this second mapping orbit, sometimes known as "the second mapping orbit" and sometimes more succinctly and confusingly as "survey orbit." As with all four of Dawn's mapping orbits, it is designed to take the spacecraft over the poles, ensuring the best possible coverage. The ship will fly from the north pole to the south over the side of Ceres facing the sun, and then loop back to the north over the side hidden in the deep dark of night. On the day side, Dawn will aim its camera and spectrometers at the lit ground, filling its memory to capacity with the readings. On the night side, it will point its main antenna to distant Earth in order to radio its findings home. At Dawn's altitude, Ceres will appear twice as wide as the camera's view. (As illustrated in this table, it will look about the size of a soccer ball seen from a yard, or a meter, away.) But as the dwarf planet rotates on its axis and Dawn sails around in its more leisurely orbit, eventually all of the landscape will come within sight of the instruments.
Only one noteworthy change has been made in the intricate plans for survey orbit since May 2014's shocking exposé. With the observations starting on June 5, the subsequent complex orbital flight to the third mapping orbit (also known as HAMO) would have begun on June 27. As we have seen, the rapidly changing orbit in the spiral descents requires a great deal of effort by the small operations team on a rigid schedule. The capable men and women flying Dawn accomplished the maneuvers flawlessly at Vesta and are well prepared for the challenges at Ceres. The work is very demanding, however, and so, just as at Vesta, the team has built into the strategy the capability to make adjustments to align most of the tasks with a conventional work schedule. The technical plans (even including the exquisitely careful husbanding of hydrazine following the loss of the two reaction wheels) fully account for such human factors. It turns out that leaving survey orbit three days later shifts a significant amount of the following work off weekends, making it more comfortable for the team members. Three days is one complete revolution, and always extracting as much from the mission as possible, they have devised another full set of observations for an eighth orbit. As a result, survey orbit may be even more extensive and productive than originally anticipated.
What awaits Dawn in the next mapping phase? The views will be three times as sharp as in the previous orbit, and exciting new discoveries are sure to come. What answers will be revealed? And what new questions (besides this one) will arise? We will know soon, as we all share in the thrill of this grand adventure. To help you keep track of Dawn's progress as it powers its way down and then conducts further observations, your correspondent writes brief (hard to believe, isn't it?) mission status updates. And although in space no one can hear you tweet, terrestrial followers can get even more frequent updates with information he provides for Twitter @NASA_Dawn.
Dawn is 3,400 miles (5,500 kilometers) from Ceres. It is also 2.30 AU (214 million miles, or 345 million kilometers) from Earth, or 855 times as far as the moon and 2.27 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 38 minutes to make the round trip.
Dr. Marc D. Rayman
12:00 p.m. PDT May 28, 2015
Let's get Dawn to business, Dear Readers,
Dawn's assignment when it embarked on its extraordinary extraterrestrial expedition in 2007 can be described quite simply: explore the two most massive uncharted worlds in the inner solar system. It conducted a spectacular mission at Vesta, orbiting the giant protoplanet for 14 months in 2011-2012, providing a wonderfully rich and detailed view. Now the sophisticated probe is performing its first intensive investigation of dwarf planet Ceres. Dawn is slowly circling the alien world of rock and ice, far from Earth and far from the sun, executing its complex operations with the prowess it has demonstrated throughout its ambitious journey.
Following an interplanetary trek of 7.5 years and 3.1 billion miles (4.9 billion kilometers), Earth's ambassador arrived in orbit on March 6, answering Ceres' two-century-old celestial invitation. With its advanced ion propulsion system and ace piloting skills, it has maneuvered extensively in orbit. Traveling mostly high over the night side of Ceres, arcing and banking, thrusting and coasting, accelerating and decelerating, climbing and diving, the spaceship flew to its first targeted orbital altitude, which it reached on April 23.
Dawn is at an altitude of about 8,400 miles (13,600 kilometers) above the mysterious terrain. This first mapping orbit is designated RC3 by the Dawn team and is a finalist in the stiff competition for the coveted title of Most Confusing Name for a Ceres Mapping Orbit. (See this table for the other contestants.) Last month we described some of the many observations Dawn will perform here, including comprehensive photography of the alien landscapes, spectra in infrared and visible wavelengths, a search for an extremely tenuous veil of water vapor and precise tracking of the orbit to measure Ceres' mass.
On the way down to this orbit, the spacecraft paused ion thrusting twice earlier this month to take pictures of Ceres, as it had seven times before in the preceding three months. (We presented and explained the schedule for photography during the three months leading up to RC3 here.) Navigators used the pictures to measure the position of Ceres against the background of stars, providing crucial data to guide the ship to its intended orbit. The Dawn team also used the pictures to learn about Ceres to aid in preparing for the more detailed observations.
We described last month, for example, adjusting the camera settings for upcoming pictures to ensure good exposures for the captivating bright spots, places that reflect significantly more sunlight than most of the dark ground. Scientists have also examined all the pictures for moons of Ceres (and many extra pictures were taken specifically for that purpose). And thanks to Dawn's pictures, everyone who longs for a perspective on the universe unavailable from our terrestrial home has been transported to a world one million times farther away than the International Space Station.
The final pictures before reaching RC3 certainly provide a unique perspective. (You can see Dawn's pictures of Ceres here.) On April 10 and April 14-15, Dawn peered down over the northern hemisphere and watched for two hours each time as Ceres turned on its axis, part of the unfamiliar cratered terrain bathed in sunlight, part in the deep dark of night. This afforded a very different view from what we are accustomed to in looking at other planets, as most depictions of planetary rotations are from nearer the equator to show more of the surface. (Indeed, Dawn acquired views like that in its February "rotation characterizations.") The latest animations of Ceres rotating beneath Dawn are powerful visual reminders that this capable interplanetary explorer really is soaring around in orbit about a distant, alien world. Following the complex flight high above the dark hemisphere, where there was nothing to see, the pictures also show us that the long night's journey into day has ended.
Gradually descending atop its blue-green beam of high velocity xenon ions, Dawn crossed over the terminator -- the boundary between the dark side and the lit side -- on April 15 almost directly over the north pole. On April 20, on final approach to RC3, it flew over the equator at an altitude of about 8,800 miles (14,000 kilometers).
The spacecraft completed its ion thrusting shortly after 1:00 a.m. PDT on April 23. What an accomplishment this was! From the time Dawn left its final mapping orbit at Vesta in July 2012, this is where it has been headed. The escape from Vesta's gravitational clutches in September 2012, the subsequent two and a half years of interplanetary travel and entering into orbit around Ceres on March 6, as genuinely exciting and important as it was, all really occurred as consequences of targeting this particular orbit.
In September 2014, the aftereffects of being struck by cosmic radiation compelled the operations team to rapidly develop a complex new approach trajectory because they still wanted to achieve this very orbit, where Dawn is now. And the eidetic reader will note that even when the innovative flight profile was presented five months ago (with many further details in subsequent months), we explained that it would conclude on April 23. And it did! Here we are! All the descriptions and figures plus a cool video elucidated a pretty neat idea, but it's also much more than an idea: it's real!! A probe from Earth is in a mapping orbit around a faraway dwarf planet.
When it had accomplished the needed ion thrusting, the veteran space traveler turned to point its main antenna to Earth so mission controllers could prepare it for the intensive mapping observations. The first task was to measure the orbital parameters so they could be transmitted to the spacecraft.
A few readers (you and I both know who you are) may have noted that in Dawn Journals during the last year, we have described the altitude of RC3 as 8,400 miles and 13,500 kilometers. Above, however, it is 13,600 kilometers. This is not a mistake. (It would be a mistake if the previous sentence were written, "Above, howevr, it is 13,600 kilometers.") This subtle difference belies several important issues about the orbits at Ceres. Let's take a further look.
As we explained when Dawn resided at Vesta, the orbital altitude we present is always an average (and rounded off, to avoid burdening readers with too many unhelpful digits). Vesta, Ceres, Earth and other planetary bodies are not perfect spheres, so even if the spacecraft traveled in a perfect circle, its altitude would change. They all are somewhat oblate, being wider across the equator than from pole to pole. In addition, they have more localized topography. Think of flying in a plane over your planet. If the pilot maintains a constant altitude above sea level, the distance above the ground changes because the elevation of the ground itself varies, coming closer to the aircraft on mountains and farther in valleys. In addition, as it turns out, orbits are not perfect circles but tend to be slightly elliptical, as if the plane flies slightly up and down occasionally, so the altitude changes even more.
In their exquisitely detailed planning, the Dawn team has had to account for the unknown nature of Ceres itself, including its mass and hence the strength of its gravitational pull. Dawn is the only spacecraft to orbit large, massive planetary bodies that were not previously visited by flyby spacecraft. Mercury, Venus, the moon, Mars, Jupiter and Saturn all were studied by spacecraft that flew past them before subsequent missions were sent to orbit them. The first probes to each provided an initial measurement of the mass and other properties that were helpful for the arrival of the first orbiters. At Vesta and Ceres, Dawn has had to discover the essential characteristics as it spirals in closer and closer. For each phase, engineers make the best measurements they can and then use them to update the plans for the subsequent phases. As a result, however, plans are based on impressive but nevertheless imperfect knowledge of what will be encountered at lower altitudes. So even if the spacecraft executes an ion thrust flight profile perfectly, it might not wind up exactly where the plan had specified.
There are other reasons as well for small differences between the predicted and the actual orbit. One is minor variations in the thrust of the ion propulsion system, as we discussed here. Another is that every time the spacecraft fires one of its small rocket thrusters to rotate or to stabilize its orientation in the zero-gravity conditions of spaceflight, that also nudges the spacecraft, changing its orbit a little. (See here for a related example of the effect of the thrusters on the trajectory.)
The Dawn flight team has a deep understanding of all the sources of orbit discrepancies, and they always ensure that their intricate plans account for them. Even if the RC3 altitude ended up more than 300 miles (500 kilometers) higher or lower than the specified value, everything would still work just fine to yield the desired pictures and other data. In fact, the actual RC3 orbit is within 25 miles (40 kilometers), or less than one tenth what the plan was designed to accommodate, so the spacecraft achieved a virtual cosmic bullseye!
In the complex preparations on April 23, one file was not radioed to Dawn on time, so late that afternoon when the robot tried to use this file, it could not find it. It responded appropriately by running protective software, stopping its activities, entering "safe mode" and beaming a signal back to distant Earth to indicate it needed further instructions. After the request arrived in mission control at JPL, engineers quickly recognized what had occurred. That night they reconfigured the spacecraft out of safe mode and back to its normal operational configuration, and they finished off the supply of ice cream in the freezer just outside the mission control room. Although Dawn was not ready to begin its intensive observation campaign in the morning of April 24, it started later that same day and has continued to be very productive.
Dawn is a mission of exploration. And rather than be constrained by a fast flight by a target for a brief glimpse, Dawn has the capability to linger in orbit for a very long time at close range. The probe will spend more than a year conducting detailed investigations to reveal as much as possible about the nature of the first dwarf planet discovered, which we had seen only with telescopes since it was first glimpsed in 1801. The pictures Dawn has sent us so far are intriguing and entrancing, but they are only the introduction to this exotic world. They started transforming it from a smudge of light into a real, physical place and one that a sophisticated, intrepid spacecraft can even reach. Being in the first mapping orbit represents the opportunity now to begin developing a richly detailed, intimate portrait of a world most people never even knew existed. Now, finally, we are ready to start uncovering the secrets Ceres has held since the dawn of the solar system.
Dawn is 8,400 miles (13,600 kilometers) from Ceres. It is also 2.66 AU (247 million miles, or 398 million kilometers) from Earth, or 985 times as far as the moon and 2.64 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 44 minutes to make the round trip.
Dr. Marc D. Rayman
10:30 p.m. PDT April 29, 2015
P.S. Our expert outreach team has done a beautiful job modernizing the website, and blog comments are no longer included. I appreciate all the very kind feedback, expressions of enthusiasm, interesting questions and engaging discussions that the community of Dawnophiles has posted over the last year or so. Now I will devote the time I had been spending responding to comments to providing more frequent mission status updates as well as fun and interesting tidbits you can follow on Twitter @NASA_Dawn.
Dear Dawnticipating Explorers,
Now orbiting high over the night side of a dwarf planet far from Earth, Dawn arrived at its new permanent residence on March 6. Ceres welcomed the newcomer from Earth with a gentle but firm gravitational embrace. The goddess of agriculture will never release her companion. Indeed, Dawn will only get closer from now on. With the ace flying skills it has demonstrated many times on this ambitious deep-space trek, the interplanetary spaceship is using its ion propulsion system to maneuver into a circular orbit 8,400 miles (13,500 kilometers) above the cratered landscape of ice and rock. Once there, it will commence its first set of intensive observations of the alien world it has traveled for so long and so far to reach.
For now, however, Dawn is not taking pictures. Even after it entered orbit, its momentum carried it to a higher altitude, from which it is now descending. From March 2 to April 9, so much of the ground beneath it is cloaked in darkness that the spacecraft is not even peering at it. Instead, it is steadfastly looking ahead to the rewards of the view it will have when its long, leisurely, elliptical orbit loops far enough around to glimpse the sunlit surface again.
Among the many sights we eagerly anticipate are those captivating bright spots. Hinted at more than a decade ago by Hubble Space Telescope, Dawn started to bring them into sharper focus after an extraordinary journey of more than seven years and three billion miles (nearly five billion kilometers). Although the spots are reflections of sunlight, they seem almost to radiate from Ceres as cosmic beacons, drawing us forth, spellbound. Like interplanetary lighthouses, their brilliant glow illuminates the way for a bold ship from Earth sailing on the celestial seas to a mysterious, uncharted port. The entrancing lights fire our imagination and remind us of the irresistible lure of exploration and the powerful anticipation of an adventure into the unknown.
As we describe below, Dawn’s extensive photographic coverage of the sunlit terrain in early May will include these bright spots. They will not be in view, however, when Dawn spies the thin crescent of Ceres in its next optical navigation session, scheduled for April 10 (as always, all dates here are in the Pacific time zone).
As the table here shows, on April 14 (and extending into April 15), Dawn will obtain its last navigational fix before it finishes maneuvering. Should we look forward to catching sight of the bright spots then? In truth, we do not yet know. The spots surely will be there, but the uncertainty is exactly where “there” is. We still have much to learn about a dwarf planet that, until recently, was little more than a fuzzy patch of light among the glowing jewels of the night sky. (For example, only last month did we determine where Ceres’north and south poles point.) Astronomers had clocked the length of its day, the time it takes to turn once on its axis, at a few minutes more than nine hours. But the last time the spots were in view of Dawn’s camera was on Feb. 19. From then until April 14, while Earth rotates more than 54 times (at 24 hours per turn), Ceres will rotate more than 140 times, which provides plenty of time for a small discrepancy in the exact rate to build up. To illustrate this, if our knowledge of the length of a Cerean day were off by one minute (or less than 0.2 percent), that would translate into more than a quarter of a turn during this period, drastically shifting the location of the spots from Dawn’s point of view. So we are not certain exactly what range of longitudes will be within view in the scheduled OpNav 7 window. Regardless, the pictures will serve their intended purpose of helping navigators establish the probe’s location in relation to its gravitational captor.
Dawn’s gradual, graceful arc down to its first mapping orbit will take the craft from the night side to the day side over the north pole, and then it will travel south. It will conclude its powered flight over the sunlit terrain at about 60 degrees south latitude. The spacecraft will finish reshaping its orbit on April 23, and when it stops its ion engine on that date, it will be in its new circular orbit, designated RC3. (We will return to the confusing names of the different orbits at Ceres below.) Then it will coast, just as the moon coasts in orbit around Earth and Earth coasts around the sun. It will take Dawn just over 15 days to complete one revolution around Ceres at this height. We had a preview of RC3 last year, and now we can take an updated look at the plans.
The dwarf planet is around 590 miles (950 kilometers) in diameter (like Earth and other planets, however, it is slightly wider at the equator than from pole to pole). At the spacecraft’s orbital altitude, it will appear to be the same size as a soccer ball seen from 10 feet (3 meters) away. Part of the basis upon which mission planners chose this distance for the first mapping campaign is that the visible disc of Ceres will just fit in the camera’s field of view. All the pictures taken at lower altitudes will cover a smaller area (but will be correspondingly more detailed). The photos from RC3 will be 3.4 times sharper than those in RC2.
There will be work to do before photography begins however. The first order of business after concluding ion thrusting will be for the flight team to perform a quick navigational update (this time, using only the radio signal) and transmit any refinements (if necessary) in Dawn’s orbital parameters, so it always has an accurate knowledge of where it is. (These will not be adjustments to the orbit but rather a precise mathematical description of the orbit it achieved.) Controllers will also reconfigure the spacecraft for its intensive observations, which will commence on April 24 as it passes over the south pole and to the night side again.
As at Vesta, even though half of each circular orbit will be over the night side of Ceres, the spacecraft itself will never enter the shadows. The operations team has carefully designed the orbits so that at Dawn’s altitude, it remains illuminated by the sun, even when the land below is not.
It may seem surprising (or even be surprising) that Dawn will conduct measurements when the ground directly beneath it is hidden in the deep darkness of night. To add to the surprise, these observations were not even envisioned when Dawn’s mission was designed, and it did not perform comparable measurements during its extensive exploration of Vesta in 2011-2012.
The measurements on the night side will serve several purposes. One of the many sophisticated techniques scientists use to elucidate the nature of planetary surfaces is to measure how much light they reflect at different angles. Over the course of the next year, Dawn will acquire tens of thousands of pictures from the day side of Ceres, when, in essence, the sun is behind the camera. When it is over the night side in RC3, carefully designed observations of the lit terrain (with the sun somewhat in front of the camera, although still at a safe angle) will significantly extend the range of angles.
In December, we described the fascinating discovery of an extremely diffuse veil of water vapor around Ceres. How the water makes its way from the dwarf planet high into space is not known. The Dawn team has devised a plan to investigate this further, even though the tiny amount of vapor was sighted long after the explorer left Earth equipped with sensors designed to study worlds without atmospheres.
It is worth emphasizing that the water vapor is exceedingly tenuous. Indeed, it is much less dense than Earth’s atmosphere at altitudes above the International Space Station, which orbits in what most people consider to be the vacuum of space. Our hero will not need to deploy its umbrella. Even comets, which are miniscule in comparison with Ceres, liberate significantly more water.
There may not even be any water vapor at all now because Ceres is farther from the sun than when the Herschel Space Observatory saw it, but if there is, detecting it will be very challenging. The best method to glimpse it is to look for its subtle effects on light passing through it. Although Dawn cannot gaze directly at the sun, it can look above the lit horizon from the night side, searching intently for faint signs of sunlight scattered by sparse water molecules (or perhaps dust lofted into space with them).
For three days in RC3 after passing over the south pole, the probe will take many pictures and visible and infrared spectra as it watches the slowly shrinking illuminated crescent and the space over it. When the spacecraft has flown to about 29 degrees south latitude over the night side, it will no longer be safe to aim its sensitive instruments in that direction, because they would be too close to the sun. With its memory full of data, Dawn will turn to point its main antenna toward distant Earth. It will take almost two days to radio its findings to NASA’s Deep Space Network. Meanwhile, the spacecraft will continue northward, gliding silently high over the dark surface.
On April 28, it will rotate again to aim its sensors at Ceres and the space above it, resuming measurements when it is about 21 degrees north of the equator and continuing almost to the north pole on May 1. By the time it turns once again to beam its data to Earth, it will have completed a wealth of measurements not even considered when the mission was being designed.
Loyal readers will recall that Dawn has lost two of its four reaction wheels, gyroscope-like devices it uses to turn and to stabilize itself. Although such a loss could be grave for some missions, the operations team overcame this very serious challenge. They now have detailed plans to accomplish all of the original Ceres objectives regardless of the condition of the reaction wheels, even the two that have not failed (yet). It is quite a testament to their creativity and resourcefulness that despite the tight constraints of flying the spacecraft differently, the team has been able to add bonus objectives to the mission.
Dawn will finish transmitting its data after its orbit takes it over the north pole and to the day side of Ceres again. For three periods during its gradual flight of more than a week over the illuminated landscape, it will take pictures (in visible and near-infrared wavelengths) and spectra. Each time, it will look down from space for a full Cerean day, watching for more than nine hours as the dwarf planet pirouettes, as if showing off to her new admirer. As the exotic features parade by, Dawn will faithfully record the sites.
It is important to set the camera exposures carefully. Most of the surface reflects nine percent of the sunlight. (For comparison, the moon reflects 12 percent on average, although as many Earthlings have noticed, there is some variation from place to place. Mars reflects 17 percent, and Vesta reflects 42 percent. Many photos seem to show that your correspondent’s forehead reflects about 100 percent.) But there are some small areas that are significantly more reflective, including the two most famous bright spots. Each spot occupies only one pixel (2.7 miles, or 4.3 kilometers across) in the best pictures so far. If each bright area on the ground is the size of a pixel, then they reflect around 40 percent of the light, providing the stark contrast with the much darker surroundings. When Dawn’s pictures show more detail, it could be that they will turn out to be even smaller and even more reflective than they have appeared so far. In RC3, each pixel will cover 0.8 miles (1.3 kilometers). To ensure the best photographic results, controllers are modifying the elaborate instructions for the camera to take pictures of the entire surface with a wider range of exposures than previously planned, providing high confidence that all dark and all bright areas will be revealed clearly.
Dawn will observe Ceres as it flies from 45 degrees to 35 degrees north latitude on May 3-4. Of course, the camera’s view will extend well north and south of the point immediately below it. (Imagine looking at a globe. Even though you are directly over one point, you can see a larger area.) The territory it will inspect will include those intriguing bright spots. The explorer will report back to Earth on May 4-5. It will perform the same observations between 5 degrees north and 5 degrees south on May 5-6 and transmit those findings on May 6-7. To complete its first global map, it will make another full set of measurements for a Cerean day as it glides between 35 degrees and 45 degrees south on May 7.
By the time it has transmitted its final measurements on May 8, the bounty from RC3 may be more than 2,500 pictures and two million spectra. Mission controllers recognize that glitches are always possible, especially in such complex activities, and they take that into account in their plans. Even if some of the scheduled pictures or spectra are not acquired, RC3 should provide an excellent new perspective on the alien world, displaying details three times smaller than what we have discerned so far.
Dawn activated its gamma ray spectrometer and neutron spectrometer on March 12, but it will not detect radiation from Ceres at this high altitude. For now, it is measuring space radiation to provide context for later measurements. Perhaps it will sense some neutrons in the third mapping orbit this summer, but its primary work to determine the atomic constituents of the material within about a yard (meter) of the surface will be in the lowest altitude orbit at the end of the year.
Dawn will conduct its studies from three lower orbital altitudes after RC3, taking advantage of the tremendous maneuverability provided by ion propulsion to spiral from one to another. We presented previews last year of each phase, and as each approaches, we will give still more up-to-date details, but now that Dawn is in orbit, let’s summarize them here. Of course, with complicated operations in the forbidding depths of space, there are always possibilities for changes, especially in the schedule. The team has developed an intricate but robust and flexible plan to extract as many secrets from Ceres as possible, and they will take any changes in stride.
Each orbit is designed to provide a better view than the one before, and Dawn will map the orb thoroughly while at each altitude. The names for the orbits – rotation characterization 3 (RC3); survey; high altitude mapping orbit (HAMO); and low altitude mapping orbit (LAMO) – are based on ancient ideas, and the origins are (or should be) lost in the mists of time. Readers should avoid trying to infer anything at all meaningful in the designations. After some careful consideration, your correspondent chose to use the same names the Dawn team uses rather than create more helpful descriptors for the purposes of these blogs. That ensures consistency with other Dawn project communications. After all, what is important is not what the different orbits are called but rather what amazing new discoveries each one enables.
The robotic explorer will make many kinds of measurements with its suite of powerful instruments. As one indication of the improving view, this table includes the resolution of the photos, and the ever finer detail may be compared with the pictures during the approach phase. For another perspective, we extend the soccer ball analogy above to illustrate how large Ceres will appear to be from the spacecraft’s orbital vantage point.
As Dawn orbits Ceres, together they orbit the sun. Closer to the master of the solar system, Earth (with its own retinue, including the moon and many artificial satellites) travels faster in its heliocentric orbit because of the sun’s stronger gravitational pull at its location. In December, Earth was on the opposite side of the sun from Dawn, and now the planet’s higher speed is causing their separation to shrink. Earth will get closer and closer until July 22, when it will pass on the inside track, and the distance will increase again.
In the meantime, on April 12, Dawn will be equidistant from the sun and Earth. The spacecraft will be 2.89 AU or 269 million miles (433 million kilometers) from both. At the same time, Earth will be 1.00 AU or 93.2 million miles (150 million kilometers) from the sun.
It will be as if Dawn is at the tip of a giant celestial arrowhead, pointing the way to a remarkable solar system spectacle. The cosmos should take note! Right there, a sophisticated spaceship from Earth is gracefully descending on a blue-green beam of xenon ions. Finally, the dwarf planet beneath it, a remote remnant from the dawn of the solar system, is lonely no more. Almost 4.6 billion years after it formed, and 214 years after inquisitive creatures on a distant planet first caught sight of it, a mysterious world is still welcoming the new arrival. And as Dawn prepares to settle into its first close orbit, ready to discover secrets Ceres has kept for so long, everyone who shares in the thrill of this grand and noble adventure eagerly awaits its findings. Together, we look forward to the excitement of new knowledge, new insight and new fuel for our passionate drive to explore the universe.
Dawn is 35,000 miles (57,000 kilometers) from Ceres, or 15 percent of the average distance between Earth and the moon. It is also 3.04 AU (282 million miles, or 454 million kilometers) from Earth, or 1,120 times as far as the moon and 3.04 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 51 minutes to make the round trip.
Dr. Marc D. Rayman
6:00 p.m. PDT March 31, 2015
This Thursday, March 19, NASA's latest mission will begin preparation for its next great milestone: making the wicked-amazing antenna rotate.
A number of spacecraft have rotating parts, such as the RapidScat mission and the Global Precipitation Measurement (GPM) mission, but those don't hold a candle to the dynamics of Soil Moisture Active Passive (SMAP).
SMAP's antenna is 20 feet in diameter. The larger the antenna, the more complex its behavior can be, which makes it more difficult to control. Just imagine swinging a 20-foot baseball bat over your head. Yikes!
Right now the antenna is locked in position until the mission "ops" (operations) team completes its checks of the entire instrument's function and confirms operability. They have taken measurements with the radar and the radiometer. They know the instruments are working by comparing the measurements to how they were tested on the ground before launch. The signals look appropriate; they're seeing what's expected. But the antenna's fixed position means it's measuring only a small strip of the ground below.
Once the antenna starts to spin, we'll be able to measure a much larger area and monitor soil moisture around the entire Earth every two to three days.
These are the three steps to achieving "spin up":
1. Engineers unlock the antenna.
2. A few days later, they spin the antenna slowly.
3. They gradually spin it faster.
At each step, they'll verify how it's performing. The engineers will then conduct a more comprehensive checkout of the instrument's systems. With the antenna spinning, they'll get to see the instrument's full performance for the first time.
After the spinning checkouts are completed ... Voilà! Bibbidi bobbidi boo! SMAP will start mapping global soil moisture and return data!
I look forward to your comments.
Dear Unprecedawnted Readers,
Since its discovery in 1801, Ceres has been known as a planet, then as an asteroid, and later as a dwarf planet. Now, after a journey of 3.1 billion miles (4.9 billion kilometers) and 7.5 years, Dawn calls it “home.”
Earth’s robotic emissary arrived at about 4:39 a.m. PST today. It will remain in residence at the alien world for the rest of its operational life, and long, long after.
Before we delve into this unprecedented milestone in the exploration of space, let’s recall that even before reaching orbit, Dawn started taking pictures of its new home. Last month we presented the updated schedule for photography. Each activity to acquire images (as well as visible spectra and infrared spectra) has executed smoothly and provided us with exciting and tantalizing new perspectives.
While there are countless questions about Ceres, the most popular now seems to be what the bright spots are. It is impossible not to be mesmerized by what appear to be glowing beacons, shining out across the cosmic seas from the uncharted lands ahead. But the answer hasn’t changed: we don’t know. There are many intriguing speculations, but we need more data, and Dawn will take photos and myriad other measurements as it spirals closer and closer during the year. For now, we simply know too little.
For example, some people ask if those spots might be lights from an alien city. That’s ridiculous! At this early stage, how could Dawn determine what kinds of groupings Cereans live in? Do they even have cities? For all we know, they may live only in rural communities, or perhaps they only have large states.
What we already know is that in more than 57 years of space exploration, Dawn is now the only spacecraft ever to orbit two extraterrestrial destinations. A true interplanetary spaceship, Dawn left Earth in Sep. 2007 and traveled on its own independent course through the solar system. It flew past Mars in Feb. 2009, robbing the red planet of some of its own orbital energy around the sun. In July 2011, the ship entered orbit around the giant protoplanet Vesta, the second most massive object in the main asteroid belt between Mars and Jupiter. (By the way, Dawn’s arrival at Vesta was exactly one Vestan year ago earlier this week.) It conducted a spectacular exploration of that fascinating world, showing it to be more closely related to the terrestrial planets (including Earth, home to many of our readers) than to the typical objects people think of as asteroids. After 14 months of intensive operations at Vesta, Dawn climbed out of orbit in Sep. 2012, resuming its interplanetary voyage. Today it arrived at its final destination, Ceres, the largest object between the sun and Pluto that had not previously been visited by a spacecraft. (Fortunately, New Horizons is soon to fly by Pluto. We are in for a great year!)
What was the scene like at JPL for Dawn’s historic achievement? It’s easy to imagine the typical setting in mission control. The tension is overwhelming. Will it succeed or will it fail? Anxious people watch their screens, monitoring telemetry carefully, frustrated that there is nothing more they can do now. Nervously biting their nails, they are thinking of each crucial step, any one of which might doom the mission to failure. At the same time, the spacecraft is executing a bone-rattling, whiplash-inducing burn of its main engine to drop into orbit. When the good news finally arrives that orbit is achieved, the room erupts! People jump up and down, punch the air, shout, tweet, cry, hug and feel the tremendous relief of overcoming a huge risk. You can imagine all that, but that’s not what happened.
If you had been in Dawn mission control, the scene would have been different. You would mostly be in the dark. (For your future reference, the light switches are to the left of the door.) The computer displays would be off, and most of the illumination would be from the digital clock and the string of decorative blue lights that indicate the ion engine is scheduled to be thrusting. You also would be alone (at least until JPL Security arrived to escort you away, because you were not cleared to enter the room, and, for that matter, how did you get past the electronic locks?). Meanwhile, most of the members of the flight team were at home and asleep! (Your correspondent was too, rare though that is. When Dawn entered orbit around Vesta, he was dancing. Ceres’ arrival happened to be at a time less conducive to consciousness.)
Why was such a significant event treated with somnolence? It is because Dawn has a unique way of entering orbit, which is connected with the nature of the journey itself. We have discussed some aspects of getting into orbit before (with this update to the nature of the approach trajectory). Let’s review some of it here.
It may be surprising that prior to Dawn, no spacecraft had even attempted to orbit two distant targets. Who wouldn’t want to study two alien worlds in detail, rather than, as previous missions, either fly by one or more for brief encounters or orbit only one? A mission like Dawn’s is an obvious kind to undertake. It happens in science fiction often: go somewhere, do whatever you need to do there (e.g., beat someone up or make out with someone) and then boldly go somewhere else. However, science fact is not always as easy as science fiction. Such missions are far, far beyond the capability of conventional propulsion.
Deep Space 1 (DS1) blazed a new trail with its successful testing of ion propulsion, which provides 10 times the efficiency of standard propulsion, showing on an operational interplanetary mission that the advanced technology really does work as expected. (This writer was fortunate enough to work on DS1, and he even documented the mission in a series of increasingly wordy blogs. But he first heard of ion propulsion from the succinct Mr. Spock and subsequently followed its use by the less logical Darth Vader.)
Dawn’s ambitious expedition would be truly impossible without ion propulsion. (For a comparison of chemical and ion propulsion for entering orbit around Mars, an easier destination to reach than either Vesta or Ceres, visit this earlier log.) So far, our advanced spacecraft has changed its own velocity by 23,800 mph (38,400 kilometers per hour) since separating from its rocket, far in excess of what any other mission has achieved propulsively. (The previous record was held by DS1.)
Dawn is exceptionally frugal in its use of xenon propellant. In this phase of the mission, the engine expends only a quarter of a pound (120 grams) per day, or the equivalent of about 2.5 fluid ounces (75 milliliters) per day. So although the thrust is very efficient, it is also very gentle. If you hold a single sheet of paper in your hand, it will push on your hand harder than the ion engine pushes on the spacecraft at maximum thrust. At today’s throttle level, it would take the distant explorer almost 11 days to accelerate from zero to 60 mph (97 kilometers per hour). That may not evoke the concept of a drag racer. But in the zero-gravity, frictionless conditions of spaceflight, the effect of this whisper-like thrust can build up. Instead of thrusting for 11 days, if we thrust for a month, or a year, or as Dawn already has, for more than five years, we can achieve fantastically high velocity. Ion propulsion delivers acceleration with patience.
Most spacecraft coast most of the time, following their repetitive orbits like planets do. They may use the main engine for a few minutes or perhaps an hour or two throughout the entire mission. With ion propulsion, in contrast, the spacecraft may spend most of its time in powered flight. Dawn has flown for 69% of its time in space emitting a cool blue-green glow from one of its ion engines. (With three ion engines, Dawn outdoes the Star Wars TIE (twin ion engine) fighters.)
The robotic probe uses its gentle thrust to gradually reshape its path through space rather than simply following the natural course that a planet would. After it escaped from Vesta’s gravitational clutches, it slowly spiraled outward from the sun, climbing the solar system hill, making its heliocentric orbit more and more and more like Ceres’. By the time it was in the vicinity of the dwarf planet today, both were traveling around the sun at more than 38,600 mph (62,100 kilometers per hour). Their trajectories were nearly identical, however, so the difference in their speeds was only 100 mph (160 kilometers per hour), or less than 0.3 percent of the total. Flying like a crackerjack spaceship pilot, Dawn elegantly used the light touch of its ion engine to be at a position and velocity that it could ease gracefully into orbit. At a distance of 37,700 miles (60,600 kilometers), Ceres reached out and tenderly took the newcomer from Earth into its permanent gravitational embrace.
If you had been in space watching the event, you would have been cold, hungry and hypoxic. But it would not have looked much different from the 1,885 days of ion thrust that had preceded it. The spacecraft was perched atop its blue-green pillar of xenon ions, patiently changing its course, as it does for so much of quiet cruise. But now, at one moment it was flying too fast for Ceres’ gravity to hang on to it, and the next moment it had slowed just enough that it was in orbit. Had it stopped thrusting at that point, it would have continued looping around the dwarf planet. But it did not stop. Instead, it is working now to reshape its orbit around Ceres. As we saw in November, its orbital acrobatics first will take it up to an altitude of 47,000 miles (75,000 kilometers) on March 19 before it swoops down to 8,400 miles (13,500 kilometers) on April 23 to begin its intensive observations in the orbit designated RC3.
In fact, Dawn’s arrival today really is simply a consequence of the route it is taking to reach that lower orbit next month. Navigators did not aim for arriving today. Rather, they plotted a course that began at Vesta and goes to RC3 (with a new design along the way), and it happens that the conditions for capture into orbit occurred this morning. As promised last month, we present here a different view of the skillful maneuvering by this veteran space traveler.
If Dawn had stopped thrusting before Ceres could exert its gravitational control, it wouldn’t have flown very far away. The spacecraft had already made their paths around the sun very similar, and the ion propulsion system provides such exceptional flexibility to the mission that controllers could have guided it into orbit some other time. This was not a one-time, all-or-nothing event.
So the flight team was not tense. They had no need to observe it or make a spectacle out of it. Mission control remained quiet. The drama is not in whether the mission will succeed or fail, in whether a single glitch could cause a catastrophic loss, in whether even a tiny mistake could spell doom. Rather, the drama is in the opportunity to unveil the wonderful secrets of a fascinating relict from the dawn of the solar system more than 4.5 billion years ago, a celestial orb that has beckoned for more than two centuries, the first dwarf planet discovered.
Dawn usually flies with its radio transmitter turned off (devoting its electricity instead to the power-hungry ion engine), and so it entered orbit silently. As it happened, a routine telecommunications session was scheduled about an hour after attaining orbit, at 5:36 a.m. PST. (It’s only coincidence it was that soon. At Vesta, it was more than 25 hours between arrival and the next radio contact.) For primary communications, Dawn pauses thrusting to point its main antenna to Earth, but other times, as in this case, it is programmed to use one of its auxiliary antennas to transmit a weaker signal without stopping its engine, whispering just enough for engineers to verify that it remains healthy.
The Deep Space Network’s exquisitely sensitive 230-foot (70-meter) diameter antenna in Goldstone, Calif., picked up the faint signal from across the solar system on schedule and relayed it to Dawn mission control. One person was in the room (and yes, he was cleared to enter). He works with the antenna operator to ensure the communications session goes smoothly, and he is always ready to contact others on the flight team if any anomalies arise. In this case, none did, and it was a quiet morning as usual. The mission director checked in with him shortly after the data started to trickle in, and they had a friendly, casual conversation that included discussing some of the telemetry that indicated the spacecraft was still performing its routine ion thrusting. The determination that Dawn was in orbit was that simple. Confirming that it was following its flight plan was all that was needed to know it had entered orbit. This beautifully choreographed celestial dance is now a pas de deux.
As casual and tranquil as all that sounds, and as logical and systematic as the whole process is, the reality is that the mission director was excited. There was no visible hoopla, no audible fanfare, but the experience was powerful fuel for the passionate fires that burn within.
As soundlessly as a spacecraft gliding through the void, the realization emerges …
Dawn made it!!
It is in orbit around a distant world!!
Yes, it’s clear from the technical details, but it is more intensely reflected in the silent pounding of a heart that has spent a lifetime yearning to know the cosmos. Years and years of hard work devoted to this grand undertaking, constant hopes and dreams and fears of all possible futures, uncounted challenges (some initially appearing insurmountable) and a seeming infinitude of decisions along the way from early concepts through a real interplanetary spacecraft flying on an ion beam beyond the sun.
And then, a short, relaxed chat over a few bits of routine data that report the same conditions as usual on the distant robot. But today they mean something different.
They mean we did it!!
Everyone on the team will experience the news that comes in a congratulatory email in their own way, in the silence and privacy of their own thoughts. But it means the same to everyone.
We did it!!
And it’s not only the flight team. Humankind!! With our relentless curiosity, our insatiable hunger for knowledge, our noble spirit of adventure, we all share in the experience of reaching out from our humble home to the stars.
Together, we did it!!!
It was a good way to begin the day. It was Dawn at Ceres.
Let’s bring into perspective the cosmic landscape on which this remarkable adventure is now taking place. Imagine Earth reduced to the size of a soccer ball. On this scale, the International Space Station would orbit at an altitude of a bit more than one-quarter of an inch (seven millimeters). The moon would be a billiard ball almost 21 feet (6.4 meters) away. The sun, the conductor of the solar system orchestra, would be 79 feet (24 meters) across at a distance of 1.6 miles (2.6 kilometers). But even more remote, Dawn would be 5.3 miles (8.6 kilometers) away. (Just a few months ago, when the spacecraft was on the opposite side of the sun from Earth, it would have been more than six miles, or almost 10 kilometers, from the soccer ball.) Tremendously far now from its erstwhile home, it would be only a little over a yard (a meter) from its new residence. (By the end of this year, Dawn will be slightly closer to it than the space station is to Earth, a quarter of an inch, or six millimeters.) That distant world, Ceres, the largest object between Mars and Jupiter, would be five-eighths of an inch (1.6 centimeters) across, about the size of a grape. Of course a grape has a higher water content than Ceres, but we can be sure that exploring this intriguing world of rock and ice will be much sweeter!
As part of getting to know its new neighborhood, Dawn has been hunting for moons of Ceres. Telescopic studies had not revealed any, but if there were a moon smaller than about half a mile (one kilometer), it probably would not have been discovered. The spacecraft’s unique vantage point provides an opportunity to look for any that might have escaped detection. Many pictures have been taken specifically for this purpose, and scientists scrutinize them and all of the other photographs for any indication of moons. While the search will continue, so far, no picture has shown evidence of companions orbiting Ceres.
And yet we know that as of today, Ceres most certainly does have one. Its name is Dawn!
Dawn is 37,800 miles (60,800 kilometers) from Ceres, or 16 percent of the average distance between Earth and the moon. It is also 3.33 AU (310 million miles, or 498 million kilometers) from Earth, or 1,230 times as far as the moon and 3.36 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 55 minutes to make the round trip.
Dr. Marc D. Rayman
6:00 a.m. PST March 6, 2015
Dear Fine and Dawndy Readers,
The Dawn spacecraft is performing flawlessly as it conducts the first exploration of the first dwarf planet. Each new picture of Ceres reveals exciting and surprising new details about a fascinating and enigmatic orb that has been glimpsed only as a smudge of light for more than two centuries. And yet as that fuzzy little blob comes into sharper focus, it seems to grow only more perplexing.
Dawn is showing us exotic scenery on a world that dates back to the dawn of the solar system, more than 4.5 billion years ago. Craters large and small remind us that Ceres lives in the rough and tumble environment of the main asteroid belt between Mars and Jupiter, and collectively they will help scientists develop a deeper understanding of the history and nature not only of Ceres itself but also of the solar system.
Even as we discover more about Ceres, some mysteries only deepen. It certainly does not require sophisticated scientific insight to be captivated by the bright spots. What are they? At this point, the clearest answer is that the answer is unknown. One of the great rewards of exploring the cosmos is uncovering new questions, and this one captures the imagination of everyone who gazes at the pictures sent back from deep space.
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Other intriguing features newly visible on the unfamiliar landscape further assure us that there will be much more to see and to learn -- and probably much more to puzzle over -- when Dawn flies in closer and acquires new photographs and myriad other measurements. Over the course of this year, as the spacecraft spirals to lower and lower orbits, the view will continue to improve. In the lowest orbit, the pictures will display detail well over one hundred times finer than the RC2 pictures returned a few days ago (and shown below). Right now, however, Dawn is not getting closer to Ceres. On course and on schedule for entering orbit on March 6, Earth's robotic ambassador is slowly separating from its destination.
"Slowly" is the key. Dawn is in the vicinity of Ceres and is not leaving. The adventurer has traveled more than 900 million miles (1.5 billion kilometers) since departing from Vesta in 2012, devoting most of the time to using its advanced ion propulsion system to reshape its orbit around the sun to match Ceres' orbit. Now that their paths are so similar, the spacecraft is receding from the massive behemoth at the leisurely pace of about 35 mph (55 kilometers per hour), even as they race around the sun together at 38,700 mph (62,300 kilometers per hour). The probe is expertly flying an intricate course that would be the envy of any hotshot spaceship pilot. To reach its first observational orbit -- a circular path from pole to pole and back at an altitude of 8,400 miles (13,500 kilometers) -- Dawn is now taking advantage not only of ion propulsion but also the gravity of Ceres.
On Feb. 23, the spacecraft was at its closest to Ceres yet, only 24,000 miles (less than 39,000 kilometers), or one-tenth of the separation between Earth and the moon. Momentum will carry it farther away for a while, so as it performs the complex cosmic choreography, Dawn will not come this close to its permanent partner again for six weeks. Well before then, it will be taken firmly and forever into Ceres' gentle gravitational hold.
The photographs Dawn takes during this approach phase serve several purposes. Besides fueling the fires of curiosity that burn within everyone who looks to the night sky in wonder or who longs to share in the discoveries of celestial secrets, the images are vital to engineers and scientists as they prepare for the next phase of exploration.
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The primary purpose of the pictures is for "optical navigation" (OpNav), to ensure the ship accurately sails to its planned orbital port. Dawn is the first spacecraft to fly into orbit around a massive solar system world that had not previously been visited by a spacecraft. Just as when it reached its first deep-space target, the fascinating protoplanet Vesta, mission controllers have to discover the nature of the destination as they proceed. They bootstrap their way in, measuring many characteristics with increasing accuracy as they go, including its location, its mass and the direction of its rotation axis.
Let's consider this last parameter. Think of a spinning ball. (If the ball is large enough, you could call it a planet.) It turns around an axis, and the two ends of the axis are the north and south poles. The precise direction of the axis is important for our mission because in each of the four observation orbits (previews of which were presented in February, May, June and August), the spacecraft needs to fly over the poles. Polar orbits ensure that as Dawn loops around, and Ceres rotates beneath it every nine hours, the explorer eventually will have the opportunity to see the entire surface. Therefore, the team needs to establish the location of the rotation axis to navigate to the desired orbit.
We can imagine extending the rotation axis far outside the ball, even all the way to the stars. Current residents of Earth, for example, know that their planet's north pole happens to point very close to a star appropriately named Polaris (or the North Star), part of an asterism known as the Little Dipper in the constellation Ursa Minor (the Little Bear). The south pole, of course, points in exactly the opposite direction, to the constellation Octans (the Octant), but is not aligned with any salient star.
With their measurements of how Ceres rotates, the team is zeroing in on the orientation of its poles. We now know that residents of (and, for that mater, visitors to) the northern hemisphere there would see the pole pointing toward an unremarkable region of the sky in Draco (the Dragon). Those in the southern hemisphere would note the pole pointing toward a similarly unimpressive part of Volans (the Flying Fish). (How appropriate it is that that pole is directed toward a constellation with that name will be known only after scientists advance their understanding of the possibility of a subsurface ocean at Ceres.)
The orientation of Ceres'; axis proves convenient for Dawn's exploration. Earthlings are familiar with the consequences of their planet's axis being tilted by about 23 degrees. Seasons are caused by the annual motion of the sun between 23 degrees north latitude and 23 degrees south. A large area around each pole remains in the dark during winter. Vesta's axis is tipped 27 degrees, and when Dawn arrived, the high northern latitudes were not illuminated by the sun. The probe took advantage of its extraordinary maneuverability to fly to a special mapping orbit late in its residence there, after the sun had shifted north. That will not be necessary at Ceres. That world's axis is tipped at a much smaller angle, so throughout a Cerean year (lasting 4.6 Earth years), the sun stays between 4 degrees north latitude and 4 degrees south. Seasons are much less dramatic. Among Dawn's many objectives is to photograph Ceres. Because the sun is always near the equator, the illumination near the poles will change little. It is near the beginning of southern hemisphere winter on Ceres now, but the region around the south pole hidden in hibernal darkness is tiny. Except for possible shadowing by local variations in topography (as in deep craters), well over 99 percent of the dwarf planet's terrain will be exposed to sunlight each day.
Guiding Dawn from afar, the operations team incorporates the new information about Ceres into occasional updates to the flight plan, providing the spacecraft with new instructions on the exact direction and throttle level to use for the ion engine. As they do so, subtle aspects of the trajectory change. Last month we described the details of the plan for observing Ceres throughout the four-month approach phase and predicted that some of the numbers could change slightly. So, careful readers, for your convenience, here is the table from January, now with minor updates.
|Beginning of activity in Pacific Time zone||Distance from Dawn to Ceres in miles (kilometers)||Ceres diameter in pixels||Resolution in miles (kilometers) per pixel||Resolution compared to Hubble||Illuminated portion of disk||Activity|
|Dec 1, 2014||740,000
|Jan 13, 2015||238,000
In addition to changes based on discoveries about the nature of Ceres, some changes are dictated by more mundane considerations (to the extent that there is anything mundane about flying a spacecraft in the vicinity of an alien world more than a thousand times farther from Earth than the moon). For example, to accommodate changes in the schedule for the use of the Deep Space Network, some of the imaging sessions shifted by a few hours, which can make small changes in the corresponding views of Ceres.
The only important difference between the table as presented in January and this month, however, is not to be found in the numbers. It is that OpNav 3, RC1 and RC2 are now in the past, each having been completed perfectly.
As always, if you prefer to save yourself the time and effort of the multi-billion-mile (multi-billion-kilometer) interplanetary journey to Ceres, you can simply go here to see the latest views from Dawn. (The Dawn project is eager to share pictures promptly with the public. The science team has the responsibility of analyzing and interpreting the images for scientific publication. The need for accuracy and scientific review of the data slows the interpretation and release of the pictures. But just as with all of the marvelous findings from Vesta, everything from Ceres will be available as soon as practicable.)
In November we delved into some of the details of Dawn's graceful approach to Ceres, and last month we considered how the trajectory affected the scene presented to Dawn's camera. Now that we have updated the table, we can enhance a figure from both months that showed the craft's path as it banks into orbit and maneuvers to its first observational orbit. (As a reminder, the diagram illustrates only two of the three dimensions of the ship's complicated route. Another diagram in November showed another perspective, and we will include a different view next month.)
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We can zoom out to see where the earlier OpNavs were.
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As the table and figures indicate, in OpNav 6, when Ceres and the sun are in the same general direction from Dawn's vantage point, only a small portion of the illuminated terrain will be visible. The left side of Ceres will be in daylight, and most of the hemisphere facing the spacecraft will be in the darkness of night. To get an idea of what the shape of the crescent will be, terrestrial readers can use the moon on March 16. It will be up much of the day, setting in the middle of the afternoon, and it will be comparable to the crescent Dawn will observe on April 10. (Of course, the exact shape will depend on your observing location and what time you look, but this serves as a rough preview.) Fortunately, our spacecraft does not have to contend with bad weather, but you might, so we have generously scheduled a backup opportunity for you. The moon will be new on March 20, and the crescent on March 23 will be similar to what it was on March 16. It will rise in the mid morning and be up until well after the sun sets.
Photographing Ceres as it arcs into orbit atop a blue-green beam of xenon ions, setting the stage for more than a year of detailed investigations with its suite of sophisticated sensors, Dawn is sailing into the history books. No spacecraft has reached a dwarf planet before. No spacecraft has orbited two extraterrestrial destinations before. This amazing mission is powered by the insatiable curiosity and extraordinary ingenuity of creatures on a planet far, far away. And it carries all of them along with it on an ambitious journey that grows only more exciting as it continues. Humankind is about to witness scenes never before seen and perhaps never even imagined. Dawn is taking all of us on a daring adventure to a remote and unknown part of the cosmos. Prepare to be awed.
Dawn is 24,600 miles (39,600 kilometers) from Ceres, or 10 percent of the average distance between Earth and the moon. It is also 3.42 AU (318 million miles, or 512 million kilometers) from Earth, or 1,330 times as far as the moon and 3.46 times as far as the sun today. Radio signals, traveling at the universal limit of the speed of light, take 57 minutes to make the round trip.
Dr. Marc D. Rayman
7:00 a.m. PST February 25, 2015
In 1964, at least two companies were working under contract to JPL on a Surveyor Lunar Roving Vehicle Study: Bendix Corporation Systems Division, and General Motors Corporation Defense Research Laboratories. This photo shows a prototype General Motors rover, one of several different approaches that were studied to determine their capabilities, limitations, and their impact on overall spacecraft design and performance. Twelve different spacecraft configurations were studied in detail, with variations in weight, power systems, communication method, and spaceframe size.
The final design of the Surveyor 1 through 7 lunar landers did not include a rover. NASA sponsored other lunar rover studies during the 1960s, with a variety of sizes and technical capabilities, and Apollo 15 astronauts became the first to drive a Lunar Roving Vehicle on the moon, during their 1971 mission. JPL continued to develop robotic spacecraft and rovers and, in 1997, landed Mars Pathfinder and its Sojourner rover on the red planet. | 0.847454 | 3.336517 |
Our modern laboratory of nuclear physics has expanded to encompass parts of the universe, or at least our Galaxy. Gamma rays emitted by the decays of radioactive nuclei testify to the production of isotopes through nuclear processes in astrophysical events. We collect measurements of the Galactic gamma-ray sky in spectral lines attributed to the decay of radioactive ^7Be, ^22Na, ^26Al, ^44Ti, ^56Ni, ^57Ni, and ^60Fe. We organize and collate these measurements with models for the production sites in novae, supernovae, stellar interiors, and interstellar cosmic-ray interactions. We discuss the physical processes and the spatial distribution of these production sites, along with models of the chemical evolution of the Galaxy. Highlights of measurements made in the last decade include detailed images of the Galaxy in ^26Al radioactivity and detection of ^56Co and ^57Co from SN 1987A, ^44Ti from Cas A, and possibly ^56Ni from SN 1991T. The ^26Al mapping of recent Galactic nucleosynthesis may be considered as a new view on the entire ensemble of massive stars in the Galaxy. The local Cygnus region shows prominent radioactive emission from well-known stellar clusters, but the absence of gamma-rays from the closest Wolf-Rayet star, WR 11, in the Vela region is puzzling. SN 1987A studies in gamma-rays measure the radioactive powering of the supernova light curve directly, which will be particularly important for the dim late phase powered by ^44Ti. The ^57Ni/^56Ni isotopic ratio determinations from gamma-rays provide additional guidance for understanding SN 1987A's complex light curve and now appear to be uniformly settling to about twice the solar ratio. Cas A ^44Ti production as measured through gamma-rays presents the interesting puzzle of hiding the expected, coproduced, and large ^56Ni radioactivity. Core-collapse supernova models need to parameterize the inner boundary conditions of the supernova in one way or another, and now enjoy another measurement of the ejecta that is definitely originating from very close to the difficult regime of the mass cut between ejecta and compact remnant. Other relevant measurements of cosmic element abundances, such as observations of atomic lines from the outer shells of the production sites or meteoritic analysis of interstellar grains, complement the rather direct measurements of penetrating gamma-rays, thus enhancing the observational constraints of nuclear astrophysics models. | 0.896251 | 4.143969 |
Viewed from outer space our home on this planet appears considerably different than it would have appeared at the glacial maximum of the Wisconsin Ice Age 22,000 years ago. Imagine we are traveling toward Earth on a spacecraft 22 millennia ago. Ice caps covered Canada entirely, a large part of northern United States, and substantial portions of Northern Europe and Asia as well as high elevation locations at lower latitudes.
A famous photograph dubbed The Blue Marble was taken by astronauts in December 1972 from 18,000 miles as they traveled toward the Moon. Earth appeared as a blue marble—a mostly water-covered, blue planet. The Apollo 17 journey was the last scientific human effort to reach and walk on the Moon. It was also a unique photographic opportunity to see Planet Earth without ice caps which recently covered large portions of the planet. Ice caps two miles thick shrouded land areas of Earth a mere geological instant ago when we were in the grip of the last deep ice age, called the Wisconsin glaciation. We say a geological instant because the last glacial maximum, the Wisconsin, persisted for a brief moment compared with the total geological time frame since the Cambrian Explosion, a burst of creation marked by the sudden appearance of nearly 100 novel phyla and thousands of individual species. The CE suddenly commenced 541 million years ago.
The Wisconsin glaciation is only one of eight distinct worldwide glacial episodes to occur in the past 800,000 years. Each glacial advance occurred on a cycle of 100,000 years. These beneficial cycles have appeared only during the last 0.017 percent of Earth’s history. The Wisconsin glaciation was one of many glacial periods beginning in the so-called Quaternary Period which began 2.59 million years ago, but its effects are significant in terms of successful Earth life in our time. Going back farther in time to the beginning of the Quaternary, many shorter ice ages occurred on a cycle of 41,000 years. There have been hundreds of ups and downs in Earth’s average temperature generally superimposed on Earth’s climate. Climate proxies such as ancient ice core data or tree ring records leave their telltale record. The Quaternary period of the last 2.59 million years is a period when glaciation of the planet occurred repeatedly.
The geological history of Earth tells the story of many unique preparations for the eventual arrival of modern humanity. We might call these preparations divine transformational miracles. Much of that history is related to changes taking place in the Quaternary Ice Age. In particular, the most recent manifestation of a well-known geological event, the Wisconsin event, evokes the thought that our Creator initiated abundant transformational miracles to prepare Earth for humans created in the Image of God.
If we consider only the recent Wisconsin glaciation we determine that its conclusion heralded the warm interglacial we enjoy today. In future posts we will discuss other transformational miracles. For example, about 12,000 years ago, the rapid change in climate from the hostile cold ice age to advancing global warmth enabled the birth of civilization with its eventual agricultural revolution. While fully modern humans existed in warmer areas of the planet for many thousands of years they were basically hunter-gatherers living a harsh life. They left artifacts of their primitive culture. Their agriculture was virtually non-existent. No writing system existed. The wheel had not yet been invented. Life in Paleolithic times, in contrast with the civilizations which arose after 12,000 years ago in the so-called Fertile Crescent, was difficult. Population density was very low, but even secular paleontologists pronounced the population “fully behaviorally and anatomically human.” Humanity had not yet begun to “subdue the earth.”
The current interglacial warm period was fully underway 12,000 years ago and sparked a population explosion as agriculture replaced hunter-gathering. The explosion paralleled new central political structures. The end of Wisconsin glaciation ushered in a period of climate stability. We are still technically in an ice age and benefit from an unusual period of climate stability—neither too hot nor too cold. Temperature graphs demonstrate this leveling off of world temperature in the most recent 10,000 or 12,000 years in contrast with earlier spikes and sudden temperature drops in the previous million years.
Our recent posts have only begun to suggest that God performed many environmental transformational miracles for specific purposes. These miracles are included in God’s ultimate plan. They do not occur instantaneously as do many less frequent transcendent miracles such as the original creation of the universe or the resurrection of Jesus Christ. A biblical expression “for such a time as this” from the Book of Esther could apply to the many transformational miracles which shaped and prepared our planetary home for today’s teeming billions of residents. This type of miracle is initiated by the timeless God of Creation, who creates all things according to His timeless schedule. | 0.881092 | 3.601206 |
For some, it will be a first. For others, a return. Either way, the moon is the most popular destination for robotic explorers in 2007 and 2008, as four countries — the United States, China, India, and Japan — prepare to launch spacecraft into lunar orbit.
From This Story
Why the moon? For one thing it’s close, which makes it an ideal technological proving ground for nations taking their initial steps beyond Earth orbit, like China and India. Another reason is that planetary scientists know surprisingly little about lunar geography, gravity, and geology. Though more than 60 spacecraft have been sent there since the Soviet Luna 1 in 1959, the moon is less well mapped than you might think. The state-of-the-art cameras, spectrometers, and other instruments on the new orbiters should quickly bring lunar scholars up to speed. “When data from the four new lunar missions are returned, we will be approaching the capabilities that we currently have for Mars,” says Brown University planetary scientist Carle Pieters, whose Moon Mineralogy Mapper will fly on India’s Chandrayaan-1.
Herewith our quick guide to the upcoming lunar derby.
Launch: Summer 2007
In a Nutshell: With 14 instruments, this may be the most scientifically comprehensive of the new moon missions.
Japan has been to the moon before, with a small satellite called Hiten in the early 1990s. But not like this. SELENE (SELenological and ENgineering Explorer) is another leap forward for a country that has been rapidly expanding its capabilities in solar system exploration with projects like the 2005 Hayabusa asteroid rendezvous. Bernard Foing, a lunar scientist with the European Space Agency, calls SELENE, with its impressive 660 pounds of instruments, “the Lexus of lunar exploration.” Scientifically, it does a bit of everything, and some things none of the rest will do, including deploying two small subsatellites to measure the gravity field on the far side of the moon—important data for fine-tuning spacecraft orbits. A radar sounder will probe deep below the surface, and a high-definition camera will return photos of Earthrise and lunar craters for the public to enjoy.
Launch: Fall 2007
In a Nutshell: This modest orbiter is the first of several lunar missions China has planned, and may be the precursor to human landings.
Chinese scientists have outlined three phases for their lunar exploration program, starting with an orbiter this year and progressing to a lander in 2012 and sample return mission in 2017. Chang’E-1 (named for a Chinese legend about a young fairy who flies to the moon) will take stereo pictures of the surface and investigate solar radiation and charged particles around the moon. Lunar resources are a special focus: Onboard spectrometers will map the abundance of metals and helium-3, a potential fuel source for future fusion reactors. A microwave radiometer—the only one on any of these four missions—will measure the thickness of the lunar soil. That’s the kind of information you’d need if you were planning a lunar base, which, according to some Chinese scientists, is the long-term plan for that country.
Country: India, with European and U.S. participation
Launch: Spring 2008
In a Nutshell: India’s first venture beyond Earth
orbit gets this technology-savvy nation into the game of deep-space exploration.
India is building the spacecraft and furnishing the launcher, although it invited international scientists to join in proposing instruments. Among the foreign contributions are a German-built infrared spectrometer modeled after one that flew on Europe’s recently ended SMART-1 lunar mission, and the NASA-supplied Moon Mineralogy Mapper, which has an even higher resolution. Between them, they will do a thorough job of mapping rock types on the lunar surface. India excels at Earth observation from space, and its homegrown Terrain Mapping Camera will return high-resolution stereo pictures that can be converted into digital terrain maps. Another U.S. instrument, called Mini-SAR, similar to the synthetic aperture radars used to explore Earth and Venus, will search for signs of water ice at the poles.
LUNAR RECONNAISSANCE ORBITER
Country: United States
Launch: Fall 2008
In a Nutshell: NASA wants better maps of the lunar surface before astronauts arrive in 2020, and LRO will discern details only a foot or two across. | 0.801126 | 3.710147 |
What’s the chance of that thump you just heard in your house was a meteorite hitting your roof? That was the case for one family in Novato, California during a fireball event that took place in the north bay area near San Francisco on October 17, 2012.
Researchers have now released new results from analysis of the meteor that fell to Earth, revealing that the “Novato meteorite” was part of numerous collisions over a span of 4 billion years.
There is nothing ordinary about a meteorite whether it just spent 4.4 billion years all alone or spent such time in a game of cosmic pinball, interacting with other small or large bodies of our Solar System. On any given night one can watch at least a couple of meteors overhead burning up, lighting up the sky but never reaching the Earth below. However, in less than two years, Dr. Peter Jenniskens, SETI Institute’s renowned meteor expert was effectively host to two meteorites within a couple hours drive from his office in Mountain View, California.
The first was the Sutter Mill meteorite, a fantastic carbonaceous chondrite full of organic compounds. The second was the Novato meteorite, identified as a L6 chondrite fragmental breccia. which is the focus of new analysis, to be released in a paper in the August issue of Meteoritics and Planetary Science. Early on, it was clear that this meteorite had been a part of a larger asteroidal parent body that had undergone impact shocks.
Analysis of the meteorite was spearheaded by Jenniskens who initially determined the trajectory and orbit of the meteoroid from the Cameras for Allsky Meteor Surveillance (CAMS) which he helped establish in the greater San Francisco bay area. Jenniskens immediately released information about the fireball to local news agencies to ask for the public’s help with the hopes of finding pieces of the meteorite. One resident recalled hearing something hit her roof, and with the help of neighbors, they investigated and soon found the first fragment in their backyard.
Finding fragments was the first step, and over a two year period, the analysis of the Novato meteorite was spread across several laboratories around the world with specific specialties.
Dr. Jenniskens, along with 50 co-authors, have concluded that the Novato meteorite had been involved in more impacts than previously thought. Dr. Qingzhu Yin, professor in the Department of Earth and Planetary Sciences at the University of California, Davis stated, “We determined that the meteorite likely got its black appearance from massive impact shocks causing a collisional resetting event 4.472 billion years ago, roughly 64-126 million years after the formation of the solar system.”
The predominant theory of the Moon’s formation involves an impact of the Earth by a Mars-sized body. The event resulted in the formation of the Moon but also the dispersal of many fragments throughout the inner Solar System. Dr. Qingzhu Yin continued, “We now suspect that the moon-forming impact may have scattered debris all over the inner solar system and hit the parent body of the Novato meteorite.”
Additionally, the researcher discovered that the parent body of the Novato meteorite experienced a massive impact event approximately 470 million years ago. This event dispersed many asteroidal fragments throughout the Asteroid Belt including a fragment from which resulted the Novato meteorite.
The trajectory analysis completed earlier by Dr. Jenniskens pointed the Novato meteorite back to the Gefion asteroid family. Dr. Kees Welten, cosmochemist at UC Berkeley, was able to further pinpoint the time, drawing the conclusion, “Novato broke from one of the Gefion family asteroids nine million years ago.” His colleague at Berkeley, cosmochemist Dr. Kunihiko Nishiizumialso added, “but may have been buried in a larger object until about one million years ago.”
There was more that could be revealed about history of the Novato meteorite. Dr. Derek Sears a meteoriticist working for the Bay Area Environmental Research Institute in Sonoma, California and stationed at NASA Ames Reserach Center applied his expertise in thermoluminescence. Dr. Sears was involved in the analysis of Lunar regolith returned by the Apollo astronauts using this analysis method.
“We can tell the rock was heated, but the cause of the heating is unclear,” said Dr. Sears, “It seems that Novato was hit again.” As stated in the NASA press release, “Scientists at Ames measured the meteorites’ thermoluminescence – the light re-emitted when heating of the material and releasing the stored energy of past electromagnetic and ionizing radiation exposure – to determine that Novato may have had another collision less than 100,000 years ago.”
From this apparent final collision one hundred thousand years ago, the Novato meteoroid completed over 10,000 orbits of the Sun and with its final Solar orbit, intercepted the Earth, entering our atmosphere and mostly burning up over California. The meteoroid is estimated to have measured 14 inches across (35 cm) and have weighed 176 pounds (80 kg). What reached the ground likely amounted to less than 5 lbs. (~ 2 kg). Only six fragments were recovered and many more remain buried or hidden in Sonoma and Napa counties.
Besides the analysis that revealed the series of likely impact events in the meteoroids history, a team led by Dr. Dan Glavin from NASA Goddard Space Flight Center undertook analysis in search of amino acids, the building blocks of life. They detected non-protein amino acids in the meteorite that are very rare on Earth. Dr. Jenniskens emphasized that the quick recovery of the fragments by scores of individuals that searched provided pristine samples for analysis.
Robert P. Moreno, Jr. in Santa Rosa, CA photographed the fireball in greatest detail with a high resolution camera. Several other photos were brought forward from other vantage points. Dr. Jenniskens stated, “These photographs show that this meteorite – now one of the best studied meteorites of its kind – broke in spurts, each time creating a flash of light as it entered Earth’s atmosphere.”
Numerous individuals and groups undertook the search for the Novato meteorite. Dr. Jenniskens trajectory analysis included a likely impact zone or strewn field. People from all walks of life roamed the streets, open fields and hillsides of the north bay in search of fragments. Despite organized searches by Dr. Jenniskens, it was the footwork from other individuals that led to finding six fragments and was the first step which led to these studies that add to the understanding of the early Solar System’s development.
For Dr. Jenniskens, Novato was part of a trifecta – the April 22, 2012, Sutter Mill meteorite in the nearby foothills of the Sierras, the Novato meteorite and the massive Chelyabinsk airburst event in Russia on February 15, 2013. Throughout this period, Dr. Jenniskens all-sky camera network continued to expand and record “falling stars” – meteors. The number of meteors recorded with calculated trajectories is now over 175,000. The SETI Institute researcher has been supported by NASA and personnel at the institute and ordinary citizens including amateur astronomers that have refined the methods for meteor orbital determination and estimating their size and mass. Several websites have compiled images and results for the Novato meteorite with Dr. Jenniskens’ – CAMS.SETI.ORG being most prominent. | 0.90295 | 3.239435 |
Because of the Kepler mission and different efforts to seek out exoplanets, we discovered lots in regards to the exoplanet inhabitants. We all know that we’re more likely to discover Neptune super-Earths and exoplanets in orbit round low-mass stars, whereas the bigger planets are round extra huge stars. This suits properly with the basic principle of the accretion of planetary formation.
However all our observations don’t conform to this principle. The invention of a Jupiter-like planet revolving round a small pink dwarf signifies that our understanding of planetary formation might not be as clear as we thought. A second principle of planetary formation, referred to as disc instability principle, may clarify this shocking discovery.
The pink dwarf star is named GJ 3512 and is about 31 light-years away from us within the Huge Dipper. GJ 3512 is zero.12 occasions the mass of our Solar and the planet, GJ 3512b, is zero.46 occasions the mass of Jupiter, at a minimal. Which means the star is barely 250 occasions extra huge than the planet. And that's not all that, but it surely's solely about zero.three AU from the star.
Evaluate that to our photo voltaic system, the place the Solar is over 1000 occasions bigger than the most important planet, Jupiter. These figures don’t add as much as the core-accretion principle.
The elemental principle of accretion is probably the most broadly accepted principle for planetary formation. Core accumulation happens when small, stable particles meet and coagulate to kind bigger our bodies. Over lengthy intervals, this builds planets. Nevertheless, there’s a restrict to the way it works.
Extra research, with extra highly effective devices, are wanted to higher perceive this method. Based on the authors, this is a wonderful alternative to refine our theories of planetary formation. As they are saying within the conclusion of the paper, "the GJ 3512 is a really promising system, as it may be absolutely characterised and thus proceed to impose strict constraints on the processes of accretion and migration, in addition to". to the effectiveness of planet formation in protoplanetary disks. mass relations between stars.
A world staff of researchers from the CARMENES consortium (Calar Alto high-resolution analysis of M nains with Exoearths with close to infrared spectroscopes and Scale optics) did this work. This consortium is in search of pink dwarfs, probably the most widespread star within the galaxy, hoping to seek out low-mass planets of their liveable areas. CARMENES not solely generates a knowledge set to know pink dwarf stars, however, by trying to find planets the dimensions of the Earth, it can present a wealthy set of monitoring objectives for future research. | 0.907879 | 3.805077 |
Space telescope offers rare glimpse of Earth-sized rocky exoplanet
By Steve Gorman
(Reuters) - Direct observations from a NASA space telescope have for the first time revealed the atmospheric void of a rocky, Earth-sized world beyond our own solar system orbiting the most common type of star in the galaxy, according to a study released on Monday.
The research, published in the scientific journal Nature, also shows the distant planet's surface is likely to resemble the barren exterior of the Earth's moon or Mercury, possibly covered in dark volcanic rock.
The planet lies about 48.6 light years from Earth and is one of more than 4,000 so-called exoplanets identified over the past two decades circling distant stars in our home galaxy, the Milky Way.
Known to astronomers as LHS 3844b, this exoplanet about 1.3 times the size of Earth is locked in a tight orbit - one revolution every 11 hours - around a small, relatively cool star called a red dwarf, the most prevalent and long-lived type of star in the galaxy.
The planet's lack of atmosphere is probably due to intense radiation from its parent red dwarf, which, though dim by stellar standards, also emits high levels of ultraviolet light, the study says.
The study will likely add to a debate among astronomers about whether the search for life-sustaining conditions beyond our solar system should focus on exoplanets around red dwarfs - accounting for 75% of all stars in the Milky Way - or less common, larger, hotter stars more like our own sun.
The principal finding is that it probably possesses little if any atmosphere - a conclusion reached by measuring the temperature difference between the side of the planet perpetually facing its star, and the cooler, dark side facing away from it.
A negligible amount of heat carried between the two sides indicates a lack of winds that would otherwise be present to transfer warmth around the planet.
"The temperature contrast on this planet is about as big as it can possibly be," said researcher Laura Kreidberg of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts. She is lead author of the study.
Similar analysis previously was used to determine that another exoplanet, 55 Cancri e, about twice as big as Earth and believed to be half-covered in molten lava, likely possesses an atmosphere thicker than Earth's. This exoplanet, unlike LHS 3844b, orbits a sun-like star.
The planet in the latest study was detected last year by NASA's newly launched Transiting Exoplanet Survey Satellite, an orbiting telescope that pinpoints distant worlds by spotting periodic, dips in the light observed from their parent stars when an object passes in front of them.
But it was follow-up observations from another orbiting instrument, the Spitzer Space Telescope, which can detect infrared light directly from an exoplanet, that provided new insights about its features.
(Reporting by Steve Gorman in Los Angeles; Editing by Bill Tarrant and Lisa Shumaker) | 0.891274 | 3.65325 |
On 28 August 1789, German-born British astronomer Frederick William Herschel decided to test drive his brand new 12m telescope and wound up discovering Saturn’s sixth-largest moon, Enceladus. So, I guess we can say that first outing was a success, no?
Herschel, to be honest, was kind of an intellectual freak. He started his adult life as an oboist in the Hannoverian Guards regiment band (an instrument both his father and his brother Jakob played). He eventually found himself in England, whose king, George II, was also elector of Hanover. In addition to the oboe, he played cello, harpsichord, and eventually the organ and violin. Not easy instruments to master. He also composed and left behind a collection of 24 symphonies, some church music, and several concertos. To give you an idea of what an impressive body of work that is, Beethoven only wrote nine symphonies; Mahler 12. And these were men who made their livings through music pretty much throughout their entire adult lives.
After settling down in Bath, where he was director of the Bath orchestra, Herschel decided to dabble in mathematics and astronomy, which isn’t a huge leap in interests, considering his love and obvious talent for music. He became acquainted with the Astronomer Royal, Nevil Maskelyne, and soon set about building his own reflecting telescopes, spending up to 16 hours a day grinding and polishing the mirrors. Because I guess he wasn’t quite busy enough already. He started seriously looking skyward in 1773 and began keeping an astronomical journal the following year.
He started off examining binary star systems, cataloguing them carefully. In all, he discovered more than 800 confirmed double or multiple star systems, and his work provided the foundation for modern binary star astronomy.
In March 1781, while searching for yet another double star to add to his collection, Herschel instead noticed something different: a nonstellar disk, which he originally thought was a comet. After observing it for some time, his findings made their way to a Russian academician, who computed the orbit and concluded it was probably a planet. Herschel agreed and called it the Georgian star, after King George III. The name was eventually changed to Uranus. Herschel was awarded the Copley Medal and elected a Fellow of the Royal Society for his discovery; in 1782 he was appointed the King’s Astronomer. Accompanied by his sister, Caroline, he moved to Buckinghamshire and cultivated an international reputation as a telescope maker.
Bored now with binary stars, Herschel looked for bigger things, eventually recording more than 2400 objects loosely defined as nebulae. He published his findings in three catalogues that were released in the late 18th and early 19th centuries. His sister also got in on the game, as did his son, though the two of them didn’t come near the number of discoveries Herschel made. Caroline, however, was honoured by the Royal Astronomical Society for her work updating and correcting an earlier work about the position of stars.
The Herschels eventually moved near London, where Herschel constructed his massive 12m telescope, at the time the largest one in the world. And the first time he used it, he found a new moon for Saturn. Not bad. He went on to discover another moon, as well as two moons of Uranus, which were named Titania and Oberon by his son, John, long after Herschel’s death. Herschel also noted that Mars’s ice caps changed size with the planet’s seasons and was the first person to realise that the solar system is moving through space. After studying the structure of the Milky Way, he concluded it was in the shape of a disk. Oh, and he also coined the word “asteroid” and discovered infrared radiation in sunlight. And he used a microscope to observe coral and bust the myth that it was a plant. Clearly, he was a man who did not like to be idle.
Herschel lived long enough to see his son found the Astronomical Society of London in 1820 (later to become the Royal Astronomical Society). On 25 August 1822, Herschel died, leaving behind an incredible legacy (even if Uranus was later downgraded from planet status). His former home in Bath, where he first observed the now dwarf planet, is home to the Herschel Museum of Astronomy. | 0.898762 | 3.306656 |
2. Wavelength/frequency/energy spectrum. Galactic and celestial coordinates. Vega and AB magnitude systems, flux and luminosity definition. Luminosity distance vs. redshift. The Sloan Sky Digital Survey. Different sets of filters and atmospheric absorption. Best sites for modern telescopes and sky observations.
3. Radio observatories, interferometry, high-energy telescopes, Cherenkov telescope. Galaxy morphology and galaxy populations. Angular size vs. redshift. Spectral Energy Distribution (SED). Dust: reddening and extinction, grain size distribution, dust extinction law and attenuation law, Galactic extinction correction.
4. Star-forming regions in galaxies, galaxy spectra, measuring redshift with spectra, interference of atmospheric absorption, sky emission and cosmic rays on galaxy spectra, dust extinction correction in galaxies, estimating the star formation rate in galaxies, photometric redshift, estimating the stellar mass of galaxies. The intergalactic medium, the Lyman-alpha forest and observations of high redshift galaxies.
8. Cosmic chemical evolution, primordial nucleosynthesis, solar chemical abundances, nucleosynthesis in massive stars, cosmic cycling of matter, measuring chemical enrichment in galaxies with emission lines, mass-metallicity relation
Python programming language
- Script I: fitting an emission line with a gaussian profile, showing the line and calculating the flux
- Script II: chi^2 minimisation with 2nd degree polynomium
- Script III: calculating dust extinction for emission lines in galaxies at redshift z > 0
- Script IV: luminosity distance calculated for a sample with redshift z
- Script V: correction of emission lines of galaxy sample for MW dust extinction and intrinsic dust extinction. Then, best-fit linear relation between log ([OII]) vs log (H-alpha). Finally, star-formation rate estimate from [OII], H-beta and H-alpha
- Script VI: SFR vs. stellar mass in a sample of galaxies
- Script VII: calculating the chemical enrichment (metallicity) of a sample of galaxies and finding the linear correlation between the metallicity and the stellar mass
- Script VIII: it shows two plots in two different windows or in the same window
1. The course-notes (in Italian) taken by Antonello Venturino, who was among my students for the year 2018
2. List of on-line tools | 0.877617 | 3.826404 |
A planet with clouds and surface water orbits a red dwarf star in this artist’s conception of the Gliese 581 star system. New findings from the University of Chicago and Northwestern University show that planets orbiting red dwarf stars are more likely to be habitable than previously believed. (Credit: Lynette Cook)
A new study that calculates the influence of cloud behavior on climate doubles the number of potentially habitable planets orbiting red dwarfs, the most common type of stars in the universe. This finding means that in the Milky Way galaxy alone, 60 billion planets may be orbiting red dwarf stars in the habitable zone.
Researchers at the University of Chicago and Northwestern University based their study, which appears in Astrophysical Journal Letters, on rigorous computer simulations of cloud behavior on alien planets. This cloud behavior dramatically expanded the habitable zone of red dwarfs, which are much smaller and fainter than stars like the sun.
Current data from NASA’s Kepler Mission, a space observatory searching for Earth-like planets orbiting other stars, suggest there is approximately one Earth-size planet in the habitable zone of each red dwarf. The UChicago-Northwestern study now doubles that number.
“Most of the planets within the Milky Way Galaxy orbit red dwarfs,” aforesaid Nicolas Cowan, a postdoctoral fellow at Northwestern’s Center for knowledge domain Exploration and analysis in uranology. “A thermostat that produces such planets a lot of clement means that we do not have to be compelled to look as way to seek out a livable planet.”
Cowan is one in every of 3 co-authors of the study, as square measure UChicago’s Greek archimandrite and Jun principle. The trio conjointly offer astronomers with a method of supportive their conclusions with the James Webb area Telescope, scheduled for launch in 2018.
The formula for conniving the livable zone of alien planets — wherever they’ll orbit their star whereas still maintaining liquid water at their surface — has remained abundant identical for many years. however the formula mostly neglects clouds, that exert a significant environmental condition influence.
“Clouds cause warming, and that they cause cooling on Earth,” aforesaid archimandrite, associate professor in geology sciences at UChicago. “They replicate daylight to chill things off, and that they absorb actinic radiation from the surface to create a atmospheric phenomenon. that is a part of what keeps the world heat enough to sustain life.”
A planet orbiting a star just like the sun would have to be compelled to complete associate orbit close to once a year to be way enough away to keep up water on its surface. “If you are orbiting around a coffee mass or dwarf star, you’ve got to orbit regarding once a month, once each 2 months to receive identical quantity of daylight that we tend to receive from the sun,” Cowan aforesaid.
Astronomers observing with the James Webb Telescope will be able to test the validity of these findings by measuring the temperature of the planet at different points in its orbit. If a tidally locked exoplanet lacks significant cloud cover, astronomers will measure the highest temperatures when the dayside of the exoplanet is facing the telescope, which occurs when the planet is on the far side of its star. Once the planet comes back around to show its dark side to the telescope, temperatures would reach their lowest point.
But if highly reflective clouds dominate the dayside of the exoplanet, they will block a lot of infrared radiation from the surface, said Yang, a postdoctoral scientist in geophysical sciences at UChicago. In that situation “you would measure the coldest temperatures when the planet is on the opposite side, and you would measure the warmest temperatures when you are looking at the night side, because there you are actually looking at the surface rather than these high clouds,” Yang said.
source : sciencedaily.com | 0.90755 | 3.923283 |
Van Allen probes begin final phase of exploration in Earth's radiation belts
Two tough, resilient, NASA spacecraft have been orbiting Earth for the past six and a half years, flying repeatedly through a hazardous zone of charged particles around our planet called the Van Allen radiation belts. The twin Van Allen Probes, launched in August 2012, have confirmed scientific theories and revealed new structures and processes at work in these dynamic regions. Now, they're starting a new and final phase in their exploration.
On Feb. 12, 2019, one of the twin Van Allen Probes begins a series of orbit descent maneuvers to bring its lowest point of orbit, called perigee, just under 190 miles closer to Earth. This will bring the perigee from about 375 miles to about 190 miles—a change that will position the spacecraft for an eventual re-entry into Earth's atmosphere about 15 years down the line.
"In order for the Van Allen Probes to have a controlled re-entry within a reasonable amount of time, we need to lower the perigee," said Nelli Mosavi, project manager for the Van Allen Probes at the Johns Hopkins Applied Physics Laboratory, or APL, in Laurel, Maryland. "At the new altitude, aerodynamic drag will bring down the satellites and eventually burn them up in the upper atmosphere. Our mission is to obtain great science data, and also to ensure that we prevent more space debris so the next generations have the opportunity to explore the space as well."
The other of the two Van Allen Probes will follow suit in March, also commanded by the mission operations team at APL, which designed and built the satellites.
The Van Allen Probes spend most of their orbit within Earth's radiation belts: doughnut-shaped bands of energized particles—protons and electrons—trapped in Earth's magnetic field. These fast-moving particles create radiation that can interfere with satellite electronics and could even pose a threat to astronauts who pass through them on interplanetary journeys. The shape, size and intensity of the radiation belts changes in response to solar activity, which makes predicting their state difficult.
Originally designated as a two-year mission—based on predictions that no spacecraft could operate much longer than that in the harsh radiation belts—these rugged spacecraft have operated without incident since 2012, and continue to enable groundbreaking discoveries about the Van Allen Belts.
"The Van Allen Probes mission has done a tremendous job in characterizing the radiation belts and providing us with the comprehensive information needed to deduce what is going on in them," said David Sibeck, mission scientist for the Van Allen Probes at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "The very survival of these spacecraft and all their instruments, virtually unscathed, after all these years is an accomplishment and a lesson learned on how to design spacecraft."
Each spacecraft will be moved to a new, lower perigee of about 190 miles above Earth through a series of five two-hour engine burns. Because the Van Allen Probes spin while in orbit, the dates of these burns had to be chosen carefully. The needed geometry happens just once or twice per year: for spacecraft B, that period falls Feb. 12-22 of this year, and for spacecraft A, it's March 11-22.
The engine burns will each use about 4.4 pounds of propellant, leaving the spacecraft with enough fuel to keep their solar panels pointed at the Sun for about one more year.
"We'll continue to operate and obtain new science in our new orbit until we are out of fuel, at which point we won't be able to point our solar panels at the Sun to power the spacecraft systems," said Mosavi.
During their last year or so of life, the Van Allen Probes will continue to gather data on Earth's dynamic radiation belts. And their new, lower passes through Earth's atmosphere will also provide new insight into how oxygen in Earth's upper atmosphere can degrade satellite instruments—information that could help engineers design more resilient satellite instruments in the future.
"The spacecraft and instruments have given us incredible insight into spacecraft operations in a high-radiation environment," said Mosavi. "Everyone on the mission feels a real sense of pride and accomplishment in the work we've done and the science we've provided to the world—even as we begin the de-orbiting maneuvers." | 0.826074 | 3.773909 |
- NASA's Transiting Exoplanet Survey Satellite telescope discovered a new planet orbiting a star in the Hydra constellation. When scientists examined the data, they noticed two other planets circling the star.
- One of these new worlds could support liquid water if its atmosphere is thick enough. Scientists need to study it further to find out whether that's the case.
- At only 31 light-years away, the newly discovered planet is among the closest exoplanets ever detected.
- Visit Business Insider's homepage for more stories.
Just 31 light-years away, one of the closest worlds ever detected could harbor liquid water on its surface.
NASA's Transiting Exoplanet Survey Satellite, or TESS — a super-powerful orbiting telescope that scouts the sky for alien worlds — spotted a new planet circling a nearby star in the Hydra constellation. When astronomers checked the star for confirmation, they discovered two more worlds orbiting it.
One of those planets, called GJ 357 d, could support liquid water if it turns out to have a thick atmosphere and be made of rock.
It's among the 45 closest exoplanets confirmed to date, out of a total 4,025 planets tallied so far outside our solar system.
A potentially watery world
This planet system is the third-closest identified using the "transit" method, in which telescopes watch for tiny dips in a star's brightness that could be caused by a planet passing in front of it. The Kepler telescope pioneered the technique, though it's been refined by TESS.
The promising planet is in its star's "habitable zone," the range of distances in which a rocky world could have the right surface temperature for liquid water to exist.
"GJ 357 d is located within the outer edge of its star's habitable zone, where it receives about the same amount of stellar energy from its star as Mars does from the Sun," Diana Kossakowski, a member of the team that discovered the planet, said in a press release.
"If the planet has a dense atmosphere, which will take future studies to determine, it could trap enough heat to warm the planet and allow liquid water on its surface," Kossakowski said.
If the planet turns out to have no atmosphere, however, its surface would be about -64 degrees Fahrenheit, well below water's freezing point.
GJ 357 d's mass is at least 6.1 times Earth's, and the planet orbits its tiny star every 55.7 days. Scientists can't say much about else about it without further study though.
TESS is only halfway done
TESS, NASA's most powerful planet-hunting telescope ever, watches thousands of stars for transits.
The telescope observes one section of the sky for 27 days at a time, before moving on to a new patch. It divides each half of the sky (the northern half and the southern half) into 13 patches, as shown in the NASA graphic below. The spacecraft completed the southern half of its journey this month and turned to the northern sky.
When the mission ends around this time next year, TESS will have observed over 85% of the sky.
So far, the telescope has found over 850 potential new planets. The next step is for ground-based telescopes to examine the stars that these planets might be orbiting and detect whether the planets indeed exert a gravitational pull.
That process is what enabled researchers to find GJ 357 d. As they were working to confirm the planet that TESS spotted, they noticed gravitational pulls from two others. (TESS didn't spot those two worlds because their orbits don't pass between their star and the telescope.)
So far, only 24 of the exoplanets that TESS has spotted have been confirmed. Earlier this week, astronomers confirmed three nearby planets the telescope detected, including a "super-Earth," though none is thought to have liquid water.
Scientists expect the telescope to identify thousands of exoplanet candidates before the mission ends. Some of those could be habitable, including GJ 357 d.
"The team is currently focused on finding the best candidates to confirm by ground-based follow-up," Natalia Guerrero, who manages the MIT team that identifies exoplanet candidates, said in a NASA press release last week. "But there are many more potential exoplanet candidates in the data yet to be analyzed, so we're really just seeing the tip of the iceberg here." | 0.888519 | 3.570246 |
Grab a group of friends, a blanket and head to a dark field away from the city this weekend for the chance to see fireballs falling from space during the year’s brightest meteor shower.
The Geminids are visible every December as Earth passes through the massive trail of debris shed by an asteroid named 3200 Phaethon. Kaurn Thanjavur, a senior astronomy lab instructor at University of Victoria, says the meteor shower is named after the direction the shooting stars come from — the constellation of Gemini.
Thanjavur says the Geminids are special and explains that normally shooting stars come from comets, often referred to as dirty snowballs, which are made of up of rock and ice. The Geminids are coming from an asteroid meaning the shooting stars are made of rock and will be more colourful and brighter for longer because they don’t burn up as quickly.
“There’s a high chance of seeing fireballs,” he says, adding they should be visible for several seconds. “If you’re fairly quick, you can even get a picture of those meteors.”
According to Thanjavur the best time to view the shower is from 11 p.m. on Friday to 2 a.m. on Saturday. “It’s nice to have few people together so everyone scans in a different direction and calls out when they see one of the fireballs,” he says.
And even if you don’t see any shooting stars, Thanjavur says it’s a great time to observe the Gemini constellation, which makes the twins. In order to find Gemini you’ll need to locate the twin stars — Castor and Pollux — which mark the heads of the twins.
According to NASA, waiting until about 10:30 p.m. when the moon’s light is less bright is best in order to see the more faint meteors, which are more numerous. Find the darkest place you can, give your eyes 30 minutes to adapt to the dark and avoid looking at your phone. Lie flat on your back with a view of the sky from horizon to horizon, taking in as much of the sky as possible and you’ll begin to see the shooting stars. | 0.847246 | 3.247781 |
by Brian Clegg
Getting to the Moon
As soon as it was realized that the Moon was more than a light in the sky, the idea of journeying to it became appealing, though early narratives of lunar travel now seem quaint in the extreme. Writers had no idea of the kind of distances involved. For that matter, they had no reason to think that air would not be readily available.
The earliest known example of a trip to the Moon stretches back 1900 years to Lucian of Samosata, a Roman living in Syria. His aim seems to have been to take a sneaky satirical poke at the Odyssey and other works of fantasy, presented as a kind of reality at the time. Lucian’s book True History was the equivalent of the Harvard Lampoon Tolkien parody, Bored of the Rings. Despite this, True History contains many features that would become prime themes of science fiction. After the first part of their journey, Lucian and his companions are lifted into the sky by a whirlwind which carries them to the surface of the Moon. Once there, the adventurers are caught up in a war between the kings of the Moon and the Sun over who should have the right to colonize Venus.
True History is unusual in surviving literature for the next 1500 years. But a whole list of fantastical journeys were made to the Moon in fiction from the seventeenth century onward. One of the first to write such a book was English bishop Francis Godwin who penned The Man in the Moone in the 1620s, though it wasn’t published until after his death in 1638. This was when Galileo was getting into trouble over his support for putting the Sun at the center of the universe. While Galileo was facing the Inquisition, Godwin wrote a story that went against the Aristotelian cosmology of the day. His Moon was very different from Aristotle’s perfect sphere: an inhabited world not unlike the Earth, with seas in the dark areas that we still give the name “mare” (sea in Latin). Godwin put the transport in the hand of gansas, an imaginary breed of swan that migrated to the Moon each year. On the other hand, he did describe the way his hero lost weight as he flew away from the Earth.
If hitching a ride with a flock of migrating birds seems unlikely, it is as nothing compared with Somnium, written by astronomer Johannes Kepler in 1634. In this, Kepler has his fictional hero cross a bridge of darkness, used by lunar demons to make the journey to Earth during eclipses. Despite this, Kepler too threw in some interesting thinking about the experience of being on the Moon. He realized that when looking back at the Earth he would see it in the lunar sky like a huge, dramatic moon. And, aware of the thinning of the atmosphere at high altitudes, he noted that the space travelers needed to have damp sponges pushed into their nostrils to breathe.
Surprisingly, though, the most scientific means of transport used to reach the Moon in this period came from Cyrano de Bergerac. We think of Cyrano as a fictional character because of the eponymous play from the end of the nineteenth century by French writer Edmond Rostand, but de Bergerac was a real seventeenth century playwright.
In his first person novel L’Autre Monde: ou les États et Empires de la Lune (The Other World: or the States and Empires of the Moon), Cyrano’s initial attempt at getting off the Earth involved flawed scientific thinking. He noted that the Sun made dew disappear, “drawing the fluid” off the surface. So, he surmised, a collection of bottles containing dew, attached to the astronaut with strings, should lift him into space. When the bottles didn’t work, a group of soldiers attached fireworks to Cyrano’s contraption, blasting him off using rocket power. Admittedly by luck, Cyrano had hit on the first vaguely realistic technological approach.
Plenty of other stories written over the next couple of centuries made use of the Moon as a backdrop to play with the possibilities of new social orders (or to mock existing ones), but the turning point from fantasy to science fiction was the arrival of the twin titans Jules Verne and H. G. Wells. Neither made use of realistic science in their respective books – but they brought the theme into the front rank of popular fiction. Within another 30 years, the science in space travel fiction was converging on reality.
Since our first true voyage to the Moon it has become a less popular destination in fiction. Yet that’s a shame. Every moonlit night we are presented with a reminder that we still haven’t truly conquered our nearest neighbor. The Moon has allure still as a destination for fiction and reality alike.
BRIAN CLEGG is the author of Ten Billion Tomorrows: How Science Fiction Technology Became Reality and Shapes the Future. He holds a physics degree from Cambridge and has written regular columns, features, and reviews for numerous magazines. He lives in Wiltshire, England, with his wife and two children.
The post Getting to the Moon: How Science Fiction Became Reality appeared first on The History Reader.
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The gray surfaces of the dwarf planet Ceres (the asteroid belt's largest resident) and Pluto's biggest moon, Charon, both show signs of containing forms of graphite, the material in pencil lead.
When NASA's Dawn spacecraft arrived at Ceres last year to embark on an orbital survey, it found a gray, icy world covered with debris left behind by impacts. Spectral observations of the object, which is both a dwarf planet and an asteroid, revealed evidence of a form of graphite called graphitized carbon on its surface, according to Amanda Hendrix, a senior scientist at the Planetary Science Institute in Arizona.
The dark carbon suggests that similar processes could change the colors of both worlds, though they're significantly different environments. [Photos: Dwarf Planet Ceres, the Solar System's Largest Asteroid]
Graphitized carbon forms when carbon is heated to high temperatures in the absence of oxygen.
Hendrix studies how carbon forms in the inner solar system. She presented the results of her ultraviolet examination of Ceres at the Lunar and Planetary Sciences Conference in The Woodlands, Texas, in March.
Throughout Ceres' history, carbon-filled meteorites and asteroids have crashed into the dwarf planet. The solar wind's charged particles have collided with the deposited carbon, repeatedly reprocessing it to release hydrogen and leaving behind a dull, gray graphitized carbon. The dark material has a low albedo, meaning it doesn't reflect a lot of light.
"It hasn't evolved to proper graphite," Hendrix told Space.com. But it's close.
Similar carbon processing may occur on other objects in the asteroid belt, she said.
And earlier this year, scientists found that Mercury's surface has high levels of carbon, suggesting that it once boasted a graphite-rich crust.
A dull moon
The inner solar system isn't the only place to find a gray world. Only a few months after Dawn reached Ceres, NASA's New Horizons spacecraftflew by Pluto and revealed that the dwarf planet's largest moon, Charon, has a grayish appearance. That color could have been caused by graphite on the moon's surface, according to lab results presented at the conference by Dale Cruikshank, a planetary scientist at NASA's Ames Research Center.
The presence of graphite at Charon presents a puzzle because New Horizons didn't spot carbon on Charon, but it did so at Pluto.
Before New Horizons arrived at Pluto, scientists hypothesized that the dwarf planet shared its atmosphere with its largest moon, and observations made by the spacecraft seem to confirm it. So carbon may travel from Pluto over to Charon, New Horizons scientists have said..
But although it is mostly gray, Charon also boasts a bright-red spot at its pole.
Cruikshank performed several experiments to learn more about this unusual color combination. In dousing ices similar to those found on the dwarf planet with radiation, Cruikshank was able to produce a residual organic gunk known as tholin. The color of this substance — named in 1979 by Carl Sagan and his colleague Bishun Khare, who performed similar space-themed experiments that left behind tholin as a sticky residue — resembles the color of Charon's red spot, as well as the color of some features seen at Pluto.
In fact, tholin may be involved in both the gray and reddish hues at Charon.
"The neutral color of Charon is consistent with taking tholin material and irradiating it," Cruikshank said during his presentation. "You end up with graphite."
The reddish region at Charon's pole is likely a newer deposit, whereas the rest of the moon is covered with an older layer, Cruikshank said.
Hendrix called these results surprising. Radiation from the solar wind should be significantly weaker at Charon than it is at Ceres, because Charon lies, on average, about 10 times farther from the sun than Ceres does. If the moon's surface is covered with graphite, she said, "it likely formed a different way."
[Editor's Note: This article previously stated that Charon lies about three times farther from the sun than Ceres does. Charon is actually, on average, about ten times farther from the sun than Ceres is.] | 0.894976 | 3.90198 |
April 8, 2016 – Astronomers have made great strides in discovering planets outside of our solar system, termed “exoplanets.” In fact, over the past 20 years more than 5,000 exoplanets have been detected beyond the eight planets that call our solar system home.
The majority of these exoplanets have been found snuggled up to their host star completing an orbit (or year) in hours, days or weeks, while some have been found orbiting as far as Earth is to the sun, taking one-Earth-year to circle. But, what about those worlds that orbit much farther out, such as Jupiter and Saturn, or, in some cases, free-floating exoplanets that are on their own and have no star to call home? In fact, some studies suggest that there may be more free-floating exoplanets than stars in our galaxy.
This week, NASA’s K2 mission, the repurposed mission of the Kepler space telescope, and other ground-based observatories have teamed up to kick-off a global experiment in exoplanet observation. Their mission: survey millions of stars toward the center of our Milky Way galaxy in search of distant stars’ planetary outposts and exoplanets wandering between the stars.
While today’s planet-hunting techniques have favored finding exoplanets near their sun, the outer regions of a planetary system have gone largely unexplored. In the exoplanet detection toolkit, scientists have a technique well suited to search these farthest outreaches and the space in between the stars. This technique is called gravitational microlensing.
For this experiment, astronomers rely on the effect of a familiar fundamental force of nature to help detect the presence of these far out worlds— gravity. The gravity of massive objects such as stars and planets produces a noticeable effect on other nearby objects.
But gravity also influences light, deflecting or warping, the direction of light that passes close to massive objects. This bending effect can make gravity act as a lens, concentrating light from a distant object, just as a magnifying glass can focus the light from the sun. Scientists can take advantage of the warping effect by measuring the light of distant stars, looking for a brightening that might be caused by a massive object, such as a planet, that passes between a telescope and a distant background star. Such a detection could reveal an otherwise hidden exoplanet.
“The chance for the K2 mission to use gravity to help us explore exoplanets is one of the most fantastic astronomical experiments of the decade,” said Steve Howell, project scientist for NASA’s Kepler and K2 missions at NASA’s Ames Research Center in California’s Silicon Valley. “I am happy to be a part of this K2 campaign and look forward to the many discoveries that will be made.”
This phenomenon of gravitational microlensing – “micro” because the angle by which the light is deflected is small – is the effect for which scientists will be looking during the next three months. As an exoplanet passes in front of a more distant star, its gravity causes the trajectory of the starlight to bend, and in some cases results in a brief brightening of the background star as seen by the observatory.
The lensing events caused by a free-floating exoplanet last on the order of a day or two, making the continuous gaze of the Kepler spacecraft an invaluable asset for this technique.
“We are seizing the opportunity to use Kepler’s uniquely sensitive camera to sniff for planets in a different way,” said Geert Barentsen, research scientist at Ames.
The ground-based observatories will record simultaneous measurements of these brief events. From their different vantage points, space and Earth, the measurements can determine the location of the lensing foreground object through a technique called parallax.
“This is a unique opportunity for the K2 mission and ground-based observatories to conduct a dedicated wide-field microlensing survey near the center of our galaxy,” said Paul Hertz, director of the astrophysics division in NASA’s Science Mission Directorate at the agency’s headquarters in Washington. “This first-of-its-kind survey serves as a proof of concept for NASA’s Wide-Field Infrared Survey Telescope (WFIRST), which will launch in the 2020s to conduct a larger and deeper microlensing survey. In addition, because the Kepler spacecraft is about 100 million miles from Earth, simultaneous space- and ground-based measurements will use the parallax technique to better characterize the systems producing these light amplifications.”
To understand parallax, extend your arm and hold up your thumb. Close one eye and focus on your thumb and then do the same with the other eye. Your thumb appears to move depending on the vantage point. For humans to determine distance and gain depth perception, the vantage points, our eyes, use parallax.
Flipping the Spacecraft
The Kepler spacecraft trails Earth as it orbits the sun and is normally pointed away from Earth during the K2 mission. But this orientation means that the part of the sky being observed by the spacecraft cannot generally be observed from Earth at the same time, since it is mostly in the daytime sky.
To allow simultaneous ground-based observations, flight operations engineers at Ball Aerospace and the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder will perform a maneuver turning the spacecraft around to point the telescope in the forward velocity vector. So, instead of looking towards where it’s been, the spacecraft will look in the direction of where it’s going.
This alignment will yield a viewing opportunity of Earth and the moon as they cross the spacecraft’s field of view. On April 14 at 11:50 a.m. PDT (18:50 UT), Kepler will record a full frame image. The result of that image will be released to the public archive in June once the data has been downloaded and processed. Kepler measures the change in brightness of objects and does not resolve color or physical characteristics of an observed object.
Observing from Earth
To achieve the objectives of this important path-finding research and community exercise in anticipation of WFIRST, approximately two-dozen ground-based observatories on six continents will observe in concert with K2. Each will contribute to various aspects of the experiment and will help explore the distribution of exoplanets across a range of stellar systems and distances.
These results will aid in our understanding of both planetary system architectures as well as the frequency of exoplanets throughout our galaxy.
For a complete list of participating observatories, reference the paper that defines the experiment: Campaign 9 of the K2 mission.
During the roughly 80-day observing period or campaign, astronomers hope to discover over 100 lensing events, ten or more of which may have signatures of exoplanets occupying relatively unexplored regimes of parameter space.
Ames manages the Kepler and K2 missions for NASA’s Science Mission Directorate. NASA’s Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder. | 0.939627 | 3.918018 |
The Atacama Desert of northern Chile is famous for being the driest place on earth. The average annual rainfall is 15mm (0.6in). Some locations, such as Arica and Iquique, average only 1 to 3mm (0.04 to 0.12in) per year. Periods of up to four years have been registered with no rainfall in the central sector, delimited by the cities of Antofagasta, Calama and Copiapó, in Chile. Evidence suggests that the Atacama may not have had any significant rainfall from 1570 to 1971.
The Atacama may well be the oldest desert on earth. Its aridity is explained by it being situated between two mountain chains (the Andes and the Chilean Coast Range) and being of high enough altitude to prevent moisture entering from either the Pacific or the Atlantic Oceans. Atacama has experienced extreme hyperaridity for at least 3 million years, making it the oldest continuously arid region on earth. The landscapes created by these conditions give the impression you are on Mars, which is probably why NASA tested its Martian rovers in the Atacama.
The Atacama covers an expansive area of 105,000 square kilometres (41,000 sq mi). The diverse landscape is made up of mostly salt lakes, sand dunes, and stony terrain. Film locations of particular interest include Death Valley Dunes, Los Flamencos National Reserve, El Tatio geysers, Coyote Lookout, Valley of the Moon, the colourful cliffs of Rainbow Valley, the lithium mines of Salar de Atacama, and the town of San Pedro.
Camanchaca is a dense fog that rolls in from the coast. Fog collection nets are used to produce running water for desert villages.
Photographing the night sky is another draw of Atacama. April through September are the best months for clear skies to see the Milky Way, Jupiter and Saturn. For the darkest of skies aim to shoot during a Lunar Eclipse.
Atacama hosts the largest astronomical project in existence, Atacama Large Millimeter Array (ALMA), a single telescope composed of 66 high-precision antennas.
The Paranal Observatory located on the mountains of Cerro Paranal is home to the Very Large Telescope (VLT). The location appeared in Quantum of Solace.
The Pan-American Highway that cuts through the Atacama is a stunning and unique location to film car commercials.
The Atacama is sparsely populated. In interior areas, oases and some valleys have been populated for millennia and were the location of the most advanced Pre-Columbian societies found in Chile. Today the Atacama is home to interesting people, such as Mane, a shaman who heals with water.
A week-long foot race called the Atacama Crossing takes place in October.
Some parts of the desert are so arid, no plant or animal life can survive. Outside of these extreme areas you can find a variety of fauna. The once endangered Vicuñas (cousins of the Llama) who’s slow growing coats are spun into some of the most expensive wool in the world, are found in this part of the world. The Atacama is also home to flamingos, viscacha, gray and culpeo foxes, desert wasps, and red scorpions.
A rich variety of over 500 flora species have evolved to live within the border of Atacama.
Getting There & Staying
San Pedro (The main inland village) is located 1670 km north of Santiago de Chile. To get there, first you need to fly to Calama. From there San Pedro (98 km) is connected by an excellent highway.
Lan Chile Airlines and Sky Airlines run five daily flights from Santiago during the weekdays and three on the weekend. The cheapest round trip tickets cost around 90,000 pesos (USD130). To get them you have to buy your ticket at least four days before the flight starts and a Saturday must be included in your stay.
Tierra Atacama is a boutique hotel on the edge of San Pedro.
Chile Production Support & Crew
Contact us if you are looking for production support for your shoot in Atacama, Chile. Our locally based fixers and producers will be able to arrange all of your film location permitting and other production requirements. If you would like to save money and work with locally based shooting crew, we have directors, DoP’s, videographers, cameramen and photographers based in Santiago. | 0.814583 | 3.197429 |
Konus, a Gamma-Ray Burst Experiment from Russia on the ISTP/Wind Spacecraft
Konus, a gamma-ray burst (GRB) monitor launched on the GGS-Wind spacecraft in November 1994, is the first Russian experiment on a NASA science mission. Dr. E. P. Mazets of the Ioffe Physico-Technical Institute in St. Petersburg, Russia is the PI and Dr. T. L. Cline of Goddard is the co-PI.
The Konus detector array consists of two unshielded gamma ray sensors located on opposing spin axes of the spacecraft. In interplanetary space far outside the magnetosphere, Konus has two advantages over Earth-orbiting GRB monitors - continuous coverage uninterrupted by Earth occultation and a steady background unaffected by passages through the trapped radiation.
Konus also provides the only full-time near-Earth vertex in the present long-baseline interplanetary GRB network (IPN), with the demise of the Compton-GRO. In addition, BeppoSAX does - and HETE-2 will - furnish partial coverage for the IPN, besides providing their own GRB alerts. The present IPN has localized a number of GRBs with sufficient precision and with adequate rapidity to enable counterpart studies that in turn have produced redshifts and other valuable GRB-associated measurements.
In addition to its GRB studies, Konus has contributed recent advances in the studies of other hard x-ray transients - soft gamma repeaters (SGRs), a giant SGR flare, and the bursting pulsar. | 0.827834 | 3.18067 |
During the same relative time period, other clues indicate more oxygen was present in the atmosphere thanfound currently
Space news (planetary science: Martian rocks containing manganese oxide minerals; indicating a wetter surface with more atmospheric oxygen than presently found on Mars) – Mars (the Red Planet), 154 million miles (249 kilometers) from Sol, or 141 million miles (228 million kilometers) from Earth, on average –
NASA’s Curiosity Mars rover has found rocks at a place called Windjana containing manganese oxide minerals according to reports from planetary scientists studying samples from the region. On Earth rocks of this type formed during the distant past in the presence of abundant water and atmospheric oxygen. This news added to previous reports of ancient lakes and other groundwater sources during Mar’s pastpoints to a wetter environment in the study region Gale Crater during this time.
Planetary scientists used the laser-firing instrument on the Curiosity Mars rover to detect high levels of manganese-oxide in mineral veins found at Windjana. “The only ways on Earth that we know how to make these manganese materials involve atmospheric oxygen or microbes,” said Nina Lanza, a planetary scientist at Los Alamos National Laboratory in New Mexico. “Now we’re seeing manganese oxides on Mars, and we’re wondering how the heck these could have formed?”
Planetary scientists are looking at other processes that could create the manganese-oxide they found in rocks in Mar’s Gale Crater region. Possible culprits at this point include microbes, but even optimistic planetary scientists are finding little fan fair accompanyingtheir ideas. Lanza said, “These high manganese materials can’t form without lots of liquid water and strongly oxidizing conditions. Here on Earth, we had lots of water but no widespread deposits of manganese oxides until after the oxygen levels in our atmosphere rose.”
Geologists have found high concentrations of manganese oxide minerals is an important marker of a major shift in Earth’s atmospheric composition, from relatively low oxygen levels during the distant past, to the oxygen-rich environment we live in today. Planetary scientists studying the rocks they found in Gale Crater suggest the presence of these materials indicates oxygen levels on Mars rose also, before declining to the present low levels detected. The question is how was Mar’s oxygen-rich atmosphere formed?
“One potential way that oxygen could have gotten into the Martian atmosphere is from the breakdown of water when Mars was losing its magnetic field,” said Lanza. “It’s thought that at this time in Mars’ history, water was much more abundant. Yet without a protective magnetic field to shield the surface, ionizing radiation started splitting water molecules into hydrogen and oxygen. Because of Mars’ relatively low gravity, the planet wasn’t able to hold onto the very light hydrogen atoms, but the heavier oxygen atoms remained behind. Much of this oxygen went into rocks, leading to the rusty red dust that covers the surface today. While Mars’ famous red iron oxides require only a mildly oxidizing environment to form, manganese oxides require a strongly oxidizing environment, more so than previously known for Mars.“
Lanza added, “It’s hard to confirm whether this scenario for Martian atmospheric oxygen actually occurred. But it’s important to note that this idea represents a departure in our understanding for how planetary atmospheres might become oxygenated. Abundant atmospheric oxygen has been treated as a so-called biosignature or a sign of extant life, but this process does not require life.“
The Curiosity rover has been investigating Gale Crater for around four years and recent evidence supports the possibilityconditions needed to form these deposits were present in other locations. The concentrations of manganese oxide discovered were found in mineral-filled cracks in sandstones in a region of the crater called “Kimberley”. NASA’s Opportunity rover has been exploring the surface of the planet since 2004 and recently reported similar high manganese deposits in a region thousands of miles away. Supporting the idea environments required to form similar deposits could be found well beyond Gale Crater.
What’s next for Curiosity?
NASA’s Curiosity rover’s currently collecting drilled rock powder from the 14th drill site called the Murray formation on the lower part of Mount Sharp. Plans call for NASA’s mobile laboratory to head uphill towards new destinations as part of a two-year mission extension starting near the beginning of October.
The rover will go forward about a-mile-and-a-half (two-and-a-half-kilometers) to a ridge capped with material rich in the iron-oxide mineral hematite first identified by observations made with NASA’s Mars Reconnaissance Orbiter. Just beyond this area, there’s also a region with clay-rich bedrock planetary scientists want to have a closer look.
NASA has been exploring these key exploration sites on lower Mount Sharp as part of an effort to investigate evidence the Red planet was once a much wetter environment, which contrasts with the pictures of Mars we have received from our orbiters and rovers. A wetter environment where life could have taken root and grown.
“We continue to reach higher and younger layers on Mount Sharp,” said Curiosity Project Scientist Ashwin Vasavada, of NASA’s Jet Propulsion Laboratory, Pasadena, California. “Even after four years of exploring near and on the mountain, it still has the potential to completely surprise us.”
Planetary scientists found the Murray formation consists primarily of mudstone, which on Earth would form from mud accumulated on the bottom on an ancient lake. This seems to indicate any lake environment that existed on the Red Planet lasted awhile, but we’ll need to investigate this possibility more. Plans are for Curiosity to investigate the upper regions of the Murray formation, ahead, for at least one year of the mission.
“We will see whether that record of lakes continues further,”Vasavada said. “The more vertical thickness we see, the longer the lakes were present, and the longer habitable conditions existed here. Did the ancient environment change over time? Will the type of evidence we’ve found so far transition to something else?”
Vasavada said, “The Hematite and the Clay units likely indicate different environments from the conditions recorded in the older rock beneath them and different from each other. It will be interesting to see whether either or both were habitable environments.”
Scientists using the Shallow Radar (SHARAD) instrument on NASA’s Mars Reconnaissance Orbiter to look beneath Mar’s north polar ice cap and get an idea of the lay of the ground think they know how Chasma Boreale and the much-discussed series of spiral troughs were formed. The formation of Chasma Boreale and enigmatic spiral troughs have been talked about for four decades by space scientists and amateur astronomers. Mar’s north polar region is really just a stack of ice and dust layers up to 2 miles thick and encompassing an area equivalent to Texas. Chasma Boreale is a distinctive land feature as long as the Grand Canyon, only wider and deeper, while the troughs spiral outward from their centers like huge pinwheels.
What did astronomers and planet scientists using SHARAD to look beneath Mar’s north polar cap reveal concerning the formation of Chasma Boreale and associated spiral troughs? The view beneath Mar’s north polar cap suggests strong winds were the main force of geological change involved in the formation of the Chasma Boreale and spiral troughs over millions of years. The geological processes involved would have formed Chasma Boreale and spiral troughs as Mar’s north polar ice cap was formed.
Professional astronomers are studying these troughs | 0.809228 | 3.792595 |
The moon will be dancing with multiple planetary partners this month, offering delights in both the morning and evening skies. And as the nights get warmer for viewers in the Northern Hemisphere, sky-watchers lingering outside will be in for a spring treat: a lovely meteor shower streaking across the constellation Lyra.
So dust off those binoculars, and mark your April calendar!
Mars passes the Pleiades—April 1
A beautiful pairing of orange-hued Mars and the Pleiades star cluster will greet viewers as soon as darkness falls on the first of the month. Both objects will dominate the western sky and will be separated by only three degrees, a gap that can be covered by your three middle fingers held at arm’s length.
If you can, definitely check out the Pleiades with binoculars or a backyard telescope. This cluster, also known as the Seven Sisters, is one of the closest to Earth at some 300 light-years away. Although it contains more than a thousand confirmed members, it gets its nickname from the seven stars that can be easily spotted with the unaided eye, even today under brightly lit city skies.
Moon meets Venus—April 2
Early risers on the second will be treated to the bright, star-like planet Venus snuggling close to the waning crescent moon. The pair will be hanging in the southeastern sky about an hour before local sunrise.
Pallas at opposition—April 9
One of the largest known asteroids, 2 Pallas, will be at its brightest in our evening skies on the 9th, and will be easy to find as it glides past one of the brightest stars in the northern spring sky. Located some 147 million miles from Earth, the giant celestial rock will be officially at opposition, when it is opposite in the sky from the sun, as seen from Earth. Roughly 326 miles wide, Pallas will be a binocular target even from light-polluted city suburbs for the next couple of weeks.
Pallas is currently sailing through the bright constellation Boötes, the herdsman, located in the southeastern evening sky. It is visible very close to the bright orange star Arcturus; their apparent separation in the sky is about equal to the width of your fist held at arm’s length.
That makes the bright star a convenient guidepost for hunting down the asteroid. Start by using binoculars to home in on Arcturus around local midnight, when the constellation will reach its highest point in the sky. Because many of the points of light in this field of view can look the same, the best way to identify an asteroid is by its telltale motion. Sketch the position of about a dozen of the stars you see. In about half an hour, observe the same star field once more and make the same sketch. The one “star” that has moved will be Pallas.
Battle of the red orbs—April 11
Evening sky-watchers will be seeing red on the 11th, as two of the brightest and reddest celestial objects huddle in the same part of the sky. Gaze toward the west after darkness falls to see ruddy Mars approaching the much brighter red star Aldebaran, also known as the eye of Taurus, the bull. The celestial duo will sit about seven degrees apart, a gap that is a bit more than the width of your fist held at arm’s length.
While they seem comparable in our skies as points of light, Mars is a third the size of Earth and is less than 190 million miles away. Meanwhile, Aldebaran is a red giant star many times larger than our sun that is located 65 light-years distant.
Lyrid meteors peak—April 22
In the predawn hours of the 22nd, the Lyrid meteor shower will reach its peak. Under ideal, dark skies, we can expect to see anywhere between 15 to 20 shooting stars an hour during this annual shower. This year, however, sky-watchers will have to contend with a waning gibbous moon—only three days past the full phase—rising just before local midnight. This means the lunar glare will wash out the fainter shooting stars around dawn, and the best views might be relegated to the darker late nights of the 21st and 22nd.
Individual shooting stars will appear to stream from the shower's namesake constellation Lyra. Meteors will seem to radiate from the area of sky occupied by the brilliant star Vega, which currently shines nearly overhead just before dawn.
The Lyrids are known to have surprise outbursts, such as one in 1982 that saw as many as 250 meteors appear in a single hour. And the 1922 performance above Europe is the stuff of legends, with records of around 500 shooting stars an hour. These spectacles can’t be predicted, so the only way to know for sure if one is happening is to go out and look up.
Moon joins Jupiter—April 23
On the 23rd, early risers will see the waning gibbous moon make a very close approach to the brilliant planet Jupiter. The pair will appear to be less than two degrees apart, meaning you could cover the cosmic duo with a just two fingers held at arm’s length. This celestial encounter will offer a great photo opportunity, with the pair hanging low in the southwestern sky about 45 minutes before local sunrise.
Moon skirts Saturn—April 25
Only a couple of mornings after Jupiter’s brush with our moon, magnificent Saturn will get its turn to hang out with Earth’s companion in our skies. Look for the brilliant moon to position itself less than half a degree from the star-like ringed world at dawn in the high southern sky. If you can, don’t forget to train your telescope on Saturn and spy those famous rings that encircle the gas giant. | 0.912048 | 3.478063 |
Nearing the end of its mission, ESA's Herschel Space Observatory has delivered a highly detailed map of extremely cold gas and dust in the iconic Andromeda Galaxy.
We've seen so many images of the grand, stately Andromeda Galaxy (Messier 31) that we sometimes forget that this giant pinwheel is alive with activity and, especially, star formation. But this just-released view, taken by the European Space Agency's Herschel spacecraft, reveals M31 in a new light.
Specifically, the space observatory recorded the galaxy's appearance at far-infrared wavelengths. The longer the wavelength, the colder the matter, and the dark-red lanes in the disk correspond to some of the very coldest dust in the galaxy (only a few tens of degrees above absolute zero). That's where future generations of stars will be born. By contrast, the bluish appearance of M31's central bulge shows that it is somewhat warmer and already dense with older stars.
Located 2½ million light-years away, the Andromeda Galaxy is about 200,000 light-years across (twice the size of our Milky Way Galaxy). Herschel's view reveals at least five concentric rings in its spiral arms. In between these are dark gaps where star-forming regions are absent.
This isn't the first time Herschel's 3.5-meter optics have been directed toward M31. Compare this view with another infrared portrait taken in late December 2010.
Launched in May 2009, the spacecraft was originally known as the Far InfraRed and Submillimetre Telescope (FIRST) but later renamed for Sir William Herschel, who in 1800 discovered infrared radiation. The spacecraft has given astronomers their most detailed views to date of cosmic targets in far-infrared and submillimeter wavelengths (from 60 to 670 microns).
While this wasn't Herschel's first look at the Andromeda Galaxy, it will likely be its last. The spacecraft is about to run out of the liquid helium that chills its optics and detectors. Once the helium is gone, now expected to occur within the next two months, the mission will end.
Here's an ESA website where you can get more information about Herschel and its mission. | 0.875848 | 3.839172 |
Recent interest in high redshift cosmology observations with the redshifted 21cm line has rekindled exploration of the VHF radio band (50-200MHz) for radio astronomy. Single antenna instruments like the ground-based EDGES and the proposed lunar orbiting DARE have the goal of characterizing the global HI signal and extracting astrophysical and cosmological information. One limitation over much of the band is strong man-made and naturally occurring interference, which DARE avoids by observing as it orbits the far side of the moon. Another advantage of space-based observing is avoidance of the ionosphere which becomes increasingly reflective at the lower end of the VHF band. Technical challenges to this type of mission include development of lower power wide-band spectrometers, better mapping of Earth originating interference, and incorporation of lessons learned from ongoing ground-based experiments. One of the main challenges faced by EDGES, observing the narrower but clean stretch of bandwidth found in Western Australia, is calibrating the spectral response of the antenna at the required 0.01dB level. | 0.846662 | 3.265578 |
On Monday (November 11), Mercury will move toward the sun and many spacecraft will have scenes in the rare event.
Spacecraft has captured incredible images of past Mercury transits, and this year promises some exciting observations from space. NASA's
Solar Dynamics Observatory (SDO) and Solar & Heliospheric Observatory (SOHO) were observing the sun during Mercury's nearly 5.5 trips, and a Japanese missions can also provide close-ups
On Earth, skyscrapers in North America, South America, Europe, Europe, and Antarctica can view the event using the ISO-certified safe
daily gear viewing ̵
1; weather permitting. Those in Alaska, the Pacific and Asia will not catch the event, as the sun will be at the bottom of the horizon when Mercury passes in front of the star like a traveling wreck. Fortunately, the teams behind many space missions will share uninterrupted views on Mercury's transit.
Related: Mercury Transit 2019: Where and How to See It on November 11
This last-minute image of Mercury transit was taken by NASA's Solar Dynamics Observatory on May 9, 2016, in association with the Atmospheric Imaging Assembly.
(Image credit: JAXA / NASA / PPARC) The SDO was designed to study changes in the activity of the sun and how it influences the Earth. Now in the ninth year of our planet's departure, the SDO continues to take measurements of the sun's interior, magnetic field and the hot outer atmosphere of the star, called the
corona . Three scientific experiments on the SDO board monitor the day's tidbits: the Atmospheric Imaging Assembly (AIA), the EUV Variability Experiment (EVE) and the Helioseismic and Magnetic Imager (HMI). During its lifetime, the entire SDO solar cycle produced over 350 million images and was used in more than 3,000 research papers, according to NASA .
A team from SDO will regularly update its website with the latest views of Mercury on November 11 in transit, accessible
here starting at 7:00 EST (1200 GMT ), about half an hour before Mercury's first contact (when the planet's silhouette was tangent to the solar disk for the first time).
NASA also operates SOHO, a 12-instrument spacecraft built in cooperation with the European Space Agency. SOHO is in the space longer than SDO, which was launched more than two decades ago. It maintains regular tabs during the day and produces many
daytime views in gif-movie format. Like SDO, they are regularly updated on the NASA website. Mercury is likely to appear in these views, even as a speeding trend in an accelerated time-lapse video. SOHO videos can be viewed here .
Japan of Japan by Hinode. spacecraft obtained this image of Mercury passing through the sun on November 8,2006, using the spacecraft's Solar Optical Telescope instrument.
(Image credit: JAXA / NASA / PPARC)
Hinode [19459005Asatellite-observationsatheatellitenatapapanJapanAerospaceExplorationAgency(JAXA)hasbeengreatlyimproved by the Mercury. The mission team will publish the images sometime after the November 11 event, a NASA spokesperson told Space.com. (Hinode is also part of the Solar Terrestrial Probes Program within the Heliophysics Division of NASA's Science Mission Directorate in Washington.) The 13-year-old mission is equipped with three powerful telescopes that assist scientists in studied how solar phenomena such as heating and magnetism affect dramatic star activity, such as solar flares .
Hinode also captured larger shadows passing before the sun, such as the
2017 Great American Solar Eclipse .
There are several newer missions that guard the sun and Mercury. The joint European-Japanese
BepiColombo mission was launched last year and has already received over 500 images ( such as this selfie ) on a lengthy journey to reach Mercury. But it's not an engineer to look at during the day, Erika Verbelen, an ESA spokeswoman, told Space.com, so it won't see solar transit on Monday.
Parker Solar Probe has the star name itself in its mission title, but so far the instruments have been turned off. Although they are turned on, which happens when the probe is near the sun in this mission orbit, the Parker Solar Probe is not designed to take direct photos of the sun, Karen C. Fox, a spokeswoman for NASA, Space.com said. Instead, it takes observations of the solar wind that flows into the sun.
Editor's Note : Visit Space.com on November 11 to see live webcast views of Mercury's rare move as shown from telescopes on Earth and in space , with the full scope of the event in heaven. If you SAFELY took a picture of the Mercury shift and you want to share it with Space.com and our news partners for a story or gallery, you can send pictures and comments to spacephotos @ space.com .
Follow Doris Elin Urrutia on Twitter @salazar_elin . Follow us on Twitter @Spacedotcom and on Facebook . | 0.828653 | 3.270587 |
Feature image: Behold! The cosmic microwave background. It was emitted just after the universe was one big plasma. Credit: Planck HFI telescope.
Welcome to the new and improved These Vibes Are Too Cosmic. Brian Kraus and Stevie christen their new time slot of 5-7pm on Tuesdays. We introduce the new format for the show – we’re switching off taking the helm each week (next week Stevie, the week after that Brian, and so on) serving up steaming offerings of science and music.
But this week, in this new show we’re so pumped about, we decided to introduce our listeners to….ourselves. We play music we love, interview each other on our respective research fields, and take questions from listeners.
Plasma physics (Brian): I work on plasmas, which are basically electrified gases. Imagine the process of melting a solid, and then boiling a liquid: in both cases, the atoms in the material are more and more free to move around as they gain energy. In a plasma, the electrons around the atoms have enough energy to escape the atomic nucleus, and what you’re left with is a gas of charged particles: negative electrons zooming around the heavier positive ions. You’d know a plasma if you saw one: they glow, like the plasma ball to the right or the lightning during a rainstorm.
The applications of plasma are numerous – from lightbulbs to space propulsion – but the most famous reason to study plasmas is to make fusion energy. This is the nuclear process where small atoms collide together to form bigger ones, which results in a huge energy gain for fused particles. Fusion energy could become a safe source of power, driving electrical grids with energy from seawater. The main issue is plasma containment, which means we have to keep the hot plasma (often at 10 million degrees C) from melting the walls of the container we keep it in. The most common device for magnetically confining a plasma is called a tokamak, which is basically a donut that keeps particles spinning around on a racetrack as they heat up.
My own work concerns measuring properties of plasmas with probes. Since the plasma is an electrified gas, it can conduct currents and respond to voltages – which are very easy to tap into by sticking a metal wire in the middle of the plasma! By varying the bias on the metal probe (putting stronger or weaker batteries on it), I can push or pull on the electrons in the plasma. Through this general method, we can deduce the plasma’s temperature and density at many points, so we have a good map of what it’s actually doing.
You can learn a lot more about plasmas, and my work studying them, by listening to an older show where Stevie interviews me about all of this in greater detail.
Observational Cosmology (Stevie): I work on the SPIDER instrument, a telescope with the aim to measure the polarization in the cosmic microwave background radiation (CMB, the featured image up top). The CMB is, believe it or not, microwave radiation that bathes our entire universe. Not only is this radiation the oldest in our universe, it serves as a snapshot of our universe at that time it was emitted – over 14 billion years ago. Since it’s
discovery in the 1960s (a great story unto itself), we’ve learned the CMB (like our universe) is almost entirely homogeneous and isotropic, but with tiny variations that map to density perturbations in
our early universe. These perturbations were the seeds of all the astrophysical structures we see around us today. Currently, the cosmic background radiation is our richest source of information on the evolution and large scale structure of our universe.
At only 2.7 degrees Kelvin, this radiation is difficult to measure, but not impossible. It is still just light with a defined energy ( = wavelength) and polarization. Through decades of effort scientists have carefully mapped the temperature of the CMB. Now, the forefront of observational cosmology is to map the polarization. Incredibly, the patterns in the polarization of the CMB have the capacity to
tell us about our universe back before the CMB was even emitted, pushing our understanding of our universe back to a time just moments after the Big Bang.
The SPIDER collaboration manages this task by cooling polarization-sensitive detectors to
less than a degree above absolute zero, and then sending them to the edge of space for a 20 day flight in weather balloon above Antarctica. SPIDER’s first flight was last January (2015). The flight was successful. We’re currently analyzing our rich new data set and preparing for a second flight in the next few years. As a grad student on this project, I’m pretty psyched. | 0.809574 | 3.398321 |
Not so long ago, there was quite a bit of skepticism about the panspermia hypothesis — the idea that life on Earth got started by using alien molecules deposited by stellar travelers like comets or asteroids. At the time, this was presented as the somewhat harebrained imagining of overzealous science fiction fans. The more grounded alternative was to assume that all molecules necessary for life sprung exclusively from the conditions on ancient Earth. These days, however, there is significantly more credence given to the idea that life got a kickstart from alien molecules, and the support is beginning to come from all corners of the scientific world.
Now, even supercomputers are getting in on the action. A forthcoming study from Lawrence Livermore National Laboratory (LLNL) claims that new supercomputer simulations of comet impacts predict the formation of some of the most crucial organic compounds for life. By making use of new and highly efficient computational models, the researchers were able to look into a comet impact for much longer than ever before — in this case, up to several hundred picoseconds. That might not sound like much, but it’s enough to see a wide array of organic molecules come together.
Conditions inside a comet impact are, as you might expect, rather extreme. By the time they reach the Earth’s surface, the exterior of a comet may be super-heated from friction with the atmosphere, but the interior would remain frozen. The shock wave that runs through this tumultuous body when it hits the Earth causes not just heat but intense pressures as well. In the case of a glancing blow, we get “moderate” figures like short periods of about 360,000 atmospheres of pressure and 4,600 degrees Fahrenheit (2,537C). Higher shock conditions can lead to much as 600,000 atmospheres as over 8,000F (4,426C). This provides a spectrum of situations that could give rise to all sorts of different molecules.
The models predicted that an oblique impact could give rise to nitrogen-containing hydrocarbon rings, the major structural component of RNA’s nitrogenous bases (DNA is thought to be a derivation of that more ancient form). On the other hand, more violent collisions could power the creation of long-chain carbon molecules like those that form the backbone of many amino acids. In the early days of the panspermia hypothesis, scientists thought many of these molecules might have been deposited intact. This study adds to an increasing body of evidence that they could be formed from carbon dioxide and other molecules we already know are present in high quantities in comets.
And what quantities they are. During the eras of greatest bombardment, comets and asteroids may have brought as much as 10 trillion kilograms of organic matter to Earth every year. That’s plenty of raw material, and these finding suggest that the mechanism of their delivery could also have provided the conditions needed to fuse that material into the complex molecules life would require. (See: Astrobiologists discover fossils in meteorite fragments, confirming extraterrestrial life.)
Comet impacts aren’t the only way to spontaneously form complex molecules from simple ones, mind you. Classical, Earth-centric explanations range from simple chemical catalysts to intense UV radiation. Even if we someday acquire irrefutable evidence for the panspermia hypothesis, it would be foolish to assume that all of life’s basic molecules came to us this way. Almost certainly, Earth’s first replicator is a mosaic made of bits both terrestrial and alien. | 0.825279 | 3.975928 |
Hi there! You may have heard of the coorbital satellites of Jupiter, or the Trojans, which share its orbit. Actually they are 60° ahead or behind it, which are equilibrium positions. Today we will see that dust is not that attached to these equilibrium. This is the opportunity to present you a study divided into two papers, Dust arcs in the region of Jupiter’s Trojan asteroids and Comparison of the orbital properties of Jupiter Trojan asteroids and Trojan dust, by Xiaodong Liu and Jürgen Schmidt. These two papers have recently been accepted for publication in Astronomy and Astrophysics.
The Trojan asteroids
Jupiter is the largest of the planets of the Solar System, it orbits the Sun in 11.86 years. On pretty the same orbit, asteroids precede and follow Jupiter, with a longitude difference of 60°. These are stable equilibrium, in which Jupiter and every asteroid are locked in a 1:1 mean-motion resonance. This means that they have the same orbital period. These two points, which are ahead and behind Jupiter on its orbit, are the Lagrange points L4 and L5. Why 4 and 5? Because three other equilibrium exist, of course. These other Lagrange points, i.e. L1, L2, and L3, are aligned with the Sun and Jupiter, and are unstable equilibrium. It is anyway possible to have orbits around them, and this is sometimes used in astrodynamics for positioning artificial satellites of the Earth, but this is beyond the scope of our study.
At present, 7,206 Trojan asteroids are list by the JPL Small Body Database, about two thirds orbiting in the L4 region. Surprisingly, no coorbital asteroid is known for Saturn, a few for Uranus, 18 for Neptune, and 8 for Mars. Some of these bodies are on unstable orbits.
Understanding the formation of these bodies is challenging, in particular explaining why Saturn has no coorbital asteroid. However, once an asteroid orbits at such a place, its motion is pretty well understood. But what about dust? This is what the authors investigated.
Production of dust
When a planetary body is hit, it produces ejecta, which size and dynamics depend on the impact, the target, and the impactor. The Solar System is the place for an intense micrometeorite bombardment, from which our atmosphere protects us. Anyway, all of the planetary bodies are impacted by micrometeorites, and the resulting ejecta are micrometeorites themselves. Their typical sizes are between 2 and 50 micrometers, this is why we can call them dust. More specifically, it is zodiacal dust, and we can sometimes see it from the Earth, as it reflects light. We call this light zodiacal light, and it can be confused with light pollution.
It is difficult to estimate the production of dust. The intensity of the micrometeorite bombardment can be estimated by spacecraft. For instance, the spacecraft Cassini around Saturn had on-board the instrument CDA, for Cosmic Dust Analyzer. This instrument not only measured the intensity of this bombardment around Saturn, but also the chemical composition of the micrometeorites.
Imagine you have the intensity of the bombardment (and we don’t have it in the L4 and L5 zones of Jupiter). This does not mean that you have the quantity of ejecta. This depends on a yield parameter, which has been studied in labs, and remains barely constrained. It should depend on the properties of the material and the impact velocity.
The small size of these particles make them sensitive to forces, which do not significantly affect the planetary bodies.
Non-gravitational forces affect the dust
Classical planetary bodies are affected (almost) only by gravitation. Their motion is due to the gravitational action of the Sun, this is why they orbit around it. On top of that, they are perturbed by the planets of the Solar System. The stability of the Lagrange points results of a balance between the gravitational actions of the Sun and of Jupiter.
This is not enough for dusty particles. They are also affected by
- the Solar radiation pressure,
- the Poynting-Robertson drag,
- the Solar wind drag,
- the magnetic Lorentz force.
The Solar radiation pressure is an exchange of momentum between our particle and the electromagnetic field of the Sun. It depends on the surface over mass ratio of the particle. The Poynting-Robertson drag is a loss of angular momentum due to the tangential radiation pressure. The Solar wind is a stream of charged particles released from the Sun’s corona, and the Lorentz force is the response to the interplanetary magnetic field.
You can see that some of these effects result in a loss of angular momentum, which means that the orbit of the particle would tend to spiral. Tend to does not mean that it will, maybe the gravitational action of Jupiter, in particular at the coorbital resonance, would compensate this effect… You need to simulate the motion of the particles to know the answer.
And this is what the authors did. They launched bunches of numerical simulations of dusty particles, initially located in the L4 region. They simulated the motion of 1,000 particles, which sizes ranged from 0.5 to 32 μm, over more than 15 kyr. And at the end of the simulations, they represented the statistics of the resulting orbital elements.
Some stay, some don’t…
This way, the authors have showed that, for each size of particles, the resulting distribution is bimodal. In other words: the initial cloud has a maximum of members close to the exact semimajor axis of Jupiter. And at the end of the simulation, the distribution has two peaks: one centered on the semimajor axis of Jupiter, and another one slightly smaller, which is a consequence of the non-gravitational forces. This shift depends on the size of the particles. As a consequence, you see this bimodal distribution for every cloud of particles of the same size, but it is visually replaced by a flat if you consider the final distribution of the whole cloud. Just because the location of the second peak depends on the size of the particles.
Moreover, dusty particles have a pericenter which is slightly closer to the one of Jupiter than the asteroids, this effect being once more sensitive to the size of the particles. However, the inclinations are barely affected by the size of the particles.
In addition to those particles, which remain in the coorbital resonance, some escape. Some eventually fall on Jupiter, some are trapped in higher-order resonances, and some even become coorbital to Saturn!
As a conclusion we could say that the cloud of Trojan asteroids is different from the cloud of Trojan dust.
All this results from numerical simulations. It would be interesting to compare with observations…
Lucy is coming
But there are no observations of dust at the Lagrange points… yet. NASA will launch the spacecraft Lucy in October 2021, which will explore Trojan asteroids at the L4 and L5 points. It will also help us to constrain the micrometeorite bombardment in these regions.
The study and its authors
You can find below the two studies:
- Dust arcs in the region of Jupiter’s Trojan asteroids,
- Comparison of the orbital properties of Jupiter Trojan asteroids and Trojan dust,
- and the homepage of Jürgen Schmidt. | 0.928453 | 3.902445 |
Hi there! Today we discuss the rotation of asteroids. You know, these small bodies are funny. When you are a big body, you are just attracted by your siblings. The Sun, the planets, etc. But when you are a small body, your life may be much more chaotic! Such small bodies not only experience the influence of gravitational perturbations, but also of thermal effects, especially when they are close enough to the Sun (Near-Earth Objects). Not only you have radiation pressure of the Sun, due to the electromagnetic field, but also a torque due to the difference of temperature between different areas of the surface of the small body.
Investigating such effects is particularly tough, since it depends on the shape of the asteroid, which could be anything. Shape, surface rugosity, thermal inertia… and the rotation state as well. When you face the Sun, you heat, but with a delay… and meanwhile, you do not face the Sun anymore… you see the nightmare for planetary scientists? Well, actually, you can say that it is not a nightmare, but something fascinating instead. You bypass such difficulties by making simplified models, and if you have the opportunity to compare with real data, i.e. observations, then you have a chance to validate your theory.
Today I present Systematic structure and sinks in the YORP effect, by Oleksiy Golubov and Daniel J. Scheeres. This study, published in The Astronomical Journal, tells us that sometimes the thermal effects may stabilize the rotational state of the asteroids.
Yarkovsky and YORP
As I said, the most important of the thermal effects, which are experienced by small asteroids (up to some 50 km), is the Yarkovsky effect. The area which faces the Sun heats, and then reemits photons while cooling. The reemission of these photons pushes the asteroids in a direction, which depends on the rotation of the body. As a consequence, this makes the prograde asteroids (rotation in the same direction as the orbit) spiral outward, while the retrograde ones spiral inward. The consequence on the orbits is a secular drift of the semimajor axis, which has been measured in some cases.
The first measurement dates back to 2003. The small asteroid (530 m) 6489 Golevka drifted by 15 km since 1991, with respect to the orbital predictions, which considered only the gravitational perturbations of the surrounding objects.
This effect had been predicted around 1900 by the Polish civil engineer Ivan Osipovich Yarkovsky.
And now: YORP. YORP stands for Yarkovsky-O’Keefe-Radzievskii-Paddack, i.e. 4 scientists. This is the thermal effect on the rotation. Most of the asteroids have irregular shapes, i.e. they do not look like ellipsoids, but rather like… anything else. Which means that the reemission of photons would not average to 0 over a rotational (or spin) period. As a consequence, if the asteroid is like a windmill, then its rotation will accelerate. Rotational data on Near-Earth Asteroids smaller than 50 km show an excess of fast rotators, with respect to larger bodies. And theoretical studies have shown that YORP could ultimately destroy an asteroid, in making it spin so fast that it would become unstable. The outcome would then be a binary object.
This is anyway a very-long-term effect.
In fact, when the rotational energy is not high enough to provoke the disruption of the asteroid, the theory of YORP predicts that the rotational states experience cycles, over several hundreds of thousands years. During these cycles, the asteroid switches from a tumbling state, i.e. rotation around 3 axes to the rotation around one single axis, and then goes back to the tumbling states. These are the YORP cycles, which are not really observed given their long duration. But the authors of this study tell us that these cycles may be disrupted.
Normal and tangential YORP
The authors recall us that the YORP effect, which generates these cycles, is in fact the normal YORP. There is a tangential YORP as well. This tangential YORP (TYORP) is due to heat transfer effects on the surface, which results in asymmetric light emission. This yields an additional force, which alters the rotation.
New equilibriums in the rotational state
And the consequence is this: when you add the TYORP in simulating the rotational dynamics of your asteroid, you get equilibriums, i.e. rotational state, which would remain constant with respect to the time. In other words, under some circumstances, the rotational state leaves the YORP cycles, to remain locked in a given state. These states would have a principal rotation axis, which would be either parallel to the orbit, or orthogonal. In this last case, the rotation could either be prograde or retrograde.
Testing the prediction
This study suggests that the authors have predicted a rotation state. It would be good to be able to test this prediction, i.e. observe this rotation state among the asteroids.
The study does not mention any observable evidence of this theory. As the authors honestly say, this is only a first taste of the complicated theory of the YORP effect. Additional features should be considered, and the mechanism of trapping into these equilibriums is not investigated… or not yet.
Anyway, this is an original study, a new step to the full understanding of the YORP effect.
The study and its authors
- You can find the study here. The authors made it freely available on arXiv, many thanks to them for sharing!
- The website of Oleksiy Golubov,
- and the one of Daniel J. Scheeres. | 0.836088 | 3.908686 |
On 28 August 1789, William Herschel began exploring the cosmos with his forty-foot telescope, which would remain the largest in the world for the next half century. Though the giant instrument gave Herschel and others greater access to the deep space of the cosmos, its cultural impact extended well beyond the realm of science.
In 1781, William Herschel’s star literally rose when his discovery of a new planet caused such excitement, the French astronomer Jérôme Lalande proposed it be named “Herschel” (Clerke 25). The discovery of Uranus catapulted Herschel into the position of the King’s Astronomer, and a few years later, with financial assistance from King George, he began work on what would be his most ambitious project: the construction of a forty-foot telescope. Herschel began the project in 1785 in Old Windsor, but less than a year later he and his sister Caroline, who was also an astronomer, were informed by the “litigious” owner of their rental house that, since the telescope would increase the property value, their rent would be raised annually (Sidgwick 129). They subsequently left Old Windsor and established a permanent residence near Windsor Castle at Slough, where they set up an observatory. Over the next few years, William oversaw the construction of the largest telescope in the world, a standing it would maintain for the next half century, and on 24 August 1789, he looked through the giant instrument for the first time. Four nights later, his telescopic viewing yielded a major discovery—the sixth satellite of Saturn—and he thereby designated 28 August 1789 as the date of completion of the forty-footer (Sidgwick 135-36; Herschel “Description” 350). The cultural impact of the giant telescope was enormous, though not for reasons anyone, including Herschel, expected. (See Fig. 1.)
During his career, Herschel was as renowned as a maker of telescopes as he was as an astronomer, and he oversaw the construction of several hundred instruments, which were sold in England and on the continent. Though he contributed significantly to popularizing astronomy through this cottage industry, his dream was not to be an entrepreneur, as his sister indicates in a recollection of 1785:
It seemed to be supposed that enough had been done when my brother was enabled to leave his profession that he might have time to make and sell telescopes. [Before receiving the patronage of King George, Herschel earned a living as a music teacher, organist, and composer.] The King ordered four ten-foot himself, and many seven-foot besides had been bespoke, and much time had already been expended on polishing the mirrors for the same. But all this was only retarding the work of a thirty or forty-foot instrument, which it was my brother’s chief object to obtain as soon as possible; for he was then on the wrong side of forty-five, and felt how great an injustice he would be doing to himself and to the cause of Astronomy by giving up his time to making telescopes for other observers. (Mary Herschel 56-57)
J. A. Bennett, who describes the evolution of Herschel’s telescopes, which ranged in size from seven-feet to forty-feet, specifies the impetus behind Herschel’s desire to construct a very large instrument: “The sweeps [performed by the twenty-foot telescope] had . . . collected a great many specimens of nebulae, but Herschel was still convinced that they were all distant clusters of stars. . . . The greater resolving power of a larger telescope would provide further evidence for his view of the heavens as a distribution of stars moulded and arranged by the force of gravity” (88).
Though a desire to test his hypothesis regarding the nature of nebulae impelled Herschel to build the forty-footer, as the largest telescope in the world it drew attention to other breakthroughs he had already made in understanding the cosmos. To this day, Herschel is best known for his discovery of Uranus, but his contributions to astronomy exceeded his sighting a new planet: he established the field of sidereal, as opposed to planetary, astronomy; he discovered thousands of nebulae and double stars; and he put forward the arresting idea that the universe, including our own galaxy, was both limitless and mutable.
Telescopic discoveries by Herschel and his fellow scientists caused theologians to reconsider conventional views of God and humankind. Thomas Dick, a Scottish minister and science teacher who makes a passing reference to Herschel’s forty-foot telescope in his book The Sidereal Heavens, writes with exhilaration of the power of such instruments:
Beyond the range of natural vision the telescope enables us to descry numerous objects of amazing magnitude; and, in proportion to the excellence of the instrument and the powers applied, objects still more remote in the spaces of immensity are unfolded to our view, leaving us no room to doubt that countless globes and masses of matter lie concealed in the still remoter regions of infinity, far beyond the utmost stretch of mortal vision. But huge masses of matter, however numerous and widely extended, if devoid of intelligent beings, could never comport with the idea of happiness being coextensive with the range of the Creator’s dominions. . . . To consider creation, therefore, in all its departments, as extending throughout regions of space illimitable to mortal view, and filled with intelligent existence, is nothing more than what comports with the idea of HIM who inhabiteth immensity, and whose perfections are boundless and past finding out. (255)
The Rev. Dionysius Lardner, an astronomy professor at the University of London, also pursues the possibility of extraterrestrial life. Referring to other “orbs” in the universe, he writes:
Have not their intelligent beings, capable of perceiving the laws of the universe, and therefore at once manifesting and glorifying the power, the wisdom, and the goodness of the infinite and incomprehensible Centre of all Existence? Are these rolling worlds like ours in all things else, and yet inferior to ours in that? Or is it not probable, that they are the habitations of classes of creatures excelling us as far in intellectual power, as some of those planets exceed ours in magnitude and apparent importance. (18)
The excitement over telescopic discoveries and their implications for other cultural arenas, such as theology, was not shared by everyone, however. To some, telescopes were aggressive instruments since they dared to intrude upon the heavens. What follows are the views of three English poets, two of whom challenged the legitimacy of the telescope and a third who accepted its authority. Other Romantic-era writers weighed in on the value of telescopes, but, through these three poets, one gets a glimpse of how Herschel’s giant instrument put astronomy front and center in public consciousness and stirred up a debate over the merits of such scientific apparatuses.
In 1797 and 1798, William and Dorothy Wordsworth and Samuel Coleridge viewed the night skies regularly in Nether Stowey, as Thomas Owens has described. Wordsworth’s interest in science has been well documented, but it is evident from the references to telescopes in his writing that he regarded them with a measure of wariness. Though, as Owens points out, Wordsworth refers to a telescope in his 1798 poem “The Thorn,” the narrator indicates he uses the instrument for lateral rather than vertical viewing: “For one day with my telescope, / To view the ocean wide and bright, / . . . / I climbed the mountain’s height . . .” (170-74). Wordsworth’s decision not to introduce the telescope in “The Thorn” as a device for stargazing is somewhat surprising in light of the history of the poem, recounted by Owens:
Inspiration for “The Thorn” came from issues of the Monthly Magazine of February to December, 1796, that were amongst the first consignment of books that Wordsworth received at Alfoxden from James Losh, and which included important source material for the poem in the form of William Taylor’s translations of poems by Bürger. . . . these papers also contained an enormous double-page illustration of Herschel’s forty-foot telescope, complete with a lengthy description of its operative and magnifying capacity. . . . (27)
The two-page spread of Herschel’s forty-footer either made little impression on Wordsworth, or the poet conveyed his tacit rejection of it by the limited use of the telescope in “The Thorn.”
In his 1806 poem “Star-Gazers,” Wordsworth is direct in communicating his skepticism of telescopes as astronomical instruments. His portrayal of a public viewing of the night sky as a theatrical event—“The Show-man chooses well his place; ‘tis Leicester’s busy Square”—reduces the telescope to a prop that turns the heavens into a spectacle (5). Though he describes everyone in the crowd as waiting impatiently to look through the instrument, the poem concludes in melancholy. With a sentiment that years later would be echoed by Walt Whitman’s Learn’d Astronomer, Wordsworth intimates that the atomizing of the cosmos through science depletes it of its soul:
Whatever be the cause, ’tis sure that they who pry and pore
Seem to meet with little gain, seem less happy than before:
One after One they take their turn, nor have I one espied
That doth not slackly go away, as if dissatisfied. (29-32)
In a note about the poem, Wordsworth writes that the event was “Observed by me in Leicester-square, as here described” (Selected Poems and Prefaces 568). Since at the viewing he chose to observe the observers rather than the stars, the stars were twice mediated for him. There is no hint in the poem that Wordsworth sees the irony in which he has implicated himself: by reading the observers’ faces, which function as a reflecting lens, he, in effect, mimics the operation of the telescope.
In Book II of The Excursion, a telescope makes a cameo appearance, but it appears only to disappear. Wordsworth’s description of the unkempt interior of a cottage includes a “shattered telescope, together linked / By cobwebs,” a visual prediction of what he evidently saw as its inevitable obsolescence (667-68). Unencumbered by astronomical devices, Wordsworth holds fast to conventional views of the universe throughout most of his poetry. In “If Thou Indeed Derive Thy Light from Heaven,” for example, he declares the stars to be “the undying offspring of one Sire,” implying that cosmic phenomena have a divine source and are as immortal as their Maker (14). The poem was first published in 1827, but the above line was one of several lines added to the poem late in his career in 1837 (Selected Poems and Prefaces 576).
Marilyn Gaull has argued that Herschel did exert some influence on Wordsworth, evidenced in a change he made to The Prelude in 1839. The amended version of a passage in Book 6 describes the effect “geometric science” had on him:
. . . I [did] meditate
On the relation those abstractions bear
To Nature’s laws, and by what process led,
Those immaterial agents bowed their heads
Duly to serve the mind of earth-born man;
From star to star, from kindred sphere to sphere,
From system on to system without end. (122-28)
Gaull’s observation that Wordsworth “contain[s] Herschel’s universe in Newton’s laws” is astute (40). To be precise, however, the poet contains one aspect of Herschel’s universe—deep space. Though Wordsworth portrays cosmic phenomena as existing “without end,” the lyrical cadence and harmonious description of the cosmos suggest he sidesteps Herschel’s more radical claim that the cosmos is in a state of dissolution. The influence of Herschel on Wordsworth is further mitigated in the poem by the context in which stars, spheres, and systems are mentioned: the narrator is meditating, not stargazing. Moreover, his meditation is inspired by mathematics, not a telescope, a point he amplifies in the passage that follows: geometric science, he argues, provided him with “A type, for finite natures, of the one / Supreme Existence, the surpassing life / Which – to the boundaries of space and time, / . . . [is] / Superior, and incapable of change . . .” (6.133-37). Wordsworth’s sublime description of the ability of math to enlarge one’s perspective suggests that it fulfilled for him the function of the telescope, rendering mechanical instruments, including Herschel’s forty-footer, unnecessary.
The dismissal of the telescopic probing of the heavens by one of England’s preeminent thinkers gives one pause. The telescopes Herschel designed and built were hardly a sideshow; they altered dramatically the stubbornly held view of the universe as an enclosed dome with stationary stars and revealed it to be unbounded space with stars in flux. Wordsworth’s resistance to such instruments was, no doubt, strengthened by his seeing more clearly than most the threat of encroaching technology, which would redefine what it meant to be human. He was not, however, the only poet to prosecute the cultural value of the telescope. William Blake also rejected it on epistemological grounds though, unlike Wordsworth, he did not have a sentimental view of the naked eye.
To Blake, seeing was an imaginative act, as he concisely states in a letter: “Every body does not see alike” (702). Though today such an observation seems obvious to the point of being unworthy of mention, for nearly two centuries, telescopes, along with microscopes, had literalized the theory that perception is mechanical and uniform, a view of perception that, to Blake, was antagonistic to both optical and imaginative vision. In his annotations to Thornton’s translation of The Lord’s Prayer, Blake makes a snide reference to “a Lawful Heaven seen thro a Lawful Telescope,” insinuating that the telescope is part of a government conspiracy to regulate perception (668). He further goes on to parody the well-known opening lines of The Lord’s Prayer: “Our Father Augustus Caesar who art in these thy <Substantial Astronomical Telescopic> Heavens” (669). Blake’s hyperbolic mockery sounds comical, but underlying those remarks is a serious concern. During the Romantic era, astronomy became a public enterprise as more telescopes were built and made accessible to people in all walks of life. From Blake’s perspective, this democratizing of science had a downside, however: it implanted a mechanical eye in people across Europe.
In his poem Milton, Blake suggests that telescopes shrink the universe of the viewer:
The Sky is an immortal Tent built by the Sons of Los
And every Space that a Man views around his dwelling-place:
Standing on his own roof, or in his garden on a mount
Of twenty-five cubits in height, such space is his Universe. (29:4-7)
Blake’s description of the dwelling-place from which a man observes the sky conveniently evokes an image of the Herschels’ viewing sites. The roof of Caroline’s cottage at Slough was a viewing platform from which she conducted sweeps of the sky with a smaller instrument while the main observatory with the giant telescope was situated nearby in a garden. But Blake’s reference to Herschel is even more acute in the above passage. To peer through the forty-footer, an observer had to climb a flight of stairs to a gallery and then scale a ladder to the observing-platform. Though the distance from the ground to the observing-platform was shorter than what Blake describes in the poem, Herschel’s giant telescope (whose tube, to be exact, was 39’, 4”) was approximately twenty-six cubits in length. Blake’s math is even more precise when one considers a detail Herschel provides in his description of the instrument: “the observer is elevated 30 or 40 feet above the assistant [who records the measurements]” (“Description” 365, 385). 25 cubits is the rounded-off average of 30 feet and 40 feet.
Blake further depicts in Milton the malleability of the universe, which, he argues, conforms to the imagination of the person who views it: “The Starry heavens reach no further but here bend and set / On all sides & the two Poles turn on their valves of gold: / And if [the observer] move his dwelling-place, his heavens also move” (29:10-12). Since the heavens move with the observer, we might transpose one of Blake’s proverbs from The Marriage of Heaven and Hell and conclude that, where man is not, the cosmos is barren (9.68). Blake’s portrayal of a person’s perception of the universe concludes with a direct critique of mechanical visual aids:
As to that false appearance which appears to the reasoner,
As of a Globe rolling thro Voidness, it is a delusion of Ulro
The Microscope knows not of this nor the Telescope. they [sic] alter
The ratio of the Spectators Organs but leave Objects untouchd. (29.15-18)
The unnamed “reasoner,” is quite likely Herschel, who, when looking through a telescope, saw stars as “Globe[s] rolling thro Voidness.” Blake rejects the claim that the telescope has the capacity to extend vision and portrays it as an instrument that does just the opposite. In his words, it contributes to the delusion of “Ulro,” his term for the lowest level of perception. In an article on Blake and scientific objects, Mark Lussier remarks on the above passage, “Instruments simply alter the ratio of ‘Organs’ yet impact not ‘Objects’ thereby widening the gap between imaginative and sensory experience . . .” (122). By altering the “ratio of the Spectators Organs,” which is what happens when you look through any configuration of convex or concave mirrors, the telescope, from a Blakean perspective, does not enhance vision; it merely creates an alternative distortion. Blake’s argument in opposition to the telescope is compelling: adding a filter to the human eye, which is already an instrument of mediation, will not lead to unmediated perception.
Ironically, Blake’s observation that “Every body does not see alike” resonates with a statement made by Herschel seventeen years earlier:
Seeing is in some respect an art, which must be learnt. To make a person see with such a power is nearly the same as if I were asked to make him play one of Handel’s fugues upon the organ. Many a night have I been practising to see, and it would be strange if one did not acquire a certain dexterity by such constant practice. (qtd. in Lubbock 101)
Anna Henchman has noted, “The act of ‘practicing to see’ is not available to a telescope; it must be performed by a human agent. Only with the help of an experienced eye and a synthesizing mind can the visual information gathered through a telescope be properly understood; the expertise of the scientist who learns to see makes this material intelligible” (24). The interplay between the viewer and the telescope is particularly interesting in light of Herschel’s intimation that the telescope performs an imaginative role for viewers. After noting the dates when he discovered two of Saturn’s satellites with the forty-footer, he admits, “It is true that both satellites are within reach of the 20-feet telescope,” and then states, “but it should be remembered, that when an object is once discovered by a superior power, an inferior one will suffice to see it afterwards” (“On the Power” 77). Though Herschel and Blake diverge on the value of the telescope, they both reject the idea that seeing is passive, mechanical, and uniform among all people and argue that it engages the imagination.
Any affinity between Herschel and Blake, empiricist and metaphysician, is counterintuitive and, therefore, all the more intriguing. Along with conceiving of seeing in a way that would later be associated with Blake, Herschel (like Blake) participates in both invention and execution, constructing the medium through which he sees the universe. In a letter to her nephew, written in 1786, Caroline Herschel provides a close-up of the building of the technological behemoth, revealing how intimately her brother was involved in the execution of his design:
It would be impossible for me, if it were required, to give a regular account of all that passed around me in the lapse of the following two years, for they were spent in a perfect chaos of business. The garden and workrooms were swarming with labourers and workmen, smiths and carpenters going to and from between the forge and the forty-foot machinery, and I ought not to forget that there is not one screw-bolt about the whole apparatus but what was fixed under the immediate eye of my brother. I have seen him lie stretched many an hour in a burning sun, across the top beam whilst the iron work for the various motions was being fixed.
At one time no less than twenty-four men (twelve and twelve relieving each other) kept polishing day and night; my brother, of course, never leaving them all the while, taking his food without allowing himself time to sit down to table. (Mary Herschel 73)
M. Pictet, a professor of astronomy from Geneva who visited Herschel in 1786, later marveled at his dual capacities: “Herschel has shown himself as great a Mechanician as a consummate Astronomer . . .” (qtd. in Lubbock 159). In an article published the following year, he provides a first-hand account of the polishing of the mirror of the forty-footer:
It follows that besides the most perfect polish the mirror of the telescope must have a parabolic figure. The work, as directed by Herschel, to achieve these two conditions, would make a subject for a picture. In the middle of his workshop there rises a sort of altar; a massive structure terminating in a convex surface on which the mirror to be polished is to rest and to be figured by rubbing. To do this the mirror is encased in a sort of twelve-sided frame, out of which protrude as many handles which are held by twelve men. . . .
The mirror is moved slowly on the mould, for several hours at a time and in certain directions, which by pressing more on certain parts of the surface than on others, tends to produce the parabolic figure.
It is then removed on a truck and carried to the tube, into which it is lowered by a machine expressly contrived for the purpose. This labour is repeated every day for a considerable time and by the observations he makes at night, Herschel judges how nearly the mirror is approaching the standard he desires. (qtd. in Lubbock 158)
Pictet’s portrayal of the work scene as an altar, as well as his note that the mirror was polished by twelve men who strived to attain the high standard set by their master, is suggestive. Herschel was revered by those close to him. As an unusually skilled seer, he was in their eyes a prophet of sorts in the biblical sense of the word. If, as Herschel suggests, seeing is indeed an art, then science, an enterprise that rests heavily on observation, is not only a religion (as Herschel’s followers and admirers conveyed by their devotion to him) but also an art, a view that Blake himself held.
Blake’s shortsightedness in recognizing the common ground he shared with Herschel was inevitable in light of his rejection of empirical science, both in theory and in practice. Even if Blake had had sufficient resources, it is improbable he would have joined the stream of visitors who visited Slough to look through the forty-footer. Those curious celestial sightseers, however, did include Lord Byron, and the effect on him was profound, as he indicates in an 1813 letter: “the comparative insignificance of ourselves & our world when placed in competition with the mighty whole of which it is an atom . . . first led me to imagine that our pretensions to eternity might be over-rated” (Letters and Journals 3: 64).
Byron’s response was hardly unique. The telescopic view of the cosmos in the nineteenth century was a jolt to an earth-centric perspective of the universe. When Herschel sighted Uranus, he gained instant celebrity among the public, as well as patronage from the king, who, as noted earlier, subsidized the building of the large telescope. Notwithstanding the enthusiastic reaction, the discovery of Uranus did not change the course of science but simply identified another cosmic body on the well-established celestial map. A few years later, however, Herschel made a discovery that all but shredded that map. Through his telescopic viewing, he recognized that some nebulae originate in the decay of other nebulae, and, as mentioned earlier, he argued that the cosmos is always in a state of dissolution and reconstitution (Scientific Papers 1: 252). In one of his papers, he zeroes in on our own galaxy and offers unsettling news: “it is evident that the milky way must be finally broken up, and cease to be a stratum of scattered stars” (Scientific Papers 2: 540). He further argues, “the breaking up of the parts of the milky way affords a proof that it cannot last for ever [and] it equally bears witness that its past duration cannot be admitted to be infinite” (Scientific Papers 2: 541). For an astronomer to announce in the late eighteenth century that our own galaxy was gradually dissolving was startling. Herschel’s high-powered telescopes, jutting into the air, pierced the calm and stable dome that had sheltered the thinking of lay people and many astronomers from time immemorial.
The evidence that Byron’s view of the cosmos was agitated by Herschel’s forty-footer is overt in his poem “Darkness,” but it can also be detected in Manfred, in which he dramatizes the cultural ramifications of Herschel’s theory. Early in the poem, Manfred invokes the “Spirits of earth and air,” declaring that they are subject to “a power . . . / Which had its birth-place in a star condemn’d, / The burning wreck of a demolish’d world, / A wandering hell in the eternal space . . .” (1.1.41-46). The seventh spirit who responds to Manfred’s call provides a backstory that suggests Manfred has the same trajectory as a stray comet:
The star which rules thy destiny
Was ruled, ere earth began, by me:
It was a world as fresh and fair
As e’er revolved round sun in air;
Its course was free and regular,
Space bosom’d not a lovelier star.
The hour arrived—and it became
A wandering mass of shapeless flame,
A pathless comet, and a curse,
The menace of the universe;
Still rolling on with innate force,
Without a sphere, without a course,
A bright deformity on high,
The monster of the upper sky!
And thou! beneath its influence born. . . . (1.1.110-24)
From Byron’s poetry, especially Manfred, it is tempting to consider that the legacy of Herschel’s telescopes (including the forty-footer)—namely, that we live in an unfathomable cosmos in a state of dissolution—may have exacerbated his mood swings between euphoria and despair. The spirit’s associating Manfred with the star that rules his destiny, a star that initially was a “fresh and fair” world but then turned into “A wandering mass of shapeless flame,” further suggests that Manfred, and by extension Byron, is bipolar because as a part of the cosmos he is also bi-solar.
Byron’s tersest description of the inescapable link between the quantum and the cosmic appears in “Heaven and Earth” where he writes of a “wandering star, which shoots through the abyss, / Whose tenants dying, while their world is falling, / Share the dim destiny of clay” (1.1.87-89). In his poem “The Dream,” Byron alludes to the role of the telescope in exposing this demise. By presenting the nature of truth through the metaphor of a telescope, he intimates the veracity of the instrument: “the telescope of truth . . . / . . . strips the distance of its phantasies, / And brings life near in utter nakedness, / Making the cold reality too real!” (180-83). He abandons the metaphor in the final stanza of “The Vision of Judgment” and states directly, “The telescope . . . / . . . kept my optics free from all delusion” (842-43). It must have come as no small surprise to Byron, who was openly dismissive of religion, to find that the telescope, which he revered for its undistorted view of the universe, had awakened in him a deeper consciousness. In a note, he writes: “The Night is also a religious concern—and even more so—when I viewed the Moon and Stars through Herschell’s [sic] telescope—and saw that they were worlds” (Letters and Journals 9: 46).
Discovering other worlds in the universe was, indeed, a religious concern. Some nineteenth-century astronomers argued that the expanded universe revealed by the telescope did not signal the obsolescence of religion but demanded a more expansive view of God. Thomas Dick (the Scottish minister and science teacher mentioned earlier) muses that it is “highly probable . . . that that portion of the universe which lies within the range of telescopic vision, and which contains so many millions of splendid suns and systems, is but a small part of the universal kingdom of Jehovah, compared with what lies beyond the utmost boundaries of human vision . . .” (284). For many, the telescope had a purpose that exceeded its empirical function: it liberated the imagination, enabling them to conceive of God in more expansive terms. Margaret Bryan, for example, declares, “most probably our system is composed of not one hundred-thousandth part of the whole creation; for, in the most crowded parts of the milky way, [Herschel] has seen 588 stars pass through the field of his large telescope in the space of one minute” (175). Earlier in her book she affirms, “God has created nothing in vain,” and later reasons that fixed stars, which have no use to Earth or other planets in our solar system, must serve other worlds (126, 169).
Herschel’s giant telescope, which caught the attention of scientists and lay people alike, had an aura even before its completion. During the construction of the telescope, the forty-foot tube, which was 15-1/3 feet in diameter, rested on the grass for a time. Caroline recalls in an 1840 letter to a niece: “Perhaps you may have heard that [on one occasion] in the early part of its existence, ‘God save the King’ was sung in it by the whole company, who got up from dinner and went into the tube . . .” (Mary Herschel 308). In a postscript to the letter, she writes: “Before the optical parts were finished, many visitors had the curiosity to walk through it, among the rest King George III., and the Archbishop of Canterbury, following the King, and finding it difficult to proceed, the King turned to give him the hand, saying, ‘Come, my Lord Bishop, I will show you the way to Heaven!’” (309). The king’s rapture was echoed by Herschel after the telescope was in use. In his paper “On the Power of Penetrating into Space by Telescopes,” he writes:
I remember, that after a considerable sweep with the 40 feet instrument, the appearance of Sirius announced itself, at a great distance, like the dawn of the morning, and came on by degrees, increasing in brightness, till this brilliant star at last entered the field of view of the telescope, with all the splendour of the rising sun, and forced me to take the eye from that beautiful sight. (54)
Though many swooned over the forty-footer, Herschel was not immune to criticism. In the January 1803 issue of the Edinburgh Review, a reviewer of his recently published papers writes: “Dr Herschel’s passion for coining words and idioms, has often struck us as a weakness wholly unworthy of him. The invention of a name is but a poor achievement for him who has discovered worlds. Why, for instance, do we hear him talking of the space-penetrating power of his instrument—a compound epithet and metaphor which he ought to have left to the poets, who, in some further ages, shall acquire glory by celebrating his name?” (qtd. in Lubbock 282). The reviewer’s concern with Herschel’s rhetoric is odd, but it does anticipate the legacy of the giant telescope. In step with the forty-footer, which penetrated space, Herschel’s coined phrase penetrated the public discourse and expanded the cultural imagination. A few years after the commentary in the Edinburgh Review, a harsh critique of the telescope came from the very astronomer who had proposed in 1781 that the newly discovered planet be named “Herschel.” Lalande, in his annual record of astronomical events for 1806, disparaged the forty-footer (Lubbock 313). Though Herschel’s brother Dietrich wrote a rebuttal, he was unable to point to any significant discoveries beyond the sighting of one of Saturn’s satellites (Lubbock 313-14).
In truth, the forty-footer did not deliver to the extent that Herschel himself had hoped it would. To perform a sweep of the skies required the telescope be moved, which was cumbersome and time-consuming to the point of hindering the sweeps. Several other factors, enumerated by Bennett, contributed to the limited value of the forty-foot instrument:
The limited zone [Herschel] could cover with the large instrument made a survey of the heavens quite impossible. . . . His other difficulties concerned the speculum. The thick mirror tarnished very quickly, a fact which is usually attributed to the large proportion of copper he used to increase its strength. Because of its size, it adjusted only slowly to changes in the surrounding temperature and so attracted much condensation, which accelerated the tarnishing. (92)
Along with the practical difficulties of operating the behemoth instrument and the tedium of its maintenance, it posed another problem: on at least one occasion it proved to be nearly lethal. In an 1807 diary entry, Caroline writes: “In taking the forty-foot mirror out of the tube, the beam to which the tackle is fixed broke in the middle, but fortunately not before it was nearly lowered into its carriage, &c., &c. Both my brothers had a narrow escape of being crushed to death” (Mary Herschel 113). But the inability of the forty-footer to fulfill the high expectations it inspired was largely due to Herschel’s own discoveries. Herschel had assumed a large telescope would be able to resolve nebulae into star clusters, but, as one biographer notes, “a year or so after its completion, Herschel recognized that many intractable nebulae are in fact gaseous and therefore, by their very nature, irresolvable” (Armitage 46).
In spite of its limitations as an instrument to advance understanding of the universe, as the largest telescope in the world, the forty-footer became an indelible image of human conquest. Oberamtmann Schroeter, an amateur German astronomer with whom Herschel corresponded for several years, articulated the symbolic value of the giant telescope in response to Herschel’s “Description of a Forty-feet Telescope”:
Your forty-foot Reflector is in truth a monument of astronomical and mechanical ingenuity. It shows how far human perseverance and zeal for the sublimest science can attain; though I am quite of your opinion that wide apertures do interfere with distinctness and that size renders the use of very large instruments more difficult and limited, yet in special cases, where increase of light is called for, they are of the greatest service, as your many important discoveries abundantly prove. (qtd. in Lubbock 215)
Late in his life Herschel, who was compelled to recognize the constraints of the giant instrument, advised his son John never to rebuild it (Bennett 101). This marked a precipitous change in his thinking since, in his 1795 description of the forty-footer, he lays out the nuts and bolts of how the giant instrument was constructed, suggesting that in the early days he saw the forty-footer as a model for future telescopes. As it happened, twenty years after Herschel published his manual on the forty-footer, the giant instrument was retired (Lubbock 342). Herschel, however, held onto the romance of his mechanical child. In less than a month before his passing, Caroline visited her brother, who was in very poor health. She notes in a diary entry that “as soon as he saw me I was sent to the Library to fetch one of his last papers and a Plate of the 40 feet telescope” (qtd. in Lubbock 360).
As a symbol, the giant telescope literally became imprinted in English culture when it was adopted as the official seal of the Royal Astronomical Society, an honor it retains to this day. As an instrument, it did not fare so well. Though Wordsworth underestimated the cultural power of the telescope, his image in “The Excursion” of one covered with cobwebs was prescient. In 1839, seventeen years after William Herschel’s death and nearly a quarter of a century after its final use, the Herschel family dismantled the forty-footer in a formal ceremony. William’s son John composed a requiem for the occasion, and, in what must have been a surreal moment, they sang the requiem from inside the giant tube (Lubbock 343). Free from the quotidian realm, their voices echoing back to themselves, the family could well have been singing a requiem to English Romanticism since only two years earlier, Victoria had begun her reign.
If one (fittingly) telescopes the lifespan of Herschel’s giant instrument, its historical moment is arresting. Six and a half weeks after the Bastille was razed to the ground, the forty-footer was raised to the heavens. If Herschel had had a stronger sense of history, he might have delayed the inauguration of his imposing instrument by a few months. (1789 would not be remembered as the year of the giant telescope.) The respective dates of the appearance and demise of the forty-footer, however, fortuitously frame the Romantic era. The heady, unbounded imagination with which the period has often been associated could hardly have a better symbol.
In that regard, one more dimension of the telescope’s cultural reach deserves mention. Though John Keats does not refer to Herschel’s forty-footer, he does allude to his discovery of Uranus in his sonnet “On First Looking into Chapman’s Homer.” In a description of the exhilaration of navigating Chapman’s translation of Homer, Keats writes:
Then felt I like some watcher of the skies
When a new planet swims into his ken;
Or like stout Cortez when with eagle eyes
He star’d at the Pacific — and all his men
Look’d at each other with a wild surmise —
Silent, upon a peak in Darien. (9-14)
Keats’s linking of cosmic exploration to the conquest of other lands exemplifies how in the European imagination, the telescope, aimed vertically at the cosmic unknown, was repositioned and directed horizontally into unknown regions of the earth. To Keats and his contemporaries, the darker side of conquest was often overlooked, however, and in 1811, when Herschel’s forty-footer was still in active use, John Bonnycastle, a professor of mathematics, offered a sublime defense for such cosmic instruments, intimating their ability to transform humanity. His words cogently describe the telescope of the imagination, an ideal to which Herschel’s colossal instrument could only aspire: “The progress of reason, and the powers of the imagination, are almost without bounds; and if we add to these, the invention of instruments, which are so many new organs of power and perception, man becomes a being worthy of admiration. . . . [He] creates to himself a new being . . .” (242).
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published July 2012
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—. Selected Poems and Prefaces. Ed. Jack Stillinger. Boston: Houghton Mifflin, 1965. Print.
—. “Star-Gazers.” Selected Poems and Prefaces. Ed. Jack Stillinger. Boston: Houghton Mifflin, 1965. 371-72. Print.
—. “The Thorn.” Selected Poems and Prefaces. Ed. Jack Stillinger. Boston: Houghton Mifflin, 1965. 70-76. Print.
Dick notes, “The lustre and brilliancy which the fixed stars exhibit when viewed with telescopes of large apertures and powers is exceedingly striking. Sir W. Herschel seldom looked at the larger stars through his forty-feet telescope, because their blaze was injurious to his sight” (230).
Among the many scholars who have pursued Wordsworth’s forays into science is Catherine Ross, who has documented the professional rivalry between Wordsworth and Humphry Davy in her essay “‘Twin Labourers and Heirs of the Same Hopes.’”
I have preserved Blake’s unorthodox spelling and punctuation, and David Erdman’s symbols. Erdman explains, “Angle brackets <thus> enclose words or letters written to replace deletions, or as additions, not including words written immediately following and in the same ink or pencil as deleted matter” (xxiv).
In a letter of 1795, Blake scorns “the pretended Philosophy which teaches that Execution is the power of One & Invention of Another” (699). He goes on to say, “he who can Invent can Execute,” and, indeed, in his illuminated poetry he performs both functions.
The writer of I Samuel notes, “[For] he that is now called a Prophet was beforetime called a Seer” (King James Bible 9.9)—a definition of “prophet,” incidentally, that Blake adopts. In his “Annotations to An Apology for the Bible,” Blake notes, “a Prophet is a Seer not an Arbitrary Dictator” (617).
In my article “A Wrinkle in Space,” I argue that Blake presents science as the art of improvisation (16).
Though Keats received a copy of John Bonnycastle’s Introduction to Astronomy as a prize, Nicholas Roe has argued, “It seems unlikely that the desiccated prose of [Bonnycastle’s book] should have quickened the marvellous vision of sidereal motion in Keats’s’ poem. More plausible, I think, is the possibility that Keats’s imagination was feeding on the memory of discoveries made at Enfield while playing in the ‘living orrery’ or gazing at a planet’s bright image through the school telescope” (37). Though Keats’s early adventures in astronomy no doubt sparked an interest in cosmic exploration, Bonnycastle’s book includes some sublime passages, one of which I quote in this essay, and he may deserve some credit for firing up Keats’s imagination. | 0.836809 | 3.365489 |
On the evening of September 8, 2016, weather permitting – and all systems go – the OSIRIS-REx mission will be launched from Cape Canaveral, Florida into outer space to play a cosmic game of tag with an asteroid named Bennu to collect a minimum of 60 grams (2 ounces) and up to 4.4 pounds of material, and return a capsule filled with what Carl Sagan might have referred to as “star stuff,” to the Utah desert in 2023. The samples will then be delivered to the Johnson Space Center in Houston, Texas, and some sent to JAXA, the Japanese Space Agency. Some of the samples will be studied in the first two years after return, but most will be preserved for study by future generations. So, in a mere nine years, this unique mission will help scientists in their efforts to solve more mysteries of the universe – and likely lead to more questions as well.
Bennu is a Near Earth Object (NEO) with a 500 meter diameter, formed about 4.5 billion years ago. OSIRIS-REx is an SUV sized spacecraft. Bennu was selected to be visited because it is accessible and has a convenient orbit for a sample return mission to Earth, is a useful size for study, and is also rich in carbon, so there is a greater chance for the discovery of organic materials and water-rich materials, such as clay. In other words, the building blocks of life on Earth may be discovered on Bennu!
So, what has this to do with herons, a favorite bird of Gene Stratton-Porter? Several years ago a contest was held to name the asteroid, formerly known as 1999R236. Among the 8000 or so entries was one from a third grader who felt the spacecraft resembled a heron in flight, when its long collection arm is outstretched. Bennu was an ancient Egyptian diety connected with the sun, creation, and rebirth – and often depicted as a heron, so the student felt the ancient name appropriate. The mission itself, OSIRIS- REx includes the name of another Eqyptian figure, Osiris, said to have brought knowledge of agriculture – and hence life, to the Nile Delta region. Just in case you're wondering, the acronym OSIRIS-REx stands for Origins Spectral Interpretation Resource Identification Security Regolith Explorer! OSIRIS-REx carries an impressive suite of scientific instruments – cameras, spectrometers, and an altimeter – to collect images, study the chemical composition of Bennu, and search for pre- biotic and biotic material. The mission is part of NASA's New Frontiers Initiative, which includes the New Horizons mission to Pluto and the Juno mission to Jupiter.
Objectives of OSIRIS-REx include understanding the formation and working of our solar system, and also a better understanding of Near Earth Objects and their hazards. The Yarkovsky Effect – in which solar energy is absorbed and released by asteroids, effecting their orbits – will also be studied as part of the mission. Scientists estimate there's a 1 in 2700 chance of Bennu impacting Earth...in the 22 nd century. So don't worry! But consider following the mission!
For more information, go to asteroidmission.org. You can watch the launch on NASA TV at NASA.gov! For more information on the Great Blue Heron of Indiana, check out Alexandra Forsythe's 7/18/2016 posting on this blog.
Adrienne Provenzano is a member of the Friends of the Limberlost and the Indiana Astronomical Society and is also a NASA Solar System Ambassador - a program of NASA JPL-CalTech. | 0.901681 | 3.496803 |
October 26, 2015 – Using a new process in planetary formation modeling, where planets grow from tiny bodies called “pebbles,” Southwest Research Institute scientists can explain why Mars is so much smaller than Earth. This same process also explains the rapid formation of the gas giants Jupiter and Saturn, as reported earlier this year.
“This numerical simulation actually reproduces the structure of the inner solar system, with Earth, Venus, and a smaller Mars,” said Hal Levison, an Institute scientist at the SwRI Planetary Science Directorate. He is the first author of a new paper published in the Proceedings of the National Academy of Sciences of the United States (PNAS) Early Edition.
The fact that Mars has only 10 percent of the mass of the Earth has been a long-standing puzzle for solar system theorists. In the standard model of planet formation, similarly sized objects accumulate and assimilate through a process called accretion; rocks incorporated other rocks, creating mountains; then mountains merged to form city-size objects, and so on. While typical accretion models generate good analogs to Earth and Venus, they predict that Mars should be of similar-size, or even larger than Earth. Additionally, these models also overestimate the overall mass of the asteroid belt.
“Understanding why Mars is smaller than expected has been a major problem that has frustrated our modeling efforts for several decades,” said Levison. “Here, we have a solution that arises directly from the planet formation process itself.”
New calculations by Levison and co-authors Katherine Kretke, Kevin Walsh and Bill Bottke, all of SwRI’s Planetary Science Directorate follow the growth and evolution of a system of planets. They demonstrate that the structure of the inner solar system is actually the natural outcome of a new mode of planetary growth known as Viscously Stirred Pebble Accretion (VSPA). With VSPA, dust readily grows to “pebbles” — objects a few inches in diameter — some of which gravitationally collapse to form asteroid-sized objects. Under the right conditions, these primordial asteroids can efficiently feed on the remaining pebbles, as aerodynamic drag pulls pebbles into orbit, where they spiral down and fuse with the growing planetary body. This allows certain asteroids to become planet-sized over relatively short time scales.
However, these new models find that not all of the primordial asteroids are equally well-positioned to accrete pebbles and grow. For example, an object the size of Ceres (about 600 miles across), which is the largest asteroid in the asteroid belt, would have grown very quickly near the current location of the Earth. But it would not have been able to grow effectively near the current location of Mars, or beyond, because aerodynamic drag is too weak for pebble capture to occur.
“This means that very few pebbles collide with objects near the current location of Mars. That provides a natural explanation for why it is so small,” said Kretke. “Similarly, even fewer hit objects in the asteroid belt, keeping its net mass small as well. The only place that growth was efficient was near the current location of Earth and Venus.”
“This model has huge implications for the history of the asteroid belt,” said Bottke. Previous models have predicted that the belt originally contained a couple of Earth-masses’ worth of material, meaning that planets began to grow there. The new model predicts that the asteroid belt never contained much mass in bodies like the currently observed asteroids.
“This presents the planetary science community with a testable prediction between this model and previous models that can be explored using data from meteorites, remote sensing, and spacecraft missions,” said Bottke.
This work complements the recent study published in Nature by Levison, Kretke, and Martin Duncan (Queen’s University), which demonstrated that pebbles can form the cores of the giant planets and explain the structure of the outer solar system. Combined, the two works present the means to produce the entire solar system from a single, unifying process.
“As far as I know, this is the first model to reproduce the structure of the solar system — Earth and Venus, a small Mars, a low-mass asteroid belt, two gas giants, two ice giants (Uranus and Neptune), and a pristine Kuiper Belt,” said Levison.
The article, “Growing the Terrestrial Planets from the Gradual Accumulation of Sub-meter Sized Objects,” is published online by PNAS. Authors H.F. Levison, K.A. Kretke, K. Walsh, and W. Bottke are all of Southwest Research Institute’s Space Science and Engineering Division.
This work was supported by the NASA Solar System Exploration Research Virtual Institute (SSERVI) through institute grant number NNA14AB03A. | 0.888942 | 3.919139 |
Saturn’s icy moon Enceladus, already known for spitting plumes of water into space, just got even more interesting. New gravity readings suggest it hosts a subsurface sea the size of Lake Superior at its south pole – and that this liquid water is in direct contact with the moon’s core, which is rich in nutrients. Both findings boost hopes that the sea hosts life.
The result comes hot on the heels of the discovery late last year that a second icy moon – Europa, which orbits Jupiter – also spews plumes of water. Both moons are now among the hottest prospects in the solar system for finding alien life – if only a suitable mission could be arranged.
NASA’s Cassini orbiter first spotted spectacular plumes at Enceladus’s south pole in 2005, shortly after arriving at Saturn. The plumes shoot into space at supersonic speeds, feeding one of Saturn’s famous rings, and are known to contain both salts and organic compounds. They make an attractive target for exploration as a craft could potentially fly through them to take samples, much simpler than landing on a moon.
Most astronomers thought that the plumes force their way out through cracks in an icy crust sitting over a sea of liquid water. But until now, no one knew how deep that sea went.
Luciano Iess at the Sapienza University of Rome in Italy and his colleagues used radar on Earth to track Cassini on three separate fly-bys of Enceladus, and watched how the spacecraft was accelerated by the moon’s gravity. This allowed them to map the distribution of mass in the moon’s interior.
Salty ice grains
They found that Enceladus has a rocky core and an icy crust. “Before, we knew almost nothing about the core beyond its likely existence. Now we know roughly how big it is, and also that it has a surprisingly low density,” says team member Francis Nimmo at the University of California, Santa Cruz. “That might be due to open fractures, or low-density hydrated minerals like clays. Either answer suggests that the rock has been in substantial contact with water, for instance allowing minerals to dissolve, and explaining the salty ice grains we see coming out of the surface.”
The team also found that the southern hemisphere has a stronger gravitational pull than its topography would suggest. That could be explained by a localised sea, sitting beneath 35 kilometres of ice and up to 8 kilometres deep. It would contain about as much water as Lake Superior in North America.
Hosting an ocean in contact with rocks boosts the chances that Enceladus hosts life, because the rocks could leach elements like potassium, sulphur and phosphorus, vital for life, into the water.
“One of the alternative models was just little pockets of water driving the jets, and in that model you wouldn’t have much in the way of life because it wouldn’t be in contact with the rock,” says team member Jonathan Lunine at Cornell University in Ithaca, New York. “This gravity map hinting at a much larger ocean is a more favourable model for having some sort of life in Enceladus’s interior.”
If there might be life there, when can we go? Cassini winds down in three years and there are no firm plans for future craft to return to Saturn. However, Cassini team member Carolyn Porco at the Space Science Institute in Boulder, Colorado, has written a paper (soon to appear in the journal Astrobiology) arguing for a mission to collect samples from Enceladus and return them to Earth. She says the new results bode well for such an effort. “The next mission there can immediately get down to the business of searching for signs of life or its precursor chemistry. It’s a big juncture!”
The subsurface-sea idea is just the simplest possible interpretation of the gravity data, cautions William McKinnon at Washington University in St Louis, who was not involved in the work. If the sea exists, there is the question of how long it has been liquid and whether it might eventually freeze – or spray itself away. The former is important as life would require the sustained presence of water to gain a toehold.
As for the possibility of the sea freezing completely, it is true that Enceladus is losing a lot of heat to space, but astronomers suspect that this is an unusual episode. “We are looking at Enceladus at a wonderful special time, where it’s very active and there’s a lot of heat,” McKinnon says.
Could the plumes deplete the sea completely? Probably not. Even if they continue at the current rate, the moon would only have lost 30 per cent of its water by mass when the sun becomes a red giant in 6 billion years. “A lot of things can happen in 6 billion years, and it may shut off long before then, although the idea of this thing blowing all of its ice away and becoming a little rocky moon is kind of nice,” Lunine says. “Some future extraterrestrials visiting our solar system will be able to look at the naked rocky core of what was once an ice moon.”
Journal reference: Science, DOI: 10.1126/science.1250551
More on these topics: | 0.834828 | 3.937242 |
This weekend, a group of astronomers made many, many headlines after giving a presentation about “a strong signal in the direction of HD164595.” HD164595 is a Sun-like star 94 light-years away, and with the RATAN-600 radio telescope in Zelenchukskaya, Russia, pointed in its direction, the astronomers picked up a blast of radio waves about 4.5 times stronger than background static. Maybe aliens? they suggested. We should investigate.
Their presentation began circulating among astronomers in slide-deck form. Paul Gilster at the website Centauri Dreams wrote about it as “an interesting SETI candidate”—meaning perhaps it came from an extraterrestrial civilization. That set off the media storm.
But I have to tell you something: Astronomers don’t know much about that “SETI candidate” signal beyond that it’s made of radio waves. And while human beings should absolutely spend some time figuring out what this signal is, they have almost no reason to conclude it came from non-human beings. Here’s why:
They don’t actually know it’s coming from that star.
As Seth Shostak, senior astronomer and director of SETI research at the SETI Institute (how’s that for credentials?) noted, the telescope doesn’t see a fine point in the sky. Every telescope has a “field of view.”
The RATAN’s view isn’t circular, though. It catches a narrow east-west section, which in this case was centered on HD164595. But the north-south view is “highly elongated,” Shostak wrote on the Institute’s website. And the actual source of the mysterious radio waves could be anywhere inside that elongation: The telescope’s “field of view” is just one strangely shaped pixel. We normally think of pixels as small, focused dots, like the kind that come from our cameras. But all “pixel” really indicates is that all of the light from a specific area gets lumped together, and basically averaged. The radio waves “from” HD 164595, then, could be coming from a little north or south of the star’s actual position, and scientists wouldn’t be able to tell the difference.
They don’t know if it’s a narrowband signal.
Historically, SETI programs have searched for “narrowband” signals spread over just a few frequencies, because scientists think it takes technology to squish a signal like that, like we do with radio-station broadcasts (nature’s narrowest radio signals seem to span around 300 Hz). A squished signal equals “Someone might have made it on purpose.” So SETI scientists collect radio waves from the sky and split them into their constituent frequencies, to see if a strong spike shows up in one or a few bands. The SETI Institute’s Allen Telescope Array splits signals into hertz-wide chunks—a billion times smaller than the RATAN-600’s data, which was in a gigahertz-wide chunk.
Like the telescope’s single pixel, which lumps all the waves from one area together, the telescope’s electronics lump 1 gigahertz’s worth of frequencies together. Was the original signal narrowband? Wideband? These data can’t—ever—tell that story. As the SETI@Home program, which uses citizens’ computers to comb through data for suspect radio waves, noted on its website, “Because the receivers used were making broad band measurements, there's really nothing about this ‘signal’ that would distinguish it from a natural radio transient (stellar flare, active galactic nucleus, microlensing of a background source, etc.).” There is, in fact, an entire field of study devoted to signals like this: time-domain astronomy, which includes, yes, SETI, but also any other signal that appears, disappears, and reappears or doesn’t. It happens a lot. Space is busy. So are human devices.
They don’t know it’s not human-generated interference.
While astronomers don’t know if this signal is squished or spread-out, they do know the middle frequency that the telescope was sensitive to: around 11 gigahertz.
Two things: Radio telescopes are supposed to catch cool waves from space. And they do that. But they also catch less cool waves from Earth, or from Earth-orbit. Airport radar, Wi-Fi, spark plugs, cell phones, and basically anything that runs on electricity emits radio waves. And satellites use these frequencies to ping and downlink. The research team has not presented data to rule out humans as the signal’s makers. In fact, one will note that 11 gigahertz is in the exact middle of a band of the radio spectrum allocated to “fixed satellites.”
“We see signals that come and go every day, all the time,” says Gerry Harp, Director of SETI Research at the SETI Institute. “We would not have given much credibility to this signal in our survey. It would be one of so many others, and they are almost always local interference.”
They don’t know it’s not a fluke.
The team, led by Nikolai Bursov of the Russian Academy of Sciences’ Special Astrophysical Observatory, scanned the star 39 times. They saw this signal once. At the Allen Telescope Array, the automated detection system checks on a candidate signal five times in a row, performing two tests each time. Those, says Harp, plus one or two at the beginning and end, mean a suspected SETI signal has to pass 12 total tests before the software tells people to pay attention (Harp says that has only happened once in the Allen Telescope’s history). The HD164595 signal, instead of passing 12/12 tests, has passed just 1/39. “In our system, we would have just forgotten about it and carried on,” says Harp.
The SETI@Home program “has seen millions of potential signals with similar characteristics, but it takes more than that to make a good candidate,” the team wrote in a blog post. “Multiple detections are a minimum criterion.” The SETI Institute hasn’t seen it again, so far, in observations their telescope began after the announcement, although they have not yet searched the full gigahertz of potential frequencies.
They didn’t tell other telescopes soon enough.
This candidate SETI signal came in more than a year ago, in May 2015. The researchers didn’t say anything until now. And if it were aliens, they may have turned their “Notice us! We’re awesome!” beacon off in June or something.
In the SETI world, one of the first items on an excited astronomer’s agenda—upon perhaps making the most meaningful cosmic discovery in the history of humans—is to ask other telescopes to look at the same star system. This can help rule out ground-based annoyances, which wouldn’t show up at an observatory following up across the country. It also rules out weird internal problems a given telescope might be having. The fact that the researchers didn’t tell anyone for more than a year, and so precluded these standard check-ups and confirmations, suggests maybe they didn’t think it was from aliens, either.
Look, I’m super pro-discovering-extraterrestrial life. It would fundamentally alter our view of the universe, ourselves, and what the two mean together. If it happens, I will cry and cry and write some article and throw a huge party, and I will invite you. But there’s almost nothing about this “candidate signal” that says “aliens,” besides that it’s a radio signal that might be from space, and it would have had to be strong to show up like this if it did come from that many light-years away.
Let’s rule out satellites and other interference; let’s cross quasars and other banging celestial objects off the list; let’s try to catch the waves again; let’s see if they look engineered or astronomical. Then we’ll talk. | 0.835951 | 3.497487 |
On Monday May 9, the planet Mercury will be out in front of the sun nearly all day. Instead of hiding in its glare, the innermost planet will pass directly across the sun’s face in an event called a transit. Our sun is big and Mercury is both small and far away (52 million miles / 83.6 million kilometers), so it takes 7 1/2 hours for the little orb to travel from one side of the solar disk to the other.
Mercury is too small to see silhouetted against the sun with the naked eye and sun filter alone, so you’ll need a scope. Anything that magnifies around 30x that’s equipped with a safe solar filter will do the trick. The planet will look like a small black dot similar to a sunspot but perfectly circular and black as midnight. No scope? If you happen to be in the Duluth, Minn. area maybe we can help.
I along with my colleagues from the Arrowhead Astronomical Society will be out in front of the Marshall W. Alworth planetarium on the University of Minnesota-Duluth campus for the transit duration. The forecast is perfect — mostly sunny skies with the temperature in the mid-50s. Some of us will be there as early as 6:15 a.m., but most, including myself, will set up shop between 9 and 10 a.m. Mercury enters the solar stage around 6:15 a.m. CDT and exits at 1:42 p.m.
I’d love it if you stopped by. With all those scopes, you won’t be able to miss us. Stay for 5 minutes or stay for an hour. We’ll be there till transit end.
When you watch the transit, you’re witnessing in real time how professional astronomers discover the majority of extrasolar planets: they measure the drop in light as a planet passes in front of its host star. Measuring the depth in the dip in brightness, scientists can determine the object’s diameter. From the time between successive transits, they measure its orbital period or how long it takes to go around the star. With the orbital period known, Kepler’s Third Law of Planetary motion yields the average distance between planet and star.
The table below lists the times of the event across the four time zones of the continental U.S. If clouds prevent you from viewing this cool and rare event, Italian astronomer Gianluca Masi will live stream it from his telescope starting at 6 a.m. CDT (11:00 UT) Monday. For more detailed information, check out this earlier blog on the topic. And though I’ve said this before, let me caution again never to look directly at the sun without a safe, secure solar filter.
I hope to see you tomorrow!
|Time Zone||Eastern (EDT)||Central (CDT)||Mountain (MDT)||Pacific (PDT)|
|Transit start||7:12 a.m.||6:12 a.m.||5:12 a.m.||Not visible|
|Mid-transit||10:57 a.m.||9:57 a.m.||8:57 a.m.||7:57 a.m.|
|Transit end||2:42 p.m.||1:42 p.m.||12:42 p.m.||11:42 a.m.| | 0.843362 | 3.640892 |
Steamy Venus-like exoplanet likely oxygen-rich, life-poor
According to new research, a very Venus-like exoplanet known as GJ 1132b might just be the first rocky planet outside our solar system where we detect oxygen in the atmosphere. But ET enthusiasts shouldn't get their hopes up – orbiting extremely close to its star, the sweltering planet's atmosphere likely has a strong greenhouse effect and a magma ocean on its surface.
When it was discovered last year, scientists were intrigued by the possibility that GJ 1132b could sustain an atmosphere. New research, led by astronomer Laura Schaefer, at the Harvard-Smithsonian Center for Astrophysics (CfA), simulated how the planet's history would pan out if it began with an atmosphere high in water content.
Thirty-nine light-years from us, GJ 1132b orbits its red dwarf parent star incredibly closely, at a distance of 1.4 million miles (2.25 million km). By comparison, the sun-hugging Mercury only ever gets as close as 29 million miles (46 million km). At that range, GJ 1132b is bombarded with UV light, which would separate water molecules into hydrogen and oxygen, creating an atmosphere full of water vapor. As a greenhouse gas, that steamy atmosphere would in turn ramp up the planet's heat even further, with temperatures tipping 450° F (232° C).
"On cooler planets, oxygen could be a sign of alien life and habitability," says Schaefer. "But on a hot planet like GJ 1132b, it's a sign of the exact opposite – a planet that's being baked and sterilized."
That steamy atmosphere could be enough to keep the surface rock molten, creating oceans of magma that absorb around 10 percent of the oxygen in the air. While some of it may linger, the vast majority of the oxygen and hydrogen atmosphere would be lost to space. Future studies of GJ 1132b could turn up traces of this leftover oxygen, thanks to next-gen instruments like the Giant Magellan Telescope and James Webb Space Telescope.
"This planet might be the first time we detect oxygen on a rocky planet outside the solar system," says co-author Robin Wordsworth.
GJ 1132b's turbulent origin story sounds remarkably like that of Venus. Our next door neighbor may once have been home to liquid water oceans as well, before they would have boiled away over billions of years and left the desolate desert we know today. While we have theories about what happened to all the oxygen on Venus, the magma ocean-atmosphere model could provide some further clues to its history, and that of similar exoplanets.
The research was published in The Astrophysical Journal.
Source: Harvard-Smithsonian CfA | 0.850266 | 3.92675 |
For a complete list, including earlier questions not listed below, click here.
You may also link from here to a listing of questions arranged by topic.
396B Posssibility of Asteroid Hitting Earth (2)
203. Superconductors work, universe expands--with no energy input. Why?(shortened message)
I am quite interested in physics in general, mainly quantum physics and the likes. One thing that to this day baffles me about physics is the whole concept of energy.
The thing I can't understand is that if you had a room temperature super-conductor (as I am aware, they haven't come up with one yet) you could have a device that produces either a repulsive or attractive force, just whilst it sits in your back garden, no extra energy required. So how is it able to produce this repulsive/attractive force without ever needing energy.
And how can the universe be expanding on limited energy and why is it not slowing down there further out it gets (Surely the further out it goes the energy has a larger void to cover so should dissipate), How do black holes consume so much energy and release none (Where does the energy go to if energy can't be created or destroyed?)
How does the Big Bang Theory work if with limited energy the universe started from something, that assumes that everything in the Universe was created from nothing, which could mean it is possible to create energy from nothing.
Any thoughts on what I have dicsussed would be most appreciated.
ReplyYou seem baffled by some phenomena, e.g. asking why does the universe expand without slowing down? How can super-conductors keep currents forever, without energy input? And so forth.
Nature owes us no explanations! WE are the ones who sometimes need change our thinking in light of observations. Nature's phenomena follow their own rules, not ours, and it's OUR job to understand them.
Ancient Greeks believed (and Copernicus still subscribed to that belief) that heavenly bodies moved in circles, because the circle had perfect symmetry, and Nature could not be anything short of perfect. Then Kepler introduced ellipses, Newton proved orbits had to be elliptical, and astronomy adjusted to a new view.
In the 19th century, science knew that material objects (sticks, stones, bones etc.) were localized, while waves filled space. Today we know electrons (say) can behave like waves or particles, depending on circumstances, and Schroedinger's equation bridges the gap between their extreme behaviors. Electromagnetic waves sometimes act as photons--particles of zero mass. Physicists had to adjust their views again.
Now about those superconductors. In everyday life, almost any physical process associated with energy transfer always suffers a loss. Motion loses energy to friction, current flow in a wire encounters ohmic resistance, and if you charge an electric battery, you can never recover all the energy invested. That happens because whenever an energy conversion process involves an large number of atoms, at least part of it that energy ends up shared by the atoms as heat. It's as if the energy had to pay a sales tax.
Processes involving single atoms are often exempt from such "taxation." The Bernoullis (I think) were the first to explain the gas laws by assuming that a gas consists of zillions of molecules or atoms, little spheres which fly through space and collide with each other. Their collisions are perfectly elastic, never losing any energy. Some larger-scale quantum phenomena--e.g. currents in a superconductor--also behave like that, they may not involve a single particle but rather a single quantum state, which seems just as good. And a bar magnet that has been magnetized stays magnetized indefinitely, with no energy input.
There is no contradiction: matter can sometimes maintain its state indefinitely. This isn't "classical" perpetual motion, as long as it cannot create more energy than it has started with.
204. Shuttle orbit and Earth rotation.Hello Dr. Stern, I have been looking all over searching for the answer to this question....please help me.
Since all things on the earth rotate with it at a constant speed, including the atmosphere (generally), how do spacecraft "recalibrate" themselves to the rotation of the earth (1000mph) upon reentry? When does it happen? What effect does it have on the passengers? I am assuming that it happens before they touch the earth since the atmosphere itself moves with the earth's rotation. Thanks for your help!
ReplyThe shuttle orbits a 5 miles per second or 18,000 mph, so 1000 mph is a relatively small part. Still, spaceflight is so difficult and expensive that any small advantage is precious.
That is why the shuttle is launched eastwards from Cape Canaveral: its orbital velocity is measured relative to space and depends only on the Earth's gravity, which is the same whether the Earth rotates or not. Therefore, an eastward launch from Cape Canaveral already has an initial velocity in the right direction, and needs only add the remaining difference.
(More at http://www.phy6.org/stargaze/StarFAQ3.htm#q62)
Same with reentry! It helps if the shuttle approaches landing from the east, because then the rotation of the ground (and of the atmosphere) is already eastward at about 1000 mph. To match velocities with the ground (and the atmosphere) the shuttle only needs to lose 17,000 mph or so, less than otherwise.
If you remember the story of the break-up of the shuttle "Columbia," it planned to land at Cape Canaveral and it approached over California: the break-up was first seen above Arizona, and most of the debris came down in eastern Texas. It was approaching its landing from the east.
Concerning re-entry, you might also look up a recent letter at http://www.phy6.org/stargaze/StarFAQ12.htm#q191
205. Worrying about Wormholes and Black HolesI have a question about space. A few weeks ago, I asked a friend if she was afraid of aliens like those seen in "War of the Worlds" and she said no, we (have) more reason to be afraid of the giant black hole at the center of the Milky Way. I knew we didn't have to worry about that, as it is billions of light years away.
But then I had a dream about it and awoke this morning with the theory that if a massive black hole opened a wormhole and sucked us right through the wormhole and into its center. Both teachers I told this to said I shouldn't worry about that (I never worry about drowning, but the supernatural is another story). But what do you think--is it at all possible? What would happen if we did get sucked in? Would it be, as my friend would call it, "an incredibly painful and excruciatingly long death" for everyone, or would it just me instant blackness? And are we at the mercy to this supposed black hole at the center of the galaxy? If so, how long does our planet have? How fast is it carrying everything in?
Okay. I'll stop bugging you now.
ReplyI am just a plain physicist and know nothing about wormholes. I know that astronomers have never seen anywhere a phenomenon which required wormholes for its explanation--and they do see some mighty weird stuff!
I looked up wormholes on the web, on "Wikipedia." There exists a lot of theoretical speculation, but I found nothing positive. Maybe it should be filed for now under science fiction, in the realm of things we cannot prove to be impossible, even though they have yet to be observed.
About the black hole at the center of the galaxy (whose distance is measured in thousands of light years, not billions), see my web page at
There exist quite a few stars orbiting it, on what seem stable orbits. I would not like to live that close to the black hole--too many X-rays--but our solar system is at a safe distance.
Neither do I worry about aliens. My greater worry is that actually, no aliens exist anywhere in the galaxy. If so, we have the only planet which harbors life--a planet which in recent years we have been treating rather shabbily. Until we know better, we ought to assume that we may be the only guardians of the flame of life, and if so, we ought to do a better job!
206. What should I study?(shortened)
I would like to find new ways to produce energy, like solar panels do, by converting some natural form of energy into electrical energy. I am enrolled in my first semester of Mechanical Engineering and working as an RN in a local hospital.
I am curious as to your advice on what I should be studying. My math is only at the level of Algebra I (I haven't had any math really in 7-8 years). Should I stay in Engineering? If so what field? Mechanical or electrical? Or should I go for a physics degree.
I would greatly appreciate your guidance, or else, ask others in your dept for their input and please write me back. I also thought about going back to school to get a degree in biology to do research in finding cures or vaccines for AIDS, Cancer, Herpes...Which I believe are all related because they have to do with changes in DNA/RNA.
Can you please give me some assistance. The tests I have taken say Engineering, then Medicine as a second choice. My family has a heavy background in electronics. I like classes like Chemistry, Physics, and Biology.
ReplyI hate to sound discouraging, especially in face of your enthusiasm, but there seems to exist a huge gap between where you are and what you are trying to reach.
Maybe I share some of the blame: the web pages I have created--carefully avoiding complex math and theory--may have done too good a job, in making the complicated seem simple to you. Front-line science is not simple, the simple stuff was all solved long ago.
This is particularly true in physics, which is very competitive, and where even reaching the starting line takes years of concentrated effort. My advice is--start with simple things. Improve your math: even the simple course in
will be useful (although a regular class ultimately gives wider grounding, besides putting pressure on you to persist). Improve your physics. Again, "Stargazers" has some useful material, but it falls short of a complete course, and is rather space-oriented. You certainly need the simple foundations: density, liquid pressure, buoyancy, levers, balanced forces, centers of gravity, calorimetry, electric circuits, basic optics.
And in any technical field these days, you may need to know about computers--also maybe to write computer code.
Anything new you learn may qualify you to a higher level. If you have some physics, math and computers, you can take a technical job. With more, and with related skills, you might get into engineering: there exist many more jobs for technicians and engineers than for physicists, an important consideration for making a living. What kind of engineering is best for you--and when you should branch off from general topics (like those mentioned above) to some specialization, that is where your judgement comes in. Such decisions depend on you, on your opportunities, perhaps on finding a good mentor or good training (with your background, maybe it will be related to the health field). Keep improving your hold on generalities until you decide you have reached that point.
If I can add something here, it is, technology and science are not everything: it also helps to get experienced in writing clearly and well. Reading books helps sharpen those skills, too.
207. The greenhouse effectI'm 35 years old, married with one kid... and just want to help a cousin in an assignment in physics.
When a photon from the sun hits the surface of the earth, it may be reflected (in which case its energy goes into making a new photon of the same wavelength) or it may be absorbed. The energy from photons that are absorbed goes into heating the earth. The earth takes some of the absorbed heat and generates new photons in the infrared part of the spectrum.
Can those photons go through the atmosphere and into space, or are they trapped by the atmosphere? If they go into space, what happens to the temperature of the earth? If they're trapped, what happens to the temperature of the earth?
ReplyYour letter sounds as if you read part of my web page
but stopped in the middle. Actually, that web page answers your question. The infra-red photons are radiated upwards from the ground, and if they could just continue to space (as they can from the surface of the Moon), they would just go on and get lost in space.
The atmosphere however absorbs those photons-- the molecules of "greenhouse gases" like water vapor, carbon dioxide and methane have "energy levels" in the infrared, able to absorb those photons. But what they absorb they can also emit, so that the infra-red bounces from one molecule to another, until it gets high enough to escape to space, around the altitude of jetliners. It's like rain hitting a forest--it does reach the ground (usually), but not before bouncing from branch to branch.
The temperature of the Earth is balanced between what comes in and what goes out--"radiation balance" in scientific language. The process is complicated by humidity and by "convection"--hot air rising, radiating some of its heat higher up, then descending. That's why we need big computers to model the weather! And as any kid nowadays knows, adding "greenhouse gases" slows down the upwards transmission of heat (in the form of infra-red photons) and shifts the radiation balance towards a warmer Earth.
Tell your cousin to read that section and maybe also the lesson plan linked from the top right corner.
208. Separation between lines of latitude and longitudeWhat is the distance in miles or kilometers between longitudes? Please and thank you!
ReplyDepends where you are! To paraphrase Neil Armstrong, it's one small step when you are near the pole, one giant leap near the equator.
Neglecting the ellipticity of the Earth, the length of the equator would be 40,000 kilometers (ellipticity adds about 74 km), making one degree of longitude 40,000/360 = 111.3 kilometers.
The average radius of the Earth is R = 6371 km (a few less than the 40,000 km value gives). At latitude L, the length of a line of latitude is 6.2832 R cosL (the factor is 2π), so one degree is (6.2832 R/360) cos L or about 111 cosL kilometers. As the latitude L increases, cos L gets smaller and smaller, and for people walking around the south pole (as some do at the South Pole Scientific Station) each degree is but one small step.
Follow-up:How stupid can I be? Quite a lot evidently. I meant to type LATITUDE! Guess my brain was in a different place. Thank you.
ReplyThat's easier. Assuming the Earth is a sphere, a line from the north pole to the southern one and back is just as long as the equator, and contains 360 degrees of latitude. So one degree of latitude corresponds to about 111 kilometres.
One degree also contains 60 minutes of arc, making one minute of latitude equal to about 1.85 kilometers. That distance is defined as a "nautical mile", and a velocity of one nautical mile per hour is "one knot", the common unit for measuring speed at sea.
Response:Thank you so much. My nephew was interested in how much further north his home town of Red Deer, Alberta was from Kingston, Ontario. Now, with your help, it will be much easier to figure out. I know he is tricking me into doing his assignment for him, but when he calls me "his favourite aunt" what else can one do?
209. Motion of air: hot to cold, or high pressure to low?I'm sitting in chemistry class right now as I type this, and I was just told that air moves from hot to cold. I already knew that matter moves from high pressure to low, so this makes no sense; cold air is of higher pressure than high. Which is true? Does are move from hot to cold or from high pressure to low pressure, and why?
ReplyAir (or any fluid, and matter too) moves in response to forces. If you want to understand motion, the question to ask is "what forces are involved?"
Pressure is force per unit area (look up in the dictionary; example: pounds per square inch, the PSI of tire pressure). So given an area A and a pressure P, the force on it is AP (A times P).
Suppose you have a cube with side equal to one unit (inch, or centimeter, or meter--whatever you work with; it helps to make a drawing here). The area A of each side is then one square unit. Suppose also that he pressure P1 in the surrounding fluid (air, water or whatever) on the cube's right side is higher than the pressure P2 on its left. So the force AP1 on the right side is greater the force AP2 on the left side. The greater force overcomes the weaker one and pushes the cube from right to left, from high pressure to lower one. That is a general rule.
The force which moves air from hot to cold is BUOYANCY--the tendency for lighter fluids to float up when surrounded by heavier (denser) ones--for example, oil floats to the top of water. You can prove (look up in a textbook) that with a cube (say) of light fluid immersed in a denser one, the net pressure P1 on the bottom is larger than the pressure P2 on the top. So it rises.
In the atmosphere, sunlight heats the ground, causing air there to heat up, too. Heated air expands and becomes less dense, and therefore rises (like a hot air balloon). As air rises, it expands and cools down. Such processes operate in the atmosphere all the time, so as you go higher (into high mountains, for instance), the air is cooler. As a result, "freshly heated" air rises only until its surroundings are just as cool.
It's more complicated, but my space here is limited. For more, look up http://www.phy6.org/stargaze/Sweather1.htm and the section which follows
210. Removing "Killer Asteroids"I just discovered your site and fully enjoyed it. I was watching a program on Canada's Discovery channel about "Killer Asteroids" and how they might be pushed off course from a collision with the Earth. They first played with the idea of using Nuclear Weapons in a near explosion to push them to a new orbit but after the discovery of very porous meteorite material found in Northern British Columbia, it was determined that these type of Asteroids would absorb any energy from a near explosion thereby not changing their orbits.
It was then suggested that a Solar Magnifier could be stationed close to the Asteroid and by focusing the sun's rays at the Asteroid, burn a hole which would release energy pushing the Asteroid in to a different orbit away from Earth.
I then had the idea of an Ion Rocket landed on the surface of the Asteroid and used to gradually increase the push away from Earth's orbit, perhaps completely out of the Solar System. Could an Ion Rocket be used for such an application? Would it be to cost prohibitive? If needed, could not the Sun's rays be used to power the Ion Rocket?
This is what brought me to your site for research on Ion Rockets. Your thoughts on this would be greatly appreciated as the program did not even mention it.
ReplyI do not know who is responsible for the program on Canada's Discovery Channel, but your message suggests some rather loose thinking. The basis for ANY changes of asteroid orbit (as well for rocket design, and a lot more) is Newton's third law:
A nuclear explosion near an asteroid would vaporize the region closest to it, and the vaporized rock would stream away from the asteroid. By Newton's law, the force moving those vaporized molecules away from the asteroid would be exactly matched by a force pushing the asteroid in the opposite direction. Whether the asteroid is hard or soft makes no difference: the momentum transmitted to the asteroid is the same.
If that would be enough to save the Earth depends on circumstances. Even small asteroids are very massive, and their orbit would probably be modified only slightly. However, if one can intercept an asteroid years before its expected impact on Earth, that may be enough. Of course, even then it would still be in an orbit which can some day again come close to Earth (unless one can make it hit the Moon).
If the asteroid material is too loose, the vapors released (they blow in all directions) may also blow some of it apart. Indeed, a bomb dug into the asteroid may conceivably blast it apart completely, so instead of a single solid impact with Earth, we may end up with multiple impacts by many smaller objects. These may perhaps burn up in the atmosphere, but would still radiate a lot of heat. Whether that makes the impact less destructive or more so, I am not sure.
A "solar magnifier" does not exist, and I cannot imagine it. A large light solar mirror will be quickly pushed away by sunlight pressure... and anyway what would it accomplish? If you want to equal the effect of a nuclear bomb by evaporating part of the surface, you need deliver a comparable amount of energy. Hard to imagine!
Ion rockets are fragile devices whose thrust is measured in grams. Not enough to move an asteroid of billions of tons! Plus, they need a source of material to create the ions, and a source of energy to accelerate them. Solar energy, again, may suffice to accelerate a spacecraft (over months of time), but not a humongous hunk of rock.
211. Strange light seen from HawaiiI live in Laie, HI. I looked out toward the east (the ocean) and noticed a bright red star. As I was looking at that star, I saw a meteor, or at least I think is a meteor. It was reddish orange in color and looked very close to the earth. It was much larger and broader looking than the meteors I'm accustomed to seeing, which are usually long, and thin. Any answers??
ReplyIt would be very hard to tell what you saw. Did it move? It could be an airplane or satellite.
Meteorites arriving near the observer would not be reddish or orange--by the time they cool down to emit that color, they are already quite dim.
If I were to guess, you may have seen a flare dropped by a military airplane or fired from a ship, as part of some training exercise or a rescue effort. Flares are very bright and are meant to illuminate large areas below, and they descend slowly by parachute. They burn with a bright, white light (produced by magnesium, or by some other burnable metal, as in a firebomb), but since the one you saw was close to the ground, it was probably far off--perhaps beyond the horizon, made visible only by the bending of its light in the atmosphere.
As you know from the setting Sun, light near the horizon, which passes through a thick atmospheric layer, tends to take a reddish-orange color. Maybe that explains what you saw. You may ask someone in the coastguard about it.
212. Is the Sun attached to another star?Good day Dr. Stern,
Would you let me know if our Sun has a central Sun? Does our Sun have a planetary orbit around another star?
Many thanks for your outstanding web page,
ReplyAs far as I know, the answer is no. If any ordinary star existed close enough to hold the Sun, it would be the brightest one in the sky, by far. It could of course be a burned-out star, or a black hole (in which case, the motion, strictly speaking would not be around that other object, but against the common center of gravity).
The problem is that the Sun and the solar system are moving through space towards the "solar apex" (look it up) at about 20 km/sec. That is more than the orbital velocity around any distant object. Of course, that distant object could move at the same velocity, too.
In my estimation, chances are very much against it. Another clue may come from tracking distant space probes: do they indicate an influence other than the gravity of the Sun and the known planets? It turns out that a small discrepancy exists with the Pioneer spacecraft, but no one has yet mentioned another star as its source.
So take it from there. My guess is, unless clear proof arrives, we are alone in space.
213. What if the Sun turned into a black hole?What would happen to the Earth if the Sun's mass suddenly collapsed to within its Schwarzschild radius and became a black hole? I know the Sun is not large enough to actually collapse to a blackhole, but it would be interesting to know what would happen to a planet orbiting a star that did become one. Would it spiral inward to be engulfed by the black hole or just move into a much smaller orbit? I'm very interested in the answer, especially after reading your articles on how hard it would be to actually reach the Sun from the Earth.
ReplyI have no special expertise in those areas, but I believe the gravitational attraction would remain the same, and therefore, so would the Earth's orbit.
Of course, life would quickly end. After being burned crisp by the energy released from the collapse, Earth would get very, very cold.
Stars near a black hole do not spiral inwards. A huge black hole exists near the center of our galaxy, and quite a few stars orbit it (in Keplerian ellipses), and apparently have been doing so for a long time. In fact, I recall reading somewhere recently that new stars appear to be forming at a high rate in that vicinity. For more, see http://www.phy6.org/stargaze/Sblkhole.htm.
214. Do absorption lines have a Doppler shift?We are studying atomic physics at school which involves the electromagnetic spectrum. We have been shown the absorption spectra for various substances. We have also been shown how if an object like a star is moving towards Earth the Fraunhofer lines will shift slightly to the blue end of the spectrum in a blue shift, and if the star is moving away the Fraunhofer lines will shift slightly to the red end of the spectrum in a red shift.
My question is why is it the Fraunhofer lines which shift, as I would have thought the atoms in the atmosphere of both Earth and the star would absorb the same frequency of light regardless of the movement of the star or Earth? I asked my physics teacher and he did not know the answer.
ReplyImagine an absorption line in the spectrum of a star. To its right and left in the spectrum are bright emissions, which get shifted by the Doppler effect due to the relative motion between the star and us, in the same direction (to the red or the blue). Would the dark gap between them shift the same way?
It would, if the dark absorption feature is caused by gas at the star. It would not, if it is caused by absorbing gas in the atmosphere of the Earth, which is one of the ways we can tell apart absorption that happens THERE from the one happening HERE.
Again, physics adds some interesting details. You know that spectral frequencies are very, very narrowly defined. One Fraunhofer line due to calcium, for instance, has a wavelength 422.6742 nanometer, defined to 7 decimal figures. However, if you split sunlight in a spectroscope and look for spectral emission lines from various elements, you will find each covers a certain spread of wavelengths. One reason is the Doppler effect: the solar envelope is hot, which means its atoms have large random velocities. Some happen to be approaching us when they emit light, some are moving away, and the Doppler effect shifts their wavelengths in opposite directions. As a result, when the wavelength spread of a spectral line is examined (and instruments exist--interferometers--which do so very well) we get a sort of bell-shaped curve, peaking at the appropriate wavelength, but spread to both sides (a pressure effect can also contribute).
However, there may be something interesting about this curve. Sometimes we see a dip right at the peak, because above that emitting region, there may be a cooler absorbing region (temperature may go down with height for a short distance before--on the Sun--it goes up again). The absorption line is narrower because, being cooler, it has less of a Doppler effect.
You must have a good school, if it teaches atomic physics! You can find more of it in "Stargazers", the section on the Sun.
215. What are "Electromagnetic Waves"?I just wanted to know how electromagnetic radiation is used to gain information about the universe. I can't seem to find what I am looking for anywhere.
ReplyScientists (unfortunately) use a somewhat technical language, and often do not realize that this creates problems for non-scientists.
Electromagnetic radiation is another name for light, and for wave phenomena which are similar to light but with longer or shorter wavelengths: radio, microwave, infra-red, ultra-violet, X-rays and gamma rays are all electromagnetic waves.
So electromagnetic waves are the ONLY source (with a few exotic exceptions) through which we get information about the universe outside Earth.
The astronomer Martin Harwit used this fact to ask, what is the maximum information such waves CAN give us about the universe? He made a chart of all the wavelengths, and the resolution we can get in each (how small and faint are the details we can see), and then pointed out where unobserved "gaps" remained. Most were in wave lengths which the atmosphere does not let through, so to fill them meant setting up observatories in space. NASA's "great observatories" programs tries to fill those gaps--for instance, the "Chandra" X-ray telescope.
What makes light etc. "electromagnetic"? The connection between light and electricity was only found by James Clerk Maxwell about 150 years ago. Look up
and sites linked there, for the intuitive meaning of the connection. It is not a simple one, and to fully understand it you would need some rather complicated math.
216. Why are the two daily tides unequal?Ocean tides on the west coast of the United States are mixed tides, usually two high tides and two low tides per day. The two highs and two lows are uneven. There is a higher high and a lower high, and a higher low and a lower low. Why do the lower low tides occur in the daytime during summer and in the night time during winter?
ReplyI am just an ordinary retired physicist, specializing in magnetic fields and trapped particles in space... not in tides! Still, I tried to find out for you by asking Google about "Atlantic Tides." On the west coast, the situation is probably similar. I regret to report that the reason is rather complicated.
A rather thorough description of tides existed on the web (but was gone in 2016), starting from
and continued to a lot of detail. Basically, the tide is a world-wide wave excited in the ocean by the gravity of the Moon and Sun, and it has two components:
the M2 component with two peaks a day, and
the K1 component with one such peak.
If we just had the Moon circling the equator, that would (according to the above web page) excite the M2 wave alone, two equal peaks a day. However, the axis of the Earth is tilted, and that adds a K1 wave.
You can see that the sum might very well give an asymmetric pair--once a day K1 adds to the M2 peak, 12 hours later it subtracts. The tilt of the northern hemisphere is opposite in the summer and winter (sunward at noon in the summer, away from the sun in winter), so maybe that explains what you claim happens.
The exact addition of the waves depends on the relative timing of the peaks, which I believe is affected by shorelines and the shapes of the ocean bottom. These factors also add higher frequency, so the calculation of tides is a complicated art, based on large collections of tide data. I would guess you can find out a lot more from that web site.
217. Why air gets cold higher up--a wrong explanationToday, I was researching why temperature drops as elevation increases and I came across an explanation on an ask-the-expert website that I just don't buy.
It said that just as a baseball loses kinetic energy and gains potential energy as it rises in its trajectory, the air molecules lose kinetic energy as they rise.
Here is the actual quote:
ReplyYou are right in questioning that "explanation." Actually, it IS correct above an altitude of about 100 kilometers, the approximate level of the last collision of air molecules. Since their thermal speed is much less than escape velocity, they rise in parabolas (more accurately, sections of ellipses) and ultimately fall back. That is the Earth's "exosphere."
But where you and I live, temperature drops with altitude for a simpler reason. The Sun heats the ground, and unless this heating were to continue indefinitely (to where the oceans would boil, etc...) that heat must be returned to space. It is a complex process, involving convection and also infra-red radiation, which is emitted, absorbed and re-emitted by greenhouse gases as it works its way up, until at about 10-12 kilometers (typically) such radiation can continue to space.
In all these processes, heat flows upwards, and as we all know, heat only flows (unaided) from higher temperature to a lower one.
For more, see
See also question #207 on this page.
Go to main list of questions (by topic) | 0.918148 | 3.181575 |
For a long time, scientists have suspected an existence of water and perhaps even life on ancient Mars; especially, since ESA‘s Mars Express discovered a lake below the planet’s South Pole last year. It is still unclear whether there really was any kind of life, but Mars Express has now revealed the first geological evidence that there were indeed large water reservoirs on the Red Planet. Launched on June 2, 2003, the Mars probe reached the planet on December 25, 2003, and has now found a system of ancient interconnected lakes that once lay deep beneath the surface. Five of which may contain minerals crucial to life. Five of these lakes may contain minerals that are crucial to life.
From time immemorial, Mars appears to be an arid world hostile to life, but there are compelling signs on the surface that large amounts of water once existed across the planet. A new study now reveals the extent of underground water on ancient Mars that was previously only predicted by models.
Large water resources
“Early Mars was a watery world, but as the planet’s climate changed this water retreated below the surface to form pools and ‘groundwater’,” says Francesco Salese of Utrecht University, lead author of the study published in the Journal of Geophysical Research – Planets. “We traced this water in our study, as its scale and role is a matter of debate, and we found the first geological evidence of a planet-wide groundwater system on Mars.”
Salese and colleagues explored 24 deep, enclosed craters in the northern hemisphere of Mars, with floors lying roughly 4000 m below Martian “sea level”. Since there are no oceans, the sea level is defined arbitrarily based only on elevation and atmospheric pressure.
Features on the floors of these craters were found that could only have formed in the presence of water. Many craters contain multiple features, all at depths of 4,000 to 4,500 meters – indicating that these craters once contained pools and flows of water that changed and receded over time.
Evidence of rivers and a Martian ocean
There are canals etched into crater walls, valleys carved out by sapping groundwater, dark, curved deltas thought to have formed as water levels rose and fell, ridged terraces within crater walls formed by standing water, and fan-shaped deposits of sediment associated with flowing water. The water level corresponds with the estimated coastlines of a presumed Martian ocean thought to have existed on Mars until three and four billion years ago.
“We think that this ocean may have connected to a system of underground lakes that spread across the entire planet,” says Gian Gabriele Ori, co-author of the study and director of the International School of Planetary Sciences at the Università D’Annunzio in Pescara, Italy. “These lakes would have existed around 3.5 billion years ago, so may have been contemporaries of a Martian ocean.”
In five of the craters, the team also discovered signs of minerals that are linked to the emergence of life on Earth: various clays, carbonates, and silicates. All these findings suggest that these water basins on Mars indeed had everything to host life. Moreover, they were the only basins deep enough to intersect with the water-saturated part of Mars’ crust for long periods of time. Evidence of this may still be buried in the sediments today.
Further research of these sites may even reveal that there were indeed suitable conditions for the existence of life on Mars. This would also be of great importance for astrobiological missions such as ExoMars – a joint ESA and Roscosmos endeavor. The ExoMars Trace Gas Orbiter has been studying Mars from above for some time, and a new mission is scheduled to start next year.
It comprises a rover – recently named after Rosalind Franklin – and a surface science platform. It will study Martian sites thought to be the most likely ones to have signs of life on Mars.
“Findings like this are hugely important; they help us to identify the regions of Mars that are the most promising for finding signs of past life,” says Dmitri Titov, ESA’s Mars Express project scientist. “It is especially exciting that a mission that has been so fruitful at the Red Planet, Mars Express, is now instrumental in helping future missions such as ExoMars explore the planet in a different way. It’s a great example of missions working together with great success.”
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Hubble finds more evidence for moon outside our solar system | 0.895317 | 3.990472 |
CELESTIAL COMPUTATIONS FOR THE NEW GREGORIAN CALENDAR
Tabulae Gregorianae Motuum Octavae Sphaerae ac Luminarium. [with] De Corrigendo Ecclesiastico Calendario.
Venice, Petrum Deheuchinum, 1580.
FIRST EDITIONS, large 4to., two works in one, ff. (viii) 50, 88 + 37 (i). Roman letter, woodcut initials and ornaments, a couple of astronomical diagrams in text. 88 leaves of astronomical and mathematical tables in first work, within printed line border, 13 of the ecclesiastical and solar calendar in second, the former printed in red and black. Jesuit library stamp and manuscript case mark in blank portion of title page, early manuscript price at head, de-accession label on fly, marginal worm trails to final leaf, well away from text. A splendid copy, with wide margins and very thick paper, crisp and clean in contemporary limp vellum, lacking ties.
Moleti (1531 – 1588) studied at the Jesuit college in Messina, where he was a pupil of mathematics, and published several works on geography and astronomy prior to his appointment as scientific tutor to the young prince of Mantua, Vincenzo Gonzaga. His important Dialogue on Mechanics discusses the problem of the speed of falling bodies of different weights, and anticipates the famous Tower of Pisa experiment of Galileo.
In 1577 he took up the chair of mathematics at Padua, and that year the Roman Congregation appointed by Pope Gregory XIII to reform the Calendar asked his opinion on the topic: his response was the second work comprised here, composed to provide technical arguments in support of the exact correction of the calendar and its astronomical tables, named the ‘Tabulae Gregorianae’ in deference to the Pope. This treatise was then published as an appendix to the astronomical tables of the motions of the fixed stars, the sun and the moon, accompanied by an explanation of the rules of astronomical calculation of the Canons for the Gregorian Tables’ proper use.
Moleti rejected the traditional computation cycles, rebasing the calendar on the real motions of the stars. Moleti’s work did not find favour with his scientific peers, but was much appreciated in Rome (to the tune of 300 Ducats), where the Pope asked him to continue his computations with the motions of the other planets. Moleti’s tables were calculated on the basis of the Copernican system which, as he first realised, Copernicus had based on the exact movements of the heavenly bodies, unlike the earlier Alphonsine tables. This was the earliest practical use by an Italian astronomer of Copernican theory. The resulting Gregorian calendar remains standard to this day. A most attractive copy of an important and very handsome book.
“Questa ediz. va noverata fra le piu splendide del sec. xvi, sia per la bellezza dei caraterri, sia per la qualita della carta e della impressione… Quest’opera redetta per ordine di Gregorio XIII fu quella che procuro all’a maggior fama di distinto astronomo,” Riccardi I 164-65.
Not in BM. STC. IT or Adams. | 0.835472 | 3.2963 |
Our Sun, like all stars, formed within a cold molecular cloud. Astronomical observations and theory provide considerable detail into this process. Yet cosmochemical observations of short lived radionuclides in primitive meteorites, in particular 60Fe, provide unequivocal evidence that the early solar system inherited fresh nucleosynthetic material from the core of a hot, massive star, almost certainly ejected in a supernova explosion. I give a short introduction to the fields of star formation and meteoritics and discuss how the reconciliation of their disparate clues to our origin places strong constraints on the environment of the Solar birthplace. Direct injection of supernova ejecta into a protoplanetary disk or a dense molecular core is unlikely since their small sizes require placement unusually close to the massive star. Lower density molecular cloud clumps can capture more ejecta but the radionuclides decay during the slow gravitational collapse. The most likely scenario is on the largest scales via the formation of enriched molecular clouds at the intersection of colliding supernova bubbles in spiral arms.
- Pub Date:
- September 2010
- Astrophysics - Earth and Planetary Astrophysics;
- Astrophysics - Galaxy Astrophysics;
- Astrophysics - Solar and Stellar Astrophysics
- 18 pages, 7 figures, invited review aimed for advanced undergraduate or beginning graduate students | 0.8691 | 3.730953 |
This image of a crescent Uranus, taken by Voyager 2 on January 24th, 1986, reveals its icy blue atmosphere. Despite Voyager 2’s close flyby, the composition of the atmosphere remained a mystery until now. Image credit: NASA/JPL
Full resolution JPEG
Gemini Observatory Press Release
For Embargoed release at 11:00am EST (5:00am HST) April 23
Hydrogen sulfide, the gas that gives rotten eggs their distinctive odor, permeates the upper atmosphere of the planet Uranus – as has been long debated, but never definitively proven. Based on sensitive spectroscopic observations with the Gemini North telescope, astronomers uncovered the noxious gas swirling high in the giant planet’s cloud tops. This result resolves a stubborn, long-standing mystery of one of our neighbors in space.
Even after decades of observations, and a visit by the Voyager 2 spacecraft, Uranus held on to one critical secret, the composition of its clouds. Now, one of the key components of the planet’s clouds has finally been verified.
Patrick Irwin from the University of Oxford, UK and global collaborators spectroscopically dissected the infrared light from Uranus captured by the 8-meter Gemini North telescope on Hawaii’s Maunakea. They found hydrogen sulfide, the odiferous gas that most people avoid, in Uranus’s cloud tops. The long-sought evidence is published in the April 23rd issue of the journal Nature Astronomy.
The Gemini data, obtained with the Near-Infrared Integral Field Spectrometer (NIFS), sampled reflected sunlight from a region immediately above the main visible cloud layer in Uranus’s atmosphere. “While the lines we were trying to detect were just barely there, we were able to detect them unambiguously thanks to the sensitivity of NIFS on Gemini, combined with the exquisite conditions on Maunakea,” said Irwin. “Although we knew these lines would be at the edge of detection, I decided to have a crack at looking for them in the Gemini data we had acquired.”
“This work is a strikingly innovative use of an instrument originally designed to study the explosive environments around huge black holes at the centers of distant galaxies,” said Chris Davis of the United State’s National Science Foundation, a leading funder of the Gemini telescope. “To use NIFS to solve a longstanding mystery in our own Solar System is a powerful extension of its use.” Davis adds.
Astronomers have long debated the composition of Uranus’s clouds and whether hydrogen sulfide or ammonia dominate the cloud deck, but lacked definitive evidence either way. “Now, thanks to improved hydrogen sulfide absorption-line data and the wonderful Gemini spectra, we have the fingerprint which caught the culprit,” says Irwin. The spectroscopic absorption lines (where the gas absorbs some of the infrared light from reflected sunlight) are especially weak and challenging to detect according to Irwin.
The detection of hydrogen sulfide high in Uranus’s cloud deck (and presumably Neptune’s) contrasts sharply with the inner gas giant planets, Jupiter and Saturn, where no hydrogen sulfide is seen above the clouds, but instead ammonia is observed. The bulk of Jupiter and Saturn’s upper clouds are comprised of ammonia ice, but it seems this is not the case for Uranus. These differences in atmospheric composition shed light on questions about the planets’ formation and history.
Leigh Fletcher, a member of the research team from the University of Leicester in the UK, adds that the differences between the cloud decks of the gas giants (Jupiter and Saturn), and the ice giants (Uranus and Neptune), were likely imprinted way back during the birth of these worlds. “During our Solar System’s formation the balance between nitrogen and sulphur (and hence ammonia and Uranus’s newly-detected hydrogen sulfide) was determined by the temperature and location of planet’s formation.”
Another factor in the early formation of Uranus is the strong evidence that our Solar System’s giant planets likely migrated from where they initially formed. Therefore, confirming this composition information is invaluable in understanding Uranus’ birthplace, evolution and refining models of planetary migrations.
According to Fletcher, when a cloud deck forms by condensation, it locks away the cloud-forming gas in a deep internal reservoir, hidden away beneath the levels that we can usually see with our telescopes. “Only a tiny amount remains above the clouds as a saturated vapour,” said Fletcher. “And this is why it is so challenging to capture the signatures of ammonia and hydrogen sulfide above cloud decks of Uranus. The superior capabilities of Gemini finally gave us that lucky break,” concludes Fletcher.
Glenn Orton, of NASA’s Jet Propulsion Laboratory, and another member of the research team notes, “We’ve strongly suspected that hydrogen sulfide gas was influencing the millimeter and radio spectrum of Uranus for some time, but we were unable to attribute the absorption needed to identify it positively. Now, that part of the puzzle is falling into place as well.”
While the results set a lower limit to the amount of hydrogen sulfide around Uranus, it is interesting to speculate what the effects would be on humans even at these concentrations. “If an unfortunate human were ever to descend through Uranus’s clouds, they would be met with very unpleasant and odiferous conditions.” But the foul stench wouldn’t be the worst of it according to Irwin. “Suffocation and exposure in the negative 200 degrees Celsius atmosphere made of mostly hydrogen, helium, and methane would take its toll long before the smell,” concludes Irwin.
The new findings indicate that although the atmosphere might be unpleasant for humans, this far-flung world is fertile ground for probing the early history of our Solar System and perhaps understanding the physical conditions on other large, icy worlds orbiting the stars beyond our Sun.
- Patrick Irwin
Professor of Planetary Physics
Department of Physics
University of Oxford, UK
Phone: +44(0) 1865 272083
Cell: +44(0) 7960752607
- Glenn Orton
Senior Research Scientist
Jet Propulsion Laboratory
California Institute of Technology
- Leigh Fletcher
Senior Research Fellow in Planetary Science
University of Leicester, UK
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The GEMMA Podcast
A podcast about Gemini Observatory and its role in the Era of Multi-Messenger Astronomy. Featuring news related to multi-messenger astronomy (MMA), time-domain astronomy (TDA), our visiting instrument program, and more through interviews with astronomers, engineers, and staff both here at Gemini (North and South) and abroad. | 0.902995 | 3.894777 |
Avi Loeb has an unorthodox new idea about how to search for alien civilizations—and it is hardly a surprise. Loeb, who chairs the astronomy department at Harvard University, has spent much of his career thinking about how the first stars came to life after the big bang, and how galaxies were born. But lately he’s become intrigued with the search for extraterrestrial intelligence, or SETI, and he tends to come at it in unusual ways.
Over the past few years, for example, Loeb has suggested searching for aliens by looking for artificial lighting on Pluto, in the admittedly unlikely event that extraterrestrials (ET) have set up an outpost there. He also has proposed trying to detect industrial pollution on distant exoplanets. His latest notion, laid out in a paper he and a co-author just put online: We should look for the microwave beams ETs might use to send light sails wafting between the planets in their home solar systems. “I don’t think it’s nuts,” says Seth Shostak, senior astronomer at the SETI Institute in California. “It’s a clever idea.” Light sails themselves are an actual thing, at least in theory; they use huge sheets of ultrathin Mylar to catch the solar wind, allowing them to carry a payload across interplanetary space without rockets. A prototype is now in the works sponsored by the Planetary Society, which has already flown a test mission and hopes to do a full-fledged demonstration flight next year..
“Unfortunately,” Loeb says, “there’s not enough push in sunlight to provide a very strong acceleration, so one can imagine using artificial radiation instead.” Loeb and his co-author, James Guillochon, a postdoctoral Einstein Fellow at the Harvard–Smithsonian Center for Astrophysics decided that microwaves would be the best candidate, based on efficiency and other factors. To move briskly between planets in an extrasolar system, they figured, you’d need a microwave beam with about a terawatt’s worth of power. “That’s about a tenth of Earth’s entire output,” says Loeb—kind of a lot. But these are aliens he’s talking about, so they could plausibly pull it off, using a powerful ground-based microwave transmitter aimed at the light sail.
Most of that power would be trapped by the light sails. Some, however, would inevitably leak around the edges, so the two astrophysicists did some calculations to see if the leakage could be detected from Earth. Their equations said yes. “It would be easily detectable out to hundreds of light-years away with existing antennas,” Loeb says. The signal would arrive as a burst of energy caused by leakage from one side of the sail, followed by a pause and then a comparable pulse from the other side—a pattern, the authors say, that would distinguish it from natural sources of microwaves.
The only time we could see the microwaves would be when the beam was pointed more or less straight at us. And since the aliens would presumably be using them to travel between planets, the two worlds in question would have to be lined up along the line of sight to Earth. That would only happen in a solar system oriented edge-on from our perspective—just the kind of solar system the Kepler space probe has been discovering by the score. It’s therefore already clear, Loeb says, where to point our antennas.
Whether it’s worth doing so, however, isn’t quite as clear. “It’s not absurd,” says Freeman Dyson, of the Institute for Advanced Study, who came up with his own outside-the-box SETI strategy in a 1960 Science paper: looking for infrared leakage from civilizations that had completely enclosed their stars in artificial, hollow “Dyson spheres” to catch every last drop of solar energy. “But it’s not enough by itself,” he says. “Any practical search program should aim to cover a multitude of possibilities, not just one.”
Since astronomer Frank Drake did the world’s very first SETI search, however, astronomers have looked mostly for extraterrestrial radio transmissions and, more recently, for alien laser beacons, figuring that we should look for technologies we ourselves have actually perfected. Light sails aren’t quite there yet, to say nothing of Dyson spheres, and there are only so many telescopes, radio and otherwise, to go around.
Still, Shostak says, any SETI search we can think of is based on our assumptions about the behavior of aliens, which we know literally nothing about. Odds are that any advanced civilization out there is more advanced than ours, given that we only discovered radio a century ago and digital computing much more recently than that. “The aliens may well have gone beyond biological intelligence, and we really don’t know what machines would choose to do.” Finding ET’s, he says, might well happen by accident, the result of some observation or experiment that had nothing to do with SETI in the first place. That being the case, he says, “I appreciate that [Loeb and Guillochon] are thinking outside the box.”
Ed Turner, a senior Princeton astrophysicist, Loeb’s co-author on the thought experiment about looking for artificial lighting on Pluto (if, by some insanely remote chance, aliens had chosen to build a city there), feels the same. “Collaborating with Avi on SETI and similarly speculative topics,” he says, “is a bit like buying a lottery ticket. It’s extremely likely to yield nothing but if you happen to be very lucky, it could end up being the most important work of your career.”
Which is very much in the original spirit of SETI, laid out in a 1959 Nature paper that inspired Frank Drake to launch the very first radio search the following year. “The probability of success is difficult to estimate,” wrote co-authors Giuseppe Cocconi and Philip Morrison, “but if we never search, the chance of success is zero." (Scientific American is part of Nature Publishing Group.) | 0.846301 | 3.475715 |
In my question How was Earth's "quasi-satellite" 2016 HO3 "first spotted" and it's orbit determined? I link to two videos of simulations of views of 2016 HO3's orbit seen in two different frames.
In this NASA JPL video (above) the view is rotating around the sun following Earth. You can see the earth move slightly closer and farther from the sun since the Earth's orbit is not quite circular.
This video (above) from http://arksky.org/calendar/alerts/714-what-is-it-the-strange-new-object-2016-ho3 shows a projection of 2016 HO3's motion against the stars as seen from Earth's location, but in a fixed direction. You can see the the sun and planets tend to follow the ecliptic, while 2016 HO3 does a figure-eight every year.
The NASA JPL news brief announcing the discovery of 2016 HO3 states:
The asteroid's orbit also undergoes a slow, back-and-forth twist over multiple decades. "The asteroid's loops around Earth drift a little ahead or behind from year to year, but when they drift too far forward or backward, Earth's gravity is just strong enough to reverse the drift and hold onto the asteroid so that it never wanders farther away than about 100 times the distance of the moon," said Chodas. "The same effect also prevents the asteroid from approaching much closer than about 38 times the distance of the moon. In effect, this small asteroid is caught in a little dance with Earth."
note: Paul Chodas is the manager of NASA's Center for Near-Earth Object (NEO) Studies
I think that the fact that it's orbit slowly oscillates on the order of decades (tens of orbital periods) with respect to Earth's orbit means it is in a 1:1 resonance with Earth. But I'm using the term orbital resonance without knowing it's exact definition - if there is one. Perhaps it's a soft term - some orbits may be clearly in resonance, others only roughly in resonance.
Is there a good working definition of orbital resonance, and is 2016 OH3's orbit in 1:1 resonance with Earth's orbit?
bonus: Are Trojan asteroids (at a planet's $L_4$ or $L_5$ triangular libration points) also considered to be in a 1:1 resonance orbit? | 0.806767 | 3.553807 |
IMAGE: NASA/ JPL
CODING IN THE CLASSROOM
CRATERING SATURATION EQUILIBRIUM EXPERIMENT
I'm interested in all the ways computer programing is able to facilitate in-depth learning of a topic. A project that changed the way I look at programing is a crater saturation equilibrium counter I developed in one of my astrophysics classes. I was really able to get a feel for how we determine the age of planetary bodies by counting craters. I ran an experiment for a certain amount of time, and compared that to the number of craters per unit area.
The purpose of this experiment is to carry out a numerical simulation of the cratering process on a planetary surface. This simulation will verify the occurrence of saturation equilibrium: that the density of craters reaches a maximum and remains constant.
This project is to model the lunar crater saturation equilibrium, which is defined as a condition when no further proportionate increase in crater density occurs as input cratering increases. Crater saturation equilibrium refers to the condition in which new impacts, on average, do no proportionately change the general crater number density (craters/km^2) on a surface because craters are packed tightly enough that old craters are destroyed by the creation of new ones. This computer model demonstrates this scenario by using a Monte Carlo simulation. We find that an identifiable saturation equilibrium occurs close to a level previously identifies for this state (Hartmann, 1984), typically fluctuating around a crater density from ~0.4 to 2 times that level. Flooding, basin ejecta blankets, and other obliterative effects can introduce structure and oscillations within this range; even after saturation equilibrium is achieved. This data can tell us more about satellite and planet surface evolution and impactor populations, which were predicated on the assumed absence of saturation equilibrium. The below simulation begins at time zero with zero impact craters, so we can observe the pure results of the Monte Carlo simulation. We should see a tapering off of the slope and it should begin to level off at an average of 70 craters per each ten square kilometers. Below you will find several figures including Python 2.7 plots, a referenced image, and Excel spreadsheet table. The last pages of this report are the code for my program.
Fig. 1) crater density on this hypothetical surface reaches equilibrium at around 400,000 years after the clock starts
Fig. 2) slope of the line decreases and levels off beginning around 300,000 years
Through this project, I have learned that crater saturation equilibrium does occur in our solar system. The impacts on average do not proportionately change the general crater number density (craters/km^2) on a surface because craters are packed tightly enough that old craters are destroyed by the creation of new ones. We need to know this information about a planetary body in order to find out more about the body’s history and how old it is today. The line of best fit in figure 2 should be fit to a different region of the graph, but I couldn’t get the code right. The line should be fixed on the region above 60 craters per 10km^2 and 300,000 years in order to clearly show that the slope was leveling off over time. Since my function for creating a best-fit line used the early data with the steeper slope, the average looks linear and positive but should in fact be logarithmic where the end slope is zero. The observation of a near-zero slope at the end of the plot demonstrates the effect of crater saturation equilibrium.
The following figure, fig. 3), is from a study by Hartmann, William K., and Robert W. Gaskell. Their simulation was somewhat more complex than my simulation, and used different starting conditions, but used roughly the same surface area (500 x 500 km). You can see that some new craters cover old craters, and some obliterate more than one small, older crater. The results of their study are similar to mine; I included this image from their report to have an interesting visual aid:
Fig. 3) nine stages of primary crater accumulation for an imaginary surface, 522 x 522 km
Hartmann, William K., and Robert W. Gaskell. "Planetary Cratering 2: Studies of Saturation Equilibrium." Meteoritics & Planetary Science 32.1 (1997): 109-21. Web. 16 Nov. 2015.
Fig. 4) first page of my excel spreadsheet (consecutive pages were far too many to include in this report) demonstrates that I printed out the time against number of craters in a table and compared the excel plot to those I made in Python.
Download the free software and give this a try for yourself! You can copy and paste the code below, and modify the initial conditions to experiment your way! And as you saw in Fig. 4, this experiment can also be conducted in Microsoft Excel. | 0.879393 | 3.748816 |
Supermoons can appear bigger and brighter than usual and there have been four so far this year. Tonight's Supermoon is the last one of 2020 and it coincides with the fifth Full Moon of the year. Also known as the Full Flower Moon, the Milk Moon and Corn Planting Moon, astronomers will not want to miss this spectacle.
The Supermoon will appear bigger and brighter because it will be near its lowest orbit of the planet.
As the Moon races around the Earth, its path is not perfectly circular and is instead elliptic.
As a result, the Moon is closer to or farther from us every night.
The Moon's lowest orbit of Earth is known as the lunar perigee and the highest is the apogee.
If a Full Moon falls within 90 percent of apogee, it is known as a Supermoon.
Supermoon tonight: Find out how to watch the Full Moon live online
How to watch the Supermoon live online tonight?
The Moon reached full illumination by the Sun at 11.45am BST (10.45am UTC) today.
For many, the peak occurred in the daytime when the Moon was still below the horizon.
But the good news is you can watch the Supermoon tonight from the comfort of your home.
Courtesy of the Virtual Telescope Project in Italy, you can watch the event in the embedded video player below.
Hosted by astrophysicist Gianluca Masi, the stream is scheduled to kick off at 7.30pm BST (6.30pm UTC).
There can be three or four Full Supermoons in a row
Dr Masi will track the Moon as it rises over the picturesque skyline of Rome.
He said: "At Virtual Telescope we will share the show with you from Rome, admiring our satellite rising above the horizon.
"We hope to bring to you, at home, the beauty of the sky, during these hard times we are living all together."
How to see the Supermoon in the UK [INSIGHT]
What is the spiritual meaning of the Full Moon? [ANALYSIS]
Starlink satellites tracker: Can you see SpaceX's Starlink tonight? [INSIGHT]
How often does a Supermoon take place?
Supermoon is not a scientific term and is only loosely defined by astronomers.
The term was coined by astrologer Richard Noelle in 1979 as a Full Moon within 90 percent of lunar perigee.
By one definition, a Supermoon is a Full Moon within 90 percent of the Moon's lowest point in a given orbit.
NASA lunar expert Gordon Johnston said: "Under this definition, in a typical year there can be three or four Full Supermoons in a row and three or four New Supermoons in a row.
"For 2020, the four Full Moons from February through May meet this 90% threshold."
Another, much narrower definition defined a Supermoon as a Full Moon within 90 percent of the Moon's lowest orbit in a given year.
By this definition, only the Full Moons in March, April and May are super.
The closest Supermoon of the year was in April - the Full Pink Moon. | 0.832804 | 3.003267 |
Astronomers Track the Birth of a ‘Super-Earth’
A new model giving rise to young planetary systems offers a fresh solution to a puzzle that has vexed astronomers ever since new detection technologies and planet-hunting missions such as NASA’s Kepler space telescope have revealed thousands of planets orbiting other stars: While the majority of these exoplanets fall into a category called super-Earths — bodies with a mass somewhere between Earth and Neptune — most of the features observed in nascent planetary systems were thought to require much more massive planets, rivaling or dwarfing Jupiter, the gas giant in our solar system.
In other words, the observed features of many planetary systems in their early stages of formation did not seem to match the type of exoplanets that make up the bulk of the planetary population in our galaxy.
“We propose a scenario that was previously deemed impossible: how a super-Earth can carve out multiple gaps in disks,” says Ruobing Dong, the Bart J. Bok postdoctoral fellow at the University of Arizona’s Steward Observatory and lead author on the study, soon to be published in the Astrophysical Journal. “For the first time, we can reconcile the mysterious disk features we observe and the population of planets most commonly found in our galaxy.”
How exactly planets form is still an open question with a number of outstanding problems, according to Dong.
“Kepler has found thousands of planets, but those are all very old, orbiting around stars a few billion years old, like our sun,” he explains. “You could say we are looking at the senior citizens of our galaxy, but we don’t know how they were born.”
To find answers, astronomers turn to the places where new planets are currently forming: protoplanetary disks — in a sense, baby sisters of our solar system.
Such disks form when a vast cloud of interstellar gas and dust condenses under the effect of gravity before collapsing into a swirling disk. At the center of the protoplanetary disk shines a young star, only a few million years old. As microscopic dust particles coalesce to sand grains, and sand grains stick together to form pebbles, and pebbles pile up to become asteroids and ultimately planets, a planetary system much like our solar system is born.
“These disks are very short-lived,” Dong explains. “Over time the material dissipates, but we don’t know exactly how that happens. What we do know is that we see disks around stars that are 1 million years old, but we don’t see them around stars that are 10 million years old.”
In the most likely scenario, much of the disk’s material gets accreted onto the star, some is blown away by stellar radiation and the rest goes into forming planets.
Although protoplanetary disks have been observed in relative proximity to the Earth, it is still extremely difficult to make out any planets that may be forming within. Rather, researchers have relied on features such as gaps and rings to infer the presence of planets.
“Among the explanations for these rings and gaps, those involving planets certainly are the most exciting and drawing the most attention,” says co-author Shengtai Li, a research scientist at Los Alamos National Laboratory in Los Alamos, New Mexico. “As the planet orbits around the star, the argument goes, it may clear a path along its orbit, resulting in the gap we see.”
Except that reality is a bit more complicated, as evidenced by two of the most prominent observations of protoplanetary disks, which were made with ALMA, the Atacama Large Millimeter/submillimeter Array in Chile. ALMA is an assembly of radio antennas between 7 and 12 meters in diameter and numbering 66 of them once completed. The images of HL Tauri and TW Hydrae, obtained in 2014 and 2016, respectively, have revealed the finest details so far in any protoplanetary disk, and they show some features that are difficult, if not impossible, to explain with current models of planetary formation, Dong says.
“Among the gaps in HL Tauri and TW Hydrae revealed by ALMA, two pairs of them are extremely narrow and very close to each other,” he explains. “In conventional theory, it is difficult for a planet to open such gaps in a disk. They can never be this narrow and this close to each other for reasons of the physics involved.”
In the case of HL Tauri and TW Hydrae, one would have to invoke two planets whose orbits hug each other very closely — a scenario that would not be stable over time and therefore is unlikely.
While previous models could explain large, single gaps believed to be indicative of planets clearing debris and dust in their path, they failed to account for the more intricate features revealed by the ALMA observations.
The model created by Dong and his co-authors results in what the team calls synthetic observations — simulations that look exactly like what ALMA would see on the sky. Dong’s team accomplished this by tweaking the parameters going into the simulation of the evolving protoplanetary disk, such as assuming a low viscosity and adding the dust to the mix. Most previous simulations were based on higher disk viscosity and accounted only for the disk’s gaseous component.
“The viscosity in protoplanetary disks may be driven by turbulence and other physical effects,” Li says. “It’s a somewhat mysterious quantity — we know it’s there, but we don’t know its origin or how large its value is, so we think our assumptions are reasonable, considering that they result in the pattern that has actually been observed on the sky.”
Even more important, the synthetic observations emerged from the simulations without the necessity to invoke gas giants the size of Jupiter or larger.
“One super-Earth turned out to be sufficient to create the multiple rings and multiple, narrow gaps we see in the actual observations,” Dong says.
As future research uncovers more of the inner workings of protoplanetary disks, Dong and his team will refine their simulations with new data. For now, their synthetic observations offer an intriguing scenario that provides a missing link between the features observed in many planetary infants and their grown-up counterparts. | 0.928273 | 3.989959 |
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