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TESS is the successor to the wildly successful Kepler/K2 Mission and is designed to find exoplanets using the same technique as Kepler – looking for their shadows as planets pass in front of their host stars, i.e. the transit technique.
Sadly, the Kepler spacecraft was officially shut down two weeks ag0 because it ran out of fuel, but TESS, launched last March, is off and running, having already discovered about half a dozen new planets.
One of those planets, we discussed in journal club on Friday – a planet orbiting the star HD1397. The gas giant planet is about the same size as Jupiter but half the mass, making it significantly less dense than Saturn.
The planet also has an unusually eccentric or stretched-out orbit that swings very near its host star, passing to within 8 stellar radii from its star at its closest point. By contrast, the Earth is 200 stellar radii away from the Sun.
If this planet had been discovered 20 years ago, it would have completely stumped astrophysicists, and many would likely have doubted its existence. Nowadays, though, such strange planets are practically the norm in exoplanet astronomy.
So with HD1397 b’s discovery, the exoplanet train rumbles on, and we should expect thousands upon thousands more bizzarities from TESS that will, like Kepler’s discoveries, again re-write the planetary rulebook.
At our research group meeting, we also discussed the art of scientific presentations. I’ve pasted the example presentation I gave below.
At our research group meeting on Friday, we discussed an interesting paper from Dr. Tom Barclay and colleagues, which explored how many and what kinds of planets we might find with the TESS mission, launched in April this year.
As Barclay et al. argue, trying to estimate the planet yield from an upcoming survey provides several benefits. For instance, knowing how many planets TESS may find can help astronomers figure out how much time to allot for follow-up observations at large observatories. Also, thinking about TESS discoveries is like staying awake on Christmas eve, anticipating all the presents – it’s just plain exciting.
And make no mistake – TESS will be another game-changer. Kepler focused on figuring out how many of each kind of planet there is in our galaxy, but as one of the trade-offs to facilitate this kind of statistical study, most of the systems found by Kepler are much too far away and dim for us to conduct follow-up studies and learn more about the systems.
TESS takes a different tack, focusing on bright, nearby stars for which additional characterization of the planets will be easier. For instance, some of the planets discovered by TESS will be observed by NASA’s next behemoth, the James Webb Space Telescope, which will reveal the planets’ atmospheres in exquisite detail.
Barclay’s paper lets us shake the presents under the TESS tree, hinting at the goodies inside. By modeling a wide variety of planets in orbit around the 3+ million stars that TESS will see, they try to simulate the kinds of observations the mission will collect and figure out which planets TESS can find easily and which ones it will struggle with.
For example, they find TESS may discover nearly 300 planets with radii smaller than twice the Earth’s. Among these potentially Earth-like planets, roughly ten will orbit in the temperate zone, making them possible oases for extraterrestrial life.
After reading these results about potentially habitable planets, I was also excited about their prediction that TESS may find 12,000+ giant (i.e. Jupiter-sized) planets. Barclay et al. caution that these objects will be especially hard to distinguish from astrophysical false positives. But these planets may also reveal some of the most interesting astrophysical phenomena, so if there are any clever tricks to extricate these planets, the effort might prove worthwhile.
Just recently returned from the meeting of the Northwestern Section of the American Physical Society, which took place on the lovely campus of the University of Puget Sound.
It was a cozy meeting of physicists and student physicists from throughout the northwest, and there was a variety of talks and posters on topics from gravitational waves to DNA computers to diversity in science.
One of the talks that really stuck out in my mind was the banquet presentation from Puget Sound’s Prof. James Evans about the antikythera mechanism, a mysterious barnacle-encrusted gearwork recovered from an ancient Grecian shipwreck.
Constructed by an unknown artisan in about 200 BC (according to Evans), the machine could track the date, follow lunar phases, predict solar eclipses, and even maybe show planetary motions — all with the turn of a single crank.
For my presentation, I gave a brief overview of exoplanet astronomy, with a focus on how these discoveries have begun to hone our ideas about alien life and extraterrestrial civilizations. I’ve posted by presentation below.
With the very first discovery of an exoplanet around a Sun-like star (51 Peg b), astronomers were introduced to hot Jupiters. These totally unexpected planets resemble Jupiter in mass, composition, and size, but they have orbits that nearly skim the surfaces of their host stars. Some of them are even losing their atmospheres under the apocalyptic glare of their host stars.
How their lives began remains a mystery, but we have a pretty good idea of how their lives will end – they will be engulfed or torn apart by their host stars. That’s because hot Jupiters are big and close enough that they can actually raise a tidal bulge on the stars (and we can actually see the bulge in a handful of cases).
This tidal interaction can cause the planets to spiral downward toward the stars, and at the same time, it causes the spins to spin faster until the planet is destroyed by the star. The same tidal effect, just in reverse, is driving the Moon away from the Earth, while slowing down the Earth’s spin. But here’s the key: we don’t know how quickly the planets are spiraling in.
Enter Prof. Kaloyan Penev of UT Dallas Physics Dept. On Valentine’s Day last week, he and his colleagues published an academic love note exploring planetary tidal decay. To do this, they modeled the evolution of planetary orbits and stellar spins under the influence of tides. The tracks in the figure at left show how a planet’s orbital period (or distance from its star) might shrink over billions of years, thanks to tides. The clump of spaghetti noodles in the figure shows that evolution for a range of assumptions about the rate of decay.
By comparing the stellar spin rate and planetary orbit predicted by their model to those we actually observe for each system, Penev and colleagues showed that the tidal decay rates might actually slow down as the planets approach their stars. So perhaps instead of an reckless death dive into the star over a few million years, the planets make like Zeno’s tortoise and tiptoe closer and closer without plunging in.
Upcoming surveys such as the TESS mission and the Large Synoptic Survey Telescope may soon allow us to test whether planets do or do not plunge into their stars. Theoretically, we expect stars that eat their planetary children dramatically brighten up by a factor of 10,000 over a few days – faster than a supernova brightens but nowhere near as bright. These surveys might able to see stars engaged in this act of cosmic infanticide.
A month ago, astronomers found, for the first time, an asteroid that definitely originated from outside our solar system.
The object, 1I/ʻOumuamua, came screaming into our solar system at 60,000 mph, took a sharp turn around the Sun, and passed within 10 million miles of Earth on Oct 18 before beginning its long journey out of our solar system and back into interstellar space.
Given its highly elongated and inclined orbit, ʻOumuamua was initially classified as a comet, but follow-up observations showed no sign of a coma, and so it was re-classified as an asteroid. Its discovery has prompted a flurry of short but exciting astronomical studies, and in our research group meeting this week, we discussed two: Ye et al. (2017) and Laughlin & Batygin (2017).
In their study, Ye and colleagues describe their observations of ʻOumuamua’s brightness and color. Their color observations indicated that ʻOumuamua is slightly but not very red, unlike many icy bodies in our Kuiper Belt. This result suggests it either formed close to its original central star (and never had much ice) or spent time near enough to its original parent star to have baked off any ice.
They also estimated that ʻOumuamua passed very near Earth’s orbit, close enough that, if any material were ejected from its surface, it may produce a meteor shower in a few hundred years.
In their study, Laughlin and Batygin took a more theoretical tact and explored possible implications of ʻOumuamua’s for the existence of planets like the putative Planet Nine.
ʻOumuamua almost definitely originated in a distant solar system and was ejected by a gravitational interaction with a planet in that system, and Laughlin and Batygin point out that most of the known exoplanet population would probably not be very good at ejecting objects like ʻOumuamua: these planets are so small and/or close to their host stars that they cannot easily liberate asteroids like ʻOumuamua from the host stars’ gravitational clutches.
But, Laughlin and Batygin suggest, if there is a sizable population of largish (several Earth masses) planets several times farther from their host stars than Earth is from the Sun, then gravitational ejections of asteroids might occur frequently enough to explain objects like ʻOumuamua.
Granted, they’re dealing with a sample size of one, but several all-sky surveys, like LSST and TESS, will arrive on the scene any day now. And we may very soon find other interstellar interlopers like ʻOumuamua. The galaxy is probably full of them.
In case you didn’t hear, late last year, astronomers confirmed a planet around our nearest stellar neighbor, Proxima Centauri, a red-dwarf star just four light years from Earth. The planet is probably about 30% more massive than Earth, probably making its composition Earth-like, and it’s in the habitable zone of its star, at a distance of about 0.05 astronomical units (AU) – all of which make it an exciting prospect for follow-up studies.
And just last week, Guillem Anglada and colleagues announced the further discovery of a debris disk around the star. The left figure up top shows the image, in radio wavelengths, of emission from the disk – the disk appears as the rainbow blob near the center, and the location of the host star Proxima is marked with a black cross.
The disk’s appears to orbit between 1 and 4 AU from its host star, which would put it between the Earth and Jupiter if it orbited in our solar system. However, since the red-dwarf star is so much smaller and cooler than our Sun, those orbital distances correspond to temperatures of only a few tens of degrees, making Proxima’s disk more akin to our Kuiper belt than our main asteroid belt.
The radio light we see from the disk is mostly due to thermal emission from dust. Using the above temperature estimate (and some other reasonable assumptions), Anglada and colleagues estimate (with large uncertainties) Proxima’s disk has about one thirtieth the mass of Ceres in dust and a lunar mass in larger bodies – almost as much mass as our Kuiper belt. There’s also marginal evidence in the data for a larger and cooler disk as well, perhaps 30 times farther from the star than the inner disk, and for something perhaps even more interesting.
In the right figure above, see the greenish blob just below and to left of the rainbow blob? That (admittedly weak) signal could be emission from a ring system orbiting a roughly Saturn-mass planet about 1.6 AU distant from the star. The authors point out that there’s a small but non-zero chance that it’s actually just a background galaxy that photobombed their observations, a possibility that can be easily tested by looking at Proxima again in a few months. But if it turns out to be a ringed planet, it would be the first exo-ring system directly imaged (other systems show possible signs of rings).
That would make Proxima an even more unusual planetary system since small stars tend to have small planets, and I’m only familiar with one other red dwarf star that hosts a big planet – NGTS-1 b, a red-dwarf hosting a hot Jupiter. But if there’s one thing that exoplanet astronomy has taught us in the last few decades, it’s to expect the unexpected.
The diagram below shows the structure of the Proxima Centauri system suggested by Anglada and colleagues.
Exoplanets are being discovered from near and far, and one way to learn more about how these planets form is to study the disk of gas and dust from which they form.
Join the Boise State Physics Department on Friday, Oct 6 at 7:30p in the Multi-Purpose Classroom Building, room 101 to hear Prof. Hannah Jang-Condell of the University of Wyoming discuss her cutting-edge research on these protoplanetary disks and how the telescopes at University of Wyoming are being used to better understand and characterize exoplanets.
At 8:30p after the presentation, we will stargaze on the roof of the Brady Street Parking Garage, weather permitting.
The event is free and open to the public. | 0.964198 | 3.775122 |
You're touching on a lot of related topics which isn't recommended for Stack Exchange. It's better to keep it to one question and specific. That said, I'll give this an answer as best I can, as I've been interested in this subject for a while and have read up on it a bit. The powers that be might close this question for being too broad and/or lacking specifics on the specific details of the rogue planet that affects Earth's orbit.
The subject of the orbital systems around different stars is of interest to astronomers and it has been modeled, many times in fact and observed, though it's very difficult to get a good look at other solar systems. Most of what has been observed is probably incomplete and a lot of what has been modeled involves some guess-work so it's an ongoing field of study.
I have to think that astronomers have simulated solar systems and come
to some conclusions about that. Is anyone familiar with that and can
say something about it?
Yes, astronomers have studied and modeled this. It's worth pointing out that models will only give the right answers if you ask the right questions. The fact that astronomers didn't expect, but found many hot Jupiters is one example of the problem with running models vs learning how real systems are likely to be set up.
This is one of my favorite videos on solar-system formation which touches on your question, though this one focuses on inner-planet formation, it's entirely mathematical modeling and it suggests that 3 gas giants tends towards instability while two can be stable. It's a little old now, but I think it's still accurate information. The modeling begins about 20 minutes into the video and the 3 gas giant chaos is shown around 24 minutes.
Scholarpedia also has a nice article on the current solar system's stability.
When you write this: "I have the idea that, in a complex system, orbits would tend toward roughly circular and in the same plane."
I think it's safe to say that there are both stable and unstable systems and an unstable system, after it kicks enough planets or other material out, will become a stable system.
I think it's also safe to say that the proto-planetary disk is what causes planets to form on the same plane, but planetary migration may change that. The sum of inclination should remain fixed, but ejected can change that.
Our solar system, the 8 known planets orbit about 6 degrees off the Sun's equator and planet 9 is one possible explanation for that, but an ejected planet could explain it too.
So I have the idea that in a complex system, where the different
bodies can affect each other's orbits,
This is probably true and it's still true in our solar system. Jupiter and Saturn affect Venus, Earth and Mars Milankovich cycles. Mars, being the closest to Jupiter is especially prone to large axial tilt shifts and eccentricity shifts. Jupiter might, in time, even pull Mercury entirely out of it's orbit where it could move significantly. The odds may be low, but if that happens, once it starts, Mercury could pass close enough to Venus or Earth and undergo a gravity assist and basically end up anywhere, possibly crashing into another planet or crashing into the sun.
There is a circularization effect caused by tides, but it only applies in 2 body systems where the rotation is faster than the Orbit and the tidal effect pushes the orbiting object outwards. There seems to be a circularizing effect for mutually tidally locked systems like Pluto-Charon but planetary perturbations prevent planets from having neat circular orbits in multi-planet systems. They can still be long term stable, but there is eccentricity variation.
The only planet in our solar system with a nearly perfect circular orbit is Neptune and I suspect it's because it's the outer-most planet. Outer planets tend to perturb the orbits of inner planets, but less so the other way around. At least, that seems true. I can't give a good mathematical reason for that, it's more loosely deducted on my part.
The inner 4 planets have eccentricity that changes over time (one of the Milankovich cycles, driven primarily by outer planets). Mars' line looks more straight, but it's on a different axis, it actually changes the most.
Source of image
they would tend to become circular and in a plane
I wouldn't make this assumption. Though the proto-planetary disk likely begins in a plane over the star's equator, some systems have been found that don't orbit in a plane. A plane may be most common, but I suspect that's because all systems begin that way more than they tend to become that way.
See here and here
To your main question,
Suppose a rogue planet came zipping through the solar system and
changed the earth's orbit a little, including the plane of the orbit.
I would think that if a rogue planet changed Earth's eccentricity, that Jupiter over time would return Earth to about where it was. Maybe with the inclination too. I couldn't find any good information on inclination changes over time by orbital perturbation.
If Earth's semi-major axis was changed, that seems to be more constant and that would change the length of Earth's year and might might be a much more permanent change. Likewise, if the Semi-major axis was moved into resonance, say with Jupiter or Venus or Mars, . . . that might be bad, as it might open the door to repeating perturbations and instability.
That's my understanding anyway. Corrections welcome. | 0.862738 | 3.262881 |
The Hubble Space Telescope has provided another remarkable view of Eta Carinae, one of the galaxy’s most massive stars as it continues a cosmic fireworks show, a slow-motion train wreck that may end with a cataclysmic supernova blast in the astronomically near future.
The show began 170 years ago when the star suddenly and dramatically brightened in an 18-year-long event now known as the “Great Eruption.” Becoming the second brightest star in the sky for more than a decade, Eta Carinae eventually faded from view, now and then brightening and dimming.
One possible explanation for the Great Eruption is that the largest member of a triple star system, one with more than 150 times the mass of the Sun, swallowed a smaller companion, throwing out two huge lobes of gas and dust that give the system its iconic appearance.
The star remains on an apparent path toward supernova, and Hubble’s latest image reveals the ultraviolet glow of magnesium between the lobes expanding to either side of the central binary and the regions just beyond the bubbles where nitrogen filaments are heated by shock waves.
“We’ve discovered a large amount of warm gas that was ejected in the Great Eruption but hasn’t yet collided with the other material surrounding Eta Carinae,” said Nathan Smith, lead investigator of the Hubble program. “Most of the emission is located where we expected to find an empty cavity. This extra material is fast, and it ‘ups the ante’ in terms of the total energy for an already powerful stellar blast.”
Hubble has studied Eta Carinae for decades in visible and infrared light, “and we thought we had a pretty full accounting of its ejected debris,” Smith said.
“But this new ultraviolet-light image looks astonishingly different, revealing gas we did not see in other visible-light or infrared images. We’re excited by the prospect that this type of ultraviolet magnesium emission may also expose previously hidden gas in other types of objects that eject material, such as protostars or other dying stars. Only Hubble can take these kinds of pictures.” | 0.853592 | 3.924319 |
One of the most famous Hubble images is a view of the Eagle Nebula dubbed “The Pillars of Creation.” Originally produced in 1995, the view showed details of three columns of gas, as NASA’s website put it, “bathed in the scorching ultraviolet light from a cluster of young, massive stars in a small region of the Eagle Nebula, or M16.” This iconic image of the wonders of Hubble exploration appeared on tee shirts and pillows, and even a postage stamp.1
To celebrate the 25th anniversary of the telescope, Hubble revisited the site, sending back data for sharper and broader images. Photographed in both visible and near-infrared light, the pillars appear as evanescent shapes containing newborn stars. As astronomers pieced together the exposures, they were amazed by the detail that was visible for the first time.
Astronomer Paul Scowen of Arizona State University at Tempe observed of the new images: “There is only one thing that can light up a neighborhood like this: massive stars kicking out enough horsepower in ultraviolet light to ionize the gas clouds and make them glow. Nebulous star-forming regions like M16 are the insterstellar neon signs that say ‘We just made a bunch of massive stars here.’ “2
Several different Hubble exposures were combined to create the 2014 visible light view. The Hubble website explains, “Streamers of gas can be seen bleeding off the pillars as the intense radiation heats and evaporates it into space. Denser regions of the pillars are shadowing material beneath them from the powerful radiation. Stars are being born deep inside the pillars, which are made of cold hydrogen gas laced with dust. The pillars are part of a small region of the Eagle Nebula, a vast star-forming region 6,500 light-years from Earth. The colors in the image highlight emission from several chemical elements. Oxygen emission is blue, sulfur is orange, and hydrogen and nitrogen are green.”3The near-infrared view reveals newly formed stars behind the nebula and inside the pillars not seen in the visible light image.
View this public domain “Hubblecast” to learn more about the photograph: | 0.837074 | 3.382337 |
A NASA spacecraft is keeping tabs on a vast dust storm on Mars that has spawned changes in the Martian atmosphere felt by two rovers on the planet's surface.
The Martian dust storm was first spotted by NASA's Mars Reconnaissance Orbiter (MRO) on Nov. 10 and has been tracked ever since. The agency's Mars rover Opportunity has seen a slight drop in atmospheric clarity due to the storm. Meanwhile the newer Curiosity rover — which has a built-in weather station — has seen a drop in air pressure and slightly increased nighttime temperatures halfway around the planet from Opportunity, NASA officials said.
"This is now a regional dust storm," Rich Zurek, NASA's chief Mars scientist at the Jet Propulsion Laboratory in Pasadena, Calif., said in a statement Wednesday (Nov. 21). "It has covered a fairly extensive region with its dust haze and it is in a part of the planet were some regional storms have grown into global dust hazes."
NASA is combining observations by the Curiosity rover and MRO to create a complete picture of the Martian dust storm. The Spain-built Rover Environmental Monitoring Station on Curiosity gives scientists a real-time look at conditions over the rover's position inside Gale Crater.
The Mars Color Imager on MRO was built by Malin Space Science Systems in San Diego. It was Malin's Bruce Cantor who first spotted the storm in photos from the powerful Mars camera on Nov. 10. [Amazing Mars Photos by MRO Spacecraft]
"For the first time since the Viking missions of the 1970s, we are studying a regional dust storm both from orbit and with a weather station on the surface," Zurek said.
Because the dust from the current storm is absorbing sunlight instead of reflecting it, a warming effect 16 miles (25 kilometers) above the Martian tempest has been seen by MRO. The effect, first recorded by MRO's Mars Climate Sounder on Nov. 16, has led to a temperature increase of 45 degrees Fahrenheit (25 degrees Celsius) so far.
Warmer temperatures are not confined to the Martian south. The circulation of the Martian atmosphere has also led to a hot spot in the planet's northern polar regions. The temperature on Mars is typically about minus 80 degrees F (minus 60 degrees C), but can vary depending on location and the Martian season.
"One thing we want to learn is why do some Martian dust storm get to this size and stop growing, while others this size keep growing and go global," Zurek said.
A global dust storm on Mars could have implications for the Opportunity and Curiosity rovers. If the current dust storm were to expand to cover the Red Planet, the dust settling on Opportunity's solar panels could reduce the rover's power supply. Opportunity has been exploring the plains of Meridiani Planum since its 2004 landing on Mars.
NASA's newer Mars rover Curiosity, meanwhile, would likely see increased haze in its photos of nearby terrain, as well as an above normal air temperature. The 1-ton Curiosity rover landed on Mars on Aug. 5 and is powered by a radioisotope thermoelectric generator that is unaffected by dust storms. | 0.825481 | 3.432816 |
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Utopia Planitia, northern lava plain on the planet Mars that was selected as the landing site of the U.S. Viking 2 planetary probe. Photographs transmitted from the Viking 2 lander, which touched down at 47.97° N, 225.74° W, on September 3, 1976, depicted a boulder-strewn plain that superficially resembles the Viking 1 landing site in Chryse Planitia. Soil-sample analyses conducted by the landers show that the soils at the two sites are nearly identical in composition, which is probably the result of a mixing of windblown dust from wide regions of the planet. The Utopia plain differs from the Chryse area in that it has a system of shallow troughs, which may be associated with ice-wedge activity as a result of permafrost. Vesicular boulders—i.e., those with small gas-formed pits, indicative of a volcanic origin—observed by the lander at the Utopia site may be either local lavas or rocks ejected from the nearby impact crater Mie.
Images from the Viking 2 lander showed the persistence of a thin layer of white ground frost, composed of water ice, for about 100 days during each of the two Martian winters observed. The frost is probably first precipitated together with carbon dioxide, which then sublimes in the sunlight, leaving only the water portion.
Learn More in these related Britannica articles:
Mars: Sparsely cratered plains…Amazonis Planitia (160° W), and Utopia Planitia (250° W). The only significant relief in this huge area is a large ancient impact basin, informally called the Utopia basin (40° N, 250° W).…
Mars, fourth planet in the solar system in order of distance from the Sun and seventh in size and mass. It is a periodically conspicuous reddish object in the night sky. Mars is designated by the symbol ♂.…
Viking, either of two robotic U.S. spacecraft launched by NASA for extended study of the planet Mars. The Viking project was the first planetary exploration mission to transmit pictures from the Martian surface. Viking… | 0.881626 | 3.191002 |
Spitzer Space Telescope, formerly also known as the Space Infrared Telescope Facility was initially launched on August 25, 2003. Originally, the mission was designed for 2.5 years, but after observing its outstanding and marvelous discoveries, it’s timespan was extended to 5 years. One of NASA’s 5 greatest observatories, Spitzer was able to see and reveal the mysterious features of the universe.
Warm objects inside our universe do not always emit radiation in the visible spectrum of light. There are different types of spectrum in which objects emit heat. Infrared radiation has wavelengths longer than that of visible light, making it significant for the observation of the cosmos.
Taking this into account, we can say that the Universe has been playing hide and seek with us. Spitzer Space Telescope worked by playing the same game with the universe and capturing these infrared radiations emitted by the distant cosmic objects. It gave us significant insight into the Universe which has led to some exciting discoveries. Here are the top 7 discoveries by Spitzer Space Telescope-
7. Light From Very First Stars
The light emitted from the first generation of stars would have been emitted around 13 billion years ago. Therefore, they would have been redshifted towards the infrared spectrum making it almost impossible to observe them with the optical telescopes but not for Spitzer. It is exciting to think that just an 85 cm long infrared telescope would have been able to detect light emitted only a few hundred million years after the big bang.
6. Buckyballs In Space
The Spitzer Space Telescope has discovered the ‘celebrity’ molecule – Buckyball. It comprises of 60 carbon atoms resembling a football. The interstellar medium between the stars seemingly contains these molecules known as Buckminsterfullerene.
5. Oldest Galaxy Ever Known
Spitzer helped discover the oldest and most distant known galaxy ever known. Its name is GN-z11.
This galaxy was identified by teams of Hubble Space Telescope and Spitzer Space Telescope. Having a stellar age of 40 million years, it is about 1/25th the size of Milky Way Galaxy and its mass is about 1% of it.
4. First-Ever Exoplanet Weather Map
Spitzer Space Telescope was able to frame the first-ever map of the surface of an exoplanet, a gas giant called HD189744b. Though Spitzer was never truly designed for this purpose, to study the planets beyond our solar system, it still has managed to surprise us with its extraordinary impressive performance.
3. Faraway Black Holes
Because of the excellent aperture and the high definition images of the Spitzer Space Telescope, NASA often used it to discover and observe the nature of the most distant nebulae as well as the black holes present inside nearby galaxies. Black Holes do not emit radiation in the visible spectrum of light but in the infrared spectrum. Therefore, Spitzer has been known to give the best observations of the black hole till now.
2. The Largest Hidden Ring Around Saturn
Spitzer was able to gather the stunning images of the hidden rings surrounding Saturn often referred to as the Phoebe ring. Originating from the satellite Phoebe, it is now more than 200 times as big as across the Saturn itself. This ring is really strange, it is tilted and probably orbits backward.
1. Seven Earth-Like Planets Around A Star
TRAPPIST-1 is an ultra-cool dwarf star located at a distance of 40 light-years away from us. At first, scientists thought that there were only 3 exoplanets orbiting the dwarf star but on Feb 22, 2017, Spitzer Space Telescope discovered that the system has 7 Earth-like planets. Apparently, the first 3 planets lie in the habitable zone of the star and could host intelligent life also.
After 16 years of unparalleled discoveries of the concealed features of the cosmos, the journey of NASA’s Spitzer Space Telescope has finally come to an end. On 30th January 2020, NASA decided to shut down the telescope. Future infrared observatories will build upon the legacy of Spitzer and will try to finish what Spitzer started.
Farewell, Spitzer. Float in Peace.
Watch this video for complete information-
This Article is Written By Sukhjit Singh & Mallika. | 0.878615 | 3.738054 |
The rule for space aesthetics has always been clear: First comes the science, then comes the art. You can’t take the most distant cosmic photographs ever captured unless you build and launch the Hubble Space telescope first. You can’t capture close-up shots of Neptune’s aquatic blue or Jupiter’s spin-painted atmosphere or Saturn’s braided rings until you get the Voyager spacecraft out to their neighborhood.
(Photos: Window on Infinity: Pictures from Space)
Now that rule is being proven again with sensational images making the rounds on the Web — and soon to be published in the new book Planetfall, by Michael Benson — that provide a cool and new and faintly eerie look at Mars. Benson is not a NASA engineer, much less an astronaut. What he is however is a photographer and media artist, one with an unusually sharp eye for images from the deep elsewhere that can dazzle terrestrial sensibilities like ours.
The pictures doing the dazzling today were shot by the Mars Reconnaissance Orbiter (MRO)in 2010 and show the predictable — if beautiful — rusty dunes of the Martian surface, sculpted like snowdrifts from the planet’s tenuous but persistent wind. The scene is broken up, however, buy strange, black, spidery blemishes scattered randomly about. From orbit they look tiny, but on the ground they’d be huge — surely larger than a football field. It’s partly their very ugliness that makes them eye-catching and partly the mystery of what causes them. Actually, however, that last part is likely no mystery at all — and the source of the features is one more indication of how complex a planet Mars is turning out to be.
While Mars can sometimes be an almost temperate place — at high noon in midsummer on the Martian equator, temperatures can reach or exceed 70º F (20º C) — at other times it can fall as low as -225º F (-153º C). This can have a dramatic effect on Mars’s two most important volatile substances: water and carbon dioxide. Last year, MRO images revealed seasonal markings on Martian slopes, with long, dark streaks appearing in the spring and summer and vanishing in the winter. The streaks emerge and retreat at cycles in the Martian year consistent with the freezing and thawing points of water, suggesting that subsurface ice deposits are intermittently melting and running and then retracting back into the soil as the thermometer falls. Said mission scientist Mike Myer at the time the finding was announced:
“Since the MRO arrived at Mars our overarching theme has been ‘follow the water.’ Now we may be catching Mars in the act. We have found repeated and predictable evidence of water flowing on the surface.”
The spidery splatters in the current images show up seasonally too, but they’re too big to be slowly flowing water and their appearance doesn’t always coincide with temperatures within water’s freeze-thaw cycle. Instead, investigators theorized as long ago as 2006, in a paper in Nature, that they could be carbon dioxide, which is present on Mars in much greater abundance than water and would not just seep to the surface, but erupt out of it, as the CO2 went suddenly from solid to gas. As the researchers wrote in the Nature paper:
We propose that the seasonal ice cap forms an impermeable, translucent slab of CO2 ice that sublimates from the base, building up high-pressure gas beneath the slab. This gas levitates the ice, which eventually ruptures, producing high-velocity CO2 vents that erupt sand-sized grains in jets to form the spots and erode the channels. These processes are unlike any observed on Earth.
And how. With MRO still orbiting Mars and two active rovers on the surface, the data stream from the Red Planet will continue. It doesn’t take the likes of Benson to make those new discoveries. But we rely on him and other media artists all the same to help us see — and appreciate — the science like we never otherwise would. | 0.869143 | 3.665257 |
The Galactic Cycle
Let us now turn to another of the major evolutionary problems: the galactic cycle. The use of the term “cycle” in this connection may seem to be putting the cart before the horse, since no evidence of any cyclic course of evolution has heretofore been recognized, but in a universe based on the Fundamental Postulates of this work a galactic cycle is mandatory. As brought out in the discussion of the permanence of the major features of the universe, half of this cycle is located in our material sector of the universe and the other half in the non-material sector.
The necessity for a means of interchange between the material and non-material sectors has already been pointed out. This, of course, involves the existence of some process whereby the rotational space displacements of the non-material universe can be converted into the rotational time displacements which we recognize as matter. The nature of this process will be discussed later, but it is evident that new matter or potential matter entering the material sector of the universe from the non-material sector as a result of such a process cannot have any preferential location in space, since the physical entities of the non-material sector are not localized in space. It will also be shown in the subsequent discussion that all of this new matter is produced in the form of individual atomic units. These newly produced atoms uniformly distributed throughout space come under the influence of gravitational forces as soon as they are formed and a process of aggregation begins. As one vast period of time follows another and gravitation continues its slow but unremitting action the aggregates grow larger, the atoms become particles, the particles become clouds, the clouds become stars, the stars gather in clusters, the clusters become galaxies, the galaxies become larger galaxies. In the meantime the space-time progression moves the galaxies outward away from each other in space and new aggregations form from new matter and remnants of the old in the areas left vacant by the larger units. In due course these new formations grow older and larger and follow in the paths of their predecessors, leaving new vacancies to be filled by still other aggregations originating in the same manner. Each generation has its period of development, comes to maturity, and finally reaches the point of reconversion into the non-material sector of the universe to start the second half of the cycle. In order to make certain that the basis for this theoretical picture is clear, let us look at the gravitational situation as defined by the Fundamental Postulates. Every location in the universe is moving outward from every other location at unit velocity because of the space-time progression resulting from the equivalence of the basic units of space and time. Simultaneously all material atoms are moving in the opposite direction, inward toward each other, because of their rotational motion. At the shorter distances the inward motion exceeds the outward motion and the atoms move closer together. As the distance increases, however, the rotational motion toward any specific location decreases according to the inverse square relation and at extreme distances the gravitational motion is reduced to the point where it is less than the oppositely-directed velocity of the space-time progression. Beyond the point of equality the net resultant motion is outward, increasing toward unity (the velocity of light) as the distance increases.
These motions control the large-scale aspects of the material universe. Within the range of effectiveness of the gravitational motion, or gravitational forces, if we wish to speak in terms of the force equivalent of the motion, all units of matter move inward toward each other and if given sufficient time must join. Various subsidiary motions may control the nature of the combinations; for instance, they may cause orbital motion rather than actual consolidation, but they cannot prevent combination other than temporarily. Within the effective gravitational range, therefore, the aggregates of matter are continually growing. At the same time the space-time progression is increasing the separation between each of these aggregates and all others which are beyond the gravitational limit. The net effect is therefore a process of aggregation and a separation of the aggregates: formation of galaxies and expansion of the universe, to use the familiar terminology.
Once more, as in the discussion of the stellar cycle, let us see how close an agreement we can find between the purely theoretical course of evolution, as derived from the Fundamental Postulates and described in the foregoing paragraphs, and the results of astronomical observations. Since we are postponing consideration of the transitions to and from the non-material sector of the universe, the question now confronting us is whether we can recognize a definite course of evolution in the galaxies and pre-galactic structures from diffuse matter to a final form of some kind.
According to the theoretical evolutionary outline which has been presented, the primary criterion of age in the galactic world is size. It must be realized, of course, that accidents of environment and other factors will affect this situation to some extent so that the principle does not necessarily apply in every individual case, but in general the ages of the various types of structures theoretically stand in the same order as their sizes. Turning from theory to observation, we find that the recognized giants among the galaxies are the spirals. There is, in fact, a rather definite lower limit below which the spiral structure does not appear at all. The other major class, the elliptical galaxies, is found all the way down to the limits imposed by the capabilities of the observational equipment but is not represented above the lower limit of the spirals, except by certain very large systems which have the shape of elliptical galaxies but are much different in other respects. The criterion of size therefore definitely places the elliptical galaxies as the younger type and the spirals as the older, as in Hubble’s original classification. It also follows on the basis of this criterion that small spirals are in general younger than larger spirals and small aggregations of the elliptical type are younger than larger elliptical galaxies.
Now let us ask what evolutionary sequence would be normal for matter subjected to the forces which exist in the galaxies. There has been a great deal of speculation as to the nature of the forces responsible for the spiral form, but the justification for such speculation is rather questionable in view of the fact that the forces which are definitely known to exist, the rotation and the gravitational attraction, are sufficient in themselves to account for the observed structure. Inasmuch as the individual units in the galaxy are independent and widely separated the aggregate has the general characteristics of a fluid. A spiral structure in a rotating fluid is not unusual; on the contrary a striated or laminar structure is almost always found in a rapidly moving heterogeneous fluid, whether the motion is rotational or translational. It is true that objections have been raised to this “coffee cup” explanation on the grounds that the spiral in the coffee cup is not an exact replica of the galactic spiral, but it must be remembered that the coffee cup lacks one of the forces that plays an important part in the galaxy: the gravitational attraction toward the center of mass. If the experiment is performed in such a manner that a force simulating gravity is introduced, say for instance by replacing the coffee cup by a bowl which has an outlet at the bottom center, the resulting structure on the surface of the water is practically a picture of the galactic spiral.
In this kind of rotational structure the spiral is the last stage, not an intermediate form. By proper adjustment of the rotational velocity and the rate of water outflow the original dispersed material on the water surface can be caused to pull in toward the center and assume a circular or elliptic shape before developing into a spiral, but the elliptic structure precedes the spiral if it appears at all. The spiral is the end product. It will be brought out later in the discussion that the manner in which the growth of the galaxy takes place has a tendency to accentuate the spiral structure, but the rotating fluid experiment shows that the spiral will develop in any event when the necessary velocity is attained. Furthermore, this spiral is dynamically stable. We frequently find the galactic spirals characterized in astronomical literature as unstable and inherently short-lived, but the experimental spiral does not support this view. From all indications the spiral structure could persist indefinitely if the rotational velocity remained constant.
However, the rotational velocity of the galaxies does not remain constant. During the early stages of galactic aggregation when the combining units are of the same general order of magnitude, it is to be expected that some rotation will develop because of non-central impacts. Once such a rotation is initiated a difference in the rate of accretion develops between the two opposite sides of the galaxy in the plane of rotation. This accretion rate is affected very materially by the velocity of the mass relative to the diffuse material through which the galaxy is moving. On one side the net velocity is the sum of the translational and tangential velocities; on the other side it is the difference. The impact of the incoming particles or aggregates is therefore asymmetric and the result is an increase in rotational velocity with the age of the structure. Here again there are individual deviations, but in general the rotational velocity is directly related to the size and age of the galaxy and it is therefore one of the criteria of age.
Closely connected with the velocity is the shape of the rotating structure. The correlation in this case is so obvious that in actual practice the velocity is generally inferred from the shape rather than measured directly, although measurements have been made in some cases where conditions are favorable. Increased rotational velocity in the elliptical galaxies results’ in greater eccentricity. Beginning with the globular clusters, which are rotating very slowly and are spherical or nearly spherical, the elliptical units pass through all stages of eccentricity down to strongly lenticular shapes. At this point the spiral disk develops. The structure of the young spiral can be described as loose: the arms are thick and widely separated and the nucleus is rather inconspicuous. As the galaxy grows older and larger the nucleus becomes more prominent and the increased rotational velocity causes the arms to thin out and wind up more tightly. In the limiting condition the galaxy is practically all nucleus and the spiral arms are wound around this central mass so tightly that in effect they become part of it. These changes in appearance in the final stage account for some of the apparent deviations from the normal relation between size and age. There are a number of very large galaxies which are classified as elliptical, although they are greatly in excess of the size which normally results in the development of the spiral structure. The logical explanation is that these are not actually elliptical galaxies; they are the tightly wound, rapidly rotating, giant spirals which have reached the end of the road as galaxies and are ready to take the next step in the evolutionary cycle. Some particularly interesting inferences along this line can be drawn from the characteristics of the giant galaxy Messier 87, one of the well-known examples of this class, and this subject will receive further attention later.
At this point it may be appropriate to digress long enough to point out that if the correlation between size and shape is as close as is indicated by this preliminary examination of the theoretical relationships, it should have some useful applications in observational astronomy, particularly in the study of the more distant galaxies. Some complications are, of course, introduced by modifications of the basic structural pattern. The most common of these modifications, the barred spiral, will be given further consideration in another connection.
The fourth criterion of age applicable to the galaxies is that of relative abundance. In the evolutionary course as outlined, each unit of aggregation is growing at the expense of its environment. The smaller units are feeding on atoms or small particles, but the larger aggregations pull in not only the particles in the immediate vicinity but also any of the small aggregates which are within reach. As a result of this cannibalism the number of units of each kind should progressively decrease with age. When we examine the existing situation we find that the order of abundance is essentially in agreement with the age as determined by other criteria. The giant spirals, the senior members of the family of galaxies according to these criteria, are relatively rare, the smaller spirals are more common, the elliptical galaxies are abundant, and the globular clusters, which may be regarded as junior elliptical galaxies, exist in enormous numbers. It is true that the observed number of small elliptical galaxies, those in the range just above the globular clusters, is considerably lower than would be predicted from this sequence, but it is evident that this is a matter of observational selection. When the majority of galaxies are observed at such distances that only the spirals and the largest of the ellipticals are big enough to be visible it is not at all strange that the observed spirals are proportionately more numerous than is predicted by theory. The number of additional elliptical galaxies discovered within the Local Group in very recent years, increasing the already high ratio of elliptical to spiral in the region most accessible to observation, emphasizes the importance of this selection process.
A fifth criterion of galactic age is provided by the ages of the constituent stars. After a galaxy has reached the stage where the complete stellar cycle is represented the evaluation of galactic age becomes a matter of determining just how many times the constituent stars have been around the cycle: a somewhat complex problem. It is, however, relatively simple to distinguish between the galaxies which are old enough to have stars in all phases of the cycle and those in which the most advanced stars have not yet reached the upper portion of the main sequence, and this distinction is all that is required for present purposes. The initial product of condensation from the primitive material is, of course, identical with the product of condensation of a diffuse mass expelled from an exploding star; that is, it is a red giant. Under normal conditions this new star, irrespective of its origin, will follow one of the usual evolutionary paths: the lines AB or AD in Figure 42.
The smallest of the stellar aggregations in the line of galactic evolution, the globular clusters, are composed primarily of stars that are in the neighborhood of the initial evolutionary line AB. In some cases the line AD is also represented and frequently there are stars along the lower portions of the main sequence, but there are no representatives of the advanced types: the hot massive stars. We therefore conclude from this evidence that the globular clusters are relatively young structures, which agrees with the testimony from other sources. The next larger aggregates, the elliptical galaxies, are composed of stars of the same general type as those of the globular clusters, the so-called Population II. Here, however, a few blue giants are occasionally found—indications that the general age level is increasing. Then when we reach the spirals the full complement of advanced type (Population I) stars makes its appearance, confirming the status of these galaxies as the oldest inhabitants of the material system.
Another possible method of identifying the age of a galaxy or other material aggregate is a determination of the proportion of heavy elements in the matter of which it is composed. As indicated in the preceding discussion, the building up of heavy elements from the hydrogen and helium atoms which are the initial products in the formation of matter is a slow but continuous process. The elements heavier than the nickel-iron group are destroyed in the stellar cycle and it can be expected that the total amount of these elements will reach an equilibrium value and will not increase above this level, but the proportion of elements in the intermediate range should continue to increase indefinitely as the aggregate grows older. If the proportion of heavy elements in an aggregate can be measured, this measurement then serves as an indication of age. Obviously an accurate determination of this quantity presents some difficult problems, but some attempts in this direction have been made and it is interesting to note that the results of these initial efforts are entirely in accord with the ages of the various structures as inferred from other data. A recent evaluation finds the percentages of elements heavier than helium ranging from 0.3 in the globular clusters, theoretically the youngest stellar aggregation available, to 4.0 in the Population I stars and interstellar dust in the solar neighborhood, theoretically the oldest material within convenient observational range.
In the preceding paragraphs we have considered six different items which should theoretically serve as criteria of galactic age: (1) size, (2) rotational velocity, (3) shape, (4) relative abundance, (5) age of the constituent stars, and (6) proportion of heavy elements. All of these criteria are in agreement that the observed galaxies and sub-galaxies can be placed in a sequence which confirms the theoretical deduction that there is a definite evolutionary path in the material universe extending from dispersed atoms and sub-material particles through particles of matter, clouds of atoms and particles, stars, clusters of stars, elliptical galaxies and small spirals to the giant spiral galaxies which constitute the final stage of the material phase of the galactic cycle. It is possible, of course, that some of these units may have remained inactive from the evolutionary standpoint for long periods of time, perhaps because of a relative scarcity of galactic “food” in their particular regions of space, and such units may be chronologically older than some of the aggregations of a more advanced type. The capture of relatively large aggregates also necessarily results in a temporary divergence from the normal relationship between age and size. Such variations as these, however, are merely minor fluctuations in a well-defined evolutionary course.
Next we turn to a different kind of evidence which gives further support to the theoretical conclusions. In the preceding discussion it has been demonstrated that the deductions as to continual growth of the material aggregates by capture of matter from the surroundings are substantiated by the fact that the ages of the various types of galaxies, as indicated by several different criteria, are definitely correlated with their respective sizes. Now we will examine some direct evidence of captures of the kind required by theory. First we will consider evidence which indicates that certain captures are about to take place, then evidence of captures actually in progress, and finally evidence of captures that have taken place so recently that their traces are still visible.
The early history of the process of aggregation must be derived principally from theory since the observation of small non-luminous aggregates is possible only to a very limited extent (at least with the facilities now available). We deduce that the atoms which constitute the initial phase of matter combine to form particles, and this deduction is confirmed by evidence of the existence of dust particles in interstellar space. We further deduce that these particles gather together into dust clouds and that stars are formed from clouds of dust and gas when the first magnetic ionization level is reached and an adequate source of heat is thereby activated. At this point the aggregates become self-luminous and the task of the observer is greatly simplified, although the enormous distances which are involved still stand as formidable obstacles to complete knowledge. From the information gathered by observation two striking facts about the formation of the stars emerge. First, we find that the stars are separated by almost fantastic distances and that the most powerful gravitational forces in the universe, those in the central regions of the largest galaxies, are not able to reduce this separation by any significant amount. (From the standpoint of this discussion binary and multiple stars are regarded as stellar units, and the term “star” should be understood as including such systems.) The second of these rather surprising facts is that, although direct observation is possible only in very limited areas, we have sufficient observational information to show that single stars and relatively large groups (globular clusters) are abundant throughout space, but there is no indication of the existence of aggregations of intermediate size.
In order to throw some light on the situation which is responsible for these somewhat bizarre relationships, let us turn back to gravitational theory. We have found that the gravitational force exerted by mass m on unit mass at distance d is m/d2. At the point where the gravitational force exerted on unit mass is unity in all effective dimensions the gravitational and space-time forces are likewise in equilibrium in all dimensions. We have previously evaluated the inter-regional ratio of effective dimensions as 156.44 and we have found that a total of 3 × (156.44)3 three-dimensional units in the time region are required to produce one effective unit parallel to the time-space region forces. The ratio of the total gravitational force to the force exerted against a single one-dimensional rotational unit is therefore
3 × (156.44)3 × 3 × 156.44 = 5.391×109.
On this basis the equilibrium equation between the gravitational force and the unit force of the space-time progression is
|1 / (5.391×109) × m/d02 = 1||
Solving for d0, we obtain
|d0 = m½ / 73420||
At this distance do the gravitational motion is equal to the space-time progression and there is no resultant motion in either direction. At distances less than d0 there is a net inward velocity. Beyond do the net velocity is outward. We thus find that for any specific mass there is a gravitational limit beyond which the net effective force reverses direction and the resultant motion is outward rather than inward.
Here, then, is the explanation for both of the extraordinary characteristics of the stellar distribution. The stars are separated by tremendous distances because each star or pre-stellar cloud continually pulls in the material within its gravitational range and this prevents the accumulation of enough matter to form another star in this space. Formation of additional stars can take place only outside the gravitational limits and when such stars originate outside these limits they move outward from all previously existing stars. The immense region within the gravitational limit of each star is therefore reserved to that star alone.
The mass of the sun has been calculated as 2×1033 g, which is equivalent to 1.205×1057 natural units of mass. The corresponding number of natural units of space is the square root of this quantity or 3.47×1028, which amounts to 1.58×1023 cm or 167,000 light years. Applying the coefficient of equation 157 we find that the gravitational limit of the sun is at 2.27 light years. The nearest star system, Alpha Centauri, is 4.2 light years distant and the average separation of the stars in the vicinity of the sun is estimated at 2 parsecs or 6.5 light years. Sirius, the nearest star larger than the sun, has its gravitational limit at 3.5 light years and the sun, 8.7 light years away, is well outside this limit. It is evident that this space distribution in which the minimum distance is two-thirds of the average requires some kind of a barrier on the low side; it cannot be the result of pure chance. The existence of a gravitational limit just below the minimum stellar separation explains the highly abnormal distribution.
From the foregoing figures and the relation indicated by equation 157 it can also be seen why small clusters of stars are not formed under normal conditions. Let us consider, for example, a hypothetical cluster of ten stars in a region in which the stars of the general field are uniformly spaced at a density equal to that in the neighborhood of the sun. On calculating the gravitational limit of the cluster we find that even the closest of the field stars are outside this limit. Since the density of matter in the dust clouds from which the stars are formed is no greater and probably less than that assumed for purposes of this calculation, it is apparent that a cluster of this size not only could not grow but could not even be formed in the first place. We deduce, therefore, that where a large number of stars form contemporaneously from a dust cloud of vast proportions a relatively large star cluster is formed, but that all other stars are formed as individual units.
Within the clusters the star density is greater than that in regions such as the one in which the solar system is located, but the nature of the force equilibrium in any aggregation of stars is such as to preclude any major increase in the density. Unlike the units of matter within the star, each of which exerts a force of attraction on all others, the individual stellar units within the cluster repel each other and the cluster is held together only by the gravitational attraction between the individual stars and the cluster as a whole. This limits the concentration toward the center and, except for the outer regions in which the density gradually drops to the near zero value of the surrounding space, it is probable that the density is nearly uniform throughout the cluster and does not increase appreciably with the cluster size. The average density of the globular clusters is estimated at one star equivalent to the sun per two cubic parsecs, which is about five times the density of the local star system. The absolute maximum, on the basis of the figures previously quoted, is 20 times the local density and the maximum density in the clusters must stay within this limit to keep the system stable. The observed average density indicates that this requirement is met by a substantial margin.
In the light of the points brought out in the foregoing discussion we may conclude that individual stars and clusters of the globular type are continually being formed throughout the vast expanse of inter-galactic space. Each of the individual stars is ultimately captured by one of the clusters or galaxies. The great majority of the clusters also come within the gravitational limit of one or another of the larger aggregates sooner or later and are absorbed, but a few manage to stay out of the way of their voracious larger neighbors long enough to develop into full-sized galaxies. It is not unlikely that the union of two large clusters is the event that marks the advance from cluster to galaxy status, since this not only provides the additional mass needed to speed up the capture of other clusters and smaller units, but also explains the origin of the increased rotational velocity which is characteristic of the galaxies.
Because of the continual pull exerted by the galaxies on all of the clusters within the galactic gravitational limits, we can expect to find each galaxy surrounded by a concentration of globular clusters moving gradually inward. Inasmuch as the original formation of the clusters took place practically uniformly throughout all of this space the concentration of clusters should theoretically continue to increase as the galaxy is approached, until the capture zone is reached. Furthermore, the number of clusters in the immediate vicinity of each galaxy should theoretically be a function of the gravitational force and the size of the region within the gravitational limits, both of which are directly related to the size of the galaxy. All of these theoretical conclusions are confirmed by observation. A few clusters have been found accompanying such small galaxies as the member of the Local Group located in 4 Fornax; there are at least 3 or 4 in the Small Magellanic Cloud and about a dozen in the Large Cloud; our Milky Way System has at least 150 when allowance is made for those which we cannot see for one reason or another; the Andromeda spiral, M 31, has about 200; NGC 4594, the “Sombrero Hat,” is reported to have “several hundred” associated clusters; while the number surrounding M 87 is estimated to be about a thousand. These numbers of clusters are definitely in the same order as the galactic sizes indicated by the criteria previously established. The Fornax-Small Cloud-Large Cloud-Milky Way sequence is not open to question. M 31 and our own galaxy are probably close to the same size but the latest information indicates that M 31 is the larger, as the relative numbers of clusters would suggest. The dominant nucleus in NGC 4594 shows that this galaxy is still older and larger, while all of the characteristics of M 87 suggest that it has reached the upper limit of galactic size.
Here again, as in the case of stellar evolution, observation gives us only what amounts to an instantaneous picture and to support the theoretical deductions we must rely primarily on the fact that the positions of the clusters as observed are strictly in accordance with the requirements of the theory. It is worthy of note, however, that such information as is available about the motions of the clusters of our Galaxy is also entirely consistent with this theory. In the words of Struve, we know “that the orbits of the clusters tend to be almost rectilinear, that they move much as freely falling bodies attracted by the galactic center.” According to the theory that has been developed herein, this is just exactly what they are.
Capture of galaxies by larger galaxies is much less common than capture of globular clusters, simply because the clusters are very much more abundant. We may deduce, however, that there should be a few galaxies on the road to capture by each of the giant spirals, and this is confirmed by the observation that the nearer spirals (the only ones we can check) have “satellites,” which are nothing more than small galaxies that have come within the gravitational field of the larger units and are being pulled in to where they can be conveniently swallowed. The Andromeda spiral, for instance, has at least four satellites: the elliptical galaxies M 32, NGC 147, NGC 185, and NGC 205. The Milky Way galaxy is also accompanied by at least four fellow travelers: the two Magellanic Clouds and the elliptical galaxies in Sculptor and Fornax. The expression “at least” must be included in both cases as it is by no means certain that all of the small elliptical galaxies in the vicinity of these two spirals have been identified.
Some of these galactic satellites not only occupy the kind of positions required by theory, and to that extent support the theoretical conclusions, but also contribute evidence of the second class: indications that the process of capture is already under way. Let us look first at the irregular galaxies. This galactic classification was not given a separate place in the age-size-shape sequence previously established as it appears reasonably certain that these irregular aggregates, which constitute only a small percentage of the total number of observed galaxies, are merely galaxies belonging to the standard classes which have been distorted out of their normal shapes by special factors. The Large Magellanic Cloud, for instance, is big enough to be a spiral and it contains the high proportion of advanced type stars which is typical of the spirals. Why then is it irregular rather than spiral? The most logical conclusion is that the answer lies in the proximity of our own giant system; that the Cloud is in the process of being swallowed by our big spiral and that it has already been greatly modified by the gravitational forces which will eventually terminate its existence as an independent unit. We can deduce that the Large Cloud was actually a spiral at one time and that the “rudimentary” spiral structure which is recognized in this system is in reality a vestigial structure.
The Small Cloud has also been greatly distorted by the same gravitational forces and its present structure has no particular significance. From the size of this Cloud we may assume that it was a late elliptical or early spiral galaxy. The conclusion that it is younger than the Large Cloud reached on the basis of the relative sizes is supported by the fact that the Small Cloud is a mixture of Population I and Population II stars, whereas the stars of the Large Cloud belong almost entirely to the types assigned to Population I in Baade’s original classification.
The long arm of the Large Cloud which extends far out into space on the side opposite our Galaxy is a visible record of the recent history of the Cloud. It should be recognized that the gravitational attraction of the Galaxy is exerted on each component of the Cloud individually, not on the structure as a whole, since the Cloud is not an integral unit but an assembly of discrete units in which the cohesive and disruptive forces are in balance, a balance which is precarious at best in view of the repulsion between the individual units. The differential forces due to the greater distances to the far side of the Cloud were unimportant when the Cloud was far away but as it approached the Galaxy the force differential increased to significant levels. As the main body was speeded up by the increasing gravitational pull it was inevitable that some stragglers would fail to keep up with the faster pace, and once they had fallen behind the force differential became even greater. We would expect, therefore, to find a luminous trail along the recent path of the incoming Cloud: just the kind of a structure that we actually observe.
This is no isolated phenomenon. Small galaxies may be pulled into the larger units without leaving visible evidence behind, as the amount of material involved is too small to be detected at great distances, but when two of the large units, the spirals, approach each other we commonly see luminous trails of the same nature as the one that has just been discussed. Figure 44 is a diagram of the structural details which can be seen in photographs of the galaxies NGC 4038 and 4039. Here we see that one galaxy has come up from the lower right of the diagram and has been pulled around in a 90 degree bend. The other has moved down from the direction of the top center and has been pulled to the right and forward. When the action is complete there will be one giant spiral moving forward to its ultimate destiny, leaving the stray stars to be picked up by some other aggregation which will come along at a later time. Several thousand “bridges” which have developed from interaction between galaxies are reported to be visible in photographs taken with the 48 inch Schmidt telescope on Mt. Palomar. Some of these are trailing arms similar to those in Figure 44. Others are advance units which are rushing ahead of the main body. The greater velocity of these advance stars is also due to the gravitational differential between the different parts of the galaxy, but in this case the detached stars are the closest to the approaching galaxy and are therefore subject to the greatest gravitational force.
In order to produce effects of this kind it is, of course, necessary that the smaller unit be well within the effective gravitational limit of the larger. It will therefore be of interest to calculate the gravitational limit of our Galaxy, a typical large spiral, and to compare this distance with the observed separations between some of the objects which are presumably undergoing gravitational distortions. The galactic masses are usually expressed in terms of a unit equal to the solar mass and since we have already evaluated the gravitational limit for this mass we may express equation 157 in the convenient form
|d0 = 2.27 (m/m8)½ light years||
The mass of our Galaxy is estimated all the way from 1011 to 5×1011 solar masses. The probable accuracy of these estimates will be discussed later, but if we accept an intermediate value for present purposes equation 158 gives us a gravitational limit of about a million light years. The distance to the Magellanic Clouds is variously estimated from about 150,000 to some 230,000 light years, but in any event it is apparent (1) that the Magellanic Clouds are well inside the gravitational limit of the Galaxy, and (2) that the diameters of the Clouds, approximately 20,000 and 30,000 light years, are large enough in proportion to the distance from the Galaxy to give rise to significant differentials in the effective gravitational forces. The calculation thus verifies the conclusion that the Magellanic Clouds are well on their way to capture by the Galaxy. The diameter of the Galaxy is about 100,000 light years and we may therefore generalize these findings for application to distant systems by observing that considerable deformation and loss of material from a large incoming unit are produced at any distance less than the equivalent of two diameters of the larger galaxy. There are many visual pairs of galaxies which show no indications of gravitational distortion although they appear to be within the two diameter range, but in these instances we must conclude that there is actually a radial separation which puts them beyond the effective distance.
Irregularities of one kind or another are relatively common in the very small galaxies but these are not usually harbingers of coming events like the gravitational distortions of the type experienced by the Magellanic Clouds. Instead they are relics of events that have already happened. Capture of a globular cluster by a small galaxy is a major step in the galactic course of evolution, consolidation with another small galaxy is a revolutionary development. Since the relatively great disturbance of the galactic structure due to either of these events is coupled with a slow return to normal because of the low rotational velocity, the structural irregularities persist for a longer time in the smaller galaxies and the number of small irregular units visible at any particular time is correspondingly large.
Although the general spiral structure of the larger galaxies is regained relatively soon after a major consolidation because of the high rotational velocity which speeds up the mixing process, there are variations in some of these structures which seem to be correlated with recent captures. We note, for instance, that a number of spirals have semi-detached masses or abnormal concentrations of mass within the spiral arms which are difficult to explain as products of the development of the spiral itself, but could easily be the results of captures. The outlying mass, NGC 5195, attached to one of the arms of M 51, for example, has the appearance of a recent acquisition. Similarly the lumpy distribution of matter in M 83 gives this galaxy the aspect of a recent mixture which has not been thoroughly stirred. A study of the structure of the so-called “barred” spirals also leads to the conclusion that these units are galactic unions which have not yet reached the normal form. The variable factor in this case appears to be the length of time required for consolidation of the central masses of the combining galaxies. If the original lines of motion of the two units intersect, the masses are undoubtedly intermixed quite thoroughly at the time of contact, but an actual intersection of this kind is not a requirement for consolidation. All that is necessary is that the directions of motion be such as to bring one galaxy well within the gravitational limit of the other at the closest point of approach. The gravitational force then takes care of the consolidation. Where the gap to be closed by gravitational action is relatively large, however, the rotational forces may establish the characteristic spiral form in the outer regions of the combined galaxies before the consolidation of the central masses is complete and in the interim the galactic structure is that of a normal spiral with a double center.
Figure 45 (a) shows the structure of the barred spiral galaxy NGC 1300. Here the two prominent arms terminate at the mass centers a and b, each of which is connected with the galactic center c by a bridge of dense material which forms the bar. On the basis of the conclusions reached in the preceding paragraph we may regard a and b as the original nuclei of Galaxies A and B, the two units whose consolidation produced NGC 1300. The gravitational forces between a and b are modifying the translational velocities of these masses in such a manner as to cause them to spiral in toward their common center of gravity, the new galactic nucleus, but this process is slowed considerably after the galaxy settles down to a steady rotation as only the excess velocity above the rotational velocity of the structure as a whole is effective in moving the mass centers a and b forward in their spiral paths. In the meantime the gravitational attraction of each mass pulls individual stars out of the other mass center and builds up the new galactic nucleus between the other two. As NGC 1300 continues on its evolutionary course we can expect it to gradually develop into a structure such as that in Figure 45 (b), which shows the arms of M 51. Figure 45 (c) indicates how M 51 would look if the central portions of the arms were removed. The structural similarity to NGC 1300 is obvious.
Another valuable source of information corroborating the theoretical deductions with respect to the capture process is provided by the globular clusters. These clusters are too small to affect the shape of the larger galaxies which may absorb them and they are also too small for the development of noticeable distortion effects within their own structures such as those which we see in the Magellanic Clouds. On the other hand the process of capture of these units is taking place practically on our doorstep and we are able to follow the clusters into the main body of the galaxy and to read their history in much greater detail than is possible in the case of the larger and more distant aggregates.
We see the globular clusters as a roughly spherical halo extending out to a distance of about 100,000 light years from the galactic center. There is no definite limit to this zone; the clusters gradually decrease in concentration until they reach the cluster density of inter-stellar space, and individual clusters have been located out as far as 500,000 light years. Since the visible diameter of the average cluster is in the neighborhood of 100 light years and the actual over-all dimensions are undoubtedly greater, there should be a substantial gravitational differential between the near and far sides of the cluster at distances within 100,000 light years. We can therefore deduce that the clusters are experiencing an increasing loss as they approach the Galaxy, both by acceleration of the closest stars and by retardation of the most distant. The effect of slow losses of this kind on the shape of a nearly spherical rotating aggregate is minor and the detached stars merge with the general field of stars which is present in the same zone as the clusters. The process of attrition is therefore unobservable from our location, but we can verify its existence by comparing the sizes of the clusters before and after losses of this kind have taken place. Studies which have been made on the clusters accessible to observation indicate that the average size of the units at 25,000 parsecs from the galactic center is 30 percent greater than the average size of those only 10,000 parsecs distant. From this it would appear that the cluster loses more than half of its mass by the time it reaches what may be regarded as the capture zone, the region in which the gravitational action is relatively rapid.
In this capture zone the losses are still greater and by the time the cluster arrives in the vicinity of the galactic plane the remaining stars are numbered in the thousands instead of in the tens or hundreds of thousands. On entry into the rapidly rotating spiral disk still further disintegration occurs, and the original globular cluster becomes a number of separate galactic clusters, the largest of which has only a few hundred members. Since the gravitational attraction of this small group is not sufficient to offset the effect of the non-uniform rotational forces of the Galaxy, the galactic clusters slowly break up and the individual stars go their separate ways. In the meantime, however, the evolutionary development of the stars is speeded up by the greatly increased amount of “food” available in the galactic disk and the stars in the older galactic clusters are quite different from those in the units just making the transition from the globular to the galactic status.
This evolution of the constituent stars is the feature which enables us to identify the relative ages of the clusters and thereby to confirm the theoretical deductions as to the history of these units. The original globular clusters are relatively young aggregates and the spread between the oldest and youngest stars in each cluster, excluding strays from older systems that may have been picked up along the path, only represents a fraction of the total evolutionary cycle. After the cluster arrives in the immediate vicinity of the Galaxy it ceases to grow and there is no further increase in the age spread. The sector of the cycle on the H-R diagram occupied by the constituent stars then simply moves forward around the circle as the cluster grows older and passes through the various evolutionary stages.
Figure 46 is a series of clusters arranged in order of increasing age. As a means of facilitating identification of the position of each group with reference to the complete evolutionary cycle, the entire stellar cycle is shown in outline in each diagram and the sectors occupied by the stars of the particular group are filled in with heavy lines. We have already noted that the globular clusters are composed of very young stars in the early evolutionary region at the upper right of the H-R diagram. In Figure 46, diagram (a) shows the composition of a typical globular cluster, M 92. Here the most advanced stars have barely reached the main sequence, the youngest are still in the formation zone, and the great majority of the constituent stars are in the intermediate region on one of the paths AB or AD. Diagram (b) is a similar representation of the globular cluster M 13, which is in a slightly more advanced stage, a larger proportion of the stars having arrived in the lower section of the main sequence. The composition of the galactic cluster M 67, diagram (c), is very similar to that of M 13, indicating that M 67 is a very recent arrival in the galactic disk, a conclusion which is corroborated by the fact that this is one of the most populous of the known galactic clusters and one of the highest above the galactic plane (about 440 parsecs). In an older cluster, the Hyades (d), a few stars still remain on the contraction path AB but the majority have reached the main sequence. Next is a still older cluster, the Pleiades (e), in which the last stragglers have attained gravitational equilibrium and the entire body of stars has moved up along the main sequence.
Further development of the Pleiades cluster in the future will bring the hottest stars in this group to the destructive limit at the top of the main sequence and will cause these stars to revert back to the red giant status via the explosion route. In the double cluster h and X Persei (f) we find that such a process has already begun. Here the main body of stars is in the region just below the upper limit but a number of red giants are also present. We can identify these giants as explosion products rather than new stars as the former explanation keeps all of the stars in the cluster in an unbroken sequence along the evolutionary path, whereas if these were young stars of cycle A they would be totally unrelated to the remainder of the cluster: a highly improbable situation.
The identification of still older clusters of stars is more difficult because the stars of the clusters separate in the course of time and there are some problems involved in recognizing these stellar associations when they are no longer compact groups. It appears probable, however, that the sun and its immediate neighbors constitute a group with a common origin and diagram (g) represents the stars of this Local Group. Here we have evidence that the group is well along in the second cycle. There are no giants among these stars but the presence of white dwarfs in such systems as Sirius and Procyon and the planets in the solar system shows that the group has been through the explosion phase. We may interpret the lack of red giants as indicating that the former giants such as Sirius have had time to get back to the main sequence while their slower white dwarf companions are still on the way. It is not certain that all of the nearby stars actually belong in this same age group, as some younger stars may also be present, but there are no obvious incongruities. Finally in diagram (h) we have the full complement of Population I stars as found in the spiral arms, an assortment which includes stars in all phases of the evolutionary cycle.
Thus far the terms Population I and Population II have been used in the customary manner to refer to the two general classes of stars first distinguished by Baade, and characterization of the stars of Figure 46 (h) as Population I follows this practice. As the diagram shows, however, classifying the stars of the spiral arms as Population I makes this category so broad that its usefulness is severely limited and it therefore seems appropriate to modify these classifications to bring them into line with the relations which have been developed in the foregoing pages. The general significance of the two designations will be retained but new definitions will be set up, based on position in the evolutionary cycle. In this revision the Population I designation will be applied to main sequence stars only, and all of the pre-main sequence stars will be assigned to Population II. These I and II classifications will then be subdivided according to the particular evolutionary cycle in which the stars are located, using the letter A to refer to the first cycle (the pre-explosion stage) and B, C, etc., to identify the subsequent cycles.
On this basis the early type first cycle stars of the globular clusters and elliptical galaxies, which were placed in Population II by Baade, will fall in Population II-A. The stars of the galactic clusters (except the very young systems such as M 67) and the other first generation main sequence stars of the spiral arms, which formed part of Baade’s Population I, will become Population I-A. In most spiral galaxies the stars of the nuclei resemble those of the globular clusters and were included in Population II in the original classification. From the facts that have been developed herein it is apparent that these are actually the oldest stars in the galaxies and they do not belong with the young stars of the clusters. They are similar to the latter in many respects only because they have gone all the way around the cycle and are back to the same position on the H-R diagram that is occupied by the young stars. Under the new definitions this position keeps the stars in Population II but since they are in the second cycle the classification is II-B. The second generation main sequence stars, the group to which the sun belongs, are Population I-B.
Theoretically the stars of the galactic nucleus should continue moving around the cycle as they grow older, until the galaxy finally reaches the end of its life span, but detailed observation of the individual stars in this region is feasible only to a very limited degree with the facilities now available and it is difficult to determine just how far this cyclic course actually extends. We do observe, however, that the light from the nucleus of a galaxy does not always have the red color characteristic of the Class II populations. In a number of galaxies, perhaps as many as ten percent of the total, the light from the galactic center is reported to be as blue as that from the disk. This indicates that in these units a large proportion of the total light is coming from the most advanced members of Population I-B. The existence of I-B stars in relatively large numbers in other nuclei may then be inferred, since the presence of the upper main sequence stars of the second generation in some nuclei means that many slightly younger galaxies must contain lower main sequence stars of the same cycle. These early I-B stars are in the same spectral classes as the II-B group and cannot be distinguished by color. The same is true of the II-C stars, the class which follows the late type I-B stars that are responsible for the blue color in galactic nuclei where it appears. We can logically infer than at least some of these II-C stars are present but we cannot identify them in the nuclei with the facilities now available, and we cannot determine whether still older populations are present.
From the foregoing it can be seen that the characteristics of the composite light emitted by a galaxy or by one of its constituent parts constitute another means of identifying the age of the aggregate, supplementing the criteria previously discussed. The integrated light from the elliptical galaxies belongs to spectral type G. In the early spirals the emission rises to type F, or even A in some cases, because of the large number of stars which move up to the higher portions of the main sequence. As these stars pass through the explosion stage and revert to the II-B status, accumulating largely in the galactic nucleus, the light gradually shifts back toward the red and in the oldest spirals the color is very much like that of the elliptical galaxies. Summarizing this color cycle, we may say that the early structures are red, there is little change in the character of the light during the development of the elliptical galaxy, then a rapid shift toward the blue as the transition from elliptical to spiral takes place, and finally a slow return to red as the spiral ages. In order to lay the foundation for an explanation of these variations in the rapidity of change it will now be necessary to take up a consideration of the behavior of the interstellar dust and gas.
Since matter is continually forming throughout all space and is moving hither and yon under the influence of gravitation and other forces, there is a certain minimum amount of material subject to accretion in any environment in which a star may be located. Immediately after the formation of a star cluster by condensation of the denser aggregates of matter in a particular volume this thin diet of primitive material is all that is available for growth and the development of the structure is correspondingly slow. As time goes on the rate of action speeds up when material begins to arrive from the more distant regions which were not stripped of their substance by the initial condensation process. Furthermore, the increasing mass accelerates the rate of progress considerably as it not only extends the gravitational limit and puts additional material within reach but also makes the capture of larger aggregates feasible. As we have already noted, observation shows that the larger elliptical galaxies have reached the point where they are beginning to pull in globular clusters in addition to single stars and diffuse material.
We cannot see what is happening to the non-luminous material, but this matter is subject to the same gravitational forces as the luminous aggregates, and we can deduce that when the elliptical galaxies reach the size that permits them to start capturing globular clusters they simultaneously begin picking up pre-stellar clouds of similar size. The dust and gas clouds arrive too late in the elliptical stage of galactic evolution to have much effect on the properties of the elliptical units, although they are no doubt responsible for the development of the small representation of hot blue stars previously mentioned. But when the elliptical structure breaks up and spreads out to form the spiral, the stars of the galaxy are thoroughly mixed with the recent acquisitions of dust and gas and the stage is set for a period of rapid advance along the path of stellar evolution. This relatively fast progress is still further magnified when it is viewed from the standpoint of light emission since the hot stars at the upper end of the main sequence may be thousands of times as luminous as the average Population II star.
The identification of these conspicuous hot and luminous stars with the spiral arms was the step which led to the original concept of two distinct stellar populations, but the new information which has been developed herein makes it clear that the galactic arms actually contain a rather heterogeneous population and a more definite correlation between the various types of stars and the general stellar populations is in order. Population I as herein defined is composed entirely of stars of the main sequence, the most conspicuous being the blue giants at the top of the sequence. The various classes of hot and massive shell stars also belong in this group and we can include the supernovae, which mark the end of the dense phase of the stellar cycle. The Population II stars of all cycles on the minimum accretion branch are the red giants and sub-giants. The white dwarfs join this group after the first explosion; that is, in Class II-B and beyond.
The rapid accretion branch of the Population II-A stars is a group of variable stars sometimes called Type II Cepheids and including, in the order of increasing age and decreasing period, the stars of the RV Tauri, W Virginis, and RR Lyrae groups. The II-B variables, the corresponding stars of the next cycle, are similar but not identical and the groups which make up this class, listed in the same order as before, are the long period variables, the semi-regular variables, and the classical Cepheids. Since these are second generation stars they are binary or multiple systems and they are shifted upward on the H-R diagram relative to the corresponding II-A stars. According to recent determinations, the average difference in luminosity for stars of the same period is about 1½ magnitudes. Population II-B also includes a similar group of variables on the other side of the main sequence which is absent from the pre-explosion Population II-A. Here we have, also in the order of increasing age, the planetaries, the classical novae, the recurrent novae, and the dwarf novae of the U Geminorum and similar types. Population II-C and later variables no doubt extend the differences between the II-B and II-A classes still farther, but this point cannot be checked against observation because the available information regarding the third cycle stars is still quite incomplete. Table CXII is a summary of the stellar types included in each classification.
Composition of Stellar Populations
|Population I (all cycles)|
|Main sequence stars|
|Stable stars (all cycles)||Red giants|
|Stable stars (II-B and later)||White dwarfs|
|Variable stars (II-A)||RV Tauri|
|Variable stars (II-B)||Long period variables|
From the nature of the growth processes as they have been described it is apparent that no aggregate consists entirely of a single stellar population, but the very young structures approach this condition quite closely since these young aggregates are formed from young stars and the only dilution by older material results from picking up an occasional stray such as one of the stars that are left behind on trails similar to those shown in Figure 44. The earlier globular clusters, under normal conditions, are therefore practically pure Population II-A and their H-R diagrams are similar to that of M 92, Figure 46 (a). The component stars are red giants, sub-giants, and variables of the RR Lyrae and other II-A groups. In the older globular clusters and the elliptical galaxies some of these same stars are present but a substantial number of stars have reached positions on the main sequence. On the basis of the classification which has been set up in this work both the older globular clusters and the elliptical galaxies will have to be regarded as being composed of mixed II-A and I-A populations. The earlier galactic clusters are in the same evolutionary stage as the elliptical galaxies and the H-R diagrams of M 67 and the Hyades, Figs. 46 (c) and (d), are to some extent representative of the phases through which the elliptical galaxies pass, although it should be remembered that the early end of the age distribution is not cut off in the growing galaxies as it is in the disintegrating clusters and the diagram for an elliptical galaxy in the same evolutionary stage as the Hyades would extend the sector occupied by the Hyades stars all the way back through the globular cluster sector to the original zone of star formation.
The rapid development in the early spiral stage eliminates most of the II-A units, except those in the incoming stream of captured material, and the stars of these early spirals are predominantly Population I-A. Further aging of these spirals then results in the appearance of second generation stars, beginning with Population II-B. The fact that the development of the spiral structure antedates the formation of the second generation stars results in a general distribution principle which has important implications for observational astronomy. With the qualification “except for strays from older systems” which will have to be understood as attached to all statements in this discussion of stellar populations, we may say that the second and later population stars, long period variables, classical Cepheids, white dwarfs, novae, etc., are confined exclusively to the stellar disks (including the nucleus). At the other extreme the early first generation stars (Population II-A) are distributed throughout all space, with the main sequence stars of the first generation (Population I-A) occupying an intermediate position.
In our own galactic system, for example, we find the typical Population II-A stars, red giants and RR Lyrae stars, in all of the observable region surrounding the Galaxy, both as individuals and in the globular clusters. On the other band, the classical Cepheids and the novae, the most easily identified of the second generation stars, are strongly concentrated toward the galactic plane and these stars are not found in the globular clusters. A few long period variables have been reported in the globular clusters and among the high velocity stars which are outside the disk of the Galaxy, but the large degree of irregularity in these stars makes it rather difficult to classify them accurately and it seems likely that these apparently misplaced second generation stars are actually long period Type II variables (Population II-A). The distribution of the white dwarfs cannot be determined from observation as they are too faint to be seen at great distances, but we can at least say that there is no evidence which conflicts with the theoretical conclusions as to the evolution of these stars.
One of the very significant points brought out by the theoretical development is that the first cycle stars should be single units whereas those of the second and later cycles should be binary or multiple systems. The second part of this conclusion is given strong support by statistical studies of the stars in the local environment. These studies indicate that about two-thirds of the near-by stars with masses greater than that of the sun are binaries or multiple stars. As the stellar mass decreases this proportion falls off rapidly but the reason for this is clearly indicated in the previous discussion of the formation of planetary systems. We know that a planetary system can be formed in lieu of a binary star when the central mass is equal to that of the sun, and it is obvious that a smaller stellar mass is still more favorable for the appearance of a planet or system of planets rather than a star as the minor component of the post-explosion star system. The drop in the proportion of binary stars as the mass decreases is merely a reflection of the shift from visible stars to invisible stars or planets; it does not indicate any actual decrease in the number of two-component systems. The absence of binary or multiple units in the first cycle stars is more difficult to establish because of the relative inaccessibility of these stars, and the evidence thus far available is somewhat spotty. There are a number of reports of binary stars in the galactic clusters, where they should theoretically be absent except in Cycle B clusters and in the post-explosion members of the most advanced Cycle A units, such as the double cluster in Perseus. If any binary stars are actually present in the early type galactic clusters they are probably stars which have become mixed with the cluster stars during the entry of the cluster into the galactic disk.
It should be recognized, however, that the identification of some of these clusters as Cycle A structures is only tentative. It appears that the break-up of the clusters should proceed more rapidly than the evolution of the stars of which they are composed and for this reason the easily distinguished, homogeneous clusters are presumed to be relatively recent additions to the Galaxy. It is not impossible, however, that some of these clusters may have evolved quite rapidly and are already in the second cycle. We have already noted that the stellar evolution speeds up considerably in regions of high dust and gas concentration. A good illustration of the way in which the normal relationship between chronological age and evolutionary age can be modified by such an environment is provided by the globular clusters which are located in the Large Magellanic Cloud. Here the gravitational distortion of the galactic structure has resulted in an irregular distribution of the dust and gas clouds and some globular clusters have entered high density regions of this kind. As a result the evolution of the stars in these clusters has been much faster than normal and while the shape, size, and location of these clusters are those of normal globular clusters, the stars are similar to those of the galactic clusters: members of Population I-A. If the high percentages of binary stars reported by some observers for such clusters as Praesepe and the Hyades are confirmed it will be necessary to revise the tentative conclusions as to the evolutionary stage of these clusters and place them in Cycle B. There are also a large number of loose, heterogeneous clusters which quite definitely belong in the second cycle. One group of this kind which has been given extensive study is NGC 6231. Here we find a large proportion of Population II stars, indicating that this cluster is either considerably older or considerably younger than a main sequence cluster such as the Pleiades. Since the structure, or lack of structure, of the cluster indicates that it has undergone severe modification since entering the Galaxy we conclude that it is older and that the Population II stars belong to Class II-B. This conclusion is supported by evidence which indicates that the stars of the cluster are largely binaries.
As mentioned in the discussion of the spiral structure, the material of which a galaxy is composed is in such a physical condition that it has the general characteristics of a fluid. In such an aggregate the heavier material moves toward the center of gravity, displacing the lighter units, which concentrate in the outer regions (the galactic disk). The dust and gas clouds and the early type stars are therefore found mainly in the disk while the older and heavier stellar systems sink into the nucleus. The segregation process is very slow and irregular because of the effects of the galactic rotation and in spite of the general separation of the older material from the younger it can be expected that many of the older star systems will be found scattered through the predominantly Cycle B population of the spiral disk. The average mass of these systems is greater than the corresponding average of any of the earlier groups but in view of the large variation between individuals within any group this characteristic is not a positive means of identification. Multiple systems are more distinctive. From the points brought out in the discussion of the formation of planetary systems it can be seen that the ultimate result of a stellar explosion is a binary star or star and planet, probably with some additional small companions. While it is possible that one of these companions may be large enough to qualify as a star, the nature of the aggregation process is such as to make this quite unlikely, and in general we may regard a multiple star system as one which has passed through the explosion stage more than once.
It has been estimated that five percent of all visual binaries are members of multiple systems. In addition to these systems in which evidence of multiplicity has been detected by observation, there are also a substantial number of observed binaries which are associations of two type A stars or two type B stars and which, according to the binary star theories that have been developed, must have additional unseen components on the other side of the main sequence. The systems of the Algol type, for instance, consist of main sequence stars paired with sub-giants of somewhat smaller mass. The main sequence star cannot be the B component because it is the larger of the two units and the more advanced from an evolutionary standpoint, and the sub-giant cannot be the B component because it is above the main sequence. We must therefore deduce that these star systems have undergone a second set of explosions and that each of the observed stars is accompanied by a small B component. As mentioned earlier, at least one and possibly both of the additional components predicted by theory have been located in Algol itself and the theory merely requires that the other systems of the same kind be similarly constructed.
We have seen that the two stars of a binary system tend to approach equality of mass as they near the upper end of the main sequence. When one explodes the other should follow suit within a relatively short time, particularly since it will receive substantial amounts of matter and thermal energy from its disintegrating companion. The great majority of multiple systems should therefore contain even numbers of stars. The normal progression is from binaries to four-member systems such as Algol and then to six-member systems on the order of Castor. The latter may be regarded as one of the oldest star systems within our field of vision.
We have found thus far in our examination of the aggregation process that the primary units of matter, the atoms, respond to the gravitational forces by continually combining until they finally build up into units of the maximum size possible for simple aggregates. These secondary units, the stars, likewise gravitate into still larger aggregates, the galaxies. The question now arises, is this the end of the aggregation process or do the galaxies again combine into super-galactic aggregates? The existence of many definite groups of galaxies with anywhere from 10 to 1000 members would seem to provide an immediate answer to this question, but the true status of these groups or clusters of galaxies is not clear as that of the stars and the galaxies. Each of the stars is a definite and tangible unit, constructed according to a specific pattern from subsidiary units which are systematically related to each other. The same can be said of the galaxies. It is by no means certain, however, that this statement can be applied to the clusters of galaxies; on the contrary, the information now available suggests that it cannot.
Let us then turn to a theoretical examination of the question. It is immediately apparent that the basic situation is very similar to that involved in the combination of stars into galaxies. All of the smaller units which are formed within the gravitational limit of a giant spiral, or are brought within it by the relatively rapid extension of the limit due to the growth of the galaxy, are ultimately consolidated with the spiral; those outside this limit are continually receding. The question then reduces to a matter of whether or not the galaxies can extend their gravitational influence still farther by the formation of super-galaxies in the same manner that the stars extend their gravitational limits by the formation of star clusters. The mathematical relations are similar and since we find that the minimum star cluster contains thousands of stars we must conclude that if there are any super-galaxies the small clusters of galaxies now recognized do not meet the requirements. On the other hand we know from observation that our Galaxy cannot be a member of a giant super-galaxy since all galaxies other than the few in our immediate vicinity are observed to be receding. (According to theory the members of the Local Group, are also moving outward away from us but this movement is so slow that it is masked by the random motions of the galaxies.) Furthermore, the recession is observed to be uniform throughout the vast space accessible to present-day telescopes and it therefore follows that super-galaxies cannot exist anywhere in this region of space.
Another line of reasoning brings us to the conclusion that the situation which we find in the observable region is typical and that there are no super-galaxies. The Fundamental Postulates require all basic processes to be cyclical, and the formation of super-galaxies is therefore impossible unless a process also exists whereby their existence can be terminated. But there are no more destructive limits on which such a process could be based. The lower and upper destructive limits of matter are reached in the supernovae and the mature galaxies respectively, and there are no others. We must therefore conclude that the existence of super-galaxies is inconsistent with the postulates.
What, then, is the nature of the observed clusters? A clue to the answer to this question can be found by examination of the contents of these groups. In our Local Group, for example, we find three major spirals, in which the bulk of the mass is concentrated, and fifteen or twenty small units. A striking contrast is supplied by the Coma cluster which contains at least 800 units, but few, if any, spirals. When we take a second look at this situation, however, it becomes apparent that the difference between the two groups is merely a matter of age. The Coma cluster is a relatively young aggregation in which the individual units are numerous but small; the Local Group is an old system in which the greater part of the mass has gravitated into a few large galaxies. Each of these giants is equivalent to 100 or more of the elliptical galaxies of the Coma cluster and when we take this factor into consideration the two groups are seen to be associations of comparable size, differing only in age and the characteristics accompanying age. We have already deduced that new galaxies are formed in regions which have been left vacant by the outward motion of the previously existing galaxies. Presumably this process can and does take place on a single galaxy basis in many, if not most, instances but the galactic associations can easily be explained if we recognize that larger regions will on occasion be left open through chance, and still further irregularities in the size of these vacant regions will be introduced through the disappearance of the mature galaxies by means of a process which will be discussed later. When an extensive region is thus left vacant new galaxies begin to develop throughout all of this empty space and because these galaxies originate at approximately the same time they pass through the various stages of evolution together and we can recognize the same kind of age characteristics in each group as a whole that we normally see in the individual galaxies.
The very early groups, those whose largest aggregates are globular clusters or the loose irregular galaxies resulting from the union of two or three clusters, are invisible unless relatively close. As the growth process continues the regular elliptical form is developed and the groups arrive at the stage represented by the Coma cluster and the cluster in Corona Borealis, in which there are a large number of small elliptical and irregular galaxies spaced relatively close together. Here the characteristics of the group as a whole are identical with the characteristics of the individual elliptical galaxy. Almost all of the component stars belong to the first generation families, Populations II-A and I-A, the composite light from the cluster is red, and there is no evidence of dust accumulations. As the group ages it decreases in numbers because of the consolidation of units but it spreads out into more space. While these processes are taking place the other signs of maturity appear: spiral galaxies are formed and go through their evolutionary stages, stars of the hot massive types are developed, and so on. In the later stages the cluster is essentially nothing more than a region of approximately average concentration in the general field of galaxies.
A highly significant fact about these mature groups of galaxies is that the giant spirals into which most of the mass has been concentrated are in general well outside the gravitational limits of their nearest contemporaries. In the-Local Group, for example, the gravitational limit of M 31 is in the neighborhood of one million light years, whereas the distance from the Milky Way is double this figure. The average distance between bright galaxies of all kinds has been estimated at 2.4 million light years. Even within the groups, therefore, the major units have a general outward motion, although this velocity is small and the direction of the net movement can be reversed in any individual case by the random motion of the galaxy.
Calculation of the velocities of recession is complicated by uncertainties as to the true masses of the galaxies and the inter-galactic distances, but we may utilize the best available information to arrive at some tentative figures for comparison with the values indicated by the spectral red shifts. As we have found previously, equilibrium between the gravitational force due to the atomic rotation and the force of the space-time progression is reached when the gravitational force has unit value in each effective time region dimension. At greater distances the gravitational force falls below the level of the space-time force, which means that from this point on the net resultant of the two forces is directed outward rather than inward. Gravitation does not actually reach zero as long as it amounts to the equivalent of unity in at least one time region dimension but it vanishes on dropping below this unit level, as less than unit force, does not exist. We may express the equilibrium at the limiting distance, d1, by substituting unity for the expression 9 × (156.44)3 in equation 156, which gives us
|m / (156.44 d12) = 1||
The limiting distance beyond which all galaxies recede with the full velocity of light then becomes
|d1 = m½ / 12.5||
which can be expressed in terms of solar masses as
|d1 = 13350 (m/m8)½ light years||
The mass of the Galaxy is a difficult quantity to measure and the most recent determinations run all the way from 1011 to 5.0×1011 solar masses. If we accept the highest value for our tentative calculations, d1 becomes 13350 (5×1011)½ = 9440×106 light years. Between d0 and d1 the decrease in gravitational velocity and the corresponding increase in the velocity of recession are linear. Disregarding the relatively short distance between the Galaxy and d0, we may then calculate the distance from our Galaxy to any other galaxy of the same or smaller mass by converting the red shift in the spectrum of that galaxy to natural units and multiplying by 9440×106 light years or 2900×1011 parsecs. In Table CXIII the distances thus obtained are compared with a few of the values calculated from observational data.
Relation of Red Shift to Distance
(millions of parsecs)
In view of all the uncertainties that enter into these calculations, the uncertainty as to the true mass of the Galaxy, the confused state of the distance determinations since the overthrow of the previously accepted yardsticks, and the possibility that some factors may have been overlooked in the very considerable extension of theory upon which the calculations are based, the best that can be expected is to arrive at comparative values which are of the same general order of magnitude and the amount of divergence between the figures in the last two columns of Table CXIII is not significant. The calculations lead to a value of 104 km/sec per million parsecs for Hubble’s constant, the relation between red shift and distance. The 1954 distances shown in Table CXIII correspond to a constant of about 150, some more recently published values fall between 80 and 90, and it has been suggested that the true figure may be as low as 55. Since the accepted value before 1952 was 540 km/sec per million parsecs it is apparent that this whole situation is rather fluid at present and no firm conclusions are warranted. The calculated value would be increased to 230 km/sec per million parsecs if the minimum estimate of 1011 solar masses were used as the mass of the Galaxy, and it could just as easily be reduced below the 104 figure by an upward revision of the Galactic mass. | 0.846954 | 3.933603 |
Jupiter is nothing but clouds, a mass of gas floating in space. So, the question of how lightning storms exist there (or, for that matter, on the “Cloud City” planet Bespin, in Star Wars) has intrigued scientists ever since NASA’s Voyager 1 probe first sent back evidence of Jovian lightning in March 1979. That data — visible light and radio signals produced by the bolts’ electrical discharges — suggested that lightning there is different from that on Earth. Now, after 39 years, a NASA study sheds light on the true nature of Jupiter’s mysterious bolts.
For the past two years, NASA’s Juno space probe has been arcing by Jupiter, swinging close enough to the gas giant’s cloud cover to solve the mystery. Juno’s findings, described in the Nature paper published Wednesday, suggest that most of NASA’s head-scratching in 1979 was warranted: Jupiter’s lightning seemed different than Earth’s because the data showed only a part of the picture. “No matter what planet you’re on, lightning bolts act like radio transmitters — sending out radio waves when they flash across a sky,” according to a statement released Wednesday by lead author Shannon Brown, Ph.D., a researcher at the Airborne Science Program at NASA’s Jet Propulsion Laboratory. NASA’s 39 years of confusion, it seems, may come down to the fact that early probes were unable to detect the relevant waves.
The original Voyager 1 data showed that Jupiter’s lightning had a curious gap in the megahertz and gigahertz ranges typical of lightning here on Earth. In particular, the data showed only emissions in the low-frequency kilohertz range; on Earth, lightning emissions are usually measured in the high-frequency gigahertz range. Juno’s sensitive Microwave Radiometer Instrument (MWR)’s recordings of the planet’s electromagnetic emissions, however, show that the relevant emissions were always there. The key was swooping close enough to the lightning to get a closer look.
“In the data from our first eight flybys, Juno’s MWR detected 377 lightning discharges,” says Brown. “They were recorded in the megahertz as well as gigahertz range, which is what you can find with terrestrial lightning emissions. We think the reason we are the only ones who can see it is because Juno is flying closer to the lightning than ever before.” Specifically, Juno reached within 3,000 miles of Jupiter’s cloud cover at the closest point in its orbit. Another reason that Juno’s MWR succeeded where many previous satellite probes — like Voyagers 1 and 2, Galileo, and Cassini — failed is, in part, because it was listening to Jupiter’s electrical storms on a radio frequency capable of passing through the charged particles in the planet’s ionosphere. (“The measurements were at 600 MHz,” Brown said in an email to Inverse.)
The new data puts to rest an older theory attempting to explain why previous probes circling Jupiter were not able to pick up megahertz or gigahertz signals: In 1985, French astrophysicist Philippe Zarka, Ph.D. speculated in an Astronomy and Astrophysics letter that Jupiter’s lightning only produced those lower-hertz range signals because it moved eerily slow compare to Earth lightning. That strange explanation can be shelved now, but there are still truly unusual things about Jupiter’s lightning. All lightning is formed, in part, as a reaction to heat, which is one of the reasons that lightning on Earth strikes most at points near the equator. But on Jupiter, the heat from the sun along the equator merely cancels out the heat emanating out from the planet’s hot core. The result is that lightning strikes most on Jupiter at the poles, where the hot/cold fronts from the core and the upper atmosphere provoke the most turbulence.
Juno will continue to collect data from Jupiter until at least July 2021, thanks to a recent extension from NASA, a good thing given that the findings continue to produce new questions. For example: “Even though we see lightning near both poles,” Brown asks, rhetorically, “why is it mostly recorded at Jupiter’s north pole?” | 0.880171 | 3.840614 |
“We must always remember with gratitude and admiration the first sailors who steered their vessels through storms and mists, and increased our knowledge of the lands … in the South.”
Less than one hundred years ago, the south pole of Earth was a land of utter mystery. Explorers labored mightily to get there, fighting scurvy, wind, disorientation and a fantastic almost-martian cold. Until Roald Amundsen and Robert F. Scott reached the Pole in 1911 and 1912, it was terra incognita.
The situation is much the same today—on the sun.
“The sun’s south pole is uncharted territory,” says solar physicist Arik Posner of NASA headquarters. “We can barely see it from Earth, and most of our sun-studying spacecraft are stationed over the sun’s equator with a poor view of higher latitudes.”
There is, however, one spacecraft that can travel over the sun’s poles: Ulysses, a joint mission of NASA and the European Space Agency. And today Ulysses is making a rare South Pole flyby.
“On February 7th, the spacecraft reaches a maximum heliographic latitude of 80oS—almost directly above the South Pole,” says Posner who is the Ulysses Program Scientist for NASA.
Right: Ulysses, an artist’s impression. Credit: David Hardy/ESA.
Solar physicists are thrilled. Ulysses has flown over the sun’s poles only twice before–in 1994-95 and 2000-01. The flybys were brief, but enough to prove that the poles are strange and interesting places.
Consider the following:
1. The sun’s north magnetic north pole sticks out the south end of the sun. Magnetically, the sun is upside down!
“Most people don’t know it, but we have the same situation here on Earth,” notes Posner. “Our magnetic north pole sticks out of the geographic south pole.”
Magnetically, Earth and sun have a lot in common. “Both the sun’s and Earth’s magnetic poles are constantly on the move, and they occasionally do a complete flip, with N and S changing places.” This flipping happens every 11 years on the sun in synch with the sunspot cycle. It happens every 300,000 years or so on Earth in synch with–what? No one knows. “Studying the polar magnetic field of the sun might give us some clues about the magnetic field of our own planet.”
2. There are holes over the sun’s poles–“coronal holes.” These are places where the sun’s magnetic field opens up and allows solar wind to escape. “Flying over the sun’s poles, you get slapped in the face by a hot, million mph stream of protons and electrons,” he says. Ulysses is experiencing and studying this polar wind right now.
(Note: Earth has a polar hole, too–the ozone hole. The chemistry of the ozone hole is totally unrelated to the magneto-physics of coronal holes, but says Posner, “it is interesting that so many poles seem to have holes.”)
3. Just as the sun’s polar magnetic field allows solar wind out, it also allows galactic cosmic rays in. Could the space above the sun’s poles be a place where we can sample interstellar matter without actually leaving the solar system? “That’s what we thought before our first polar flyby in 1994,” recalls Posner. “But we were wrong. Something is keeping cosmic rays out of the sun’s polar regions. The current flyby gives us a chance to investigate this phenomenon.”
4. Another mystery: There is evidence from earlier flybys that the north pole and the south pole of the sun have different temperatures. “We’re not sure why this should be,” says Posner, “and we’re anxious to learn if it is still the case.” Today’s south polar flyby will be followed by a north polar flyby in early 2008, allowing a direct north vs. south comparison.
In a sense, Ulysses is more like Richard E. Byrd than Amundsen or Scott. In November 1929, Byrd flew over Earth’s south pole in a Ford Trimotor airplane named the Floyd Bennett. The plane barely gained enough altitude to overfly the high polar plateau, clearing some mountain peaks and glaciers by little more than a few hundred feet. Compasses were useless for direction-finding so close to the magnetic pole, and there were few landmarks in the white expanse below. Nevertheless, he managed to guide the plane straight to latitude 90 S.
Like Byrd, Ulysses is a flier. “Today the spacecraft is gliding 300 million km (2 AU) above the sun’s ‘Antarctic.’ That’s a safe distance and a good place to sample the sun’s polar winds and magnetic fields.”
In the long run, however, Ulysses will follow Scott: “Had we lived I should have had a tale to tell of hardihood, endurance and courage…,” Scott wrote shortly before his entire party perished from cold. They reached the pole, famously chasing Amundsen, but never made it home again. Ulysses will never come home either, eventually perishing in the cold of space when its internal power sources fail. (For more on this, see Science@NASA’s “Cold Peril”).
To honor the common heritage of exploration, NASA’s Science Mission Directorate dedicates its efforts during the Ulysses’ South Pole flyby to Roald Amundsen, Robert F. Scott and Richard E. Byrd.
Amundsen, Scott, Byrd, and now Ulysses. Says Posner, “their stories will inspire generations to come.” | 0.877251 | 3.384463 |
Press Release: ARGOS Mission Seeks New Information about Black Holes and Neutron Stars
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Date Issued:March 02, 1999
Relevant Web URLs:
A collaboration of astrophysicists from the Department of Defense's Naval Research Laboratory (NRL), and particle physicists from the Department of Energy's Stanford Linear Accelerator Center (SLAC), Stanford University, have built an experiment to study black holes and neutron stars that was launched today on board the Air Force Space Test Program's (STP's) Advanced Research and Global Observation Satellite (ARGOS). The instruments were integrated onto a Delta II rocket for the satellite's launch, from Vandenberg AFB, CA, into a polar orbit in the early morning on February 23, 1999. ARGOS, which has a 3-year planned operational life, will carry nine primary experiments that contain 31 different sensors and sub-experiments.
The Unconventional Stellar Aspect (USA) experiment, one of the primary experiments, was designed to observe bright x-ray sources to further our understanding of these exotic objects, which are mostly binary systems in our Galaxy containing black holes, neutron stars or white dwarf stars. Studying these systems allows particle astrophysicists to glimpse matter in its most extreme states where densities can be higher than in an atomic nucleus, and extraordinarily strong and relativistic gravitational forces and enormous magnetic fields are acting in concert to produce dramatic phenomena not observable in earth based laboratories.
USA will make significant contributions to applied science, environmental science, and engineering research as well. It will use these same x-ray sources to test new approaches to satellite navigation, conduct the first x-ray tomographic survey of the Earth's atmosphere, and will test new concepts for fault-tolerant computing in space.
"This is the first time that SLAC has been directly involved in a space based experiment. USA gives us the chance to do in-depth particle astrophysics research on many different black hole and neutron star systems in our Galaxy. The collaboration between particle physicists at SLAC and astrophysicists at the Naval Research Laboratory, which began in 1991, gives us a unique approach to studying these systems" said Prof. Elliott Bloom, spokesperson for the SLAC collaboration who helped to build the USA hardware.
The USA sensors are sensitive to x-ray wavelengths of about 1 to 10 Angstroms. USA observations of celestial black hole and neutron star binaries will provide information about the behavior of relativistic gravity near black holes where the fields are very strong. USA can also test the standard model of particle physics under extreme conditions of temperature and density and perhaps find evidence for new types of matter. To probe new regions of physics, USA can observe time variable phenomena in these sources with a time resolution of less than 100 microseconds.
USA is an x-ray telescope consisting of two large area x-ray sensors and a gimbaled mounting. With a field-of-view of about 1.5 degrees, and an area of about 2000 cm^2, the detectors will measure the time-varying x-ray output of celestial sources with excellent timing information and reasonable energy resolution. To accomplish its mission, USA will observe a small number of targets, selected prior to launch, and re-measure the X-rays from these targets repeatedly. The scientists anticipate that each of approximately 30 bright sources will be observed several times during the first month of operation. Two to four observations are planned for each orbit, depending on particle background and source location.
As part of its engineering research goals the USA Experimental team will test new concepts for fault-tolerant computing in space. To achieve this goal, USA carries a two-computer testbed that consists of a military radiation-hardened processor side-by-side with a commercial off-the-shelf (COTS) processor. This testbed will allow scientists to demonstrate the capability of using advanced fault tolerant software algorithms to enable the COTS processor to be used for high-performance space-based computing tasks.
The Principal Investigator for the USA experiment is Dr. Kent S. Wood from the US Naval Research Laboratory (NRL). Dr. Michael N. Lovellette, also from NRL, is the Project Scientist. Dr. Michael Wolff and Dr. Paul Ray of NRL have also been prominent in the construction phase of USA. Professor Elliott Bloom, Stanford Linear Accelerator Center (Stanford University), is the lead Co-investigator for the Stanford part of the collaboration, which also includes Dr. Gary Godfrey of SLAC, Stanford Physics Professor Peter Michelson, Visiting Professor Lynn Cominsky (Sonoma State University), and a growing number of Stanford graduate students. There is also a broader membership in the USA collaboration poised to analyze the prolific data soon to be beamed down from the spacecraft. Besides those at NRL, Stanford and Sonoma State, these include scientists at Calgary University, MIT, and NASA AMES. The Department of Defense and the Department of Energy have provided funds for USA. | 0.906802 | 3.458923 |
For a relatively small celestial object, Pluto has been spotlighted in an enormous ongoing debate about what constitutes planetary status (or the lack thereof)—could our moon be next?
Planetary scientist Alan Stern, Pluto’s #1 fan and now possibly the moon’s, thinks so. Both famous and infamous for sending NASA’s New Horizons mission to Pluto, his probe only reached it the once-planet by the time it got demoted by the International Astronomical Union (IAU). This prompted backlash from Stern that may or may not have involved a certain eight-letter word regarding his opinion on the validity of Pluto’s downgraded status, along with the pressing question of why New Horizons was even sent to study Pluto if its subject was no longer a planet.
“To mitigate this unfortunate perception,” declared Stern and NASA colleagues in a controversial proposal, “we propose a new definition of ‘planet’, which has historical precedence. In keeping with both sound scientific classification and people’s intuition, we propose a geophysically-based definition of 'planet' that importantly emphasizes a body’s intrinsic physical properties over its extrinsic orbital properties."
So what exactly does this mean for the moon?
Backtrack several thousand years. Stern evidently had supporters even before humanity could launch anything into space. Even Aristotle believed the moon to be a planet. While the mystery factor of the “man in the moon” enticed the ancients into observing it, an anomalous astronomical coincidence convinced them it was more than just a satellite in Earth’s shadow. We apparently have a rebel moon, because it doesn’t orbit in (or extremely close to) the equatorial plane of our planet as other moons do. Even the Greek word for moon has nothing to do with sub-planetary objects; it literally translates to “thing that shines”, referring to the sunlight it reflects in the night sky.
Unfortunately for Aristotle (and Stern), the Renaissance saw a rebirth of ideas as to what the moon should be classified as. Copernicus’ telescope told of a heavenly body that orbited Earth rather than the sun. This is how it first got downgraded to a satellite, which derives from “satelles”, meaning “servant”. Arguments between astronomical purists who believed moons were planets and more radical thinkers who insisted they were satellites hardly helped. Galileo’s then-groundbreaking discovery of Jupiter’s moons made it lose even more of its luster, because it was no longer "the" moon.
Stern believes that astronomers’ opinions of planets are too obscured by their studies of every other floating object and cosmic phenomenon in space, while planetary scientists such as himself zero in exclusively on moons, planets, and planetary systems. He even likened asking an astronomer for an opinion on Pluto or the moon’s planetary status to expecting brain surgery from a podiatrist. An apology to podiatrists everywhere, but the IAU’s definition of planethood is relatively narrow. Planets have to orbit the sun, need enough gravity to assume a round shape and should be gravitationally dominant enough to clear their orbital zone. Now, wait for the irony. Comets and other smaller cosmic objects are always shooting through planetary orbits—which makes absolute zone clearing impossible.
Taking the obvious zone clearing flaw into account, Stern proposes that “a planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters.” Read: planets are any round objects in space smaller than stars. That would qualify both Pluto and the moon.
Whether or not the IAU will accept this proposal, the planet Luna is now at least a possibility. | 0.908602 | 3.683544 |
The decisive contribution of researchers from the Universities of Trieste and Udine, the Trieste section of the INFN, the Trieste Astronomical Observatory of the INAF.
On January 14, 2019, for the first time ever, high-energy photons emitted by a flash of gamma rays, or GRB, were revealed. These photons, which have reached energies of the order of teraelettronvolt, that is thousands of billions of times higher than those of visible light, were captured by the MAGIC telescopes on the Canary Islands. The Italian scientific contribution was fundamental for the discovery, also in this case. In the international team, researchers from the Universities of Trieste and Udine, researchers from the Trieste section of the INFN, the Trieste Astronomical Observatory and involved in the GRB project of the Institute for Fundamental Physics of the Universe (IFPU) played a leading role.
A new light on the phenomenon of GRBs
Gamma-ray burst (GRB) are short but powerful cosmic explosions that suddenly appear in the sky, about once a day. The flashes of gamma rays are characterized by a very bright initial flash in gamma rays that has a typical duration ranging from fractions of a second to a few hundred seconds. This initial flash is followed by the so-called afterglow, an emission of light observable at all wavelengths that is dimming over time. The study of afterglow was done at all wavelengths using instrumentation from both ground and space. Today we know that GRBs are the result of the explosion of very massive stars or the fusion of neutron stars in distant galaxies. Although we have identified the origin of these phenomena still much is the mystery that surrounds the phenomenon itself and the physics that characterizes it.
In particular, observations with high-energy gamma-ray telescopes are fundamental to solve these still mysterious aspects because they allow us to observe directly the heart of the phenomenon. Exactly what happened with the observations of the GRB190114C made by MAGIC telescopes in the Canary Islands that for the first time revealed the emission of photons from this source to the energy of the teraelettronvolt.
"The event observed by various space telescopes, including AGILE and Fermi, was called GRB 190114C and its coordinates, which identified its position in the sky, were distributed via the internet to astronomers around the world in 22 seconds from the detection of the explosion," says Prof. Francesco Longo, of the University and INFN of Trieste and a member of the collaborations AGILE, Fermi and MAGIC.
To receive the alert there were two MAGIC telescopes, Cherenkov light telescopes, each with a mirror diameter of 17 m, located on the island of La Palma, in the Canary Islands (Spain). MAGIC telescopes are designed to respond quickly to GRB alerts and also have a dedicated follow-up strategy. In the case of the GRB 190114C, MAGIC was able to start the observation about 30 seconds after the arrival of the GRB alert from the satellites, i.e. about 50 seconds after the detection of the phenomenon.
After pointing in the direction of the GRB 190114C, the MAGIC telescopes captured for the first time the highest energy photons ever measured for this type of celestial event. An unprecedented result, which provides new information essential for understanding the physical processes taking place in GRBs. "The photons revealed by MAGIC must in fact originate from a different process than the radiation commonly observed in the afterglow of GRBs, distinct from the physical process responsible for the emission of GRBs at the lowest energies" - says Davide Miceli, PhD student at the University of Udine, in the group of astroparticle physics coordinated by Prof. Barbara De Lotto.
Although the emission up to the energies of TeV in GRBs had been provided for in some theoretical studies, it had remained unnoticed until now despite the numerous researches carried out in recent decades with various instruments that work on these energies, including MAGIC.
The high-energy photons were observed by MAGIC until half an hour after the explosion of the GRB so, thanks to both the intensity of the signal received and the procedure for analyzing data in real time available at the observatory, it was possible to communicate within a few hours of observation to the international astronomical community the discovery of the first unequivocal detection of high-energy photons from a GRB. This communication highlighted the importance of this astronomical event and gave rise to an extensive campaign of follow-up observations at all wavelengths of the GRB 190114C by more than two dozen observers or instruments from the radio band to TeV energies.
All the observations made offer a very complete multifrequency overview for this event and provide unequivocal evidence that the high energy emission observed by MAGIC originates from a further, distinct emission process in the afterglow so far never observed: "From our analysis, the favorite candidate for explaining the very high energy emission is the so-called reverse Compton process in which the photons gain a considerable amount of energy in the collisions with even higher energy electrons that have been accelerated by the collision with the material surrounding the GRB" says Dr. Lara Nava of the INAF of Brera and associated with the INFN and the INAF of Trieste, which continues: "Vice versa, the low-energy photons observed in afterglows originate from the so-called synchrotron process in which the observed photons are generated by the interaction between electrons and magnetic fields".
MAGIC has opened a new window to study GRBs. These results indicate that we are certainly able to detect many more GRBs to TeV energies with both MAGIC and the new generation Cherenkov instruments.
The direct news for the MAGIC experiment:
Francesco Longo: [email protected]
Department of Physics - University of Trieste
Davide Miceli: [email protected]
Lara Nava: [email protected] | 0.809828 | 4.11032 |
Image credit: Cornell
According to researchers from Cornell University, binary asteroids – where a small asteroid orbits a larger one – are actually pretty common in Earth crossing orbits. In fact, they think that gravitational interactions with the Earth might actually help to cause the arrangement. The researchers estimate that 16% of asteroids larger than 200 metres in diameter have a companion – so far they’ve found five using two of the world’s largest radio telescopes.
Binary asteroids — two rocky objects orbiting about one another — appear to be common in Earth-crossing orbits, astronomers using the world’s two most powerful astronomical radar telescopes report. And it is probable, they say, that these double asteroid systems have been formed as a result of gravitational effects during close encounters with at least two of the inner planets, including Earth.
Writing in a report published by the journalScience on its Science Express web site (April 11, 2002), the researchers estimate that about 16 percent of so-called near-Earth asteroids (NEAs) larger than 200 meters (219 yards) in diameter are likely to be binary systems, with about a three-to-one relative size of the two encircling bodies. To date, five such binary systems have been identified by radar, says lead researcher Jean-Luc Margot, an O.K. Earl postdoctoral fellow in the Division of Geological and Planetary Sciences at the California Institute of Technology.
Margot, who at the time of the observations was a research associate in the planetary studies/radar group at the National Science Foundation’s (NSF) Arecibo Observatory in Puerto Rico (managed at Cornell University), says that theoretical and modeling results show the binary asteroids appear to be formed extremely close to Earth — within a distance equal to a few times the planet’s radius (6,378 kilometers or 3,963 miles). “The fact that one out of every six large NEAs is a binary and that they typically survive on the order of 10 million years, implies that these close encounters must happen frequently compared to the lifetime of the binary asteroids,” says Margot.
The Science article, “Binary Asteroids in the Near-Earth Object Population,” is coauthored by Michael Nolan, research associate at Arecibo; Lance Benner, Steven Ostro, Raymond Jurgens, Jon Giorgini and Martin Slade at the Jet Propulsion Laboratory (JPL); and Donald Campbell, professor of astronomy at Cornell. The observations were made at the 70-meter Goldstone NASA tracking telescope in California and at Arecibo Observatory.
NEAs are formed in the asteroid belt, between the orbits of Mars and Jupiter, and nudged by the gravitational attraction of nearby planets, largely Jupiter, into orbits that allow them to enter the Earth’s neighborhood. Most of the asteroids are the remnants of the initial agglomeration of the inner planets.
Astronomers have long speculated about the existence of binary NEAs, based in part on impact craters on Earth. Of about 28 known terrestrial impact craters with diameters greater than 20 kilometers, at least three are double craters formed by impacts of objects about the same size as the newly discovered binaries. Astronomers also have noted the changes in brightness of reflected sunlight for some NEAs, indicating a double system was causing an eclipse or occultation of one by the other.
In 2000, Margot and his co-researchers, using measurements from the Goldstone radar, found that a small, roughly 800-meter-diameter (half-a-mile) asteroid, 2000 DP107 (discovered only months before by a team from the Massachusetts Institute of Technology), was a binary system. Observations over eight days last October with the much more sensitive Arecibo telescope clearly established the physical characteristics of DP107’s two asteroids as well as their orbit about each other. The smaller object called the secondary, it was found, is about 300 meters (1,000 feet) in diameter and is orbiting the larger asteroid, the primary, every 42 hours at a distance of 2.6 kilometers (1.6 miles). The two asteroids appear to be locked in synchronous rotation, with the smaller always with the same face oriented to the larger.
Since that observation, says Margot, four more binary NEAs have been discovered, all in Earth-crossing orbits and each with a main asteroid significantly larger than the smaller body. “The primary is rotating much faster than most NEAs in all five binaries that have been discovered,” says Cornell’s Campbell. The Science Express article speculates that the most likely way the binaries are created is by close encounters of asteroids with the inner planets Earth or Mars. Of the five binary NEAs discovered to date, none has an orbit that brings it as close to the sun as Venus or Mercury.
NEAs, basically piles of rubble held together by gravity, are on trajectories that bring them within a few thousand miles of the planets, where tidal forces —- essentially the pull of gravity — can increase the spin rate of the asteroid, causing it to fly apart. The ejected rubble then reforms in orbit around the larger asteroid.
“The asteroid is already rotating very quickly as it approaches the planet. A little extra boost from tidal forces can be enough to exceed its breakup limits, and it sheds mass. This mass can end up forming another object in orbit around the asteroid. Right now this seems the most likely explanation,” says Margot.
There is an important reason for studying binary asteroids, says JPL’s Ostro: their potential for colliding with Earth. Knowing the density of so-called PHAs (for potentially hazardous asteroids), he observes, “is an extremely important input to any mitigation plans.” He says, “Getting NEA densities from radar is dirt cheap compared with getting a density with a spacecraft. Of course, the most important thing to know about any PHA is whether it is two objects or one, and this is why we want to observe these binaries with radar whenever possible.”
Margot notes, “Radar gives us very precise measurements of the size of the objects and their shape. The radar measurements of the distance and velocity of each component allows us to obtain precise information on their orbits. From this we can obtain the mass of each of the objects allowing, for the ?rst time, measurements of NEA densities, a very important indicator of their composition and internal structure.”
Arecibo Observatory is operated by the National Astronomy and Ionosphere Center at Cornell under a cooperative agreement with the NSF. The research was supported by the NSF, with NASA providing additional support for the planetary radar program at Arecibo.
Original Source: Cornell News Release | 0.899432 | 3.859281 |
Breakthrough Watch, the global astronomical program looking for Earth-like planets around nearby stars, and the European Southern Observatory (ESO), Europe’s foremost intergovernmental astronomical organisation, today announced “first light” on a newly-built planet-finding instrument at ESO’s Very Large Telescope in the Atacama Desert, Chile.
The instrument, called NEAR (Near Earths in the AlphaCen Region), is designed to hunt for exoplanets in our neighbouring star system, Alpha Centauri, within the “habitable zones” of its two Sun-like stars, where water could potentially exist in liquid form. It has been developed over the last three years and was built in collaboration with the University of Uppsala in Sweden, the University of Liège in Belgium, the California Institute of Technology in the US, and Kampf Telescope Optics in Munich, Germany.
Since 23 May ESO’s astronomers at ESO’s Very Large Telescope (VLT) have been conducting a ten-day observing run to establish the presence or absence of one or more planets in the star system. Observations will conclude tomorrow, 11 June. Planets in the system (twice the size of Earth or bigger), would be detectable with the upgraded instrumentation. The near- to thermal-infrared range is significant as it corresponds to the heat emitted by a candidate planet, and so enables astronomers to determine whether the planet’s temperature allows liquid water.
Alpha Centauri is the closest star system to our Solar System, at 4.37 light-years (about 25 trillion miles) away. It consists of two Sun-like stars, Alpha Centauri A and B, plus the red dwarf star, Proxima Centauri. Current knowledge of Alpha Centauri’s planetary systems is sparse. In 2016, a team using ESO instruments discovered one Earth-like planet orbiting Proxima Centauri. But Alpha Centauri A and B remain unknown quantities; it is not clear how stable such binary star systems are for Earth-like planets, and the most promising way to establish whether they exist around these nearby stars is to attempt to observe them.
Imaging such planets, however, is a major technical challenge, since the starlight that reflects off them is generally billions of times dimmer than the light coming to us directly from their host stars; resolving a small planet close to its star at a distance of several light-years has been compared to spotting a moth circling a street lamp dozens of miles away. To solve this problem, in 2016 Breakthrough Watch and ESO launched a collaboration to build a special instrument called a thermal infrared coronagraph, designed to block out most of the light coming from the star and optimised to capture the infrared light emitted by the warm surface of an orbiting planet, rather than the small amount of starlight it reflects. Just as objects near to the Sun (normally hidden by its glare) can be seen during a total eclipse, so the coronagraph creates a kind of artificial eclipse of its target star, blocking its light and allowing much dimmer objects in its vicinity to be detected. This marks a significant advance in observational capabilities.
The coronagraph has been installed on one of the VLT’s four 8-metre-aperture telescopes, upgrading and modifying an existing instrument, called VISIR, to optimise its sensitivity to infrared wavelengths associated with potentially habitable exoplanets. It will therefore be able to search for heat signatures similar to that of the Earth, which absorbs energy from the Sun and emits it in the thermal infrared wavelength range. NEAR modifies the existing VISIR instrument in three ways, combining several cutting-edge astronomical engineering achievements. First, it adapts the instrument for coronagraphy, enabling it to drastically reduce the light of the target star and thereby reveal the signatures of potential terrestrial planets. Second, it uses a technique called adaptive optics to strategically deform the telescope’s secondary mirror, compensating for the blur produced by the Earth’s atmosphere. Third, it employs novel chopping strategies that also reduce noise, as well as potentially allowing the instrument to switch rapidly between target stars -— as fast as every 100 milliseconds — maximising the available telescope time.
Pete Worden, Executive Director of the Breakthrough Initiatives, said: “We’re delighted to collaborate with the ESO in designing, building, installing and now using this innovative new instrument. If there are Earth-like planets around Alpha Centauri A and B, that’s huge news for everyone on our planet.”
“ESO is glad to bring its expertise, existing infrastructure, and observing time on the Very Large Telescope to the NEAR project,” commented ESO project manager Robin Arsenault.
“This is a valuable opportunity, as — in addition to its own science goals — the NEAR experiment is also a pathfinder for future planet-hunting instruments for the upcoming Extremely Large Telescope,” says Markus Kasper, ESO’s lead scientist for NEAR.
“NEAR is the first and (currently) only project that could directly image a habitable exoplanet. It marks an important milestone. Fingers crossed — we are hoping a large habitable planet is orbiting Alpha Cen A or B” commented Olivier Guyon, lead scientist for Breakthrough Watch.
“Human beings are natural explorers,” said Yuri Milner, founder of the Breakthrough Initiatives, “It is time we found out what lies beyond the next valley. This telescope will let us gaze across.”
Source: European Southern Observatory
Date: Jun 10, 2019 | 0.821047 | 3.837562 |
This time of year is full of music, with carol singers out in force and the ubiquitous Christmas “hits” playing on loop in every store, but a recent discovery has brought music to mind in a different way…
The music of the spheres – Pythagorean theory of the universe
The ancient Greeks described music in terms of a seven-note scale, to which have been assigned the letters A through G, where the main intervals could be expressed as simple mathematical ratios between the first four integers, with: octave (eighth)=2:1, fifth=3:2, fourth=4:3 (the counting system was inclusive, of the original numbers, which is how to get eight notes in a seven-note system – the fourth and fifth reduce to three and four as numbers, which then do add up to seven). These ratios harmonise musically as well as mathematically ie they are pleasing to the mind and the ear.
However, when extending this tuning however, a problem arises since no stack of 3:2 intervals (perfect fifths) will fit exactly into any stack of 2:1 intervals (octaves). Although there is a suggestion that the Pythagoreans were unaware of this, the philosopher Arthur Schopenhauer, described the problem:
“…thus, a perfectly pure harmonious system of tones is impossible not only physically, but even arithmetically. The numbers themselves, by which the tones can be expressed, have insoluable irrationalities,”
– The World as Will and Representation, Volume I, §52, E.F.J. Payne translation, Dover Publications, 1966, p.266
By considering a scale to consist of 12 equal intervals, a solution to stacking of the fifths can be found from the 12th root…if the seventh octave is 128:1 or 27, then the fifth is 27/12 or 1.4983:1. This is close to, but not the same as 3:2 (1.5). This “equal semitones” approach was developed simultaneously in Europe and China in the 16th century.
“Middle C” is the reference point for all the keys on a piano, and for the musical scale in general. “A above Middle C” is the benchmark note for which there is a definition in terms of physics, with a sound frequency now set at exactly 440 Hz.
This tuning approach suits other intervals better…while the Pythagorean approach works well tonally for fifths – a 3:2 ratio having a pleasing sound, other intervals such as thirds – 81:64 for major thirds and 32:27 for minor thirds sound much less pleasing, and as a result, Pythagorean tuning is rarely found after around 1510.
Pythagoras was the first to identify that the pitch of a musical note is in inverse proportion to the length of the string that produces it.
According to Dr George N. Gibson of the University of Connecticut Pythagoras “got lucky”: he did not actually study the frequencies that made up pleasing intervals and the musical scale – he just made observations about the lengths of the strings that made intervals and scales, and by coincidence, the frequency of a string has a simple relationship to its length. So, all the conclusions he reached about ratios of lengths of strings for different intervals, also apply to the ratios of the frequencies in the intervals. Unfortunately, this is not true for the tension in a string, or for the length of vibrating bars such as those on a xylophone.
This woodcut was made in the Middle Ages to explain illustrate Pythagorean ratios and how they applied to musical instruments:
The lower right panel shows flutes whose lengths correspond to the Pythagorean ratios. This works because, like a string, the frequency of an air column is simply related to its length. However, the panel on the lower left is problematic since the weights on the ends of the strings change their tension – as the frequency of the strings is not simply related to the tension, weighted strings will not sound in accordance with Pythagorean intervals. The examples in the upper panels are even more complicated, but bells, water glasses, and anvils also would not produce the correct intervals.
Unfortunately, the reverence for ancient Greek philosophers meant their theories were widely applied without any testing to see if the theories applied to any given situation….as Gibson puts it in his notes, “had anyone bothered to build any of the instruments (except for the flute) in the ratios prescribed in the woodcut, they would have found that the intervals were all wrong.”
It was actually Vincenzo Galilei, Galileo Galilie’s father, who first noticed that there was something wrong with the woodcut, which is interesting considering how Pythagoras’ theories about music and astronomy were to be challenged by his son.
Greek astronomers had identified certain “fixed” stars whose relative position in the sky did not change through the seasons. They also noted that there were “wanderers” or planets which moved relative to the background stars. To explain these observations, the astronomers theorised that the fixed stars were attached to a large black sphere that defined the edge of the universe, while the planets were attached to moving spheres, with each planet on its own sphere. In order for the fixed stars to be visible through these spheres, the Greeks believed they were made of crystal.
The known “planets” at the time were the moon, Mercury, Venus, the sun, Mars, Jupiter, and Saturn…seven, in total, so there were seven crystal spheres. This chimed with the seven notes in the musical scale discovered by Pythagoras, so the Greeks combined the two ideas into the concept of the “Music of the Spheres”.
Pythagoras proposed that the Sun, Moon and planets all emit their own unique hum based on their orbital revolution, and that the quality of life on Earth reflects the tenor of celestial sounds which were imperceptible to the human ear.
This idea dominated astronomy for the next 15 centuries, and many great physicists were convinced that universe had an order that was musical in nature. The astronomer Johannes Kepler became obsessed with trying to fit the orbits of the planets to a musical scale, and in the process discovered his eponymous laws of planetary motion.
Recent discoveries herald the Earth’s own music
While the music of the spheres may have been generally discounted, it turns out the Earth actually does have its own hum. This was confirmed in 1998 when a research team found the Earth constantly generates a low-frequency vibrational signal in the absence of earthquakes.
Since then, seismologists have proposed a number of different theories to explain the existence of this vibration, from atmospheric disturbances to the movement of ocean waves over the sea floor. A 2015 paper found that two marine factors are primarily responsible for the imperceptible planetary drone: the ebb and flow of ocean waves reaching the seafloor, and the vibrations caused by the collision of ocean waves add up to produce the hum. The result is a strange ultralow frequency that resonates almost identically all over the planet.
The vibration has been measured using seismometers on land, but now a new study has measured the vibrations beneath the sea, and determined that Earth’s natural vibration peaks at several frequencies between 2.9 and 4.5 millihertz – about 10,000 times smaller than the lower hearing threshold of the human ear, which is 20 hertz.
Closer to home and more familiar is the hum of electricity
The electricity hum (also called the “mains hum”) is more familiar, but what most of us don’t think about is that this hum has its own musical pitch associated with the frequency of the system. In a 50 Hz system such as the UK, this pitch is close to a G on the musical scale, whereas in the 60 Hz US system it is almost exactly halfway between A♯ and B.
This mains hum can be heard in audio equipment, and also from power grid equipment such as transformers. The intensity of the hum is a function of the applied voltage.
Hums can also appear at the frequency harmonics, though with a much lower intensity. In the case of a 50 Hz current, there could be humming at 100 Hz, 200 Hz, and so on, up until very high frequencies creating an entire spectrum of electrical hum with sound both at the original pitch, and higher octaves.
The hum is generally considered to be a nuisance, particularly in electrical musical instruments, however it does have some uses…forensic analysts use a technique called Electrical Network Frequency which allows them to validate audio recordings by comparing how the frequency changes in the background mains hum to a pre-existing database. This allows them to identify when a recording was created and help detect any edits in the recording.
Science has come a long way since the ancient Greeks theorised about a fundamental connection between music and astronomy, and yet we find that our planet does in fact have a natural hum, and we are also surrounded by a man-made humming from our electricity system. It’s not quite as romantic as the harmony of the spheres, but it’s curious nonetheless.
I would like to thank everyone who has read and commented on my blog over the past year, and wish you all a very merry (and musical!) Christmas, and a happy and prosperous New Year! | 0.847887 | 3.030567 |
To the human eye, the Rosette nebula appears as a vague ghost of a cloud around a bright star cluster in the constellation Monoceros, the Unicorn.
But to the infrared eye of the Herschel Space Observatory, this cosmic rose lights up with astonishing color:
—Image courtesy ESA/PACS & SPIRE Consortium/HOBYS Key Programme Consortia
More precisely, this epic picture was created by color-coding different infrared wavelengths based on the changing temperatures within the dust-and-gas cloud.
The bright regions are massive stars being born inside the nebula, each one shrouded by a dusty cocoon.
Herschel is offering astronomers some of the first views of these so-called protostars, which will grow up to become what are known collectively as OB class stars.
Once they reach adulthood, these very hot, very massive stars won’t live for long. But during their lifetimes, O and B stars emit some of the most energetic radiation that comes from living stars, usually in the form of ultraviolet light.
UV radiation from these stars can quickly ionize—or charge—the gases in the clouds around them, creating what are known as H II regions, such as the Rosette nebula.
H II regions in turn become nurseries for stars great and small, giving birth to thousands of stars over a few million years. Understanding how OB stars are born, live, and die can therefore help astronomers better understand the origins of less massive, longer-lived stars such as our own sun.
On the flip side, previous studies of the Rosette nebula also showed how O stars in particular can effectively halt planet formation around sunlike stars.
Some newborn stars are surrounded by swirling disks of dust and gas. Given enough time, gravity can pull clumps of matter together so that the disks coalesce into planets.
But O stars can create planetary “danger zones,” because the radiation streaming from the bright, massive monsters is so strong it can blow away any embryonic disks surrounding younger stars that formed too close by. | 0.841791 | 3.814933 |
Two sources tens of millions of light-years away have sent puzzling X-ray flares blazing our way. Now astronomers think they might have the answer: intermediate-mass black holes.
During every second of daylight, more than a trillion photons flood through the pupil of your eye. Yet it took only a dozen or so X-rays to reveal brilliant flashes coming from an unknown source tens of millions of light-years away.
X-rays are hard to come by. They’re only produced in the most energetic and violent processes, such as you might find in the magnetic field around a neutron star or in a black hole’s relativistic jet. So when a source emitted a whopping six X-ray photons in 22 seconds, compared to its usual rate of six photons per hour, astronomers took notice. Six photons may not sound like a lot, but if they’re coming from millions of light-years away, they point to a whole bunch of energy, of which we’re only seeing a small fraction.
When the same team found another source with similar behavior, but recurring every few years, they began narrowing down the possible explanations. Soon they had eliminated all but one: intermediate-mass black holes, the long-looked-for “inbetweener” beasts too large to have been formed by a single star’s death but much smaller than the supermassive black holes in galaxies’ centers. The results and reasoning are published in the October 20th Nature (full text here).
When three undergraduate students began working with Jimmy Irwin at the University of Alabama’s astronomy department, they only had a few hours a week to devote to research. So Irwin set them to work on a simple project: trawl through the Chandra X-ray Observatory archive and look for things that “twinkle.” What they were looking for were black holes with stellar companions — these sources are common and frequently double or triple in brightness over an hour or so before fading away again.
“A handful of such objects had been found previously,” Irwin says, “Searching through the Chandra archive for more examples seemed like a suitably straightforward project for undergraduates.”
Instead, the students happened upon something completely different: two spectacular sources that brightened by a factor of 100 or 200 over less than a minute. After the first source’s flare, they spotted a second source near Centaurs A that went from ten photons every three hours to 10 photons in a 51-second timespan. Both sources slowly faded over an hour before they returned to pre-flash levels.
“We were quite surprised,” Irwin says. “We’ve never seen anything like this.”
And that wasn’t all — going back through the Chandra archives showed that the second source actually had erupted four previous times, twice in 2007 and once each in 2009 and 2014. That immediately pointed to some “non-cataclysmic event”: whatever was generating these brilliant flashes wasn’t destroying itself.
Whatever is behind the brilliant, repeat flashes, it’s not common: Irwin’s students analyzed the X-rays from 70 nearby galaxies, as well as the Milky Way, and found no other flares.
Previous observations had already zeroed in on where the flashes hail from: the first source is probably a globular cluster, an old ball of stars neighboring the elliptical galaxy NGC 4636; the second source, possibly a dwarf galaxy, lives near the active galaxy Centaurus A.
Intermediate Monster Black Holes
What boosts its brightness by at least 100 times in mere seconds, fades over an hour, and lives among old stars such as found in globular clusters and dwarf galaxies?
At first, the team was inclined to look at neutron stars. After all, these crushed stellar remnants host powerful magnetic fields and can flash and flare in myriad ways depending on their age and environment. But even the most powerfully magnetized neutron stars simply don’t have the power to generate the energy inherent in these brief flares.
Which leaves one remaining option: “All of these observations seem to suggest the presence of a black hole,” says Sergio Campana (Astronomical Observatory of Brera, Italy), who wrote a perspective piece to accompany the study in Nature.
Intermediate mass black holes between 100 and 1,000 times the mass of the Sun — those not quite small enough to come from a collapsed star and not quite big enough to sink to its galaxy’s center — provide an easy explanation for some bright X-ray sources. But even if black holes provide enough energy to power these flares, it’s still unclear why they would be flaring.
Irwin and colleagues have already applied for X-ray and visible-light followup observations of the two sources, both to better determine their origins and perhaps to catch another flare in action. The discovery also points to the legacy value of Chandra’s data archive — if a first search found these two, could a wider search of, say, the XMM-Newton archive find more?
“Now that we know these strange objects are out there,” Campana says, “they will remain on the watch list.” | 0.811003 | 4.052379 |
Aldebaran joins the crescent Moon at dawn for its last occultation in 15 years — it's sure to be a beautiful sight.
Forty-nine consecutive months. That's how many times the Moon will have covered the bright star Aldebaran when the current series of occultations — begun on January 29, 2015 — ends on September 3rd. If you haven't seen one of these stunning stellar cover-ups, Tuesday morning, July 10th, will be your last chance until the next series begins in 2033.
During its 18.6 year nodal cycle, the Moon weaves between 5.1° north and south of the ecliptic because of its inclined orbit, putting it within reach of four first magnitude stars: Spica, Antares, Aldebaran and Regulus. Of these, Aldebaran is the brightest at magnitude 0.9. Because Aldebaran lies 5.5° south of the ecliptic, the Moon should theoretically pass nearly ½° north of the star every go-round. It doesn't, though, thanks to parallax.
Because the Moon is relatively close to Earth, it shifts position against the background stars depending on one's location. For instance, if viewed from diametrically opposite ends of Earth, say the poles, its position varies by 1.54° or three full moon diameters. From equator to pole, it's still about ¾° or 1.5 moon diameters — plenty of reach to cloak Aldebaran.
What makes Tuesday's event even more special is that none of four bright stars will be occulted again until the next Antares series begins on August 25, 2023, five years from now! What a bummer. All the more reason to set the alarm Tuesday, rub the sleep from your eyes and watch the 11% waning crescent rise next to the bright pink star.
Now for a bit of bad news. This last accessible Aldebaran occultation — the remaining two occur across the Arctic wilderness — will only be visible for observers in the Western Great Lakes region from Ontario as far west as North Dakota, Iowa, and southern Manitoba. At the western end, the Moon rises with Aldebaran already occulted, so those places will only witness the star's reappearance, which is the best part anyway.
Since the Moon will be just 2.5 days before new, it will be low in the sky for everyone — only 3° high for Minneapolis and 7° for Mackinaw City, Mich. at reappearance — so find a location with an unobstructed eastern horizon. You'll find a list of cities and times of the star's disappearance and reappearance here. Times are Universal Time, so remember to subtract 4 hours for Eastern, 5 for Central and so on.
The good news is that even if you aren't in the path, you can still see a close conjunction of star and Moon. In New Orleans the two will be only 20′ apart shortly after local moonrise, 1° in San Francisco and a scant 4′ apart in New York when closest at 4:28 a.m. in morning twilight. You can easily find out exactly where to look and how close the two will be for your location by downloading an app for your iPhone or Android. I use Star Chart (free) and the recently introduced free version of Sky Safari. Just Google 'em up. Be sure to bring a camera to capture this beautiful pairing.
An occultation of a bright star is a wonderful thing to witness in binoculars or a telescope. As the Moon moves eastward in its orbit, it edges ever closer to the star. Moments before disappearance, the star hovers at the limb of the Moon for what seems like forever. Then all at once, it vanishes in a flash. Minutes later, we're treated to an equally sudden "star rise" along the Moon's darkened, earth-lit limb. An incredible sight.
Catch a Grazing Occultation
You want an even more amazing sight? Travel to the graze line, where Aldebaran will scrape along the Moon's southern limb, flashing in and out of view as it alternately disappears behind mountain peaks and reappears as they travel past. Depending on your location, you may witness several to more than a dozen flashes.
Keen-eyed skywatchers may notice that Aldebaran — unlike lots of other occulted stars — won't blink out in an instant. With a radius 43 times that of the Sun, it has a true angular size, it will take a moment for the star to disappear and reappear. David Dunham, a founder of the International Occultation Timing Association (IOTA), described Aldebaran's return to view in a 1962 occultation as "appearing like a drop of water coming out of a faucet."
Check here for detailed graze paths and times for specific cities and regions including Green Bay and Appleton, Wisconsin; Mackinaw City, Michigan; and Iron Bridge, Ontario. To help plan your outing, check the latest forecast at the National Weather Service site by typing in your town's name in the local forecast box.
A delicate, Earth-lit Moon and bright orange star fused in the growing light of dawn — I think this is going to be a beautiful event. I'd love to hear about your experience, so drop by later with a comment or photo. | 0.869294 | 3.543328 |
A primordial galaxy could yield insight into the elusive process of early galaxy formation.
The further back in time astronomers look, the foggier the universe becomes. This cosmic cloudiness has prevented us from observing galaxies forming in the early universe — and by early, I mean less than a billion years after the Big Bang. But new research into a strange object lying near Mira in the constellation Cetus might yield some much-needed insight into the young universe.
First spotted in 2009, this object originally seemed to be a big bubble of ionized gas. Further observations suggested it was a galaxy whose light had taken 13 billion years to reach Earth, shining at us from a redshift of 6.6. And yet more refined observations revealed it to be a much rarer object: a merging triple system of infant galaxies, on course to possibly evolve into a galaxy akin to our Milky Way.
The triad of star-forming regions, named Himiko for a famous queen of ancient Japan, existed when the universe was only an infantine 800 million years old. Astronomers often refer to this era as the cosmic dawn, when the earliest galaxies were churning out stars. We’ve observed very few galaxies around this time, including one less than 500 million years after the Big Bang . The most active period of star formation came later, when the universe was a sprightly 2 to 3 billion years old.
The three star-forming regions of this soon-to-be galaxy also give Himiko its notability. Together, they produce 100 Suns per year (give or take a few) — an order of magnitude more than most galaxies seen by the Hubble Space Telescope (HST) at similar cosmic times. To put it in perspective: the titanic expanse of our Milky Way creates only one Sun’s worth of stellar mass each year. Only a couple of known early galaxies match or exceed Himiko’s rate, and it’s not clear whether these few incredibles hint at something surprising in the early universe.
Such active star-forming regions should show evidence of heavy elements, such as carbon. These heavier chemical building blocks are formed inside the furnaces of hot, massive, short-lived stars as they age, then are dispersed by the stars’ violent deaths. However, observations of the infant trinity from the Atacama Large Millimeter/submillimeter Array (ALMA) and HST completely lack any indication of carbon.
While a single missing element sounds innocuous, it could actually be a big deal. Astronomers have long been on the hunt for the most primordial stars and galaxies, which would only contain hydrogen and helium and (maybe) a trace of lithium. If the gas cloud surrounding the three clumps is as heavy-element free as the data suggest, then Himiko is a crucial example of a primordial galaxy seen during its formation.
Read the full paper on Himiko. | 0.844477 | 4.161699 |
Voyager had crossed the heliopause, where the river of solar particles meets the vast ocean of interstellar space. It is now beyond the bubble of our sun’s influence, NASA announced Monday.
For the second time, a human-made object has ventured into the void between the stars.
Its companion probe, Voyager 1, crossed that threshold in 2012. But Voyager 2 has a scientific leg up on its predecessor: It still possesses a working plasma instrument. This allows the spacecraft to sense a different kind of charged particle, called galactic cosmic rays.
After decades of looking at the galaxy “through the clouded lens of our heliosphere,” NASA physicist Georgia de Nolfo said, “we’re now able to take a step outside with Voyager and contemplate the vistas of our local galactic neighborhood.”
The spacecraft is about 11 billion miles from Earth — so far it takes signals traveling at the speed of light 16.5 hours to reach mission control at the Jet Propulsion Laboratory in California. That’s more than twice as distant as Pluto and 37 times farther than the journey from Earth to Mars.
Neither of the Voyager probes has technically left the solar system, said Ed Stone, who has been the project scientist for the mission since 1972. In about 300 years, they will reach the edge of the Oort cloud — a halo of icy bodies loosely bound by the sun’s gravity that is thought to be the source of comets. It will take another 40,000 years for the spacecraft to exit that cloud and come under the influence of another star.
For all their long years of travel, both spacecraft are essentially still on the solar system’s doormat.
But even from this vantage point, the probes are gaining new insights about how our corner of the cosmos works. Each left the heliosphere at a different location, and encountered slightly different conditions when they reached interstellar space. This suggests that there are complex interactions between the solar wind and interstellar space that affect the shape of the sun’s bubble, said NASA heliophysicist Nicola Fox.
“It’s a whole new view from the other side of that boundary,” she said.
Out there, highly energetic particles blow through space’s dark expanse like a strange cosmic breeze. These galactic cosmic rays have tremendous energy and travel close to the speed of light; if they ever reached astronauts or spacecraft, the consequences could be severe. Fortunately, most of these particles are deflected from our solar system by the sun’s magnetic field.
But scientists have to get beyond the sun’s protective bubble if they want to study these rays. So that’s what Voyager did.
With its plasma instrument and other tools, Voyager 2 will use these cosmic rays as “galactic messengers,” de Nolfo said, revealing clues about the stellar explosions that formed them.
But both spacecraft are living on borrowed time. “I like to say that they’re healthy, if you consider them as senior citizens,” said Suzanne Dodd, longtime project manager for the mission. Though the probes are functional, they are running out of the plutonium that powers them.
Voyager 2 is especially vulnerable, Dodd said, because it’s so cold — a few degrees above the freezing point of the hydrazine that powers its thrusters. Soon, researchers must make trade-offs about how to use the reserves that remain: Will they keep the spacecraft warm or continue to do science?
“We have difficult decisions ahead,” she said.
Scientists expect to receive their last signal from both Voyagers in the next five to 10 years. But their mission will not end then. Each spacecraft carries a copy of the Golden Record, a gold plated copper disk inscribed with sounds and images meant to communicate what life is like on Earth.
As they drift through space, to the next star and beyond, they will always bear this message — a postcard, to whomever finds them, from the world their creators call home. | 0.903118 | 3.897222 |
The blue-to-green approximate oval in the centre of this image is a phenomenon long theorised but never before directly seen.
It is a thick, dusty “doughnut” surrounding a rotating disk of material that is itself falling into the maw of a supermassive black hole that lies at the centre of Cygnus A, a galaxy some 760 million light-years from Earth.
In the so-called “unified model” for black holes, the existence of the torus, which is positioned approximately at right angles to the titanic jets extending fore and aft, is deployed to explain why the structures can look to different to observers, despite being pretty much identical.
All black holes, astronomers conclude, are surrounded by a ring of infalling material, and spew outflowing jets. Together, this set of features is called the active galactic nucleus (AGN).
However, black holes in different parts of the universe, and set at different angles of view to terrestrial or orbiting telescopes, don’t all look the same – a condition that led to them being divided into categories, such as quasars, blazars, or Seyfert galaxies.
The AGN model works on the assumption that such divisions represent a false taxonomy. To explain this, the notion of the torus was introduced. All black hole-powered “central engines” are basically similar (except in the matter of mass), the theory runs, but the torus is massive and thick, and obscures whatever is behind or inside it, relative to an observer, altering their appearance.
And now, astronomers led by Chris Carilli, of the National Radio Astronomy Observatory (NRAO) in Virginia, US, have succeeded in directly observing one for the first time.
“The torus is an essential part of the AGN phenomenon, and evidence exists for such structures in nearby AGN of lower luminosity, but we’ve never before directly seen one in such a brightly-emitting radio galaxy,” Carilli says.
“The torus helps explain why objects known by different names actually are the same thing, just observed from a different perspective.”
To obtain the image, the researchers used the Karl G Jansky Very Large Array (VLA) radio-astronomy observatory in New Mexico, US.
The result clearly shows the supermassive black hole – 2.5 billion times more massive than the sun – at the centre of the structure, in the form of two red circles. The orange and yellow rings represent a swirling, orbiting mass of infalling material, inside the darker torus.
Jets flying from either side of the structure can also clearly be shown. Also of interest is a smaller bright object in the lower right-hand part of the image. It was first observed in 2016 and, at present, its exact nature remains unknown.
“Cygnus A is the closest example of a powerful radio-emitting galaxy — 10 times closer than any other with comparably powerful radio emission,” says researcher Rick Perley.
“Doing more work of this type on weaker and more distant objects will almost certainly need the order-of-magnitude improvement in sensitivity and resolution that the proposed Next Generation Very Large Array (ngVLA) would bring,” he added.
Carilli and colleagues plan to publish their findings in The Astrophysical Journal Letters.
Andrew Masterson is a former editor of Cosmos.
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Has NASA discovered another Earth? Perhaps
- This newly found world, Kepler-1649c, is 300 light-years away from Earth.
- This world is similar to Earth both in size and estimated temperature, NASA said.
- "This intriguing, distant world gives us even greater hope that a second Earth lies among the stars."
Astronomers have discovered a planet nearly the same size as Earth that orbits in its star’s habitable zone, where liquid water could exist on its surface, a new study said.
The presence of liquid water also indicates the planet could support life.
This newly found world, Kepler-1649c, is 300 light-years away from Earth and orbits a star that is about one-fourth the size of our sun.
What's exciting is that out of all the 2,000 plus exoplanets that have been discovered using observations from the Kepler Space Telescope, this world is most similar to Earth both in size and estimated temperature, NASA said.
An exoplanet is a planet that's outside of our solar system.
"This intriguing, distant world gives us even greater hope that a second Earth lies among the stars, waiting to be found,” said Thomas Zurbuchen, associate administrator of NASA’s science mission directorate in Washington, D.C.
Although NASA said that there are other exoplanets estimated to be closer to Earth in size – and others may be closer to Earth in temperature – there is no other exoplanet that's closer to Earth in both of these values that also lies in the habitable zone of its system.
This newly revealed world is only 1.06 times larger than our own planet. Also, the amount of starlight it receives from its host star is 75% of the amount of light Earth receives from our sun – meaning the exoplanet's temperature may be similar to our planet’s, as well.
But unlike Earth, it orbits a red dwarf. Though none have been observed in this system, this type of star is known for stellar flare-ups that may make a planet's environment challenging for any potential life.
Scientists discovered this planet when looking through old observations from the Kepler Space Telescope, which the agency retired in 2018. (Although NASA’s Kepler mission ended in 2018 when it ran out of fuel, scientists are still making discoveries as they continue to examine the information that Kepler sent back to Earth.)
"The more data we get, the more signs we see pointing to the notion that potentially habitable and Earth-size exoplanets are common around these kinds of stars," said study lead author Andrew Vanderburg, a researcher at the University of Texas at Austin.
"With red dwarfs almost everywhere around our galaxy, and these small, potentially habitable and rocky planets around them, the chance one of them isn't too different than our Earth looks a bit brighter," he said.
The new study was published Wednesday in The Astrophysical Journal Letters. | 0.844705 | 3.537596 |
Fast radio bursts are having a moment in the science community.
After another repeating fast radio signal was traced to a nearby galaxy last month, a new study found that this burst occurs in a regular pattern -- sending signals to Earth every 16 days.
According to the new study published Feb. 3, this is the first time astronomers have identified a steady pattern in the FRBs. The first 28 cycles were detected between September 2018 and October 2019.
"We find that bursts arrive in a 4.0-day phase window, with some cycles showing no bursts, and some showing multiple bursts, within CHIME’s limited daily exposure," the study's authors wrote.
Where is this signal coming from? Besides tracing it to a galaxy 500 million light-years away (relatively nearby), scientists don't yet know. But, detecting the pattern is an important step to pinpointing an origin.
This repeating FRB was first detected in January 2020 using eight telescopes from around the world. The repeating pattern was discovered by the Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst Project (CHIME/FRB).
Canadian telescope CHIME is the same one that detected eight FRBs flashing from deep space in August 2019.
FRBs last only a few milliseconds but can expel more energy than 500 million suns. The first FRB was detected in 2007.
Theories about the precise origins of FRBs include two neutron stars or black holes colliding, evaporating black holes, interstellar explosions called supernovae or a fast-spinning neutron star with a strong magnetic field.
Yes, some suggest they could come from alien life. However, NASA's Jet Propulsion Laboratory says new data being collected doesn't fit quite right with any of these theories.
And, the discovery of an FRB repeating in a pattern definitely doesn't fit neatly into any of these explanations for the signal origins.
According to Space.com, patterns like this signal in astrophysics indicated a spinning or orbiting celestial objects.
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The recent launch of Gaia gave a boost of popularity to astronomy missions. Blasting from the Guiana Space Center in French Guiana, the Soyuz-STK rocket carrying the European Space Agency flagship mission delivered its cargo to orbit on December 19th last year. After a month-long travel to its final orbit, the Gaia mission is finally ready to start mapping a billion stars close to our Sun. Doing astronomy in space is no small deal, even for a state of the art satellite, as we will see.
Space astronomy missions are one of the most well known uses for space. While astronomers back on Earth are struggling to get past the interferences created by the atmosphere, or having to wait for an inconvenient cloud to get past, telescopes in space have a 24-hour day of clear sky. But this dream-come-true situation for astronomers is a challenge for engineers building the space platforms and telescopes. As for any other space mission, safety is an issue that is discussed, studied, and tested before any systems are launched and operated.
Any satellite is divided in two parts: the payload and the platform. Platforms are doing the boring but vital tasks, like providing electricity, propulsion, or guidance to the satellite. Payloads, on the other end, make it to the first page of the corporate brochures, and for a good reason: they are doing the mission. Payload tasks go from providing worldwide transmissions, to giving you the means to tell on which road you’re driving, or, for Hubble or other astronomy missions, providing gorgeous images of the cosmos that tend to become desktop wallpapers.
Behind the lens
Payloads in space astronomy are usually an instrument of some sort, like a giant telescope, or a very sharp radio antenna, or in the case of Gaia a combination of a Sky Mapper, a photometer, and a Radial Velocity Spectometer. Simply put, it is a precise measuring ruler to evaluate distances between stars. It is also why the Gaia mission is actually doing astrometry, the science of evaluating distances between celestial objects.
While space safety usually brings images of exploding rockets to the mind, this magazine proves on a regular basis how much larger the scope of space safety is. It can sometimes take very subtle forms, and space astronomy (or astrometry) is a good example.
Stability is key…
For any astronomy mission, one of the most important issues is to remain still. Very, very still. We all tried the very simple experiment of taking, on the go, a picture from a moving car of a charming cottage on the side of the street, only to discover a few hundred meters later that the picture was all blurred. You then have to go through the process of kindly asking to “please drive back,” and try again, only this time at a full stop.
The same is true for space telescopes, only the distance to the object we try to observe is far greater, which means that the stability of the telescope is a main design and operational issue. Lose the capability of keeping your satellite very stable, and every shot you take (or every part of space you listen to), will be white noise.
There are two kinds of stability needed: structural stability and control stability.
Structural stability is the hardest to achieve as it requires a very good knowledge of how your structure will react in space. Materials in space tend to have different properties than on Earth: plastics for instance can become very fragile, metal layers can join without fusion (cold welding), etc. The thermal environment of a satellite adds to the complexity of the situation, with parts facing the sun for too long heating up to nearly 260°C, while parts in the shadows can go below -100°C (colder than solid CO2, or “dry ice” on Earth). Any material will change volume if submitted to these extreme temperatures and will bend if the gradient of temperature is sharp. Should you not believe it, try a simple experiment next time you roast a meal: try pouring a large amount of cold water in the ceramic plate just out of the oven… And have an extra meal ready to cook in your fridge, because in all probability, the plate will break apart instantly.
On a spacecraft, keeping structures steady is assured in large part by a rigorous design that tries to average thermal conditions around the spacecraft. Some parts are designed to conduct heat while others act as a shield. Heat pipes are also used to conduct heat to radiators, sending the heat back into space. On some spacecraft, like Gaia, deployable solar shields are even mounted to guarantee that the instrument remains cold.
Once your satellite is well designed and its structure steady, you still have to ensure the pointing of your satellite and its stability. This task goes to the platform and more specifically to the GNC subsystem. GNC is short for the three basic tasks of this subsystem: Guidance (Where do I go?), Navigation (Where am I?), and Control (What do I do?). The GNC subsystem requires sensors and actuators. All of this equipment (and especially actuators) are prone to failure since they have mechanical parts in movement. Redundancy of all GNC equipment is therefore a must. Triple redundancy is usual, quadruple redundancy quite common, especially if you want your mission to be a long one.
Reaction wheels are a usual choice as rotation actuators. They basically use the same science as ice skaters spinning: when the ice skater moves his arms away from his body, the spin reduces and when he pulls them in, the spin accelerates. Several other solutions can be used such as spinning the entire satellite, thus giving it stability around one axis, or using Earth’s magnetic field, if close to the Earth, just to mention a few.
The Hubble space telescope, one of the most famous astronomy missions, is a good example of how critical this equipment can be. Hubble has been serviced five times by the space shuttle during which at least ten parts related to the GNC subsystem were replaced.
With the retirement of the Space Shuttle and advances in electronics, optics, and other astronomy related technologies, an increased number of next generation missions are bound to leave low Earth orbit (LEO) mostly to be located around the second Sun-Earth Lagrangian point (L2 for short), which is permanently located on the far side of the Earth as seen from Sun. But as much as being away from Mother Earth has its advantages, it also means that you are all alone now and that your parents will not support you anymore. No more reaction wheels for Christmas.
You could argue that with the end of the Space Shuttle era, servicing satellites is a thing of the past anyway, which is partly true. However, even if servicing is so 2010, Earth also protects satellites in LEO from cosmic radiation, solar winds, and other nasty particles. These events are nice to look at when they take the form of northern lights but can do critical damage to electronic systems when experienced in space and away from Earth.
Should a space agency lose its 100-million-dollar digital camera in space because of a solar flare two weeks into operations, tax payers and their representatives will no longer be that enthusiastic when paying the bill. Hardened electronics are therefore required. These electronic systems can detect and automatically solve single event upsets (SEU). SEUs happen when a charged particle has changed the property of your onboard electronics by changing a 0 to a 1 or the other way around.
But with all its solar storms, L2 is undoubtedly a nice place to do astronomy: while orbiting L2, the satellite remains at the same distance to the Sun, and to the Earth. With the Earth only 1.5 million km away, communications going at light speed are not too long, nor do they require a big transmitter. Another nice fact is that the satellite does not have a big blue ball that prevents it from watching half the sky. Any telescope in LEO has a hard time observing targets for a long time, as their orbit inevitably puts Earth in the field of observation at some point. Satellites in LEO also have to deal with the upper atmosphere and the Earth’s magnetic field, which can be as devastating as solar storms in the long run.
Let us get out and see the world !
L2 is getting crowded. And that is a good thing because getting our telescopes farther create some challenges, some of which we have approached in this article, and clearly we are overcoming them. It is easy to be nostalgic of an era of astronomy closer to home where giant telescopes where deployed from giant space vessels. While that is now a thing of the past, the next step still holds a lot of promise, and even if it is not as photogenic, it should excite us.
The mere fact that we can work in L2 with automated science missions of unparalleled complexity proves that space engineering is advancing in the right direction. In these missions, safety, and a very good knowledge of your system, is the key. Getting away from Earth’s immediate suburbs with cutting edge automated missions shows that agencies and space industries are getting more confident in their designs and concepts of operations.
We have seen over the last few years a sharp shift in priorities in western space programs. With the International Space Station (ISS) now at full capacity, and private corporations such as Arianespace, SpaceX, and Orbital Sciences in charge of launching cargo to the ISS on a regular basis, the target of next generation space missions is basically to be decided by our governments’ funding policies.
Asteroids are a recurring theme that holds promise from a scientific point of view and offer a target still unvisited by humans. If the decision is made to send our next generation of astronauts to these free flying rocks, we will have to build up from the experience of our automated missions in L2, including astronomy missions.
Getting away from LEO is the ultimate proof that the ever cautious and pessimistic engineers are getting confident in their technologies. It is a sign of optimism for the future of space exploration, and in these times of uncertainty, it is very good news. | 0.858504 | 3.398339 |
Creating New Stars
“To an engineer, fan belts exist between the crankshaft and the water pump. To a physicist, fan belts exist, briefly, in the intervals between stars.”
That’s beautiful, I thought, after reading the quote above. But . . . What’s it really mean?
This quote appears at the end of the following story, in the acknowledgements section of George Dyson’s book Turing’s Cathedral: The Origins of the Digital Universe:
In 1956, at the age of three, I was walking home with my father, physicist Freeman Dyson, from his office at the Institute for Advanced Study in Princeton, New Jersey, when I found a broken fan belt lying in the road. I asked my father what it was. “It’s a piece of the sun,” he replied.
My father was a field theorist, and protégé of Hans Bethe, former wartime leader of the Theoretical Division at Los Alamos, who, when accepting his Nobel Prize for discovering the carbon cycle that fuels the stars, explained that “stars have a life cycle much like animals. They get born, they grow, they go through a definite internal development, and finally they die, to give back the material of which they are made so that new stars may live.” To an engineer, fan belts exist between the crankshaft and the water pump. To a physicist, fan belts exist, briefly, in the intervals between stars.
The sun is the star upon which so much of this world relies, which explains why Dyson’s father called the fan belt “a piece of the sun.” The fan belt exists between the life of —and arguably because of— the sun.
What Bethe also explained in his speech is that,
“The ejected material probably contains the heavy elements which have been formed in the interior of the massive star. Thus heavy elements get into the interstellar gas, and can then be collected again by newly forming stars. It is believed that this is the way how stars get their heavy elements. This means that most of the stars we see, including our sun, are at least second generation stars, which have collected the debris of earlier stars which have suffered a supernova explosion.”
Why am I sharing this on a site that most-often discusses publishing, doing the work, being creative?
Jon Udell’s article “Names That Mean Things, Names That Do Things,” pointed me toward Dyson’s book, but his article 3D Printing Isn’t the Digital Literacy that Libraries Need to Teach was the one that spun me into researching Bethe’s work, as well as the work of William A. Fowler, and how the core materials of stars are gathered by new stars.
What does 3D printing and digital literacy have to do with the creation of stars?
One has the potential to feed the other.
Take the concept of a star and break it down to an individual level. You’re a star. The core of what you create in your lifetime has the potential to help other stars form.
I spend much of my time researching, brainstorming and/or implementing the creation, conservation and sharing of stories and other forms of information (a.k.a. the “heavy elements” or “materials), which are, or have been, at the core of so many individual stars.
What scares me is that much of the material from older stars has been boxed and stored in a relative’s attic, warehoused and forgotten (or in a long que awaiting digitization) in a library’s warehouse, or is disintegrating in full view, with little action to preserve it.
“At a gathering of makers and hackers last year I sat in a session on the future of libraries. The entire discussion revolved around 3D printers and maker spaces. I asked about other creative literacies: media, webmaking, curation, research. Nobody was interested. It was all about 3D printing.”
Udell goes on to discuss the maker movement and 3D printers and his conclusion that they are “being marketed with great success.”
We are starting to realize that you can’t build a house, or heat it, or feed the family that lives in it, by manipulating bits. You need to lay hands on atoms. As we re-engage with the physical world we will help heal our economies and our cultures. That’s all good. But it’s not the first thing that comes to mind when libraries seek to transform themselves from centers of consumption into centers of production.
Libraries really are about bits. They are uniquely positioned to adopt and promote digital literacies. Why don’t they? Those literacies aren’t yet being marketed as effectively as 3D printing. We who care need to figure out how to fix that.
My conclusion on why there’s a push for 3D printers instead of curation/preservation by libraries?
Money and manpower.
Invest in a 3D printer and you’re likely to get people in the library making/using it. Spend the same money on curation/preservation and you’ll cover not even a dime in the dollar of materials that previous stars have created.
“When people say everything’s online, they’re woefully uninformed,” said Jerry Dupont, of the Law Library Microform Consortium, as quoted in the well-titled ABA Journal article “Fading Past: Are Digitization and Budget Cuts Compromising History?”
Why should you care?
So much of what is created today is inspired by materials created by yesterday’s stars.
So much of the problems we face have solutions in past experiences.
So much of where we’d like to go, has been traveled by those in the past.
While making and creating and doing is important, the second and third steps of sharing and preserving are equally important.
Like Udell, I’d like to see a solution and am muddling through my own ideas/solutions.
If you’ve ever incorporated—or have been inspired by (or learned from)—past stars, how would you keep their core materials available for the future? What would be of greatest importance to you?
One last thought from a completely different source:
When interviewed by Jimmy Fallon this past week, Bruce Springsteen said (check out the 2:40 mark):
“It’s not the time in your life, it’s the life in your time.”
There have been some big stars with one-hit lives and small stars packed to the gills with life.
Preserving their materials isn’t just a good thing to do — it has the potential to help grow stars for the future.
One thing you can do? Support the libraries and encourage digital literacy. I know they don’t buy as many books as authors and publishers would always like, but they do have the potential to provide those authors and those publishers the resources, inspiration and stars for the future. | 0.821642 | 3.103232 |
Is there a more complicated and sophisticated technological engineering project than a spacecraft? Maybe a particle accelerator or a fusion power project. But other than those two, the answer is probably no.
Spacecraft like the ESA’s JUICE don’t just pop out of the lab ready to go. Each spacecraft like JUICE is a singular design, and they require years—or even a decade or more—of work before they ever see a launch pad. With a scheduled launch date of 2022, JUICE is in the middle of all that work. Now its cameras are capturing images of Jupiter and its icy moons as part of its navigation calibration and fine-tuning.
JUICE stands for Jupiter Icy Moons Explorer. Its mission is to orbit Jupiter and to perform repeated fly-bys of the gas giant’s ocean-bearing moons: Callisto, Ganymede, and Europa. For the final phase of its mission, JUICE will settle into an orbit around Ganymede, the Solar System’s largest moon, for an extended look. (JUICE will be the first spacecraft to orbit another planet’s moon.) At the end of its mission in February 2034, the spacecraft will be decommissioned by impacting Ganymede.
Its mission profile is pretty complex, and all of that complexity requires precise navigation. The spacecraft’s NavCam (Navigation Camera) will play a major role in finding JUICE’s position and velocity in relation to the moons it visits. (Radio tracking will help too, of course.) A round-trip radio signal between Earth and Jupiter takes about 1 hour and 45 minutes, so an autonomous navigation system is necessary. NavCam is a critical part of that system.
These images of Jupiter and its moons were taken with NavCam, but not while it was attached to the spacecraft. A team of engineers at Airbus, the JUICE mission’s primary contractor, took NavCam to the roof of a building at the Airbus Facility in Toulouse, France. The goal was to test NavCam in real sky conditions.
They were testing an engineering model of NavCam, and they focused on the various software and hardware interfaces, including image processing and on-board navigation software. They not only observed the Moon and other objects, but the spacecraft’s eventual target, Jupiter and its moons.
“Unsurprisingly, some 640 million kilometres away, the moons of Jupiter are seen only as a mere pixel or two, and Jupiter itself appears saturated in the long exposure images needed to capture both the moons and background stars, but these images are useful to fine-tune our image processing software that will run autonomously onboard the spacecraft,” says Gregory Jonniaux, Vision-Based Navigation expert at Airbus Defence and Space, in a press release. “It felt particularly meaningful to conduct our tests already on our destination!”
The environment around Jupiter is particularly nasty when it comes to radiation. NavCam, as well as all the spacecraft’s other systems, need to be protected from that radiation. All of the instrumentation and systems are critical, but perhaps none is as critical as the navigation equipment like NavCam.
NavCam’s purpose to provide the finely-tuned navigation required to operate in the region. Not only will JUICE be the first spacecraft to orbit the moon of another planet, but its flybys will take it very near to the moons—between 200 km and 400 km from the surfaces. NavCam’s precision navigation will allow JUICE to travel safely and effectively around Jupiter, and also to conserve fuel.
Of course, things will look much different once the spacecraft is at Jupiter. During flybys, and during the orbit of Ganymede, NavCam will be able to see surface features on the moons. Part of NavCam’s testing involved feeding it simulated images of what it’ll see once it’s there.
“The simulated views of the moons of Jupiter give a more realistic impression of what our NavCam will capture during flybys,” added Daniele Gherardi, ESA Guidance, Navigation and Control expert, in the same press release. “Of course, the high-resolution scientific camera suite will impress us with even more detail of these enigmatic moons.”
The imaging system Gherardi is referring to is called JANUS (Jovis, Amorum ac Natorum Undique Scrutator.) It’s a sophisticated, high-resolution imaging system with a spatial resolution down to 2.4 m/pixel (7.9 ft/pixel.) It also provides stereo imaging, and will integrate with spectral, laser, and radar data to provide geomorphology measurements.
This isn’t the only testing that NavCam will undergo as the ESA and Airbus work their way towards the mission’s eventual launch in 2022. By the end of the year, NavCam will be tested with a “full flight representative performance optics assembly.” Following that, it will be tested for integration with the rest of the JUICE spacecraft. And after launch, the ESA will use an engineering model of NavCam to support mission ops.
It’s a ways to go before JUICE is launched, but these dates have a way of sneaking up on us. It wasn’t that long ago that we were waiting patiently for NASA’s JUNO spacecraft to launch to Jupiter. Now, JUNO has been orbiting Jupiter for over three years, and NASA has extended its mission to July 2021.
But while JUNO is mostly all about Jupiter itself, JUICE is focusing on the ocean-bearing moons around Jupiter, trying to establish their potential to support life. But it can’t do that without precision navigation, and that’s what NavCam is all about.
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What is a gravity assist or a swingby for a spacecraft? I've heard about spacecraft gaining velocity from passing close to planets and being 'sling shot'-ed into a higher orbit. Where does this energy come from?
Gravity assist is a technique used to speed up, slow down or change the direction of a spacecraft as it approaches a planet within our solar system. This technique saves fuel that would otherwise have to be used to make these adjustments.
The basic principles behind gravity assist have to do with the relative velocities of the spacecraft and of the planets involved and the conservation of angular momentum. The spacecraft approaches the planet. Because the planet is moving too (while orbiting the Sun), it actually transfers some of its angular momentum to the spacecraft. What the craft gains in velocity, the planet loses. The mass of the planet is huge compared to that of the spacecraft so the loss is imperceptible. For example, Galileo increased its speed at Earth by 11,620 mph in 1990 and 8,280 mph in 1992. The Earth slowed down in its orbit by a speed of about 5 billionths of an inch per year from the two events.
The technique of gravity assist or swingby approach for a spacecraft was used as early as the Mariner 10 mission in 1973-1974 and has been used recently to create unique orbits such as with the Ulysses spacecraft.
Submitted by Mark (Maryland, USA)
Submitted by Jean-Marc (Oullins, France)
(September 3, 1998)
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- KELT-9b is a hot Jupiter.
- It is one of the hottest exoplanets ever discovered.
- It has a daytime temperature of 7,800 degrees Fahrenheit (4,600 Kelvin).
This artist's concept shows planet KELT-9b orbiting its host star, KELT-9. It is one of the hottest gas giant planets discovered so far.
With a dayside temperature of more than 7,800 degrees Fahrenheit (4,600 Kelvin), KELT-9b is a planet that is hotter than most stars. But its star, called KELT-9, is even hotter – a blue A-type star that is likely unraveling the planet through evaporation.
KELT-9b is a gas giant 2.8 times more massive than Jupiter, but only half as dense. Scientists would expect the planet to have a smaller radius, but the extreme radiation from its host star has caused the planet's atmosphere to puff up like a balloon.
The planet is also unusual in that it orbits perpendicular to the spin axis of the star. That would be analogous to the planet orbiting perpendicular to the plane of our solar system. One "year" on this planet is less than two days long.
The KELT-9 star is only 300 million years old, which is young in star time. It is more than twice as large, and nearly twice as hot, as our sun. Given that the planet's atmosphere is constantly blasted with high levels of ultraviolet radiation, the planet may even be shedding a tail of evaporated planetary material like a comet.
The study reporting the KELT-9 discovery was largely funded by the National Science Foundation (NSF) through an NSF CAREER Grant, NSF PAARE Grant and an NSF Graduate Research Fellowship. Additional support came from NASA via the Jet Propulsion Laboratory and the Exoplanet Exploration Program; the Harvard Future Faculty Leaders Postdoctoral Fellowship; Theodore Dunham, Jr., Grant from the Fund for Astronomical Research; and the Japan Society for the Promotion of Science. | 0.864029 | 3.635557 |
Doug Lowe’s 1st Law states that when an object maintains a stable orbit around another object, the force of gravity between the objects is counter balanced by a propulsive force generated by the orbiting object at right angles to the force of gravity in the direction of motion of the orbiting object.
Doug Lowe’s 2nd Law states that if an orbiting object generates a propulsive force in excess of that required to maintain a stable orbit, the surplus force will be used up in the production of rotational motion
Yet again in the commentary by Lisa Grossman (New Scientist 2 November 2013 page 11), Dark Matter fails to become visible. This expensive failure sits in a long string of failures to discover the source of the vast bulk of the energy sloshing about in our universe.
The scientific herd should come out of denial and dig a big hole for Dark Matter, bury it forever and save a few billions of world currency because it does not exist.
Dark matter does not exist because of Lowe’s Law of Equilibrium for Orbiting Objects. It is worth repeating because it puts a very different slant on how we deal with gravity and matter!
Lowe’s Law states that when an object maintains a stable orbit around another object, the force of gravity between the objects will be counter balanced by a propulsive force generated by the orbiting object at right angles to the force of gravity in the direction of motion of the orbiting object
If you recognise that dark matter does not exist but so called dark energy does exist then it is a short step to say that the 80% of all the energy in our universe is in fact attached to the matter all around us. So now you have to accept that matter all around us has 3 fundamental properties not two: mass, gravity and propulsion and you have found your dark energy.
Without the propulsion vector, matter would be a permanent singularity and alternatively comets would always impact directly with the sun because without the propulsion force giving it the boost to take a straight line around the sun (instead of curving into it), the comet having momentum only could not resist the sun's gravity so would be dragged straight into it.
What I am hoping to start in this discussion is ideas for how the free energy of gravity can be converted into the 3rd fundamental property of matter - propulsion.
The other line of discussion which you may be thinking about is how the FREE energy of magnetism (like gravity) can be converted into a force of propulsion based on Lowe's law. By understanding this law I think we might have the key that the megalithic builders had and our scientists have blanked since Newton formulated his laws.
I believe that engaging the force of free magnetism with matter of a particular kind in a particular way will result in harnessing its free propulsive forces - maybe with a bit of electro-mechanical help.
Finding the combinations of magnetism and matter which will give us the propulsive force is what our quest is about. I am on the case, are you?
This force is what enabled the builders of Stonehenge to transport their huge blocks of stone - without roads - a distance of 160 miles. Even in the unlikely event that they did build a special road from West Wales (Carn Goedog near the west coast of Wales) across rivers estuaries mountains and valleys, what kind of machines must they have had to move 60 blocks of stone 4 tons in weight amounting to 240 tons. Even if they were moved first over land and then by sea it would have been a monumental achievement with primitive sledges etc and barges - AND how would they have propelled them?
Then there are the sarsens which come from about 25 miles away. These stones numbered about 80 originally and an average of about 30 tons; one was estimated to be 50 tons and 100 feet long.That's a total of of about 2400 tons they had to move without any evidence of roads having been built to transport them.
Even today our roads and vehicles are too flimsy to move a 50 ton rock 100 feet long: It would take 3 x 40ft trailers loaded end to end pulled by 2 tractors at each end and they would struggle to move it up hill and down and our bridges would not be able to take the weight. Are you convinced?
Check out this link:
You can check out my blog on the subject of dark matter and energy at: | 0.834984 | 3.609238 |
By Kathryn Harriss | –
(The Conversation) – NASA’s spacecraft OSIRIS-REx has finally reached the asteroid 101955 Bennu – which may be on collision course with the Earth – after travelling for just over two years since its launch in September 2016. This mission, which will bring grains back for us to study on Earth, is latest to return asteroid samples to Earth after the Japanese Space Agency’s missions Hayabusa 1 and 2 and StarDust. The data will help unveil more about the origins of the solar system and how to protect the Earth from possible asteroid impact.
Bennu seen on November 16. NASA/Goddard/University of Arizona.
The spacecraft will spend the next year completing a detailed survey of the surface of Bennu (492 metres in diameter) – including locating the most suitable landing sites. Once a site is selected, the spacecraft will land for about five seconds to collect a sample of the surface material using a burst of nitrogen gas to liberate material from the surface into the sampler head.
The spacecraft has enough gas to attempt three sample collections from the surface. This will hopefully provide a sample of between 60g and 2,000g of surface regolith material (the layer of material covering solid rock). It will start heading back to Earth in 2021 – getting here in 2023.
Asteroids are material left over from the early solar system, which means they offer a unique look into its early composition. Bennu orbits the sun between the Earth and Mars. Its composition is of particular interest as we already know it is rich in carbon. This means it may contain organic materials that have remained unaltered since the formation of the solar system. It is not impossible that asteroids like it delivered the building blocks of life to the early Earth – the mission could help us investigate this theory.
Though sample return is a major and complex part of this mission, OSIRIS-REx will study other aspects of the asteroid too. During the survey of the surface the spacecraft will also be looking out for plumes and natural satellites orbiting the body. Instruments on board will allow enable us to identify different chemicals on it. This will help finding the most interesting and richest sample sites to a resolution of about two metres.
The asteroid Bennu is of interest to Earth for another reason. Bennu may be on collision course with Earth in the future. It is theorised from the study of the orbit of Bennu that gravity interaction between the two bodies during a close approach to Earth in 2060 (750,000km) will slightly alter its course. This means that there is a cumulative one in 2,700 chance of an Earth impact between 2175 and 2199.
OSIRIS-REx may be able to aid in preventing such events. One of the thing it will measure is the body’s “Yarkovsky acceleration”. This effect is a force that acts on a rotating body in space, caused by the uneven release of heat from the surface of the asteroid. Once this is known, it will be possible to investigate whether we could use this force to change the orbit of Bennu and other threatening asteroids. For example, it may be possible to use solar radiation to heat up one side of the rock more than the other – changing its rotation and the orbit trajectory.
The next two years is going to be an exciting one for small body research. This mission will provide the most detailed analysis of carbon rich asteroids and will provide answers about the evolution of the solar system and our own planet. Analysis of the regolith will also tell us more about the effects of space weathering on the surface of small bodies from harsh solar radiation.
The collection method for the mission is called “Touch and Go Sample Acquisition Mechanism”. And touch and go is exactly what the spacecraft must achieve, rather than a full landing. This will be extremely difficult and we will have to wait a year to see if the new method is successful. Let’s keep our fingers crossed that it all goes according to plan.
Bonus video added by Informed Comment: | 0.876542 | 3.561821 |
Black holes are famous for being inescapable. Within the event horizon of these celestial objects, matter and even light enter and then disappear forever. However, beyond the event horizon, black holes are known to form accretion disks from which light can escape. In fact, this is how astronomers are able to confirm the presence of black holes and determine their properties (i.e. mass, spin rate, etc.)
However, according to a recent NASA-funded study led by researchers from the California Institute of Technology (Caltech), there is evidence that not all light emanating from a black hole’s disk simply escapes. According to their observations, some of the light escaping from the disk is pulled back in by the black hole’s gravity and reflected off the disk again. These observations confirm something astronomers have theorized for about forty years.
When astronomers talk about an optical telescope, they often mention the size of its mirror. That’s because the larger your mirror, the sharper your view of the heavens can be. It’s known as resolving power, and it is due to a property of light known as diffraction. When light passes through an opening, such as the opening of the telescope, it will tend to spread out or diffract. The smaller the opening, the more the light spreads making your image more blurry. This is why larger telescopes can capture a sharper image than smaller ones.
There’s a lot going on at the center of our galaxy. A supermassive black hole named Sagittarius A-Star resides there, drawing material in with its inexorable gravitational attraction. In that mind-bending neighbourhood, where the laws of physics are stretched beyond comprehension, astronomers have detected a ring of cool gas.
“We have taken the first picture of a black hole.”
EHT project director Sheperd S. Doeleman of the Center for Astrophysics | Harvard & Smithsonian.
What was once un-seeable can now be seen. Black holes, those difficult-to-understand singularities that may reside at the center of every galaxy, are becoming seeable. The Event Horizon Telescope (EHT) has revealed the first-ever image of a black hole, and with this image, and all the science behind it, they may help crack open one of the biggest mysteries in the Universe.
An almost unimaginably enormous black hole is situated at the heart of the Milky Way. It’s called a Supermassive Black Hole (SMBH), and astronomers think that almost all massive galaxies have one at their center. But of course, nobody’s ever seen one (sort of, more on that later): It’s all based on evidence other than direct observation.
The Milky Way’s SMBH is called Sagittarius A* (Sgr. A*) and it’s about 4 million times more massive than the Sun. Scientists know it’s there because we can observe the effect it has on matter that gets too close to it. Now, we have one of our best views yet of Sgr. A*, thanks to a team of scientists using a technique called interferometry.
Shortly after Einstein published his Theory of General Relativity in 1915, physicists began to speculate about the existence of black holes. These regions of space-time from which nothing (not even light) can escape are what naturally occur at the end of most massive stars’ life cycle. While black holes are generally thought to be voracious eaters, some physicists have wondered if they could also support planetary systems of their own.
Looking to address this question, Dr. Sean Raymond – an American physicist currently at the University of Bourdeaux – created a hypothetical planetary system where a black hole lies at the center. Based on a series of gravitational calculations, he determined that a black hole would be capable of keeping nine individual Suns in a stable orbit around it, which would be able to support 550 planets within a habitable zone.
As Raymond indicates, one of the immediate advantages of having this black hole at the center of a system is that it can support a large number of Suns. For the sake of his system, Raymond chose 9, thought he indicates that many more could be sustained thanks to the sheer gravitational influence of the central black hole. As he wrote on his website:
“Given how massive the black hole is, one ring could hold up to 75 Suns! But that would move the habitable zone outward pretty far and I don’t want the system to get too spread out. So I’ll use 9 Suns in the ring, which moves everything out by a factor of 3. Let’s put the ring at 0.5 AU, well outside the innermost stable circular orbit (at about 0.02 AU) but well inside the habitable zone (from about 2.7 to 5.4 AU).”
Another major advantage of having a black hole at the center of a system is that it shrinks what is known as the “Hill radius” (aka. Hill sphere, or Roche sphere). This is essentially the region around a planet where its gravity is dominant over that of the star it orbits, and can therefore attract satellites. According to Raymond, a planet’s Hill radius would be 100 times smaller around a million-sun black hole than around the Sun.
This means that a given region of space could stably fit 100 times more planets if they orbited a black hole instead of the Sun. As he explained:
“Planets can be super close to each other because the black hole’s gravity is so strong! If planets are little toy Hot wheels cars, most planetary systems are laid out like normal highways (side note: I love Hot wheels). Each car stays in its own lane, but the cars are much much smaller than the distance between them. Around a black hole, planetary systems can be shrunk way down to Hot wheels-sized tracks. The Hot wheels cars — our planets — don’t change at all, but they can remain stable while being much closer together. They don’t touch (that would not be stable), they are just closer together.”
This is what allows for many planets to be placed with the system’s habitable zone. Based on the Earth’s Hill radius, Raymond estimates that about six Earth-mass planets could fit into stable orbits within the same zone around our Sun. This is based on the fact that Earth-mass planets could be spaced roughly 0.1 AU from each other and maintain a stable orbit.
Given that the Sun’s habitable zone corresponds roughly to the distances between Venus and Mars – which are 0.3 and 0.5 AU away, respectively – this means there is 0.8 AUs of room to work with. However, around a black hole with 1 million Solar Masses, the closest neighboring planet could be just 1/1000th (0.001) of an AU away and still have a stable orbit.
Doing the math, this means that roughly 550 Earths could fit in the same region orbiting the black hole and its nine Suns. There is one minor drawback to this whole scenario, which is that the black hole would have to remain at its current mass. If it were to become any larger, it would cause the Hill radii of its 550 planets to shrink down further and further.
Once the Hill radius got down to the point where it was the same size as any of the Earth-mass planets, the black hole would begin to tear them apart. But at 1 million Solar masses, the black hole is capable of supporting a massive system of planets comfortably. “With our million-Sun black hole the Earth’s Hill radius (on its current orbit) would already be down to the limit, just a bit more than twice Earth’s actual radius,” he says.
Lastly, Raymond considers the implications that living in such a system would have. For one, a year on any planet within the system’s habitable zone would be much shorter, owing to the fact their orbital periods would be much faster. Basically, a year would last roughly 1.6 days for planets at the inner edge of the habitable zone and 4.6 days for planets at the outer edge of the habitable zone.
In addition, on the surface of any planet in the system, the sky would be a lot more crowded! With so many planets in close orbit together, they would pass very close to one another. That essentially means that from the surface of any individual Earth, people would be able to see nearby Earths as clear as we see the Moon on some days. As Raymond illustrated:
“At closest approach (conjunction) the distance between planets is about twice the Earth-Moon distance. These planets are all Earth-sized, about 4 times larger than the Moon. This means that at conjunction each planet’s closest neighbor appears about twice the size of the full Moon in the sky. And there are two nearest neighbors, the inner and outer one. Plus, the next-nearest neighbors are twice as far away so they are still as big as the full Moon during conjunction. And four more planets that would be at least half the full Moon in size during conjunction.”
He also indicates that conjunctions would occur almost once per orbit, which would mean that every few days, there would be no shortage of giant objects passing across the sky. And of course, there would be the Sun’s themselves. Recall that scene in Star Wars where a young Luke Skywalker is watching two suns set in the desert? Well, it would a little like that, except way more cool!
According to Raymond’s calculations, the nine Suns would complete an orbit around the black hole every three hours. Every twenty minutes, one of these Suns would pass behind the black hole, taking just 49 seconds to do so. At this point, gravitational lensing would occur, where the black hole would focus the Sun’s light toward the planet and distort the apparent shape of the Sun.
To illustrate what this would look like, he provides an animation (shown above) created by @GregroxMun – a planet modeller who develops space graphics for Kerbal and other programs – using Space Engine.
While such a system may never occur in nature, it is interesting to know that such a system would be physically possible. And who knows? Perhaps a sufficiently advanced species, with the ability to tow stars and planets from one system and place them in orbit around a black hole, could fashion this Ultimate Solar System. Something for SETI researchers to be on the lookout for, perhaps?
This hypothetical exercise was the second installment in two-part series by Raymond, titled “Black holes and planets”. In the first installment, “The Black Hole Solar System“, Raymond considered what it would be like if our system orbited around a black hole-Sun binary. As he indicated, the consequences for Earth and the other Solar planets would be interesting, to say the least!
At the center of our galaxy resides a Supermassive Black Hole (SMBH) known as Sagittarius A. Based on ongoing observations, astronomers have determined that this SMBH measures 44 million km (27.34 million mi) in diameter and has an estimated mass of 4.31 million Solar Masses. On occasion, a star will wander too close to Sag A and be torn apart in a violent process known as a tidal disruption event (TDE).
These events cause the release of bright flares of radiation, which let astronomers know that a star has been consumed. Unfortunately, for decades, astronomers have been unable to distinguish these events from other galactic phenomena. But thanks to a new study from by an international team of astrophysicists, astronomers now have a unified model that explains recent observations of these extreme events.
As Enrico Ramirez-Ruiz – the professor and chair of astronomy and astrophysics at UC Santa Cruz, the Niels Bohr Professor at the University of Copenhagen, and a co-author on the paper – explained in a UCSC press release:
“Only in the last decade or so have we been able to distinguish TDEs from other galactic phenomena, and the new model will provide us with the basic framework for understanding these rare events.”
In most galaxies, SMBHs do not actively consume any material and therefore do not emit any light, which distinguishes them from galaxies that have Active Galactic Nuclei (AGNs). Tidal disruption events are therefore rare, occurring only once about every 10,000 years in a typical galaxy. However, when a star does get torn apart, it results in the release of an intense amount of radiation. As Dr. Dai explained:
“It is interesting to see how materials get their way into the black hole under such extreme conditions. As the black hole is eating the stellar gas, a vast amount of radiation is emitted. The radiation is what we can observe, and using it we can understand the physics and calculate the black hole properties. This makes it extremely interesting to go hunting for tidal disruption events.”
In the past few years, a few dozen candidates for tidal disruption events (TDEs) have been detected using wide-field optical and UV transient surveys as well as X-ray telescopes. While the physics are expected to be the same for all TDEs, astronomers have noted that a few distinct classes of TDEs appear to exist. While some emit mostly x-rays, others emit mostly visible and ultraviolet light.
As a result, theorists have struggled to understand the diverse properties observed and create a coherent model that can explain them all. For the sake of their model, Dr. Dai and her colleagues combined elements from general relativity, magnetic fields, radiation, and gas hydrodynamics. The team also relied on state-of-the-art computational tools and some recently-acquired large computer clusters funded by the Villum Foundation for Jens Hjorth (head of DARK Cosmology Center), the U.S. National Science Foundation and NASA.
Using the model that resulted, the team concluded that it is the viewing angle of the observer that accounts for the differences in observation. Essentially, different galaxies are oriented randomly with respect to observers on Earth, who see different aspects of TDEs depending on their orientation. As Ramirez-Ruiz explained:
“It is like there is a veil that covers part of a beast. From some angles we see an exposed beast, but from other angles we see a covered beast. The beast is the same, but our perceptions are different.”
In the coming years, a number of planned survey projects are expected to provide much more data on TDEs, which will help expand the field of research into this phenomena. These include the Young Supernova Experiment (YSE) transient survey, which will be led by the DARK Cosmology Center at the Niels Bohr Institute and UC Santa Cruz, and the Large Synoptic Survey Telescopes (LSST) being built in Chile.
According to Dr. Dai, this new model shows what astronomers can expect to see when viewing TDEs from different angles and will allow them to fit different events into a coherent framework. “We will observe hundreds to thousands of tidal disruption events in a few years,” she said. “This will give us a lot of ‘laboratories’ to test our model and use it to understand more about black holes.”
This improved understanding of how black holes occasionally consume stars will also provide additional tests for general relativity, gravitational wave research, and help astronomers to learn more about the evolution of galaxies.
In August of 2017, a major breakthrough occurred when scientists at the Laser Interferometer Gravitational-Wave Observatory (LIGO) detected gravitational waves that were believed to be caused by the collision of two neutron stars. This source, known as GW170817/GRB, was the first gravitational wave (GW) event that was not caused by the merger of two black holes, and was even believed to have led to the formation of one.
As such, scientists from all over the world have been studying this event ever since to learn what they can from it. For example, according to a new study led by the McGill Space Institute and Department of Physics, GW170817/GRB has shown some rather strange behavior since the two neutron stars colliding last August. Instead of dimming, as was expected, it has been gradually growing brighter.
For the sake of their study, the team relied on data obtained by NASA’s Chandra X-ray Observatory, which showed that the remnant has been brightening in the X-ray and radio wavelengths in the months since the collision took place. As Daryl Haggard, an astrophysicist with McGill University whose research group led the new study, said in a recent Chandra press release:
“Usually when we see a short gamma-ray burst, the jet emission generated gets bright for a short time as it smashes into the surrounding medium – then fades as the system stops injecting energy into the outflow. This one is different; it’s definitely not a simple, plain-Jane narrow jet.”
What’s more, these X-ray observations are consistent with radiowave data reported last month by another team of scientists, who also indicated that it was continuing to brighten during the three months since the collision. During this same period, X-ray and optical observatories were unable to monitor GW170817/GRB because it was too close to the Sun at the time.
However, once this period ended, Chandra was able to gather data again, which was consistent with these other observations. As John Ruan explained:
“When the source emerged from that blind spot in the sky in early December, our Chandra team jumped at the chance to see what was going on. Sure enough, the afterglow turned out to be brighter in the X-ray wavelengths, just as it was in the radio.”
This unexpected behavior has led to a serious buzz in the scientific community, with astronomers trying to come up with explanations as to what type of physics could be driving these emissions. One theory is a complex model for neutron star mergers known as “cocoon theory”. In accordance with this theory, the merger of two neutron stars could trigger the release of a jet that shock-heats the surrounding gaseous debris.
This hot “cocoon” around the jet would glow brightly, which would explain the increase in X-ray and radiowave emissions. In the coming months, additional observations are sure to be made for the sake of confirming or denying this explanation. Regardless of whether or not the “cocoon theory” holds up, any and all future studies are sure to reveal a great deal more about this mysterious remnant and its strange behavior.
As Melania Nynka, another McGill postdoctoral researcher and a co-author on the paper indicated, GW170817/GRB presents some truly unique opportunities for astrophysical research. “This neutron-star merger is unlike anything we’ve seen before,” she said. “For astrophysicists, it’s a gift that seems to keep on giving.”
It is no exaggeration to say that the first-ever detection of gravitational waves, which took place in February of 2016, has led to a new era in astronomy. But the detection of two neutron stars colliding was also a revolutionary accomplishment. For the first time, astronomers were able to observe such an event in both light waves and gravitational waves.
In the end, the combination of improved technology, improved methodology, and closer cooperation between institutions and observatories is allowing scientists to study cosmic phenomena that was once merely theoretical. Looking ahead, the possibilities seem almost limitless! | 0.936849 | 4.053639 |
Saturn’s auroras may heat its atmosphere like an electric toaster.
Measurements from NASA’s Cassini spacecraft’s final orbits show that Saturn’s upper atmosphere is hottest where its auroras shine, a finding that could help solve a long-standing mystery about the outer planets.
Saturn’s upper atmosphere is much hotter than scientists first expected based on the planet’s distance from the sun. In fact, all the gas giant planets — Saturn, Jupiter, Uranus and Neptune — were thought to have chilly upper atmospheres around 150 kelvins (–123° Celsius). But data from the Voyager spacecraft, which flew past the outer planets in the 1970s and 1980s (SN: 8/7/17), showed a surprisingly toasty upper atmosphere of 400 to 600 kelvins (125° C to 325° C) on Saturn, and even higher temperatures on Jupiter and Neptune.
Planetary scientists dub this mismatch an “energy crisis.” Something injects extra energy into the gas giants’ atmospheres, but no one knew what. “Trying to explain why these temperatures are so high has long been a goal in planetary atmospheric physics,” says planetary scientist Ron Vervack of Johns Hopkins University’s Applied Physics Laboratory.
Data from the Cassini spacecraft’s waning weeks might point to an answer, planetary scientist Zarah Brown of the University of Arizona in Tucson and colleagues report April 6 in Nature Astronomy.
After orbiting Saturn for 13 years, Cassini finished its mission with a daredevil series of dips between the planet and its rings before plunging into Saturn’s atmosphere in September 2017 (SN: 9/15/17). During those final orbits, the spacecraft probed the planet’s upper atmosphere by watching stars in the background. Measuring the amount of starlight that the atmosphere blocks told Brown and colleagues how dense the atmosphere is at different points, a clue to its temperatures.
Using 30 of these stellar measurements, 22 of which came from the last six weeks of Cassini’s mission, the team mapped Saturn’s atmospheric temperatures across the whole planet and at different depths. “For the outer planets, this is an unprecedented data set,” says planetary scientist Tommi Koskinen, also of the University of Arizona.
The atmosphere was hottest around 60° N and 60° S latitudes — roughly where Saturn’s glowing auroras show up (SN: 2/16/05). Auroras are brilliant lights that sparkle when charged particles from the sun interact with a planet’s magnetosphere, the region defined by a planet’s magnetic field. Unlike Earth’s visible auroras, Saturn’s auroras glow mainly in ultraviolet light.
The auroras’ light doesn’t emit much heat on its own, but is accompanied by electric currents that can generate heat like the wires in a toaster. This process, called Joule heating, also happens in Earth’s atmosphere.
If Jupiter, Uranus and Neptune’s auroras also coincide with extra heat, then auroras may solve the mystery of hot atmospheres across the solar system. The same process could even take place on exoplanets, Brown says.
Vervack, who has worked with the Voyager dataset but was not involved in the new work, thinks this study marks “a big step in our understanding” of these hot upper atmospheres.
“The real test of whether they’re right will be when you go out to Uranus or Neptune,” whose magnetospheres are more complicated than Saturn’s, he says. “Being able to see how our understanding from Saturn holds up when we get to these more complicated systems is going to be really key to knowing if we’ve licked this problem or not.” | 0.895581 | 3.994435 |
Supernova Caught in the Act
Earliest-ever Detection Made Possible by Computing, Networks
August 25, 2011
Contact: Linda Vu, +1 510 495 2402, [email protected]
A supernova discovered yesterday is closer to Earth—approximately 21 million light-years away—than any other of its kind in a generation. Astronomers believe they caught the supernova within hours of its explosion, a rare feat made possible by a specialized survey telescope and state-of-the-art computational tools.
The discovery of such a supernova so early and so close has energized the astronomical community as they are scrambling to observe it with as many telescopes as possible, including the Hubble Space Telescope.
Joshua Bloom, assistant professor of astronomy at the University of California, Berkeley, called it “the supernova of a generation.” Astronomers at Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley, who made the discovery predict that it will be a target for research for the next decade, making it one of the most-studied supernova in history.
The supernova, dubbed PTF 11kly, occurred in the Pinwheel Galaxy, located in the “Big Dipper,” otherwise known as the Ursa Major constellation. It was discovered by the Palomar Transient Factory (PTF) survey, which is designed to observe and uncover astronomical events as they happen.
Want to see it for yourself? Berkeley Lab astronomer Peter Nugent explains how
“We caught this supernova very soon after explosion. PTF 11kly is getting brighter by the minute. It’s already 20 times brighter than it was yesterday,” said Peter Nugent, the senior scientist at Berkeley Lab who first spotted the supernova. Nugent is also an adjunct professor of astronomy at UC Berkeley. “Observing PTF 11kly unfold should be a wild ride. It is an instant cosmic classic.”
He credits supercomputers at the National Energy Research Scientific Computing Center (NERSC), a Department of Energy supercomputing center at Berkeley Lab, as well as high-speed networks with uncovering this rare event in the nick of time.
The PTF survey uses a robotic telescope mounted on the 48-inch Samuel Oschin Telescope at Palomar Observatory in Southern California to scan the sky nightly. As soon as the observations are taken, the data travels more than 400 miles to NERSC via the National Science Foundation’s High Performance Wireless Research and Education Network and DOE’s Energy Sciences Network (ESnet). At NERSC, computers running machine learning algorithms in the Real-time Transient Detection Pipeline scan through the data and identify events to follow up on. Within hours of identifying PTF 11kly, this automated system sent the coordinates to telescopes around the world for follow-up observations.
Three hours after the automated PTF pipeline identified this supernova candidate, telescopes in the Canary Islands (Spain) had captured unique “light signatures,” or spectra, of the event. Twelve hours later, his team had observed the event with a suite of telescopes including the Lick Observatory (California), and Keck Observatory (Hawaii) had determined the supernova belongs to a special category, called Type Ia. Nugent notes that this is the earliest spectrum ever taken of a Type Ia supernova.
“Type Ia supernova are the kind we use to measure the expansion of the Universe. Seeing one explode so close by allows us to study these events in unprecedented detail,” said Mark Sullivan, the Oxford University team leader who was among the first to follow up on this detection.
“We still do not know for sure what causes such explosions,” said Weidong Li, senior scientist at UC Berkeley and collaborator of Nugent. “We are using images from the Hubble Space Telescope, taken fortuitously years before an explosion to search for clues to the event’s origin.”
The team will be watching carefully over the next few weeks, and an urgent request to NASA yesterday means the Hubble Space Telescope will begin studying the supernova’s chemistry and physics this weekend.
Catching supernovae so early allows a rare glimpse at the outer layers of the explosion, which contain hints about the star it once was. “When you catch them this early, mixed in with the explosion you can actually see unburned bits from the star that exploded! It is remarkable,” said Andrew Howell of UC Santa Barbara/Las Cumbres Global Telescope Network. “We are finding new clues to solving the mystery of the origin of these supernovae that has perplexed us for 70 years. Despite looking at thousands of supernovae, I’ve never seen anything like this before.”
“The ability to process all of this data in near real-time and share our results with collaborators around the globe through the Deep Sky Science Gateway at NERSC is an invaluable tool for following up on supernova events,” says Nugent. “We wouldn’t have been able to detect and observe this candidate as soon as we did without the resources at NERSC.”
At a mere 21 million light-years from Earth, a relatively small distance by astronomical standards, the supernova is still getting brighter, and might even be visible with good binoculars in ten days' time, appearing brighter than any other supernova of its type in the last 30 years.
“The best time to see this exploding star will be just after evening twilight in the Northern hemisphere in a week or so,” said Oxford’s Sullivan. “You’ll need dark skies and a good pair of binoculars, although a small telescope would be even better.”
The scientists in the PTF have discovered more than 1,000 supernovae since it started operating in 2008, but they believe this could be their most significant discovery yet. The last time a supernova of this sort occurred so close was in 1986, but Nugent notes that this one was peculiar and heavily obscured by dust.
"Before that, you'd have to go back to 1972, 1937 and 1572 to find more nearby Type Ia supernovae,” says Nugent.
The Palomar Transient Factory is a survey operated a Palomar Observatory by the California Institute of Technology on behalf of a worldwide consortium of partner institutions. Collaborators on PTF 11kly with Nugent, Bloom and Li are Brad Cenko, Alex V. Filippenko, Geoffrey Marcy, Adam Miller (UC Berkeley), Rollin C. Thomas (Lawrence Berkeley National Laboratory), Sullivan (Oxford University), and Andrew Howell (UC Santa Barbara/Las Cumbres Global Telescope Network).
Read more about how NERSC supports the Palomar Transient Factory.
About NERSC and Berkeley Lab
The National Energy Research Scientific Computing Center (NERSC) is a U.S. Department of Energy Office of Science User Facility that serves as the primary high-performance computing center for scientific research sponsored by the Office of Science. Located at Lawrence Berkeley National Laboratory, the NERSC Center serves more than 7,000 scientists at national laboratories and universities researching a wide range of problems in combustion, climate modeling, fusion energy, materials science, physics, chemistry, computational biology, and other disciplines. Berkeley Lab is a DOE national laboratory located in Berkeley, California. It conducts unclassified scientific research and is managed by the University of California for the U.S. Department of Energy. »Learn more about computing sciences at Berkeley Lab. | 0.856872 | 3.490916 |
Dust is a major annoyance for most of us, but to scientists it can be precious. Over the summer researchers identified seven specks of dust returned to Earth by the Stardust spacecraft, which spent 12 years in space and tried to collect samples from the wake of a comet. The seven dust motes may come from interstellar space. Determining their true origin, however, has proven problematic.
Three of the microscopic grains are locked in a foam material called aerogel, from the outside covering of Stardust. Aerogel is great at catching the particles, but scientists have not yet figured out a good way to extract the grains without damaging them. For now, the grains, and the researchers, are stuck.
The other four interstellar dust candidates were found in the grid of aluminum foil that held the aerogel. When the grains hit, the foil melted and formed miniature craters. Scientists chemically analyzed two of these craters, but the findings are inconclusive.
The impactors might come from interstellar space, or they could be local. Unfortunately, the analysis destroyed those two grains. And the other two foil-embedded candidates were lost while being transported between labs.
Scientists hope to find still more microscopic particles in the Stardust collector. And they have keep NASA cleaning crews from doing any dusting. | 0.803323 | 3.147129 |
- Open Access
Morphologies of omega band auroras
Earth, Planets and Space volume 69, Article number: 103 (2017)
We examined the morphological signatures of 315 omega band aurora events observed using the Time History of Events and Macroscale Interactions during Substorm ground-based all-sky imager network over a period of 8 years. We find that omega bands can be classified into the following three subtypes: (1) classical (O-type) omega bands, (2) torch or tongue (T-type) omega bands, and (3) combinations of classical and torch or tongue (O/T-type) omega bands. The statistical results show that T-type bands occur the most frequently (45%), followed by O/T-type bands (35%) and O-type bands (18%). We also examined the morphologies of the omega bands during their formation, from the growth period to the declining period through the maximum period. Interestingly, the omega bands are not stable, but rather exhibit dynamic changes in shape, intensity, and motion. They grow from small-scale bumps (seeds) at the poleward boundary of preexisting east–west-aligned auroras, rather than via the rotation or shear motion of preexisting east–west-aligned auroras, and do not exhibit any shear motion during the periods of auroral activity growth. Furthermore, the auroral luminosity is observed to increase during the declining period, and the total time from the start of the growth period to the end of the declining period is found to be about 20 min. Such dynamical signatures may be important in determining the mechanism responsible for omega band formation.
Auroral luminosity undulations of the poleward boundaries of diffuse auroras were first described by Akasofu and Kimball (1964) and were named “omega bands” due to the similarity of their shapes to inverted (poleward-opening) versions of the Greek letter Ω. Omega bands are generally observed in the post-midnight and morning sectors during the recovery phases of magnetospheric substorms. They typically have sizes of 400–1000 km and usually drift eastward at speeds of 0.3–2 km/s.
The ionospheric electrodynamic characteristics of omega bands have been described in several papers (see, e.g., Wild et al. 2000, 2011; Syrjäsuo and Donovan 2004; Amm et al. 2005; Vanhamäki et al. 2009, and references therein), all of which support the overall picture of a sequence of upward and downward field-aligned currents (FACs) located in the bright and dark regions, respectively, of such structures. As the band structure with its temporally stationary current system moves above ground-based magnetometers, Ps6-type magnetic pulsations (with periods of 5–40 min) are observed (Saito 1978; Rostoker and Barichello 1980). Omega bands generally consist of intense pulsating auroras (Oguti et al. 1981; Sato et al. 2015). However, the mechanism responsible for omega band formation remains unclear.
The classification of omega bands has gradually evolved. Oguti et al. (1981) and Lyons and Walterscheid (1985) described omega bands as “torch-like” structures extending from the poleward boundaries of post-midnight diffuse auroras. Lühr and Schlegel (1994) described omega bands as “tongue-like” protrusions extending northward.
Unlike auroral arcs, which are indeed the predominant form of auroras, omega bands are observed rather rarely. Consequently, relatively little attention has been paid to omega bands and only a limited number of related reports have been published. Furthermore, satellite images, which can provide larger geographical coverage, had significantly lower spatial and temporal resolution than all-sky TV cameras on the ground. Thus, the main morphological features of omega bands during formation have not yet been well established. To identify these features, it is important to examine the dynamic and morphological signatures of as many omega band events as possible.
In this study, we analyzed 315 omega band events that were observed using the Time History of Events and Macroscale Interactions during Substorm (THEMIS) ground-based all-sky imager (ASI) network. We examined the optical signatures occurring during the generation of the omega bands, from the growth period to the declining period through the maximum period, and classified the omega bands based on their morphological forms.
In this study, we employed optical ASI data obtained at the THEMIS ground-based observatories (GBOs) (Angelopoulos 2008; Mende et al. 2008). Combining all of the ground-based THEMIS, ASI data yielded global aurora data, covering broad latitude and longitude ranges with high spatial (~1 km near the zenith) and temporal (3 s) resolutions. The white light all-sky imagers covered a wide wavelength range of about 400–700 nm, and the images were projected onto an ionospheric altitude of 110 km.
To identify “omega band-like” aurora events in this study, we firstly examined a summary plot of the THEMIS data (example of March 1, 2011, <http://themis.ssl.berkeley.edu/gbo/display.py?date=2011.03.01&view_type=summary&submit=Start >) acquired over a period of 8 years, from January 2007 to December 2014. Our selection method is based on a qualitative visual inspection of the images. First, we checked the aurora keogram. Omega band-like events can be easily identified in the keogram because most omega auroras display a “wedge-shaped” or “triangle-shaped” structure with duration of several tens of minutes. Omega band auroras display such peculiar shapes in the keogram and usually drift eastward and cross the meridian plane of ASI (see examples shown in Figs. 2 and 5 of Sato et al. 2015). Subsequently, we analyzed the auroral shapes using a sequence of ASI images to check whether or not the shapes of the auroras looked like omega bands. Finally, we selected 315 events that exhibited the specific characteristics of omega bands. Events whose activity declined before arriving at the meridian plane of ASI were not counted as omega band events.
To examine the morphological and dynamic signatures of the shapes and motions of the omega bands, we produced movie files using the original 3-s-resolution ASI data.
After selecting the events and obtaining the movie files, we classified the omega bands based on their morphologies and examined the optical characteristics occurring during their generation, from the growth period (the period over which the undulation area increased from the start of the appearance of the protrusions) to the declining period (the period of decreasing or shrinking undulation area and the period over which the undulation loses its omega shape until it disappears all together) through the maximum period (the period over which the spatial size of the omega is at its maximum).
Classification of omega bands and their growth signatures
Using the data from the 315 selected events, we determined that omega bands can be classified into the following three subtypes based on the morphological signatures: (1) classical (O-type) omega bands, (2) torch or tongue (T-type) omega bands, and (3) combinations of classical and torch or tongue (O/T-type) omega bands. Figure 1 presents typical examples of the three types of omega bands that we identified. Auroras with O-type bands are diffuse auroras whose poleward boundaries exhibit two undulating shapes resembling inverted versions of the Greek letter Ω (Akasofu and Kimball 1964). Auroras containing T-type omega bands are also diffuse auroras whose poleward boundaries exhibit undulating shapes extending northward; in these cases, the undulating shapes resemble torches or tongues. Although the shapes of torches and tongues are very similar to each other, torches are usually larger and show more rapid movements of their shape and luminosity as compared to tongues, as shown later in Fig. 4 and also in Additional file 3: Movie S3 and Additional file 4: Movie S4. O/T-type omega band auroras exhibit the undulating shapes of both O-type and T-type omega band auroras simultaneously. That is, the boundaries in the dark sections between torches (or tongues) resemble inverted Ω shapes.
Figure 2 presents an example of the growth signature of an O-type omega band aurora, which was observed at Gillam (GILL) in Canada (Mag. Lat. 66.0°, Long. 333.2°) on February 27, 2009. The two undulating shapes of the poleward boundary of the diffuse aurora, which resembles an inverted Ω, become brighter and clearer with time. Notably, the poleward boundary of this aurora contrasts sharply with the dark region, which is located on the poleward side of the undulating aurora. An additional movie file shows this in more detail (see Additional file 1: Movie S1).
Figure 3 provides an example of the growth signature of a T-type aurora. This particular aurora was observed at Gakona (GAKO) in Alaska (Mag. Lat. 63.1°, Long. 269.5°) on March 1, 2011. The poleward boundary of the part of the diffuse aurora in the western portion of the field of view expands poleward with time between 1422:00 UT and 1428:00 UT. Notably, the torch-shaped poleward boundary does not exhibit shear motion, but rather simply extends poleward. It may be important to examine this signature to identify the mechanism responsible for omega band aurora formation. The 3-s-resolution movie corresponding to this event revealed an intense, pulsating aurora consistent with the inside of a torch aurora. An additional movie file shows this in more detail (see Additional file 2: Movie S2).
The upper panels of Fig. 4 depict an O/T-type aurora whose T-type structure is tongue-shaped. This aurora was observed at Kiana (KIAN) in Alaska (Mag. Lat. 65.0°, Long. 251.5°) on October 2, 2011. At 1214:00 UT, the aurora mainly exhibits O-type omega band characteristics, and the size of the dark part of the omega band decreases with time. Meanwhile, the signature of a T-type omega band, which appears in the western portion of the field of view, grows and becomes clearer with time. The characteristics of both O-type and T-type omega bands are observable in the images acquired at 1216:00 UT and 1217:00 UT; in other words, the aurora is an O/T-type omega band aurora at those times. In this case, the tongue-shaped poleward boundary does not rotate, but rather simply extends poleward. An additional movie file shows this in more detail (see Additional file 3: Movie S3). The lower panels of Fig. 4 present another example of an O/T-type omega band aurora. In this event, which was observed at Goose Bay (GBAY) in Canada (Mag. Lat. 60.4°, Long. 23.0°) on March 9, 2008, the T-type structure is torch-shaped. An O-type omega band is evident from 0504:00 UT until 0510:00 UT in the central to western portion of the field of view. Furthermore, a very active torch is observable in the western part of the O-type omega band and drifts eastward. The eastward drift speed between 0504:00 UT and 0510:00 UT is ~800 m/s. An additional movie file shows this in more detail (see Additional file 4: Movie S4).
Figure 5 provides an example of an O&O/T&T-type omega band aurora, which means that O-type, O/T-type, and T-type omega bands all appeared during the same event. The left panel is an image of an O-type omega band aurora that was acquired at GBAY at 0428:00 UT on March 9, 2008. The middle and right panels are images of the O/T-type omega band aurora at 0431:00 UT and the T-type omega band aurora at 0433:00 UT, respectively. The frequencies with which auroras with multiple types of omega bands, namely O&O/T&T-type and O/T&T-type omega band auroras, were observed are provided in Fig. 6. It may be very interesting and important to examine the signatures of such auroras to determine the mechanism responsible for the formation of omega bands. An additional movie file shows this in more detail (see Additional file 5: Movie S5).
Statistics of the observed auroras
Figure 6 illustrates the occurrence rates of the different types of auroras among the 315 selected events. The left panel includes the occurrence rates of all of the possible omega band event types. The total number of events in this chart is 315, and each event can consist of multiple types of omega auroras. For example, O&O/T&T-type means that O-type, O/T-type, and T-type omega bands appeared during one event. As shown, O/T&T-type events occur the most often, with a frequency of 34% (104 events), followed by T-type events, which have a frequency of 29% (89 events). O&O/T&T-type, O/T-type, O-type, and O&O/T-type events have frequencies of 15% (46 events), 8% (24 events), 7% (23 events), and 7% (21 events), respectively. On the other hand, the right panel provides the occurrence rates of only the three subtypes of omega bands, O-type, O/T-type, and T-type, as described in the classification. In this statistics, the total number of identified aurora of either type exceeds the total number of events (i.e., periods displaying omega auroras) because multiple types of omega auroras may occur during each event. The results show that O-type, O/T-type, and T-type omega bands occur with frequencies of 18% (90 events), 35% (174 events), and 47% (239 events), respectively. That is, T-type omega bands occur the most often, followed by O/T-type bands and finally O-type bands. It is important to note that when the auroras change their type, they always evolve along the following sequences: from O to O/T, then T-type or from O/T- to T-type. These morphological signatures may be important for the determination of the mechanism responsible for omega band formation.
Life cycles of omega bands from the growth period to the declining period through the maximum period
It is interesting to examine the dynamic signatures of omega band auroras from the growth period to the declining period through the maximum period, examples of which are presented in Fig. 7. The upper panels depict the event observed at GBAY on March 9, 2008, which is designated as Event 1. Between 0428:00 UT (0051:00 MLT) and 0431:00 UT, the aurora exhibits an O/T-type omega band form, and the torch structure expands with time and drifts eastward. The torch reaches its maximum degree of formation at 0434:00 UT and then dissipates with time between 0442:00 UT and 0443:30 UT. During this declining period, the undulating part at the poleward edge suddenly intensifies in luminosity with more dynamic movement and then gradually disappears. Notably, the auroral luminosity increases during the declining period. Dynamical signatures of this event are shown in Additional file 5: Movie S5. Such signatures could be important to understand the formation mechanism of omega band auroras, as discussed later. The entire process from the start of the growth period to the end of the declining period lasts about 20 min, judging from the original image data (not shown here). The middle panels illustrate the life cycle of the T-type omega band observed during the event at GAKO on March 1, 2011, which is defined as Event 2. The seed of a torch aurora structure appears in the western portion of the east–west-aligned aurora at 1309:00 UT (0224:00 MLT) and expands poleward with time. The torch structure reaches its maximum degree of formation around 1317:00–1321:00 UT and then dissipates with time between 1328:00 UT and 1330:00 UT. During this declining period, the auroral luminosity increases, while the shape is destroyed by 1330:00 UT, as in Event 1. Dynamical signatures of this event are shown in Additional file 6: Movie S6. Again, the duration of the event from the start of the growth period to the end of the declining period is about 20 min, judging from the original image data. The bottom panels show an event similar to Event 2 that was observed at GAKO on March 1, 2011, and is designated as Event 3. The seed of a torch aurora structure appears in the western part of the east–west-aligned aurora at 1420:00 UT (0335:00 MLT). The seed grows with time and expands poleward, forming a torch structure. The torch structure reaches its maximum height of formation between 1420:00 UT and 1427:00 UT and then dissipates with time between 1429:00 UT and 1433:00 UT. As in Events 1 and 2, the aurora luminosity increases with time and the shape is destroyed during the declining period. Dynamical signatures of this event are shown in Additional file 7: Movie S7. The entire event lasts about 20 min from the start of the growth period to the end of the declining period, judging from the original image data.
The statistical results show that about 55% of events occur within a duration of 15–25 min, while 28, 11, and 6% have durations of 25–35, 5–15, and more than 35 min, respectively (not shown). In these statistics, we selected only those events that displayed their entire lifetime from their growth period to their declining period in the field of view of the “single” all-sky imager. We excluded those events where omega auroras drifted outside of the field of view of ASI before full declination of the omega shape. We also excluded those events where omega-shaped auroras appeared from the horizon. Although the background drift speed varies from event to event, typically it takes ~30–40 min for an auroral structure to pass by the field of view of the all-sky camera. Thus, the lifetime of omega band auroras identified here could be bounded by the ~30–40 min of time required for the omega to cross the field of view of the all-sky imager.
Figure 8 presents schematic illustrations of the dynamic signatures from the growth and expansion period to declining period through maximum period. In the left panel, which shows the pattern during the growth and expansion period, the poleward boundary of the east–west-aligned aurora expands with time and forms a tongue or torch shape. The time interval between the dotted line labeled 1 and the solid line designated as line 2 is about 3–5 min. The middle panel, which depicts the pattern during the maximum period of torch or tongue shape formation, shows the poleward boundary extended to its maximum height. In many cases, the maximum period lasts for 2–4 min. In the right panel, which corresponds to the declining period, the poleward boundary of the torch or tongue shape decreases in height and bends eastward with time. The time interval between the dotted line defined as line 4 and the solid line labeled 5 is about 2–5 min. Notably, the auroral intensity often increases during the declining period, as demonstrated in Fig. 7.
Dynamic signatures during the initial phase of the growth of omega bands
Initial growth signatures of omega band auroras provide important information that may be useful in understanding their formation mechanism. However, analysis of these signatures has some limitations due to the fact that such signatures are very complex in most cases, and it is rare to be able to observe a clear, complete shape of omega band auroras near the zenith in field of view of ASI during the initial growth. Under these observational limitations, we have found some examples that demonstrate clear morphological evolutions during the initial growth phase of omega bands, as presented in Fig. 9. The top panels demonstrate the event observed at Kiana (KIAN) in Alaska (Mag. Lat. 65.0°, Long. 251.5°) on March 23, 2007, which is designated as Event 1. The leftmost image at 1405:12 UT (0205:12 MLT) shows east–west-aligned discrete arc auroras, just before the start of omega band auroras. At 1406:54 UT, a small bump/protrusion appears at the poleward boundary of the western part of the preexisting east–west-aligned auroras in the field of view of ASI. Then, this bump expands poleward with time (see panel at 1408:33 UT), and the auroras acquire a tongue-type form at 1410:09 UT. In the images, artificial light contaminates the aurora in the northern part of the image and the artificial light has been masked with a gray area. It is important to note here that the omega band auroras are found to grow from a small-scale bump (a seed) at the poleward boundary of pre-east–west-aligned arc auroras, not via the rotation or shear motion of preexisting east–west-aligned auroras. The second row of images labeled Event 2 shows the growth phase of tongue-type omegas along with intense pulsating auroral patches observed at McGrath (MCCR) in Alaska (Mag. Lat. 61.7°, Long. 260.3°) on March 1, 2011. The leftmost image at 1418:30 UT (0248:30 MLT) demonstrates preexisting east–west-aligned band auroras consisting of pulsating auroras, just before the appearance of the omega band aurora. At 1420:21 UT, a small bump/protrusion appears at the poleward boundary of the western part of the preexisting east–west-aligned band auroras. Then, this bump expands poleward with time and forms the tongue-type omega bands, with a similar behavior as that for Event 1. In these images, artificial light contaminates the western edge. This area has been masked with a gray patch. Dynamical signatures of this event are shown in Additional file 8: Movie S8. The third row panels show the growth signature of torch-type omega bands that were observed at Pinawa (PINA) in Canada (Mag. Lat. 60.0°, Long. 331.9°) on March 9, 2008, and is designated as Event 3. At 0616:30 UT (2339:30 MLT), just before the appearance of the omega band aurora, there are two types of east–west-aligned auroras. One type is the east–west-aligned discrete arc auroras, which are observed on the poleward side. The other type of auroras is observed on the equatorward side forming the east–west-aligned pulsating auroras. At 0620:00 UT, a small-scale torch-like auroral structure (a seed) appears at the western side of the poleward east–west-aligned discrete aurora. Then, the torch-like auroral structure expands poleward and increases in height and intensity with time, as seen at 0622:27 UT and 0627:18 UT. When this torch-type omega aurora reaches a maximum area at about 0627:18 UT, the pulsating auroral regions can be seen embedded within the torch-type omega (see Additional file 9: Movie S9). The bottom panels show the growth signature of omega band auroras consisting of intense patch pulsating auroras that were observed at Fort Yukon (FYKN) in Alaska (Mag. Lat. 67.3°, Long. 266.7°) on February 23, 2014, and is referred to as Event 4. The leftmost panel shows an image at 1229:00 UT (0132:00 MLT), just before the start of the omega band aurora. In this time interval, the intense pulsating auroras cover half of the equatorward region. A weak, non-pulsating auroral element appeared on the western side at the poleward edge of the east–west-aligned pulsating aurora. This weak auroral element drifts eastward as seen in the subsequent images. At 1232:30 UT, the seed of an omega band aurora, which consists of pulsating patches, appears at the poleward side of the east–west-aligned pulsating aurora near the zenith of ASI. This seed grows with time expanding poleward, increasing its intensity, as seen in the images at 1233:42 UT and 1235:27 UT. The growth signatures and the movements of pulsating aurora elements of this event are very similar to the omega event shown in Figs. 3 and 7 of Sato et al. (2015). The dynamics of this event are shown in Additional file 10: Movie S10. It is worth noting here that there are no auroral streamers in any of the events in Fig. 9, and we will discuss this observation later.
Summary and discussion
To the best of the authors’ knowledge on the past studies, the main morphological features of omega bands during formation have not yet been well established. In order to identify these features, it is important to examine the dynamic and morphological signatures of as many omega band events as possible. In this study, we have examined morphological signatures of 315 omega band aurora events observed using the THEMIS ground-based ASI network during an 8-year period from January 2007 to December 2014. We have for the first time found that omega bands can be classified as O-type, T-type, and O/T-type bands. Auroras with T-type omega bands occurred the most frequently (45%), followed by those exhibiting O/T-type bands (35%) and finally O-type bands (18%). Accounting for the events in which multiple omega band types appeared, O/T&T-type events were the most common, occurring with a frequency of 34% (104 events), followed by T-type events 29% (89 events). O&O/T&T-type, O/T-type, O-type, and O&O/T-type events occurred with frequencies of 15% (46 events), 8% (24 events), 7% (23 events), and 7% (21 events), respectively.
The reason why the occurrence rate of T-type bands is higher than the rates for other types is not clear at this moment. We need to investigate the relationship between the occurrence of each type of omega band and further examine the occurrence conditions of each type of omega aurora in terms of the magnetic local time, geomagnetic activity, interplanetary magnetic field components (By and Bz), solar wind velocity, ionospheric convection velocity, etc.
Even though identifying the formation mechanisms of omega auroras is beyond the scope of this article, we briefly review previous studies and then make suggestions regarding the mechanisms that may explain the evidence shown in the present work. A number of generation mechanisms, which are reviewed in Amm et al. (2005), have been proposed. The most widely accepted generation mechanisms are that omega bands correspond to waves resulting from a Kelvin–Helmholtz (KH) instability arising in sheared flows in the equatorial regions of the tail (Rostoker and Samson 1984) or the hybrid Kelvin–Helmholtz/Rayleigh–Taylor instability in the plasma sheet (Yamamoto 2011 ) and, alternatively, that omega bands form as a direct consequence of auroral streamer activity (high-speed flows) in the magnetotail (Henderson 2009, 2012). Weygand et al. (2015) examined these two source mechanisms using the data observed with the THEMIS ground-based observatory and onboard spacecraft. They concluded that the KH instability mechanism could not explain their observational evidence and that the high-speed flow shear mechanism is the most likely cause of the omega band aurora, but the study lacked observations in regions where the KH instability might have occurred. On the other hand, the auroral streamer mechanism could explain only a fraction of their observational signatures.
In our study with high spatial (~1 km near the zenith) and temporal (3 s) resolution data, we examined the morphological signatures of omega band formation from the growth period to the declining period through the maximum period. Interestingly, the omega bands were observed not to be stable, but rather to exhibit highly dynamical changes in shape, intensity, and motion. We found the following dynamical signatures that may be important to enable determination of the mechanisms responsible for omega band formation: (1) the omega band auroras grow from small-scale bumps (seeds) at the poleward boundary of preexisting east–west-aligned auroras, rather than via the rotation or shear motion of the preexisting east–west-aligned auroras; (2) the auroras did not exhibit any shear motion during the growth of omega auroral activity; (3) the auroral luminosity consistently increased during the declining period; (4) the entire process from the beginning of the growth period to the end of the declining period typically lasted about 20 min; (5) when the auroras changed their type, they always evolved along the following sequences, from O-type to O/T-type, then to T-type or O/T-type to T-type.
It is worth noting that we could not find any auroral streamer events in this study, as shown in Figs. 7 and 9. Because we used single all-sky imager data, there is a possibility that we missed auroral streamer events that prolonged along the north–south direction in the higher latitude region of omega auroras.
During growth and expansion periods of the O-type and O/T-type omega bands, a clear contrast was evident between the regions of light and darkness along the poleward boundaries, which may be the boundaries between the upward and downward FACs, as suggested in previous papers (Lühr and Schlegel 1994; Wild et al. 2000; Amm et al. 2005).
The morphological and dynamical signatures analyzed in this study, especially such characteristics as the highly dynamical changes in shape, intensity, and motion, suggest that the sources of generation and formation of omega bands are not only located near the tail region in the magnetosphere but also the ionosphere may play an important role. That is, the enhancement of auroral luminosity could be caused by the field-aligned acceleration of auroral electrons, which is widely accepted to be caused by magnetosphere–ionosphere coupling processes (Evans 1974; Mozer et al. 1980). A fully magnetospheric model for the formation of omega band auroras may have difficultly explaining the enhancement of auroral luminosity during the declining period, even if it can explain the shape and motion of omega band auroras. Both the KH instability model and auroral streamer model are generation mechanisms that take place in the magnetotail. We strongly propose that the magnetosphere–ionosphere coupling should also play an important role for formation of omega band auroras, especially during the declining period. In order to confirm these generation mechanisms, coordinated observations on the ground and onboard spacecraft located at the equatorial region in the magnetotail and in the ionosphere along the same geomagnetic field lines could be very important.
The statistical signatures of omega band auroras in terms of magnetic local time, duration, recurrence period, drift speed, and relationships to the interplanetary magnetic field components (By and Bz) will be reported in a subsequent article.
Time History of Events and Macroscale Interactions during Substorm
Inter-university Upper atmosphere Global Observation NETwork
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NS analyzed THEMIS GBO all-sky imager data. TH and YT arranged data analysis software. AY discussed about the ionospheric convection. All authors read and approved the final manuscript.
This work was partially supported by a Grant-in-Aid for Scientific Research C (15K05305), B (25287129) and the Inter-university Upper atmosphere Global Observation NETwork (IUGONET) project funded by the Ministry of Education, Culture, Sports, Science and Technology of Japan. We would like to thank A. Kadokura for useful comments. Part of the work of TH has been conducted at ERG-Science Center (ERG-SC) operated by ISAS/JAXA and ISEE/Nagoya University. The authors acknowledge NASA contract NAS5-02099 for the use of data from the THEMIS Mission. Specifically, we thank S. Mende and E. Donovan for use of the ASI data. Deployment and data retrieval of the THEMIS ASIs were partly supported by CSA contract 9F007‐046101. THEMIS all-sky image data are available through the open data repository at UC Berkeley at http://themis.ssl.berkeley.edu/index.shtml.
The authors declare that they have no competing interests.
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Sato, N., Yukimatu, A.S., Tanaka, Y. et al. Morphologies of omega band auroras. Earth Planets Space 69, 103 (2017). https://doi.org/10.1186/s40623-017-0688-1
- Omega band aurora
- Torch aurora
- Tongue aurora
- Pulsating aurora
- All-sky imager
- Field-aligned current | 0.810878 | 3.648621 |
Lesson Plans: Make a Comet
I love hands-on science demos. One of my favorites is the “Make your own comet” that I often do for public events with kids, adults, anyone! I perfected my comet making skills while I was a part of Dark Skies, Bright Kids in Virginia, and I’ll share the not-so-secret recipe with you here. It’s fairly simple… once you practice it and get the mixtures right. It is also being included in the new CosmoQuest unit called In-VESTA-Gate where we talk about all the “little things” in the solar system. (P.S. We’re looking for teachers to look over and/or beta test the unit, so please check it out!)
Comets are the dirty snowballs of the solar system. You know that lump of YUCK left on the side of the road several days after it snows? Yeah, it’s kind of like that. Though when seen in the night sky, these objects can be quite spectacular, such as when Comet McNaught graced the Southern skies in 2007.
So what is a comet made of? We can look at comets with various telescopes and tell what’s in them by looking at their spectra. They become active as they get close to the sun, sporting tails and jets. These give off emission lines of carbon-containing molecules, or “organics” as well as volatiles (things that turn into a gas at “ordinary” temperatures) such as water, carbon dioxide, and ammonia.
We’ve also sent spacecraft to get a close of look at several comet nuclei. And here’s the surprising thing: They are very, very dark. In fact, these generally are the least reflective objects in the solar system. Dark surface full of volatiles that turn to gas as it gets close to the Sun? Sounds like a dirty snowball to me. But it’s not just any ordinary ice that makes a comet, so here is how to do this really cool demo.
First, you need to gather your materials. Comets are made of dirt and rock, so grab some! Powdered charcoal briskets get you an excellent dark color, but I just grad a bag of soil from a home and garden store to use in a pinch. Really desperate? Try not to get caught digging up your neighbor’s yard…
You’ll also want some water, a glass cleaner containing ammonia, some sort of “organic” compound such as soda or corn syrup, and the best ingredient, dry ice. Now, the dry ice needs to be powdered, so whether you get it in pellet or block form, it helps to bang on it for a while with a rubber mallet while it is double, or even triple garbage bagged. You may be able to get dry ice at your local grocery store, a willing university science department, or a local distributer. To finish up materials, you’ll need a large bowl, a cooler in which to store the dry ice, a large serving spoon, gallon sized baggies for every person making a comet, paper towels (for the mess) and, very importantly, protective gloves for anyone handling dry ice. Oven mitts work, despite being unwieldy.
SAFETY NOTE: Dry ice can be dangerous and children should never handle unsupervised. It can and will burn your skin. It can and will explode a sealed container. Seriously, respect the stuff.
For each comet, show off and describe each ingredient and how it is analogous to what is in a comet: dirt, rocks, water, ammonia, organics. You only need a tiny bit of ammonia and organics for show and add just enough water to make mushy, but not runny, mud. These all go into your gallon-sized plastic baggie. Now get your gloves on and get ready for the fun part. Pour in some of the crushed dry ice, about as much as you have mud mixture, and quickly much the bag around to mix the ingredients. DO NOT SEAL THE BAG. Now crush it into a ball with your gloved hands while still inside the bag and squeeze. At this point, I like to mention that I’m too lazy to wait millions of years for this stuff to accrete on its own, so I put a little pressure on it. Now, still with gloved hands, pull the new comet out of the bag.
Notice that your comet is outgassing a bit, especially where there are still little chunks of dry ice. Go ahead and blow on it to make more! This is a process called sublimation, when a solid turns directly into a gas. This happens to the volatiles in comet when it gets close enough to the sun to be heated up. This is part of what makes the comet tail! Interesting fact: the comet’s tail always points away from the Sun and does not indicate direction of motion.
The most recent, full set of instructions from DSBK can be found here (pdf), while the current draft of that day’s lesson in In-VESTA-Gate can be found here (doc).
And, oh look, my buddy Phil Plait made this comet for his Discovery Channel special. And then he one-ups me by blasting it with a super high-powered laser! Or, trying to, at least.
Be sure to use this demo when talking about Comet ISON, a recently discovered comet that looks like it will put on a lovely show as it gets closer to the Sun through November, and, if it survives, on its way back in December. Check out this viewing guide by David Dickinson of Universe Today. And have fun holding a piece of the cosmos in your hand! Your gloved hand, that is… | 0.802519 | 3.461937 |
Launching an accelerating fragment of the thin disk at 7 percent of the speed of light
Space news (July 25, 2015) – 7,500 light-years away in the constellation Centaurus
The majority of lights in the night sky above are double star systems composed of two suns orbiting each other. NASA space scientists using the Chandra X-ray Observatory observed the unusual double star system PSR B1259-63/LS 2883 (B1259 is the short version) three times between December 2011 and February 2014 looking for clues to its nature.
“These two objects are in an unusual cosmic arrangement and have given us a chance to witness something special,” said George Pavlov of Penn State University in State College, Pennsylvania, lead author of a paper describing these results. “As the pulsar moved through the disk, it appears that it punched a clump of material out and flung it away into space.”
Composed of a pulsar and companion star 30 times the mass of the Sun, B1259 is in a weird looking cosmic arrangement that has been kicking up a little dust lately. Recent data indicates the high-energy particle winds created by the combination of rapid rotation and intense magnetic field of the pulsar appears to have punched a hole in the disk of gas surrounding the companion star. A hole composed of gas that has been ejected from the disk at 4 million miles per hour and accelerated from 7 percent of the speed of light to 15 percent between the second and third observation periods.
“After this clump of stellar material was knocked out, the pulsar’s wind appears to have accelerated it, almost as if it had a rocket attached,” said co-author Oleg Kargaltsev of George Washington University (GWU) in Washington, DC.
The pulsar is an ultra-dense neutron star orbiting its companion star in a highly elliptical orbit that makes its closest approach every 41 months. The companion star is rotating at a speed resulting in a disk of material spinning off, creating the thin disk of gas surrounding the massive sun. The pulsar is expected to pass through the disk of material as it makes its next approach to B1259. NASA scientists expect to view the event and collect data on the unusual nature of this double star system.
41 months is enough time for NASA scientists to plan their next move and get other telescopes and spacecraft in place to view the event. NASA scientists will collect data on the effects of the stellar winds of the pulsar on the gas disk surrounding the companion star as it passes through. There could be another ejection of gas material as it passes close to B1259, next time, which is an opportunity to learn more about double star systems and the cosmos.
“This just shows how powerful the wind blasting off a pulsar can be,” said co-author Jeremy Hare, also of GWU. “The pulsar’s wind is so strong that it could ultimately eviscerate the entire disk around its companion star over time.”
NASA space scientists will next view double star system B1259, later in the year, and sometime in 2016. The next passing of the pulsar through the disk of gas surrounding its companion star could be even more spectacular and unusual in nature.
You can learn more about the Chandra X-ray Observatory here.
To learn more about double star systems go here.
To learn more about NASA’s space mission visit here.
Learn more about possible plate tectonic forces operating on the surface of Europa. | 0.801233 | 3.784422 |
NASA has caught a “space ghost” on it’s Hubble Space Telescope as cosmologists saw something gazing back at them.
In the picture, an uncanny pair of shining eyes glares menacingly toward us. The penetrating “eyes” are the most conspicuous element of what takes after the essence of an extraordinary animal. Be that as it may, this is no spooky nebulous vision. Hubble is taking a gander at a titanic head-on crash between two worlds.
The picture shows a layout of a face in a ring of blue stars with further gatherings of new stars structure a nose and mouth.
Each “eye” is the brilliant center of a cosmic system, one of which hammered into another.
The brutal experience gives the framework a capturing “ring” structure for just a short measure of time, around 100 million years.
The accident pulled and extended the universes’ plates of gas, residue, and stars outward.
This activity framed the ring of extraordinary star arrangement that shapes the nose and face.
The whole framework, named AM 2026-424, is 704 million light-years from Earth.
Ring universes are uncommon; just two or three hundred of them exist in the enormous inestimable neighborhood.
These cosmic systems have needed to crash at the perfect direction to make the ring.
They will blend totally in around 1 to 2 billion years, stowing away their chaotic past.
The next to each other juxtaposition of the two focal lumps of stars from the two systems additionally is irregular.
The lumps that cause the eyes to give off an impression of being a similar size recommends that two cosmic systems of about equivalent extents were associated with the accident.
This is progressively regular impacts where little worlds are eaten up by their bigger neighbors.
Hubble watched this special framework as a component of a “snapshot” program that exploits incidental holes in the telescope’s watching timetable to press in extra pictures.
Space experts intend to utilize this imaginative Hubble program to investigate numerous other irregular interfacing cosmic systems.
The objective is to order a strong example of close by interfacing cosmic systems, which could offer knowledge into how universes developed after some time through galactic mergers.
By dissecting these itemized Hubble perceptions, cosmologists could then pick which frameworks are practical objectives for catch up with NASA’s James Webb Space Telescope, planned to dispatch in 2021. | 0.861911 | 3.412073 |
Think of London in 1600, a pivotal year in Shakespeare’s canon, as a mash up of Canada circa 1967 (Expo, Trudeau, a blasting economy, and lots of kids with hardly anything to worry about) and contemporary Palo Alto, the app startup incubator of the world. Throbbing with British bravado, the sinking of the Armada, religious freedom, explorations of the New World, 1600 was a time when princes, ruffians and pickpockets equally enjoyed bear baiting (an appallingly sadistic sport) and flowery poetry.
This was when the distinctions between religion, astronomy, astrology and magic were fluid; when “science” wasn’t science yet; when adventurous thinkers were pulling away from ancient ideas and increasingly relying on mathematics and observation.
In November 1572, when Shakespeare was eight, a supernova, a massive dying star shone in the sky for months, shaking up the idea of immutable heavenly spheres. It signaled the slow death of magical thinking and the birth of paradigm-shaking revelations: the distinction between electricity and magnetism; the law of inertia; the magnetic pull of Earth; the theory of lenses; Galileo’s telescopic discoveries (born the same year as WS); the laws of planetary motion; the law of hydrostatic pressure; and the law behind the swinging of a pendulum.
How curious then that scholars came so late to considering if and how this scientific exuberance might have found its way into Shakespeare’s plays. This is the subject of an excellent book, by Dan Falk. It’s a scholarly guide to some of the best thinking —and a refutation of some of the more loony ideas— about Shakespeare’s canon and the “science” of his times.
The science-bard link was first made by Peter Usher, an astronomer, in a paper he presented at a conference in Toronto in 1997, which he followed up with a book, Shakespeare and the Dawn of Modern Science, in 2010. He claimed that “Hamlet” was actually a gigantic face-off between the Ptolemaic and heliocentric/Copernican concepts of the Earth’s place in the universe, whether it be at the centre where the Ancients had put it, or farther out, a mere planet rotating around the sun.
“Perhaps the biggest riddle of the time was whether the universe was small, comfortable and human-centered—or whether, as a handful of bold thinkers had suggested, it was enormous, with mankind a mere speck and our planet, on a cosmic scale, little more than a dot,” writes Falk. “No wonder Hamlet sees ‘this goodly frame the earth’ as nothing more than a ‘congregation of vapours’, ‘a sterile promontory.’”
The scholarly community was prepared to buyin to this notion at least a little, but as for the more radical picture, that Hamlet was actually a secret allegorical code that Shakespeare had created with the idea of dodging the (non-existent) religious police, well as one Harvard prof put it, Shakespeare doesn’t do allegories.
At the opposite end of the argument, it now seems absurd to suppose that Shakespeare, living within a few cramped dank city blocks of the world’s greatest pre-telescope astronomers, socializing as he did up and down and sideways across society as only celebrity entertainers could do, wouldn’t work in some scientific fervor into his plays. And this view seems to have won out, according to Falk.
The Science of Shakespeare is your time machine to a deeper appreciation of the plays and the history of science, especially regarding Copernicus’ De revolutionibus, the book that moved Earth away from the centre of the God-created galaxy. Fortunately, the book stays away from the aggressive fact-twisting that imbues the attempts by the lunatic fringe to prove Shakespeare misogynistic or anti-Semitic or a literary fraud or something else that suits the temper of our times. Falk’s book is definitely a cut above all that.
But back to “Hamlet”, Falk does draw lines between specific references in the play to contemporary people and events. “Yond same star that’s westward from the pole” in the opening scene probably referred to the supernova of WS’s childhood. Hamlet’s pals, Rosencrantz and Guildenstern, were names plucked from a list on a 1590 engraving of the Danish astronomer Tycho Brahe, the greatest of the pre-telescopic astronomers. (Tycho is thought to have been the model for Prospero in the “Tempest.”)
More telling is Hamlet describing himself as the king of infinite space. “Infinite” applied to “space” was new. It’s his fussing over his role in the psychic and cosmic abyss that has kept “Hamlet” at the forefront of Shakespeare’s plays.
But just as “Hamlet” looks forward, “Macbeth” looks back to an older world of magic and witches. Falk describes them, these vectors of bad magic/science, as something of a national obsession. Witches could be male or female but they were usually described as old women, elderly, helpless, crippled, wrinkled, hairy-lipped, squinty-eyed, squeaky-voiced and with a scolding tongue. Their most intense persecution coincided with the scientific revolution, as people joined their need for vengeance with scraps of emerging science.
“Magnetism seems almost tailor-made for mystical interpretations…The very idea of magnetic forces ‘seemed to open the possibility of telepathy, magical healing and action at a distance.’ For example, if someone was injured by the use of a weapon, it made sense to apply the healing ointment not only to the wound, but also to the weapon; after all, if magnetic forces could affect planetary orbits, might not vital spirits readily traverse the short distance between weapon and wound?”
The same arguments for why you should read this book hold for why you should read Shakespeare. Because you need a rest from thinking bad thoughts about the ultimate legacy that human beings will leave the planet. Because understanding how the Copernican worldview picked us up and put us down in a different place throws some useful light on how we have “received” evolution, the last time we were reminded that our specialness is only relative.
I remember someone from my university days exclaiming that it was remarkable what WS could write, considering he didn’t have the benefit of modern psychology. She got it backwards of course. We can’t know what Shakespeare thought, but we think we know what kings among others think, because Shakespeare convinced us of it.
The Science of Shakespeare: A New Look at the Playwright’s Universe, by Dan Falk, published by Goose Lane in Canada and Thomas Dunne Books, St. Martin’s Press in the U.S.
Author photo by Sara Desjardins Photography | 0.90758 | 3.313631 |
Stargazers are in for a once in a 150-year treat this week, with a super red blue Moon illuminating the night sky on January 31.
In a rare piece of cosmic synergy the second full Moon of the month, which is known as a blue Moon, coincides with a total lunar eclipse (red Moon) and the Moon being at one of its closest points to earth in its orbit, called a supermoon.
Viewers will see a blood Moon - a Moon coloured bright red as the Earth's shadow passes over it.
ANU Astrobiologist Associate Professor Charley Lineweaver said Australians will have the best seats on Earth to view the super red blue Moon.
"Unlike most of the world, we will be able to see the eclipse from beginning to end," said Associate Professor Lineweaver from the ANU Research School of Astronomy and Astrophysics (RSAA).
"Another perk of this celestial show is that the earth's shadow will not pass over any old full Moon, rather, it will pass over a super Moon - it will be closer and brighter than usual.
"Thus, we will witness a super red blue Moon ... a cosmic syzygy even rarer than a blue Moon."
Astrophysicist Dr Brad Tucker from the RSAA said the super red blue Moon was a great chance for people to develop an interest in astronomy without needing to invest in a telescope.
"Lunar eclipses are great as you do not need any special equipment. A camera is good to take some great shots but you can also enjoy it safely with your eyes, unlike a solar eclipse," Dr Tucker said.
"Since the orbit of the Moon varies (wobbles) by about five degrees, the Moon is not always in perfect alignment with the Sun and the Earth, so that is why we do not get a lunar eclipse every lunar cycle.
"For those in the east of Australia, the eclipse will start just before 10pm, with the total lunar eclipse (when it is red) starting just before midnight, and lasting just over an hour until around 1am." | 0.875395 | 3.15125 |
In colliding galaxies, a pipsqueak shines bright
In the nearby Whirlpool galaxy and its companion galaxy, M51b, two supermassive black holes heat up and devour surrounding material. These two monsters should be the most luminous X-ray sources in sight, but a new study using observations from NASA's NuSTAR (Nuclear Spectroscopic Telescope Array) mission shows that a much smaller object is competing with the two behemoths.
The most stunning features of the Whirlpool galaxy—officially known as M51a—are the two long, star-filled "arms" curling around the galactic center like ribbons. The much smaller M51b clings like a barnacle to the edge of the Whirlpool. Collectively known as M51, the two galaxies are merging.
At the center of each galaxy is a supermassive black hole millions of times more massive than the Sun. The galactic merger should push huge amounts of gas and dust into those black holes and into orbit around them. In turn, the intense gravity of the black holes should cause that orbiting material to heat up and radiate, forming bright disks around each that can outshine all the stars in their galaxies.
But neither black hole is radiating as brightly in the X-ray range as scientists would expect during a merger. Based on earlier observations from satellites that detect low-energy X-rays, such as NASA's Chandra X-ray Observatory, scientists believed that layers of gas and dust around the black hole in the larger galaxy were blocking extra emission. But the new study, published in the Astrophysical Journal, used NuSTAR's high-energy X-ray vision to peer below those layers and found that the black hole is still dimmer than expected.
"I'm still surprised by this finding," said study lead author Murray Brightman, a researcher at Caltech in Pasadena, California. "Galactic mergers are supposed to generate black hole growth, and the evidence of that would be strong emission of high-energy X-rays. But we're not seeing that here."
Brightman thinks the most likely explanation is that black holes "flicker" during galactic mergers rather than radiate with a more or less constant brightness throughout the process.
"The flickering hypothesis is a new idea in the field," said Daniel Stern, a research scientist at NASA's Jet Propulsion Laboratory in Pasadena and the project scientist for NuSTAR. "We used to think that the black hole variability occurred on timescales of millions of years, but now we're thinking those timescales could be much shorter. Figuring out how short is an area of active study."
Small but Brilliant
Along with the two black holes radiating less than scientists anticipated in M51a and M51b, the former also hosts an object that is millions of times smaller than either black hole yet is shining with equal intensity. The two phenomena are not connected, but they do create a surprising X-ray landscape in M51.
The small X-ray source is a neutron star, an incredibly dense nugget of material left over after a massive star explodes at the end of its life. A typical neutron star is hundreds of thousands of times smaller in diameter than the Sun—only as wide as a large city—yet has one to two times the mass. A teaspoon of neutron star material would weigh more than 1 billion tons.
Despite their size, neutron stars often make themselves known through intense light emissions. The neutron star found in M51 is even brighter than average and belongs to a newly discovered class known as ultraluminous neutron stars. Brightman said some scientists have proposed that strong magnetic fields generated by the neutron star could be responsible for the luminous emission; a previous paper by Brightman and colleagues about this neutron star supports that hypothesis. Some of the other bright, high-energy X-ray sources seen in these two galaxies could also be neutron stars. | 0.833931 | 4.111366 |
The age of the Earth in the twentieth century:: a problem (mostly) solved
Published:January 01, 2001
In the early twentieth century the Earth’s age was unknown and scientific estimates, none of which were based on valid premises, varied typically from a few millions to billions of years. This important question was answered only after more than half a century of innovation in both theory and instrumentation. Critical developments along this path included not only a better understanding of the fundamental properties of matter, but also: (a) the suggestion and first demonstration by Rutherford in 1904 that radioactivity might be used as a geological timekeeper; (b) the development of the first mass analyser and the discovery of isotopes by J. J. Thomson in 1914; (c) the idea by Russell in 1921 that the age of a planetary reservoir like the Earth’s crust might be measured from the relative abundances of a radioactive parent element (uranium) and its daughter product (lead); (d) the development of the idea by Gerling in 1942 that the age of the Earth could be calculated from the isotopic composition of a lead ore of known age; (e) the ideas of Houtermans and Brown in 1947 that the isotopic composition of primordial lead might be found in iron meteorites; and (f) the first calculation by Patterson in 1953 of a valid age for the Earth of 4.55Ga, using the primordial meteoritic lead composition and samples representing the composition of modern Earth lead. The value for the age of the Earth in wide use today was determined by Tera in 1980, who found a value of 4.54 Ga from a clever analysis of the lead isotopic compositions of four ancient conformable lead deposits. Whether this age represents the age of the Earth’s accretion, of core formation, or of the material from which the Earth formed is not yet known, but recent evidence suggests it may approximate the latter.
Figures & Tables
The Age of the Earth: From 4004 BC to AD 2002
The age of the Earth has long been a subject of great interest to scientists from many disciplines, particularly geologists, biologists, physicists and astronomers. This volume, The Age of the Earth: from 4004 BC to AD 2002, brings together contributors from these different subjects, along with historians, to produce a comprehensive review of how the Earth’s age has been perceived since ancient times. Touching on the works of eminent scholars from the seventeenth to nineteenth centuries, it describes how concepts of the Earth’s history changed as geology slowly separated itself from religious orthodoxy to emerge as a rigorous and self-contained science. Fossils soon became established as useful markers of relative age, while deductions made from geomorphological processes enabled the discussion of time in terms of years. By the end of the nineteenth century biologists and geologists were fiercely debating the issue with physicists who were unwilling to give them the time needed for evolution or uniformitarianism.
With the discovery of radioactivity, attempts to calculate the Earth’s age entered a new era, although these early pioneers in radiometric dating encountered many difficulties, both technical and intellectual, before the enormity of geological time was fully recognized. This effort affected both the theory and practice of geology. Geochronology was largely responsible for it maturing into a professional scientific discipline, as increasingly refined techniques measured not only the age of the rocks, but the rate of processes which now elucidate many aspects of the Earth’s evolution.
Even today the Earth’s chronology remains a contentious topic — particularly for those dating the oldest rocks — and it is implicated in debates surrounding our hominid ancestors, the origins and development of life, and the age of the universe.
The Age of the Earth: from 4004 bc to AD 2002 will be of particular interest to geologists, geochemists, and historians of science, as well as astronomers, archaeologists, biologists and the general reader with an interest in science. | 0.804685 | 3.331043 |
Solar System/Extraterrestrial Water
Extraterrestrial Water is a topic of the event Solar System. It covers several planets and moons in the solar system that are candidates for possible extraterrestrial water, or have the possibility of sustaining extraterrestrial life.
- 1 Extraterrestrial Water
- 2 Properties of Water
- 2.1 Phase Diagram
- 2.2 Water Ice Forms
- 2.2.1 Low Density Amorphous
- 2.2.2 High Density Amorphous
- 2.2.3 Very High Density Amorphous
- 2.2.4 Hexagonal (Ih)
- 2.2.5 Cubic (Ic)
- 2.2.6 Ice II
- 2.2.7 Ice III
- 2.2.8 Ice IV
- 2.2.9 Ice V
- 2.2.10 Ice VI
- 2.2.11 Ice VII
- 2.2.12 Ice VIII
- 2.2.13 Ice IX
- 2.2.14 Ice X
- 2.2.15 Ice XI
- 2.2.16 Ice XII
- 2.2.17 Ice XIII
- 2.2.18 Ice XIV
- 2.2.19 Ice XV
- 2.2.20 Ice XVI
- 2.3 Liquid Water
- 2.4 Gaseous Water (Water Vapor)
- 3 Sites of Possible Extraterrestrial Life
During the 2014 and 2015 seasons, Solar System focused on extraterrestrial water within the solar system. This section only goes over the aspects of the celestial bodies that are associated with water.
Water on Mars is very rarely found as a liquid, as the pressure is too low at the surface for it to form. Water is mainly found as solid ice, but there is some gaseous water vapor in the thin atmosphere. Ancient Mars could have had a denser atmosphere, allowing liquid water to be present at the surface. Channels eroded by floods, ancient river valley networks, deltas, and lake beds all point to the idea of ancient liquid water. Water has been found in ice form at the bottom of some craters in the mid latitudes, most notably in the Vastitas Borealis crater with the Mars Express orbiter. In the southern Elysium Planitia, there is what appears to be plates of broken ice. The ice is speculated to have been formed from water that had spewed out of the fault Cerberus Fossae about 2 to 10 million years ago. The poles have water ice layers that vary in thickness from summer to winter. In the summer, the amount of water ice decreases in the poles as it sublimates into the atmosphere.
Discovery of Water
The Mars Express, using its MARSIS radar sounder, targeted the south ice cap and confirmed that ice is present at the cap in 2004. The OMEGA instrument indicated that the ice was separated into three parts; the top, reflective part, the slopes called scarps that fall away to the surrounding plains, and the permafrost that stretches for kilometers away from the cap. The Phoenix lander discovered the presence of water within its landing site near the north ice cap in July 2008. The Mars Reconnaissance Orbiter two years later found that the volume of ice in the north ice cap was 821,000 cubic kilometers.
Furthermore, patterned grounds characteristics of Earth's periglacial regions have been found on some Martian surfaces. A radar study in January 2009 looking at lobate debris aprons in Deuteronilus Mensae found evidence for ice lying beneath a few meters of rock.
Glaciers have been reported in numerous Martian craters. The Gamma Ray Spectrometer on Mars Odyssey and measurements on the surface from the Phoenix lander have pointed to the idea of ground water under Mars's surface. Areas of Mars in mid to high latitudes are thought to have large amounts of water ice. Recent evidence has shown that glaciers could be hidden under insulating rocks and/or dust.
Evidence found by the Mars Reconnaissance Orbiter have shown that sometime in the past ten years, a liquid had deposited sediment within a gully. This was found in the craters Terra Sirenum and Centauri Montes. In August 2011, a Nepalese student, Lujendra Ojha, found seasonal changes on slopes near crater rims in the Southern hemisphere. These streaks seemed to grow in the summer, and fade the rest of the year. It is thought that salty water (or brines) flow downhill and evaporate, leaving a mineral deposit. These slope lines are in sync with the heat flux of the Martian surface. The rate of growth with the features are consistent with groundwater flow through a sandy stratum.
Europa is thought to have more water on and under its surface than Earth. Europa has an outer layer of frozen water ice. Below that, it is theorized that there is a liquid saltwater ocean. Galileo orbiter found that the ocean creates a magnetic field out of Jupiter's. The surface ice floats on top of the ocean and drifts, much like the Earth's lithosphere on the asthenosphere.
Tidal heating exerted by Jupiter and the other Galilean moons is the leading explanation for Europa's liquid ocean. Jupiter's large gravitational force slightly stretches the moon and as the moon rotates around the planet, different parts of the moon stretch and compress. The other moons add to this as they pass by. This creates heat within the moon's interior and thus melts the lower layers of Europa's ice sheet. Water on Europa, solid or liquid, creates a layer about 100 km thick in total.
There are two models on how this water layer behaves, the "thick ice" theory and the "thin ice" theory. The thick ice theory states that there is an outer layer comprised of solid ice and plastic "warm ice" layer, and that the rest of the water layer is a liquid ocean. This theory shows that the ocean has rarely interacted with the surface. The thin ice theory states that Europa has a solid outer layer only a few kilometers thick. The model considers only the topmost layer that acts elastically under Jupiter's tides, and considers the interaction of Europa's surface and the ocean. According to the model, the ocean could interact with the surface through open ridges and form chaotic terrain.
Much like the moon of Enceladus, Europa has reoccurring plumes of water around 200 km high, which occur at Europa's aphelion and disappear at perihelion, due to the tidal force of Jupiter and its cycle.
Enceladus, much like Europa, is thought to have an ocean under surface ice. This ocean, unlike Europa's, is located near the South pole, and is thought to have around the same volume of water as Lake Superior. The ocean is thought to be caused by tidal heating from Saturn. It is also speculated that the area has other origins of heat, such as radioactive heating, sublimation of ice, shear heating, and that certain chemicals within the ocean (such as ammonia) lower the freezing point of water.
Enceladus's surface is made of water ice. It is fairly active with its relatively smooth surface, which is especially smooth around the southern tiger stripes. The tiger stripes are areas of high cryovolcanism, which involves the eruption of water and other volatiles that are not silicate rock. The geysers on Enceladus release mostly water vapor and some other components such as nitrogen, methane, and carbon dioxide. The materials are deposited around the geysers, covering most rugged terrain in the area. The geysers are thought to be created much like geysers here on Earth, and emit from pressurized water chambers that are heated from tidal heating or other heating methods listed above.
The eruptions are correlated with Enceladus's orbit and its distance from Saturn. When the moon is at aphelion, more material erupts from the geysers, and at perihelion, the geysers release less material. This is due to the tidal effects of Saturn which pull the tiger stripes open at aphelion and compress them at perihelion. These geysers are thought to be a factor in the formation of Saturn's E ring.
Enceladus has a thick atmosphere compared to the other moons of Saturn, besides Titan. The atmosphere could be formed from cryovolcanism or escaped particles from the surface or interior. The atmosphere consists of mostly water vapor (91%) and some nitrogen (4%), carbon dioxide (3.2%), and methane (1.7%).
Iapetus is thought to be composed mostly of ice, as it has a low density. The moon is known for its two tone coloration, that one side is darker than the other. The dark side is called Cassini Regio and the light side is separated into two parts: Roncevaux Terra in the north and Saragossa Terra in the south. This coloration is likely caused by sublimation of ice on the darker, warmer side, which produces vapor that deposits on the lighter, cooler side. As more ice sublimates on the dark side, darker material is shown and the temperature increases, which in turn kick-starts more sublimation and deposition.
This cycle occurs on both sides, but more intensely on Cassini Regio. It has been calculated that every billion years at current temperatures, Cassini Regio looses 20 meters of ice while the other side loses 10 centimeters. Ice does move from the light side to the dark side but at a slower rate.
The sublimation leaves lag (residue) on the dark side, giving the side its characteristic reddish color. The lag consists of organic materials much like on meteorites from the early solar system. It has been found that the lag creates a foot-deep layer above a layer of ice. The distribution of sublimation processes (described in the final sentences of the previous paragraphs) is the cause for the thinness of the layer. Cassini Regio also remains dark from the impact sunlight has on the lag; sunlight darkens the particles as they reside on the surface or travel in orbit around the moon.
Iapetus is also known for its equatorial ridge, which resides along the center of Cassini Regio. There is a theory that states that the ridge was formed from an upwelling of icy material below the surface that solidified. Other theories say it was formed from Iapetus's supposed early oblate shape, the deposition of a ring system around the moon, or a convective overturn.
Triton is the largest moon of Neptune and has a surface covered with various ices. Most of the surface is frozen nitrogen (55%) with water ice coming in at second (15-35%), and carbon dioxide making up the remaining 10-20%. Water comprises Triton's mantle, which is above a core of rock. Scientists believe that if Triton has a large enough core, radioactive decay and tidal heating could create enough heat for convection to occur in the mantle, or even the ocean proposed above, meaning that life could occur in the moon.
Water ice is what comprises the "cantaloupe" terrain on the western hemisphere of the moon. More specifically, the ice is dirty water ice, with frozen gases and dust mixed in. This cantaloupe terrain is the oldest terrain on the moon and consists of many depressions that are not impact craters due to their similar size and smoothness. Scientists theorize it could be caused by diapirism, the rising of lumps of less dense materials within more dense materials.
Other theories suggest that the terrain is caused by collapses or flooding from cryovolcanism. On Triton, nitrogen erupts into the atmosphere through the process of cryovolcanism. It is thought to be caused by the same method as most examples of this on other bodies in the solar system, through some sort of heat source. Tidal heating could heat nitrogen beneath the surface, making it expand and force its way up to the surface through vents. Another source could be a greenhouse effect created by solid materials on the moons icy surface. Solar radiation passes through the ice, heating nitrogen below and within it, and pressure from the nitrogen continues until it erupts.
Cryovolcanism on Triton does not release water, but water can be found in supposed icy lava on the surface. Cipango Planum on the eastern hemisphere is a high plain thought to be caused by the accumulation of icy lava, which is thought to be comprised of ammonia and water.
Ceres is the largest object in the asteroid belt, being the only dwarf planet there. It is also one of the listed potential sites of extraterrestrial life, although it has not been considered as much as other bodies. Ceres's surface has been found to be composed of some hydrated minerals (minerals with water in their chemical structure), which is evidence for water in the interior.
Ceres has an oblate shape that is common with a differentiated body, which points to the idea that Ceres may consist of a rocky core with an icy mantle above. As found by the Keck Telescope in 2002, this mantle contains 200 million cubic kilometers of water, more than the amount of fresh water on Earth. Characteristics of its surface points to the possibility of volatile materials in the body. Some still speculate that Ceres could only be partially or not differentiated with a porous composition. This theory states that a rock layer on a mantle of ice would sink down and create salt deposits, something not found on Ceres. Theorists say that Ceres doesn't have an ice shell, but has water mixed throughout the body.
Ceres's atmosphere is thin but is comprised of water vapor, which is speculated to have been released by the sublimation of water ice that has migrated from the interior. Some evidence for this was found in the 1990s at Ceres's north pole but was never proven. The IUE spacecraft found hydroxide ions near the pole through ultraviolet observations, which are released when water vapor is split apart by solar radiation. It also has been found that there could be a water vapor source(s) at the mid-latitudes. The Herschel Space Observatory in early 2014 found that localized water sources in this area give off around 3 kilograms of water vapor a second. It is thought that this water is released from sublimation of surface ice or even cryovolcanism created by supposed radioactive energy. The Dawn spacecraft arrived at Ceres in 2015 and continues to help our understanding of the planet.
Titan is the largest moon in our solar system. Like Europa and Enceladus, it is thought to have a subsurface water ocean. Titan is thought to have a rocky center surrounded by a water layer that is thought to be differentiated. The lowest layer is comprised of high-pressure ice, such as Ice VI with tetrahedron crystals. The next layer is comprised of liquid water and the top layer is normal ice 1. The topmost layer of Titan is thought to be very rigid and varying in thickness, based on gravity field tests taken by Cassini. The gravity tests also show that the moon must have a high density, showing that the subsurface ocean most likely a dense, salty brine. The varying thickness could possibly be caused by an ocean that is slowly crystallizing.
The liquid layer is thought to be almost like a magma made of liquid water and ammonia. The ammonia is thought to make the water buoyant enough to bubble up through the icy crust, like magma on Earth. The ocean is also thought to have a high amount of dissolved salts made out of sulfur, sodium, and potassium. This makes the ocean almost like a brine and around as salty as the saltiest bodies of water on Earth (like the Dead Sea and the Great Salt Lake). Because of the characteristics of this ocean, it is likely that when it is forced through the crust, it takes methane from the ice. The ocean could also be a reservoir for methane. This could be a reason for the high amount of methane in the atmosphere and on the surface.
Evidence for this ocean comes from the Cassini probe. The probe detected extremely low-frequency radio waves in the atmosphere, whereas the surface of Titan is thought to be a poor reflector of low-frequency waves. The waves in the atmosphere are thought to have been reflected off of a liquid-ice boundary of a subsurface ocean. Cassini also found that the surface of Titan has solid tides up to 30 feet in height, which would not be possible for a body with a solid rocky composition. Because of this, scientists theorize that a liquid layer allows the tides to occur this high.
Researchers also speculate that Titan has cryovolcanism at its surface, which most likely would spew out the ammonia-water of Titan's supposed ocean. But because Titan's outer layer is comprised of ice 1, which is less dense than liquid water, there would have to be a large amount of energy powering cryovolcanism. There would have to be tidal heating from Saturn and radioactive decay for there to possibly be enough energy for this activity to work.
Pressure from underplating of ice plates at the surface could also drive cryovolcanism. Underplating occurs when one tectonic plate subducts under another and partially melts. This melting could create some plume events much like what happens at Earth's subduction zones. This theory could only be true if Titan has tectonic activity occurring at its surface, but data taken from the moon provides evidence for tectonic activity.
Comets consist of a nucleus (a solid, core structure), coma ("atmosphere" around the nucleus), and two tails (a gas tail and a dust tail). The nucleus consists of a conglomerate of rock, dust, water ice, and other frozen gases (carbon dioxide, carbon monoxide, methane, etc). The nucleus's water ice is hidden under a surface crust around several meters thick. This crust reflects little light as it is comprised mostly of organic compounds, which allows more heat to be absorbed. Solar heating drives off lighter volatiles, leaving heavy dark compounds much like tar or crude oil.
The solar heating enables the process of outgassing to occur. Outgassing is the process by which gases that are trapped, dissolved, frozen, or absorbed are released. Gases on a comet are released as jets off of the nucleus's surface, which are formed from the uneven heating of the nucleus's surface. These jets consist of water vapor and ice, carbon dioxide, and other trapped gases within the comet (listed above). The outgassing process creates a coma of water and dust from the comet's nucleus, which forms around the nucleus. As the comet travels closer to the sun, more water is released from the nucleus, increasing its amount in the coma.
Due to the amount of water in most comets, scientists have theorized that they contributed to the introduction of water to the Earth. However, tests on comets have shown evidence that says otherwise. Water on comets includes a higher amount of heavy hydrogen (hydrogen with a neutron with the proton) than Earth's water, around 300 ppm instead of 150 ppm on Earth. Even though some comets have water much like Earth's, most tested comets have the wrong amount. Comets also have been speculated to be what brought amino acids to Earth due to the high amount of organic chemicals in most comet's nuclei. Some even speculate comets brought organisms to early Earth. However, scientists believe that meteorites brought water and organic compounds to Earth. Specifically, meteorites called carbonaceous chondrites have water much like Earth's, leading to theories that say these brought water to Earth. Yet, comets are still not out of the picture as a potential source of water on Earth.
Properties of Water
For the 2014-15 Solar event, it is crucial to know the properties of water in all phases.
Water Ice Forms
Ice may be in an amorphous solid state at various densities or any one of the 17 known solid crystalline phases of water.
Subjected to high pressures and varying temperatures, ice can form in sixteen separate known phases. The types are differentiated by their crystalline structure, ordering and density. There are also two metastable phases of ice under pressure, both fully hydrogen-disordered; these are IV and XII. Ice XII was discovered in 1996. In 2006, XIII and XIV were discovered. Ices XI, XIII, and XIV are hydrogen-ordered forms of ices Ih, V, and XII respectively. In 2009, ice XV was found at extremely high pressures and −143°C. At even higher pressures, ice is predicted to become a metal; this has been variously estimated to occur at 1.55 TPa or 5.62 TPa.
As well as crystalline forms, solid water can exist in amorphous states as amorphous ice (ASW) of varying densities. Water in the interstellar medium is dominated by amorphous ice, making it likely the most common form of water in the universe. Low-density ASW (LDA), also known as hyperquenched glassy water, may be responsible for noctilucent clouds on earth and is usually formed by deposition of water vapor in cold or vacuum conditions. High density ASW (HDA) is formed by compression of ordinary ice Ih or LDA at GPa pressures. Very-high density ASW (VHDA) is HDA slightly warmed to 160K under 1–2 GPa pressures.
In outer space, hexagonal crystalline ice (the predominant form found on Earth) is extremely rare. Amorphous ice is most common.
Low Density Amorphous
Low-density amorphous ice, also called LDA, vapor-deposited amorphous water ice, amorphous solid water (ASW) or hyperquenched glassy water (HGW), is usually formed in the laboratory by a slow accumulation of water vapor molecules (physical vapor deposition) onto a very smooth metal crystal surface under 120 K. In outer space it is expected to be formed in a similar manner on a variety of cold substrates, such as dust particles. It is expected to be common in the subsurface of exterior planets and comets.
Melting past its glass transition temperature (Tg) between 120 and 140 K, LDA is more viscous than normal water. Recent studies have shown the viscous liquid stays in this alternative form of liquid water up to somewhere between 140 and 210 K, a temperature range that is also inhabited by ice Ic. LDA has a density of 0.94 g/cm3, less dense than the densest water (1.00 g/cm3 at 277 K), but denser than ordinary ice (ice Ih).
Hyperquenched glassy water (HGW) is formed by spraying a fine mist of water droplets into a liquid such as propane around 80 K or by hyperquenching fine micrometer-sized droplets on a sample-holder kept at liquid nitrogen temperature, 77 K, in a vacuum. Cooling rates above 104 K/s are required to prevent crystallization of the droplets. At liquid nitrogen temperature, 77 K, HGW is kinetically stable and can be stored for many years.
High Density Amorphous
High-density amorphous ice (HDA) can be formed by compressing ice Ih at temperatures below ~140 K. At 77 K, HDA forms from ice Ih at around 1.6 GPa and from LDA at around 0.5 GPa (approximately 5,000 atm). At this temperature, it can be recovered back to ambient pressure and kept indefinitely. At these conditions (ambient pressure and 77 K), HDA has a density of 1.17 g/cm3.
Peter Jenniskens and David F. Blake demonstrated in 1994 that a form of high-density amorphous ice is also created during vapor deposition of water on low-temperature (< 30 K) surfaces such as interstellar grains. The water molecules do not fully align to create the open cage structure of low-density amorphous ice. Many water molecules end up at interstitial positions. When warmed above 30 K, the structure re-aligns and transforms into the low-density form.
Very High Density Amorphous
Very-high-density amorphous ice (VHDA) was discovered in 1996 by Mishima who observed that HDA became denser if warmed to 160 K at pressures between 1 and 2 GPa and has a density of 1.26 g/cm3 at ambient pressure and temperature of 77 K. More recently it was suggested that this denser amorphous ice was a third amorphous form of water, distinct from HDA, and was named VHDA.
This form of ice is the form all natural ice on Earth conforms to. It has a hexagonal crystal structure and has a low density structure. It has a low packing efficiency compared to other ices, such as cubic. This ice forms in sheets, much like mica. This sheeted structure is characteristic to minerals with basal cleavage. The hardness varies with temperature. At 0°C, the hardness is about or below 2 on the Mohs scale and at -80°C it is at 6 on the scale. Crystals of this ice forms hexagonal plates and/or columns. With increasing pressure, thermal conductivity of the ice decreases. This is caused by changes in the bonding of hydrogen that decreases the transverse sound velocity. The nucleation of this ice is enhanced at the air-water surface than within the water (by a factor of 10^10). Crystals grow in the direction of the c-axis. They either grow inside vertical freezing pipes or grow down vertically from platelets already nucleated. They can also grow from prism faces in an agitated environment. The speeds of growth depends on the ability for the crystal faces to form greater amounts of cooperative hydration. The temperature of the surrounding water determines to amount of branching in the crystal. There is more branching at a low degree (<2°C) and more needle like growth at a higher degree (>4°C). Solutes in the water cannot be incorporated in a hexagonal structure. The solutes are expelled to the surface or the amorphous layer between microcrystalline crystals.
Cubic ice is a form of water ice commonly found in high clouds in the Earth's atmosphere. It is a metastable form of ice that can be formed by condensing water vapor at ambient pressure and low temperatures (generally less than -80 degrees Celsius), at -38 degrees Celsius in small droplets, or by reducing the pressure on high pressure ices at 77 K. Cubic ice has a higher vapor pressure than ice Ih. It is often found in freezing confined aqueous systems. It is thought that this ice may be the preferred form for water droplets under 15 nm radius at around 160-220 K. This is due to how cubic ice has lower interfacial free energy than hexagonal ice. Large cubic crystals convert slowly to hexagonal ice at 170-220 K. Cubic ice consists of a face centered cubic lattice. The ice has a fairly open, low density structure. Cubic ice has a staggered arrangement of hydrogen bonding, instead of hexagonal ice's 3/4 arrangement of hydrogen bonding. All molecules have identical environments. All atoms have four tetrahedrally arranged nearest neighbors and twelve second neighbors. The H-O-H angle of the water molecules do not change much from the isolate form of the molecule. The hydrogen bonds are not straight in the ice structure. Cubic ice, much like hexagonal, shows a reduction in thermal conductivity with increasing pressure. This is caused, just like hexagonal, by changes in hydrogen bonding decreasing the transverse sound velocity.
Ice II is a rhombohedral crystalline form of ice with highly ordered structure. It is formed from ice Ih by compressing it at temperature of 198 K at 300 MPa or by decompressing ice V at 238K. When heated it undergoes transformation to ice III, but it is not easily formed by cooling ice III. It is thought that the cores of icy moons like Jupiter's Ganymede may be made of ice II. In ice II, all water molecules are hydrogen bonded to four others, two as donor and two as acceptor. Ice-two may exist metastably below ~100 K between ambient pressure and ~5 GPa. At ambient pressure it irreversibly transforms into ice Ic above 160 K. As the H-O-H angle does not vary much from that of the isolated molecule, the hydrogen bonds are not straight. Half the open hexagonal channels of ice Ih have collapsed in ice II. The relationship of the ice II structure to ice Ih can be visualized by detaching the columns of hexameric ice Ih rings, moving them relatively up or down at right angles to their plane, rotating them about 30° around this axis and re-linking the hydrogen bonds in a more compact way to give a density of 1.16 g/cm3. The hydrogen bonding is ordered and fixed in ice II. There is no corresponding disordered phase, in contrast to the other ordered ices VIII, IX, XI and XV. The lack of a disordered phase has been correlated with the high energy difference between the most and the second most stable ice configurations. Some of ice II's hydrogen bonds are bent and, consequentially, much weaker than the hydrogen bonds in hexagonal ice.
Ice III is a type of ice that is formed from water at 300 MPa with a temperature lowered to 250 K. The unit cell forms tetragonal crystals with a space group of P41212 92, a Laue class symmetry of 4/mmm, and analogous to keatite silica. All the water molecules are hydrogen bonded to four others and the ICE III contains five membered rings joined as bicylo-heptamers with a density of 1.16 g cm-3. The disorder hydrogen bonding constantly changes with the tetragonal crystal being pseudo-cubic with cell dimensions 6.666 angstroms and 6.936 angstroms
Ice IV is a type of water formed by the heating of high-density amorphous ice slowly (0.4 K min-1) at 145 K and at a constant pressure of 0.81 GPa. Ice IV formed a rhombohedral cr
Gaseous Water (Water Vapor)
Sites of Possible Extraterrestrial Life
For the 2014-15 Solar event, it is useful to know which celestial bodies in our solar system could possibly have life living on (or in) them.
Life needs many things to survive. It needs water, which Mars has in the form of ice at its poles. If life ever evolved on Mars, it did so in a place with a source of liquid water. Ice caps at the poles will not sustain life, but other sources of water might work, such as hydrothermal pools, not unlike those at Yellowstone National Park in Wyoming, or any other place that will have the temperature to sustain liquid water.
Life also needs energy to thrive. The presence of energy on Mars other than sunlight is rare, since there are superoxides that break down organic matter that life is based on. Besides sunlight, there is little evidence of other energy, such as chemical or geothermal energy like Earth, but it may still be there. On Earth, life can be sustained in many places where the sunlight never reaches, such as abysses, trenches, and caves with chemical energy, or in the Earth's crust with geothermal energy. There is a chance that the same phenomenons can happen on Mars like they did on Earth.
NASA (National Aeronautics and Space Administration) is looking for signs of life on Mars. They are looking for signs that will allude to the conditions on Mars that may have allowed life to be sustained there, such as carbon. The element carbon (C) is the building block of life. All living things use carbon. Dead organisms turn into peat, which turns into coal, which has a high carbon percentage, and then we humans burn the coal to produce carbon energy. It is known that the atmosphere of Mars is carbon dioxide (CO2). If NASA finds carbonate minerals on Mars, we will know that there was once liquid water on Mars because the reaction between water (H2O) and the atmosphere (CO2) will react to form carbonic acid, or H2CO3, hydrogen carbonate. If these are found, then we will know that liquid water has existed on Mars for a long time, maybe even enough for life to have developed. On Earth, fossils can be used to tell our geologic and biologic history. Maybe Mars will have fossils, too. NASA is currently looking into dried lake/riverbeds for possible evidence of life in fossils.
The moon of Europa is one of the top locations in the solar system for the potential of extraterrestrial life. Life has three main requirements for survival, the presence of natural elements and chemicals, the presence of a universal solvent, and an ample supply of energy. Europa has the potential of all of these three. The theorized water ocean under the moon's surface is the perfect solvent for natural chemicals. Ridges on Europa's surface have a reddish color created by certain natural elements. This may be an indication of the presence of these chemicals in the underground ocean. Tidal heating from Jupiter, radioactive decay, and hydrothermal vents at the ocean floor all are supposed energy sources for life on the moon. Because all three requirements are present in the supposed ocean, if life is on Europa, it would most likely be located in the ocean. Where they are located in the ocean could vary. Life here would be extremophiles living either near hydrothermal vents on the ocean floor, on the underside of the icy surface, freely floating in the ocean, or even within the rock of the ocean floor (like endoliths on Earth) Life could also be found in lakes encased by the ice layer, separate from the ocean. Life on the moon would be single cellular or small multi cellular extremophiles. If the ocean environment was extremely salty, only extreme halophiles would be able to thrive. If life isn't on Europa now, it could appear later due to changes in the composition of the ocean salinity.
Saturn's moon Enceladus is another possible source of extraterrestrial life. Since the discovery in 2005 that Enceladus actively vents gas, the spacecraft Cassini has provided NASA with more information that will help them determine if life can be sustained on this remote moon.
Many flybys and analyses by Cassini of the plumes of water that stream through Enceladus have revealed that there are chemicals like carbon, hydrogen, nitrogen, and oxygen present underneath the ice shell of Enceladus' crust, which is a giant ocean. This information was only further confirmed when, in 2015, Cassini flew into a plume of water and used its chemical detector to confirm that there is molecular hydrogen (H2) on Enceladus. On Earth, molecular hydrogen sprouts from the hydrothermal vents on the ocean floor, entering the ocean. The chemistry between elements in the water and the molecular hydrogen supports life forms such as one-celled microbes, tube worms, and crabs. If this can occur on Earth, then there is a very high chance of it occurring on Enceladus. Three things are required for life to be sustained, and Enceladus has the potential for all of them: chemicals (existing), water (from the acidic water under the 5km shell of ice), and energy (from the plumes of water). | 0.903568 | 3.601939 |
Europe’s Rosetta mission finally came to an end last week with the planned collision of the spacecraft with the object it had been monitoring for the last two years: comet 67P/Churyumov-Gerasimenko. Rosetta was on its sixth orbit around the Sun since launching in 2004, a journey that included three Earth fly-bys, one Mars fly-by, and two asteroid encounters. It also endured 31 months in deep-space hibernation before waking up in January 2014 prior to its arrival at comet 67P in August of that year. There it deployed the Philae lander, which achieved the first ever soft-landing on a comet (although in a sub-optimal location that resulted in lost communication).
Among the mission’s noteworthy scientific results were the discovery and analyses of gases streaming from the comet’s nucleus, which included molecular oxygen, nitrogen, and water. The water, though, was found to be enriched in deuterium (the heavy isotope of hydrogen), which means it isn’t the same type of water that exists today in Earth’s oceans. That in turn suggests that not all the water on Earth comes from comets, as one earlier hypothesis had held, and that a large proportion of Earth’s water must have derived from volcanic exhalations and mantle degassing early in the planet’s lifetime.
Taken together, Rosetta’s scientific findings so far indicate that the comet formed in a cold region of the early solar system more than 4.5 billion years ago, at a time when the planets were still forming. Thus, it contains some of the oldest material we can find, including amino acids, the building blocks of life.
During much of the two-year mission, many of Rosetta’s instruments were still too far away from the comet to do a detailed compositional analysis of 67P.
That changed when the spacecraft crashed into the comet last week, however; Rosetta’s last hours will most likely yield its most valuable scientific return. Not only are the final high-resolution images, some of them taken a few seconds before impact, stunning, the compositional analyses should be even more intriguing. We may have to wait years for the treasure trove of data to be fully harvested, however, and to gain a fuller picture of the organic content that comets likely delivered to early Earth, and their possible role in the origin of life. | 0.838083 | 3.849433 |
Supernova Dust Found in Antarctic Could Be 20 Million year old
Remnants of a supernova were found in Antarctic snow. The space dust could be 20 million years old.
A star collapses when it dies, spewing out space dust in a giant cloud of elements that make for very beautiful Hubble Telescope photos. The “explosion,” called a supernova, results in either a black hole or an incredibly small, dense star that no longer generates heat.
A supernova also shoots space dust out in all directions that travels through the universe, occasionally coming into contact with other stars, planets — whatever happens, to be in its path.
Earth has been around long enough to collect particles from exploding stars, even though it’s difficult to find the evidence. But sometime in the past 20 years, space dust from a supernova intersected with Earth and settled in Antarctica. The dust itself could be as old as 20 million years.
Scientists found a strange version of iron in relatively fresh Antarctic snow, according to a study published in the journal Physical Review Letters. Specifically, it was an isotope of iron, Fe-60, that astronomers know was present when our solar system formed. The discovery of the iron-laden dust could help scientists form a clearer timeline of our solar system.
Gunther Korschinek and his colleagues at institutes in Germany and Austria were hunting for evidence on Earth of a supernova in space. They chose Antarctica, Korschinek said, because they wanted a sample from “a very clean area, that is not disturbed by dust from surrounding material.”
They ended up hauling a half-ton of snow from the nearly uninhabited, frozen continent to their labs in Europe, under the hypothesis that they might find such stardust evidence. And their methods were relatively rudimentary. Researchers found the best snow samples in unfrequented areas of Antarctica, of which there are many. The snow had to stay frozen on the trip for this analysis to work, so they scooped it into plastic-foam containers and kept the temperature low on the roughly 10,000-mile trek.
From the research station, the snow was loaded onto a plane and then headed to the shore of Antarctica’s coast. From there, it was taken by a research boat to South Africa, before getting on another boat to Europe.
Finally, the boxes made their way into a van and on their way to a lab, where the snow was melted and filtered. Korschinek was able to receive small samples so his team could analyze the elements found in the snow.
The iron-60 was there, but they had to rule out other potential sources — such as residue from nuclear bombs or power plants — before they could determine it was interstellar. In the second half of the 20th century, nuclear weapons and their testing sent particles all over the planet, and those reactions also produced iron-60.
Ruling out other sources allowed scientists to confirm it was space dust. The process was slow and included many steps, Korschinek said, but the closer they got to confirmation, the more excited the team became. The discovery opens up the window of possibilities for research.
“We can hopefully learn more about supernovae, from this specific supernova,” Korschinek said. | 0.841297 | 3.736532 |
Easter, you may have noticed, is not a fixed day in the calendar. While Christmas, in contrast, occurs reliably every year on Dec. 25, Easter wanders around on a given Sunday in late March or April. This year Easter will be celebrated on March 31, but in 2014 it will occur on April 20. The reason has to do with the mismatch between the periodicity of the sun and the moon and the long history of human efforts to create a reliable and consistent calendar.
The Earth takes approximately 365.25 days to complete its orbit around the sun. The moon, on the other hand, completes its monthly cycle in approximately 28 days. Twenty-eight is neatly divided into a month consisting of four seven-day weeks (and now you know why there are seven days in a week instead of six or 10 or…). If the annual solar cycle were evenly divisible by the “monthly” lunar cycle, creating an accurate calendar would be easy. Instead, 365.25 solar days divided by 28 lunar days equals 13.0446 months.
Calculating the seasons was vitally important in the growing agricultural societies of the past and to the religious-political hierarchies that presided over these expanding civilizations. Without this perplexing mismatch between the periodicity of the sun and the moon to challenge their imaginations, observations and calculations, our ancestors might never have developed advanced mathematics and the astronomical sciences.
Most of the early calendars created by humans were based on the lunar cycle (13 months of 28 days, each month divided into four seven-day weeks). Religious Muslims and Jews today still use modified lunar calendars with an occasional leap month thrown in to prevent the months from wandering too far away from their solar seasons.
In 46 A.D., Julius Caesar instituted the Julian calendar throughout the Roman Empire. It would be the predominant calendar used throughout Europe for 1,500 years. The Julian calendar is a solar calendar consisting of 12 months of varying lengths (28 days, 30 days, and 31 days) with a leap day added to February every fourth year (i.e., 29 days instead of 28 days).
The problem is that the annual periodicity of the sun is not exactly 365.25 days, as the Greek astronomer Hipparchus had calculated back in the second century B.C. The actual solar year is 365 days, five hours, 55 minutes and 12 seconds. Hipparchus’ calculations were off by only a few minutes, which is pretty impressive for 2,200 years ago. But this tiny discrepancy in the sun’s actual periodicity resulted in a gain of about three days every four centuries under the Julian calendar as compared with the observed equinoxes and solstices.
The First Council of Nicaea in 325 A.D. established that Easter should occur on the first Sunday after the full moon that follows the vernal equinox. This year, the spring equinox occurred on March 20 with the full moon on March 27, ergo Sunday, March 31 is Easter. This formulation also linked Easter in proximity to the Jewish Passover, from which the Christian holiday is symbolically derived. But there was another problem: Over many centuries under the Julian calendar, in which a Julian year differed slightly from an actual year, the vernal equinox wandered 10 days earlier to around March 10.
The Gregorian calendar was instituted in 1582 by the Catholic Church to correct these accumulated discrepancies. Pope Gregory’s bull began by skipping 10 calendar days to restore Easter to its “proper” place in the calendar — late March or April.
Imagine the ruckus that would be created today if, by decree, we simply skipped 10 days in March. In 1582, Europe was already hot in the midst of the Reformation. Protestants couldn’t care less for the “Popish” bull on esoteric astronomy. A Euro crisis ensued, not over a common currency, but over the lack of a common calendar. This crisis lasted for centuries. The Catholic countries had lost 10 days in the “New Style” Gregorian reform, but the Protestant countries continued to follow the “Old Style” Julian calendar.
The Gregorian calendar had one major improvement over the earlier Julian calendar. It modified leap years to fine-tune the actual solar periodicity. Every year divisible by four is still a leap year (i.e., 29 days in February instead of 28) with the exception of centurial years that are not divisible by 400. Thus, the years 1700, 1800, 1900 and 2100 are not leap years, but 1600, 2000 and 2400 are. This latter adjustment made the calendar more consistent and it could hold up for millennia in keeping with the solar year.
The Gregorian calendar is now the Civil Calendar of the world, but the road to its acceptance was not easy. The British Empire finally adopted the “New Style” Gregorian calendar in 1752, by which time the discrepancy had grown from 10 days to 11 days. By decree, London eliminated these 11 days, and resynchronized their dates with Catholicism and the sun. President George Washington, for instance, was born on Feb. 11, 1732 in the Virginia colony under the “Old Style” calendar, which would be reckoned as Feb. 22, 1732 under the “New Style” calendar.
Today, there remains a 13-day difference between the Gregorian calendar and the Julian calendar still used by Eastern Christianity. Thus, Orthodox Christianity celebrates Christmas on Jan. 7, 13 days after Dec. 25. As for Easter — the moveable feast with no fixed date — this year, Orthodox Christians will celebrate the holiday on May 5. Curiously, Western and Eastern Christianity will celebrate Easter together in 2014 on Sunday, April 20. I have no idea how often that happy confluence occurs.
Today, the relative movements of the Earth, moon and sun can be measured more precisely than our ancestors were capable of doing or knowing. We also know these periodicities to be more uneven. A lunar month, for instance, is actually quite variable and is on average 29 days, 12 hours and 44 minutes (not 28 days).
Time in our techno-scientific, global civilization is even more precious and precise, such that we measure it reliably in scales from nanoseconds to light-years. Someday our descendants will no doubt have to adjust their calendars again, but something of the rising and setting sun and the phases of the moon will always govern our existential understanding of the passing of time in ways that matters most in our human-scale experience.
The history of telling time is an education in the education of our species on a finely tuned, slightly quirky and fantastically blessed planet teeming with life and consciousness. It is a planet that wobbles on its axis in elliptical orbit around the sun even as it is pushed and pulled by the gravitation of the moon. It is a planet governed by the periodicity of the sun and the moon, but also cycles of birth, death and renewal of life. It is a planet governed by the Great Eucharistic law — eat and be eaten. Earth itself, we now understand, is literally a moving feast.
Chag Sameach and Happy Easter. | 0.815556 | 3.522148 |
As the Kepler space telescope begins finding its first Earth-sized exoplanets, with the ultimate goal of finding ones that are actually Earth-like, it would seem natural that the SETI (Search for Extraterrestrial Intelligence) program would take a look at them as well, in the continuing search for alien radio signals. That is exactly what SETI scientists are doing, and they’ve started releasing some of their preliminary results.
They are processing the data taken by Kepler since early 2011; some interesting signals have been found (a candidate signal is referred to as a Kepler Object of Interest or KOI), but as they are quick to point out, these signals so far can all be explained by terrestrial interference. If a single signal comes from multiple positions in the sky, as these ones do, it is most likely to be interference.
They do, however, also share characteristics which would be expected of alien artificial signals.
A couple of examples are from KOI 817 and KOI 812. They are of a very narrow frequency, as would be expected from a signal of artificial origin. They also change in frequency over time, due to the doppler effect – the motion of the alien signal source relative to the radio telescope on Earth. If a signal is found with these characteristics but also does not appear to be just interference, that would be a good candidate for an actual artificial signal of extraterrestrial origin.
These are only the results of the first observations and many more will come during the next weeks and months.
Looking for signals has always been like looking for a needle in the cosmic haystack; until now we were searching pretty much blind, starting even before we knew if there were any other planets out there or not. What if our solar system was the only one? Now we know that it is only one of many, with new estimates of billions of planets in our galaxy alone, based on early Kepler data. Plus the fact that the majority of those are thought to be smaller, rocky worlds like Earth, Mars, etc. How many of them are actually habitable is still an open question, but finding them narrows down the search, providing more probable actual targets to turn the radio telescopes toward instead of just trying to search billions of stars overall.
All twelve signal examples so far can be downloaded here (PDF). | 0.86666 | 3.521892 |
Stardust has finally solved a mystery as unfathomably old as the creation of our solar system.
Scientists from all over Europe collaborated at Italy's underground Laboratory for Underground Nuclear Astrophysics (LUNA) in a study that ended up illuminating more of the mystery behind the nebulous origins of our solar system. Published in the journal Nature Astronomy, this study has chemically linked cosmic dust found in meteorites to the immense dust cloud that astronomers believe our Solar system emerged from some 4.6 billion years ago. This stellar finding glows especially brightly because most of the grains that were thought to swirl in the chaos of that antediluvian dust cloud were destroyed as space rocks and planets were born.
"The long-standing question of the missing dust was making us very uncomfortable: it undermined what we know about the origin and evolution of dust in the Galaxy," said team lead Dr. Maria Lugaro of Hungary's Konkoly Observatory. "It is a relief to have finally identified this dust thanks to the renewed LUNA investigation of a crucial nuclear reaction."
Evidence of specific chemical reactions identified the dust as originating from Asymptotic Giant Branch (AGB) stars, celestial bodies 6-8 times the size of the sun that were in their death throes at the time of the embryonic solar system. After a star has been in the red giant phase for a stretch of time, its helium core contracts and heats up at an astonishing rate, eventually skyrocketing to temperatures hot enough to ignite what is called the helium flash. The star becomes a red giant again — entering the AGB phase — after the helium in its core eventually burns out. As these ancient stars degenerated, their outer layers were blown off into space and the refuse is believed to have accumulated into a cloud of cosmic gas and dust.
Nuclear reactions specific to AGB stars left a lasting mark on the chemical composition of the dust grains for billions of years. Nuclear physicists were also surprised to determine that there had been twice as many fusion reactions between protons and type of oxygen known as 17O that is much heavier than that floating in the Earth's atmosphere (and nowhere near breathable). Proton-capture nucleosynthesis, in which protons are 'captured' and consumed by the nucleus of an atom, was one of the reactions they sought out the most. Stardust grains have the effect of such reactions imprinted in their astral DNA.
"It is a great satisfaction to know that we have helped to solve a long-standing puzzle on the origin of these key stardust grains," said UK team lead Professor Marialuisa Aliotta of the University of Edinburgh's School of Physics and Astronomy. "Our study proves once again the importance of precise and accurate measurements of the nuclear reactions that take place inside stars."
(via Science Daily) | 0.885746 | 4.055258 |
Professor Chris Arumainayagam has recently published results suggesting that low-energy, electron-induced condensed phase reactions may have contributed to the interstellar synthesis of prebiotic molecules. These molecules were previously thought to form only through UV photons. His work coincides with the idea that we, as humans, come from stardust and is the first unambiguous detection of glycine in a comet as reported in May 2016.
The goal of his research was to understand the “chemistry of the heavens”, as he so poetically put it. He wanted to do so by recreating what happens in interstellar space when high-energy cosmic rays impact ices surrounding micron-size dust grains in dark dense molecular clouds. In such locations the pressure is around ten trillion times lower than that of atmospheric pressure. The interaction of high-energy cosmic rays with matter creates massive amounts of low-energy electrons.
Arumainayagam’s results demonstrate that low-energy electron and UV irradiation of methanol ices yield just about the same reaction products. His studies thus far have identified one possible electron-induced cosmic ice chemistry tracer, known as methoxymethanol. This tracer is a complex organic molecule that is not identified in UV laboratory photolysis studies of condensed methanol. Future astronomical identification of methoxymethanol within interstellar or circumstellar clouds may be able to provide even more evidence to the role of low-energy electrons in astrochemistry. His complete findings back up a very important need for astrochemical models to include the details of low-energy electron-induced reactions in addition to those driven by UV photons.
Jyoti Campbell, a Wellesley College Sophomore will give an oral presentation at the conference called “The Role of Low-Energy Electrons in Astrochemistry: A Tale of Two Molecules.” Campbell has been offered access to technologies and equipment that are rarely something undergraduates can go near.
Arumainaygam is currently working on upgrading his UHV chamber to explore the fundamental differences between chemical reactions initiated by photons and electrons. The study was published in Surface Science journal. | 0.817255 | 3.842731 |
The 21 and 22 of April is the peak of a shower of meteors – or shooting stars – known as the Lyrids.
All the time small pieces of interplanetary debris – meteoroids – burn up in the Earth’s atmosphere. Most of them are very small, around the size of a grain of sand, but they enter the atmosphere at anything from 10 to 70 kilometres each second, or up to 250,000 kilometres an hour.
At this speed even such tiny particles quickly heat up and are destroyed as they run into the air around our planet. The air around them glows briefly as a streak of light, which is then seen as a meteor from the ground.
RAS Deputy Executive Director Robert Massey explains how to see the Lyrids.
On any clear night a few random meteors called ‘sporadics’ are visible each hour. But at certain times of year there are also showers of meteors, where activity is enhanced. The second half of April sees the Lyrid meteor shower.
The Lyrids come from the tail of Comet Thatcher, which last came close to the Sun in 1861. This comet takes more than 400 years to complete its orbit, so will next be close to the Earth in the 23rd century.
Like all comets, Thatcher leaves a stream of debris in its wake. When the Earth runs into that material, some of it burns up in our atmosphere – meaning we see more meteors than usual.
The way we intercept the trail of material also means that the meteors appear to come from a point in the sky – the radiant – in the constellation of Lyra, so are called the Lyrids.
This year the Lyrids peak on the night of 21-22 April. The best view should be around 0300 local time, when the radiant is high overhead in the northern hemisphere.
Observers with a good dark sky might see around 10 Lyrid meteors each hour, on top of the sporadics. The shower tends to produce quite bright meteors, which makes things a bit easier in towns and cities, and there’s also no Moon visible to interfere with the view.
Meteor showers are easy to observe. Unlike many astronomical phenomena, a telescope or pair of binoculars actually make it much harder to see meteors. The best way to watch them is simply with your eyes, as you can see a large area of sky at once.
More information on the Lyrids from the International Meteor Organisation. | 0.860253 | 3.725307 |
Ever since their discovery more than a decade ago, enigmatic flashes of radio waves have puzzled astronomers. These “fast radio bursts” (FRBs) pop up with startling frequency and intensity all across the sky, each emerging from unknown faraway extragalactic sources and packing the power output of up to hundreds of millions of suns into just a few fleeting milliseconds.
Now researchers are closing in on their origins.
A team studying one particular FRB some three billion light-years from Earth—known as FRB 121102, the only ever seen to repeat—has found it is engulfed by an extremely strong magnetic field. Such extreme magnetic fields have only previously been seen near neutron stars around the supermassive black hole at the center of our galaxy. The team suggests this FRB’s mysterious source is a very young and fast-spinning, highly magnetized neutron star—a magnetar—that may be orbiting a massive black hole. The findings are published in the January 11 Nature.
“For the first time, we’re getting some sense of the environment around the burst’s source—remote sensing from three billion light-years away!” says study co-author Shami Chatterjee, an astronomer at Cornell University. “We recognize this is piling one exotic thing atop another: We want an energetic magnetar without precedent, and we also want to put it next to a massive black hole. But we do have a similar example in our own galaxy. ”The magnetars near the Milky Way’s center, however, have yet to be seen emitting FRBs, which tend to come from much, much further away.
A curious property of FRBs confirms their vast distance from us—their radio waves have been “dispersed” by their passage through clouds of electrons that fill the space between stars and galaxies, smeared out in proportion to how far they have journeyed to reach Earth. That means FRBs could become best-in-class probes of cosmic structure, allowing researchers to determine not only the distance to any given FRB but also how much intervening material lies in interstellar and intergalactic space along its path. But to fully realize that revolutionary potential, astronomers must better understand what gives rise to FRBs in the first place, and whether the lone known repeating burster, FRB 121102, is a typical example or a fluke.
To learn more, the team periodically monitored the repeater across several months using two of the world’s largest radio telescopes, Arecibo Observatory in Puerto Rico and the Green Bank Telescope in West Virginia. FRB 121102 does not repeat with clockwork regularity; instead, its bursts are intermittent and, so far, impossible to precisely predict. The team ultimately captured and analyzed 16 bursts. The durations of each burst, which ranged from nine to 30 milliseconds, suggested the source is perhaps 10 kilometers across—the size of a typical neutron star.
Besides looking at the timing and dispersion of each radio burst, the researchers also measured its polarization—the way the burst’s light oscillated up or down, left or right, perpendicular to its direction of travel. When polarized radio waves pass through magnetic fields and charged particles, their polarization becomes twisted like a corkscrew—the denser the particles and the more intense the magnetic field, the greater the twisting. Polarization measurements showed FRB 121102’s twisting was enormous, rivaling the largest ever seen from an astrophysical source. The twisting was also rapidly changing, declining by 10 percent across a roughly half-year period. Whatever the source is, it must be a compact object surrounded by a dense, intensely magnetized cloud of plasma (a hot, ionized gas) moving at very high speeds.
“Can we maybe now understand how this extreme environment is related to the fact that this is the only known repeating FRB?” asks study co-author Jason Hessels, an astronomer at the University of Amsterdam and ASTRON Netherlands Institute for Radio Astronomy. “Maybe that extreme environment includes structures that can boost the brightnesses of the bursts like a magnifying lens.” Those structures could be particularly dense tendrils and knots of plasma whipping through the cloud surrounding the FRB source, so-called “plasma lenses” that would occasionally amplify ongoing radio emissions to help produce the repetitions. Without such a magnifying effect, repeated bursts are hard to explain—FRBs are so powerful that many models suggest their production would require the total physical destruction of their sources, such as the cataclysmic collision of two neutron stars.
The first inklings of FRB 121102’s true nature trace back to early 2017, when this so-far singular FRB was definitively linked to a region of intense star formation in a dwarf galaxy some three billion light-years from Earth. Such dwarfs are rich in pristine gas scarcely altered since the universe sprang into being during the big bang nearly 14 billion years ago—and that gas tends to form especially massive and short-lived stars, which end their lives by exploding with astonishing violence as “superluminous supernovae.” Those explosions, in turn, can leave behind particularly extreme remnants—stellar-mass black holes, for one thing, but also run-of-the-mill neutron stars and their supercharged kin, magnetars. What’s more, when astronomers zoomed in on the FRB’s locale within the dwarf galaxy, they saw something else nearby—a softer, steadier radio glow from a roiling cloud of plasma that could have been material ejected from a recent magnetar-forming supernova or burped out by a voraciously feeding black hole. At the time no one knew whether the FRB was actually associated with this cloud; this latest study all but confirms it lies embedded within.
“Last year’s localization was a game changer in a very direct way,” says Jim Cordes, a study co-author and astronomer at Cornell. “This latest result is more drilling into the FRB and its surroundings to tell us something about the environment surrounding what we call the ‘engine,’ the object producing these high-energy radio bursts.” That fearsome engine, Cordes and other co-authors say, is most likely a magnetar less than a century old—a relative newborn in comparison with those we know in the Milky Way, which are thought to have formed thousands of years ago. A magnetar so young should be spinning extremely fast, perhaps once per millisecond, but will rapidly lose rotational speed as its whirling magnetic field dumps immense amounts of energy into a surrounding shell of expanding plasma left over from the supernova that birthed it.
“As the magnetar spins down its magnetic field moves. And the field is so strong it takes the magnetar’s ironlike crust with it, cracking the crust to generate ‘starquakes’ and flares that drive energy like a piston out into the surrounding, dynamic nebula,” Cordes says. “That’s one possibility.” The other, he says, is a magnetar orbiting a massive black hole that is feeding on huge volumes of gas and dust. In that more general scenario the magnetar could periodically pass through debris disks and particle jets surrounding the black hole as it feeds, being bathed in material that is then ejected at high speed by the intense magnetic fields. In either case, the result could be a repeating FRB. If FRB 121102’s twisted polarization continues to unwind (following the 10 percent reduction across a half year already seen), that would suggest a surrounding nebula slowly expanding and dissipating, in support of the first scenario. If instead its surroundings continue displaying wild magnetic oscillations, that could be better evidence for something more like the black hole scenario.
Although these results go a long way toward solving the mystery of FRB 121102, Chatterjee says, they still remain frustratingly silent about the bigger questions: Do all FRBs come from one type of physical source? Do all FRBs repeat? “This is a ‘nature versus nurture’ problem,” he says. “Is it in the nature of FRBs that they all originate in this sort of extreme environment—or is this more of a nurture situation, where this one repeats because of its extreme environment, this strong magnetic field and plasma lensing? Both possibilities remain tantalizingly open.”
More answers should come soon, via new wide-field radio telescopes now coming online that should excel at detecting more FRBs, pinpointing their cosmic origins and charting their possible repetitions. One in particular, called CHIME (Canadian Hydrogen Intensity Mapping Experiment), is projected to detect anywhere between a few and a few dozen FRBs per day when it begins operations later this year, giving astronomers fresh hopes for peering deeper than ever before into the mysterious hearts of FRBs across the universe. | 0.918881 | 4.070541 |
The sun's polarity is getting closer to flipping. The star's northern hemisphere's polarity has already reversed, and the southern hemisphere should follow suit soon, scientists say.
Every 11 years or so, the two hemispheres of the sun reverse their polarity, creating a ripple effect that can be felt throughout the far reaches of the solar system. The sun is currently going through one of those flips in its cycle, said scientists working at Stanford University's Wilcox Solar Observatory, which has monitored the sun's magnetic field since 1975.
"The sun's poles are reversing, and this is a large-scale process that takes place over a few months, but it happens once every 11 years," Todd Hoeksema, a solar physicist at Stanford said in a video about the polarity reversal. "What we're looking at is really a reversal of the whole heliosphere, everything from the sun out past the planets."
The polarity reversal builds up over time. A sunspot spreads out, causing the sun's magnetic field to migrate from the equator of the star to one of the sun's poles. As this change occurs, the sun's magnetic field reduces to zero and then comes back with the opposite polarity, Hoeksema said in a statement. [Solar Max: Photos of the Active Sun in 2013]
"When that reverses it effects us here on Earth because not only do we see more cosmic rays, but there's also more activity on the sun," Hoeksema said. "That activity comes in and it affects the Earth's magnetic field."
The planet's magnetic field affects technology on Earth like GPS systems and power grids, Hoeksema said. The uptick in solar activity can also create brilliant auroras on Earth and on certain planets of the solar system.
"We also see the effects of this on other planets," Hoeksema said in a statement. "Jupiter has storms, Saturn has auroras, and this is all driven by activity of the sun."
This part of the sun's cycle is known as the "solar maximum." The solar max marks the peak in the star's activity. Usually, the sun's polarity reversal happens during this period of the solar cycle, however, the reversal isn't responsible for the increased number of solar flares and eruptions known as coronal mass ejections usually observed around solar max.
The increased activity acts as an indicator that the polarity reversal will occur, but it doesn't cause the sun to become more active, Hoeksema said in an earlier interview with SPACE.com.
The polarity reversal probably won't harmfully impact Earth, in fact, it could even protect the planet in some ways, scientists have said.
The sun's huge "current sheet" — a surface extending out from the sun's equator — becomes wavier as the poles reverse. The sheet's crinkles can create a better barrier against the cosmic rays that can damage satellites, other spacecraft and people in orbit, scientists said. | 0.803707 | 3.650352 |
As within the different sciences, astronomers within the Muslim lands constructed upon and significantly expanded earlier traditions. The middle of our galaxy is about 30,000 gentle years from Earth. Comet Kohoutek was a new comet, and astronomers anticipated it to be quite vivid when it passed by the Sun on perhaps its first go to to the internal solar system. As with telescopes, the bigger the aperture (the diameter of the objective lens), the extra gentle will be captured and therefore the brighter objects will appear.
Astrometry, probably the most historic branch of astronomy, is the measure of the sun , moon and planets The exact calculations of these motions allows astronomers in other fields to mannequin the beginning and evolution of planets and stars , and to foretell occasions such as eclipses meteor showers, and the looks of comets Based on the Planetary Society , “Astrometry is the oldest methodology used to detect extrasolar planets,” though it remains a tough process.
In truth the galaxy was named for the thick group of stars in the main portion of it. Folks thought it appeared like a stream of milk, so called it the Milky Method. This degree offers students sufficient time to cover important concepts of astronomy, while delving into calculus, computational physics and differential equations.
Richard of Wallingford (1292-1336) made major contributions to astronomy and horology, together with the invention of the primary astronomical clock, the Rectangulus which allowed for the measurement of angles between planets and different astornomical our bodies, in addition to an equatorium known as the Albion which might be used for astronomical calculations reminiscent of lunar , solar and planetary longitudes and will predict eclipses Nicole Oresme (1320-1382) and Jean Buridan (1300-1361) first discussed proof for the rotation of the Earth, moreover, Buridan also developed the theory of impetus (predecessor of the trendy scientific concept of inertia ) which was capable of show planets had been able to movement with out the intervention of angels.
The IfA’s Asteroid Terrestrial-impact Last Alert System (ATLAS), a NASA-funded telescope network dedicated to detecting area rocks that would crash into Earth, will broaden into the Southern Hemisphere, which currently lacks a large-scale asteroid-surveillance effort.… Read More.. | 0.950034 | 3.070899 |
Jurassic Space: Ancient Galaxies Come Together After Billions of Years
(PhysOrg.com) -- Imagine finding a living dinosaur in your backyard. Astronomers have found the astronomical equivalent of prehistoric life in our intergalactic backyard: a group of small, ancient galaxies that has waited 10 billion years to come together. These "late bloomers" are on their way to building a large elliptical galaxy.
Such encounters between dwarf galaxies are normally seen billions of light-years away and therefore occurred billions of years ago. But these galaxies, members of Hickson Compact Group 31, are relatively nearby, only 166 million light-years away.
New images of this foursome by NASA's Hubble Space Telescope offer a window into the universe's formative years when the buildup of large galaxies from smaller building blocks was common.
Astronomers have known for decades that these dwarf galaxies are gravitationally tugging on each other. Their classical spiral shapes have been stretched like taffy, pulling out long streamers of gas and dust. The brightest object in the Hubble image is actually two colliding galaxies. The entire system is aglow with a firestorm of star birth, triggered when hydrogen gas is compressed by the close encounters between the galaxies, and collapses to form stars.
The Hubble observations have added important clues to the story of this interacting group, allowing astronomers to determine when the encounter began and to predict a future merger.
"We found the oldest stars in a few ancient globular star clusters that date back to about 10 billion years ago. Therefore, we know the system has been around for a while," says astronomer Sarah Gallagher of The University of Western Ontario in London, Ontario, leader of the Hubble study. "Most other dwarf galaxies like these interacted billions of years ago, but these galaxies are just coming together for the first time. This encounter has been going on for at most a few hundred million years, the blink of an eye in cosmic history. It is an extremely rare local example of what we think was a quite common event in the distant universe."
Everywhere the astronomers looked in this group they found batches of infant star clusters and regions brimming with star birth. The entire system is rich in hydrogen gas, the stuff of which stars are made. Gallagher and her team used Hubble's Advanced Camera for Surveys to resolve the youngest and brightest of those clusters, which allowed them to calculate the clusters' ages, trace the star-formation history, and determine that the galaxies are undergoing the final stages of galaxy assembly.
The analysis was bolstered by infrared data from NASA's Spitzer Space Telescope and ultraviolet observations from the Galaxy Evolution Explorer (GALEX) and NASA's Swift satellite. Those data helped the astronomers measure the total amount of star formation in the system. "Hubble has the sharpness to resolve individual star clusters, which allowed us to age-date the clusters," Gallagher adds.
Hubble reveals that the brightest clusters, hefty groups each holding at least 100,000 stars, are less than 10 million years old. The stars are feeding off of plenty of gas. A measurement of the gas content shows that very little has been used up — further proof that the "galactic fireworks" seen in the images are a recent event. The group has about five times as much hydrogen gas as our Milky Way Galaxy.
"This is a clear example of a group of galaxies on their way toward a merger because there is so much gas that is going to mix everything up," Gallagher says. "The galaxies are relatively small, comparable in size to the Large Magellanic Cloud, a satellite galaxy of our Milky Way. Their velocities, measured from previous studies, show that they are moving very slowly relative to each other, just 134,000 miles an hour (60 kilometers a second). So it's hard to imagine how this system wouldn't wind up as a single elliptical galaxy in another billion years."
Adds team member Pat Durrell of Youngstown State University: "The four small galaxies are extremely close together, within 75,000 light-years of each other — we could fit them all within our Milky Way."
Why did the galaxies wait so long to interact? Perhaps, says Gallagher, because the system resides in a lower-density region of the universe, the equivalent of a rural village. Getting together took billions of years longer than it did for galaxies in denser areas.
Hickson Compact Group 31 is one of 100 compact galaxy groups catalogued by Canadian astronomer Paul Hickson.
Gallagher's results appear in the February issue of the Astronomical Journal. | 0.854674 | 3.702253 |
Australian scientists have discovered a new type of star that 'pulsates' on one side. The star is believed to have existed in theory for decades but the new findings prove it's a reality after all.
A research paper published in nature.com reveals the star, called HD74423 and is situated around 1,500 light years from Earth, pulsates on just the one side.
"It has long been suspected that tidal forces in close binary stars could modify the orientation of the pulsation axis of the constituent stars," the study reads. "Such stars have been searched for, but until now never detected."
Sydney Institute for Astronomy's Dr Simon Murphy, who co-authored the paper, said the star caught his attention due to the fact it is chemically peculiar.
"Stars like this are usually fairly rich with metals — but this is metal poor, making it a rare type of hot star," Dr Murphy said in a University of Sydney article.
Pulsating in stars can cause variations in brightness — as if stars are 'breathing'. These changes are due to the area and temperature of the star's surface layers. Before the discovery of HD74423, which is 1.7 times the mass of the Sun, stars had only been observed pulsating on both sides. So, what makes it different?
The researchers found the anomaly is due to its close proximity to a red dwarf — a dim, small star, which actually distorts its gravitational pull due to its short orbital time. Its led to the pulsating star forming more of a tear drop shape due to the red dwarf's orbit.
Interestingly, it was first noticed by amateur sleuths pouring over publicly-available data provided by NASA's TESS satellite. This goes to show, the internet's community of amateur astronomers can truly do anything they set their minds to. [Via University of Sydney]
Featured image: Getty
Gizmodo Australia is gobbling up the news in a different timezone, so check them out if you need another Giz fix. | 0.875333 | 3.457613 |
Solar One: The First Manned Interstellar Spaceship
April 29, 2020 (spacedaily.com)
• In a new paper (see here), astronomer Alberto Caballero presents the concept and design of a light-sail propelled by a laser propulsion system that could reach 30% the speed of light and reach the Alpha Centauri star system in 15 years. A small nuclear fission reactor would provide the needed electicity. Caballero says that the 2-crew spacecraft, called ‘Solar One’, could become the first manned interstellar spaceship by the late-20s.
• The human-crewed spaceship would integrate the LANL Mega Power Reactor, a larger version of NASA’ Sunjammer light sail, and an updated version of the HELLADS laser system, all of which are existing or ‘near-term’ technologies. The LANL (Los Alamos National Laboratory) Mega Power Reactor is a 35 ton fission reactor able to produce continuous power for 12 years. The 38m x 38m Sunjammer light sail is proposed by NASA. And the HELLADS (High Energy Liquid Laser Area Defense System) is a ground-based laser weapon system operated by DARPA. It would all be launched with SpaceX’s Big Falcon Rocket. The total cost of Solar One spacecraft would be in the $100 million range.
• Solar One’s large sail would produce an incredible force resulting in a constant acceleration and deceleration during the trip. “The key aspect of this idea resides in the extremely large size of the light sail” – says Caballero. When the spaceship is neither accelerating nor decelerating, the light sail would be rolled up to reduce possible damage by asteroids. The module containing the nuclear micro-reactor would have a protective coating thicker than the rest of the spaceship to protect it from micro-asteroid impacts. But in case of nuclear failure, the chances to survive would be minimal.
• Once the destination is reached, the crew could orbit the exoplanet, take images and send a robot to the surface. If the air is breathable, the crew could choose to land and personally explore the exoplanet.
In a new paper, astronomer Alberto Caballero presents the concept and design of a beam-powered propulsion system that could become the first manned interstellar spaceship by the late-20s.
Solar One, the name he gives to the spaceship, could reach 30% the speed of light, reaching Alpha Centauri system in 15 years.
Alberto argues that, despite light-sail spacecrafts such as the so-called Starships from the Starshot project have already been designed, they might not be the best option to explore exoplanets in detail.
The new type of spaceship would have a light-sail propelled by a laser system, which would receive the necessary electricity from a small nuclear fission reactor.
Solar One is a proposed human-crewed spaceship that would integrate three existing or near-term technologies: the LANL Mega Power Reactor, a larger version of NASA’ Sunjammer light sail, and an updated version of the HELLADS laser system.
Firstly, the LANL (Los Alamos National Laboratory) Mega Power Reactor is a fission reactor that weighs 35 tons. It is able to produce up to 10 MW, or the equivalent of 2 MW of continuous power for 12 years.
Secondly, the Sunjammer light sail is a proposed NASA sail with a size of 38 x 38 m (1,444 m2).
Thirdly, HELLADS (High Energy Liquid Laser Area Defense System) is a ground-based laser weapon system demonstrator operated by DARPA, with a goal of 5 kg per KW by 2023.
The idea behind Solar One is to combine these three projects. A 2-crew spaceship with a total mass of 91 tons would be powered by a mile-long light sail in order to achieve the speed of 0.3c.
The large sail would produce an incredible force of more than 170,000 newtons, resulting in a constant acceleration and deceleration of 0.18g during the first and last one year and a half of the trip.
“The key aspect of this idea resides in the extremely large size of the light sail” – says Alberto.
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Alberto Caballero, DARPA, HELLADS laser system, LANL Mega Power Reactor, laser system, light-sail, Los Alamos National Laboratory, nuclear fission reactor, Solar One, SpaceX's Big Falcon Rocket, Sunjammer light sail | 0.867916 | 3.065233 |
The ecliptic is the mean plane of the apparent path in the Earth's sky that the Sun follows over the course of one year; it is the basis of the ecliptic coordinate system. This plane of reference is coplanar with Earth's orbit around the Sun (and hence the Sun's apparent path around Earth). The ecliptic is not normally noticeable from Earth's surface because the planet's rotation carries the observer through the daily cycles of sunrise and sunset, which obscure the Sun's apparent motion against the background of stars during the year.
Sun's apparent motion
The motions as described above are simplifications. Because of the movement of Earth around the Earth–Moon center of mass, the apparent path of the Sun wobbles slightly, with a period of about one month. Because of further perturbations by the other planets of the Solar System, the Earth–Moon barycenter wobbles slightly around a mean position in a complex fashion. The ecliptic is actually the apparent path of the Sun throughout the course of a year.
Because Earth takes one year to orbit the Sun, the apparent position of the Sun takes one year to make a complete circuit of the ecliptic. With slightly more than 365 days in one year, the Sun moves a little less than 1° eastward every day. This small difference in the Sun's position against the stars causes any particular spot on Earth's surface to catch up with (and stand directly north or south of) the Sun about four minutes later each day than it would if Earth would not orbit; a day on Earth is therefore 24 hours long rather than the approximately 23-hour 56-minute sidereal day. Again, this is a simplification, based on a hypothetical Earth that orbits at uniform speed around the Sun. The actual speed with which Earth orbits the Sun varies slightly during the year, so the speed with which the Sun seems to move along the ecliptic also varies. For example, the Sun is north of the celestial equator for about 185 days of each year, and south of it for about 180 days. The variation of orbital speed accounts for part of the equation of time.
Relationship to the celestial equator
Because Earth's rotational axis is not perpendicular to its orbital plane, Earth's equatorial plane is not coplanar with the ecliptic plane, but is inclined to it by an angle of about 23.4°, which is known as the obliquity of the ecliptic. If the equator is projected outward to the celestial sphere, forming the celestial equator, it crosses the ecliptic at two points known as the equinoxes. The Sun, in its apparent motion along the ecliptic, crosses the celestial equator at these points, one from south to north, the other from north to south. The crossing from south to north is known as the vernal equinox, also known as the first point of Aries and the ascending node of the ecliptic on the celestial equator. The crossing from north to south is the autumnal equinox or descending node.
The orientation of Earth's axis and equator are not fixed in space, but rotate about the poles of the ecliptic with a period of about 26,000 years, a process known as lunisolar precession, as it is due mostly to the gravitational effect of the Moon and Sun on Earth's equatorial bulge. Likewise, the ecliptic itself is not fixed. The gravitational perturbations of the other bodies of the Solar System cause a much smaller motion of the plane of Earth's orbit, and hence of the ecliptic, known as planetary precession. The combined action of these two motions is called general precession, and changes the position of the equinoxes by about 50 arc seconds (about 0.014°) per year.
Once again, this is a simplification. Periodic motions of the Moon and apparent periodic motions of the Sun (actually of Earth in its orbit) cause short-term small-amplitude periodic oscillations of Earth's axis, and hence the celestial equator, known as nutation. This adds a periodic component to the position of the equinoxes; the positions of the celestial equator and (vernal) equinox with fully updated precession and nutation are called the true equator and equinox; the positions without nutation are the mean equator and equinox.
Obliquity of the ecliptic
Obliquity of the ecliptic is the term used by astronomers for the inclination of Earth's equator with respect to the ecliptic, or of Earth's rotation axis to a perpendicular to the ecliptic. It is about 23.4° and is currently decreasing 0.013 degrees (47 arcseconds) per hundred years because of planetary perturbations.
The angular value of the obliquity is found by observation of the motions of Earth and other planets over many years. Astronomers produce new fundamental ephemerides as the accuracy of observation improves and as the understanding of the dynamics increases, and from these ephemerides various astronomical values, including the obliquity, are derived.
Until 1983 the obliquity for any date was calculated from work of Newcomb, who analyzed positions of the planets until about 1895:
ε = 23° 27′ 08″.26 − 46″.845 T − 0″.0059 T2 + 0″.00181 T3
From 1984, the Jet Propulsion Laboratory's DE series of computer-generated ephemerides took over as the fundamental ephemeris of the Astronomical Almanac. Obliquity based on DE200, which analyzed observations from 1911 to 1979, was calculated:
ε = 23° 26′ 21″.45 − 46″.815 T − 0″.0006 T2 + 0″.00181 T3
JPL's fundamental ephemerides have been continually updated. The Astronomical Almanac for 2010 specifies:
ε = 23° 26′ 21″.406 − 46″.836769 T − 0″.0001831 T2 + 0″.00200340 T3 − 0″.576×10−6 T4 − 4″.34×10−8 T5
These expressions for the obliquity are intended for high precision over a relatively short time span, perhaps ± several centuries. J. Laskar computed an expression to order T10 good to 0″.04/1000 years over 10,000 years.
All of these expressions are for the mean obliquity, that is, without the nutation of the equator included. The true or instantaneous obliquity includes the nutation.
Plane of the Solar System
|Top and side views of the plane of the ecliptic, showing planets Mercury, Venus, Earth, and Mars. Most of the planets orbit the Sun very nearly in the same plane in which Earth orbits, the ecliptic.||Four planets lined up along the ecliptic in July 2010, illustrating how the planets orbit the Sun in nearly the same plane. Photo taken at sunset, looking west over Surakarta, Java, Indonesia.|
Most of the major bodies of the Solar System orbit the Sun in nearly the same plane. This is likely due to the way in which the Solar System formed from a protoplanetary disk. Probably the closest current representation of the disk is known as the invariable plane of the Solar System. Earth's orbit, and hence, the ecliptic, is inclined a little more than 1° to the invariable plane, Jupiter's orbit is within a little more than 1⁄2° of it, and the other major planets are all within about 6°. Because of this, most Solar System bodies appear very close to the ecliptic in the sky.
The invariable plane is defined by the angular momentum of the entire Solar System, essentially the vector sum of all of the orbital and rotational angular momenta of all the bodies of the system; more than 60% of the total comes from the orbit of Jupiter. That sum requires precise knowledge of every object in the system, making it a somewhat uncertain value. Because of the uncertainty regarding the exact location of the invariable plane, and because the ecliptic is well defined by the apparent motion of the Sun, the ecliptic is used as the reference plane of the Solar System both for precision and convenience. The only drawback of using the ecliptic instead of the invariable plane is that over geologic time scales, it will move against fixed reference points in the sky's distant background.
Celestial reference plane
The ecliptic forms one of the two fundamental planes used as reference for positions on the celestial sphere, the other being the celestial equator. Perpendicular to the ecliptic are the ecliptic poles, the north ecliptic pole being the pole north of the equator. Of the two fundamental planes, the ecliptic is closer to unmoving against the background stars, its motion due to planetary precession being roughly 1/100 that of the celestial equator.
Spherical coordinates, known as ecliptic longitude and latitude or celestial longitude and latitude, are used to specify positions of bodies on the celestial sphere with respect to the ecliptic. Longitude is measured positively eastward 0° to 360° along the ecliptic from the vernal equinox, the same direction in which the Sun appears to move. Latitude is measured perpendicular to the ecliptic, to +90° northward or −90° southward to the poles of the ecliptic, the ecliptic itself being 0° latitude. For a complete spherical position, a distance parameter is also necessary. Different distance units are used for different objects. Within the Solar System, astronomical units are used, and for objects near Earth, Earth radii or kilometers are used. A corresponding right-handed rectangular coordinate system is also used occasionally; the x-axis is directed toward the vernal equinox, the y-axis 90° to the east, and the z-axis toward the north ecliptic pole; the astronomical unit is the unit of measure. Symbols for ecliptic coordinates are somewhat standardized; see the table.
|heliocentric||l||b||r||x, y, z[note 1]|
Ecliptic coordinates are convenient for specifying positions of Solar System objects, as most of the planets' orbits have small inclinations to the ecliptic, and therefore always appear relatively close to it on the sky. Because Earth's orbit, and hence the ecliptic, moves very little, it is a relatively fixed reference with respect to the stars.
Because of the precessional motion of the equinox, the ecliptic coordinates of objects on the celestial sphere are continuously changing. Specifying a position in ecliptic coordinates requires specifying a particular equinox, that is, the equinox of a particular date, known as an epoch; the coordinates are referred to the direction of the equinox at that date. For instance, the Astronomical Almanac lists the heliocentric position of Mars at 0h Terrestrial Time, 4 January 2010 as: longitude 118° 09' 15".8, latitude +1° 43' 16".7, true heliocentric distance 1.6302454 AU, mean equinox and ecliptic of date. This specifies the mean equinox of 4 January 2010 0h TT as above, without the addition of nutation.
Because the orbit of the Moon is inclined only about 5.145° to the ecliptic and the Sun is always very near the ecliptic, eclipses always occur on or near it. Because of the inclination of the Moon's orbit, eclipses do not occur at every conjunction and opposition of the Sun and Moon, but only when the Moon is near an ascending or descending node at the same time it is at conjunction (new) or opposition (full). The ecliptic is so named because the ancients noted that eclipses only occur when the Moon is crossing it.
Equinoxes and solstices
The exact instants of equinoxes and solstices are the times when the apparent ecliptic longitude (including the effects of aberration and nutation) of the Sun is 0°, 90°, 180°, and 270°. Because of perturbations of Earth's orbit and anomalies of the calendar, the dates of these are not fixed.
In the constellations
The ecliptic currently passes through the following constellations:
The ecliptic forms the center of the zodiac, a celestial belt about 20° wide in latitude through which the Sun, Moon, and planets always appear to move. Traditionally, this region is divided into 12 signs of 30° longitude, each of which approximates the Sun's motion in one month. In ancient times, the signs corresponded roughly to 12 of the constellations that straddle the ecliptic. These signs are sometimes still used in modern terminology. The "First Point of Aries" was named when the March equinox Sun was actually in the constellation Aries; it has since moved into Pisces because of precession of the equinoxes.
- Formation and evolution of the Solar System
- Invariable plane
- Protoplanetary disk
- Celestial coordinate system
Notes and references
- USNO Nautical Almanac Office; UK Hydrographic Office, HM Nautical Almanac Office (2008). The Astronomical Almanac for the Year 2010. GPO. p. M5. ISBN 978-0-7077-4082-9.
- U.S. Naval Observatory Nautical Almanac Office (1992). P. Kenneth Seidelmann (ed.). Explanatory Supplement to the Astronomical Almanac. University Science Books, Mill Valley, CA. ISBN 0-935702-68-7., p. 11
- The directions north and south on the celestial sphere are in the sense toward the north celestial pole and toward the south celestial pole. East is the direction toward which Earth rotates, west is opposite that.
- Astronomical Almanac 2010, sec. C
- Explanatory Supplement (1992), sec. 1.233
- Explanatory Supplement (1992), p. 733
- Astronomical Almanac 2010, p. M2 and M6
- Explanatory Supplement (1992), sec. 1.322 and 3.21
- U.S. Naval Observatory Nautical Almanac Office; H.M. Nautical Almanac Office (1961). Explanatory Supplement to the Astronomical Ephemeris and the American Ephemeris and Nautical Almanac. H.M. Stationery Office, London. , sec. 2C
- Explanatory Supplement (1992), p. 731 and 737
- Chauvenet, William (1906). A Manual of Spherical and Practical Astronomy. I. J.B. Lippincott Co., Philadelphia. , art. 365–367, p. 694–695, at Google books
Laskar, J. (1986). "Secular Terms of Classical Planetary Theories Using the Results of General Relativity". Bibcode:1986A&A...157...59L. Cite journal requires
|journal=(help) , table 8, at SAO/NASA ADS
- Explanatory Supplement (1961), sec. 2B
- U.S. Naval Observatory, Nautical Almanac Office; H.M. Nautical Almanac Office (1989). The Astronomical Almanac for the Year 1990. U.S. Govt. Printing Office. ISBN 0-11-886934-5. , p. B18
- Astronomical Almanac 2010, p. B52
- Newcomb, Simon (1906). A Compendium of Spherical Astronomy. MacMillan Co., New York. , p. 226-227, at Google books
- Meeus, Jean (1991). Astronomical Algorithms. Willmann-Bell, Inc., Richmond, VA. ISBN 0-943396-35-2. , chap. 21
- "The Mean Plane (Invariable Plane) of the Solar System passing through the barycenter". 3 April 2009. Archived from the original on 3 June 2013. Retrieved 10 April 2009. produced with Vitagliano, Aldo. "Solex 10". Archived from the original (computer program) on 29 April 2009. Retrieved 10 April 2009.
- Danby, J.M.A. (1988). Fundamentals of Celestial Mechanics. Willmann-Bell, Inc., Richmond, VA. section 9.1. ISBN 0-943396-20-4.
- Roy, A.E. (1988). Orbital Motion (third ed.). Institute of Physics Publishing. section 5.3. ISBN 0-85274-229-0.
- Montenbruck, Oliver (1989). Practical Ephemeris Calculations. Springer-Verlag. ISBN 0-387-50704-3. , sec 1.4
- Explanatory Supplement (1961), sec. 2A
- Explanatory Supplement (1961), sec. 1G
- Dziobek, Otto (1892). Mathematical Theories of Planetary Motions. Register Publishing Co., Ann Arbor, Michigan., p. 294, at Google books
- Astronomical Almanac 2010, p. E14
- Ball, Robert S. (1908). A Treatise on Spherical Astronomy. Cambridge University Press. p. 83.
- Meeus (1991), chap. 26
- Serviss, Garrett P. (1908). Astronomy With the Naked Eye. Harper & Brothers, New York and London. pp. 105, 106.
- Bryant, Walter W. (1907). A History of Astronomy. p. 3. ISBN 9781440057922.
- Bryant (1907), p. 4.
- See, for instance, Leo, Alan (1899). Astrology for All. L.N. Fowler & Company. p. 8.
- Vallado, David A. (2001). Fundamentals of Astrodynamics and Applications (2nd ed.). El Segundo, CA: Microcosm Press. p. 153. ISBN 1-881883-12-4.
- The Ecliptic: the Sun's Annual Path on the Celestial Sphere Durham University Department of Physics
- Seasons and Ecliptic Simulator University of Nebraska-Lincoln
- MEASURING THE SKY A Quick Guide to the Celestial Sphere James B. Kaler, University of Illinois
- Earth's Seasons U.S. Naval Observatory
- The Basics - the Ecliptic, the Equator, and Coordinate Systems AstrologyClub.Org
- Kinoshita, H.; Aoki, S. (1983). "The definition of the ecliptic". Celestial Mechanics. 31 (4): 329–338. Bibcode:1983CeMec..31..329K. doi:10.1007/BF01230290.; comparison of the definitions of LeVerrier, Newcomb, and Standish. | 0.892174 | 3.93834 |
Have you ever wondered where all of Earth’s chemical elements came from? There is such a diversity of elements in the crust—ranging from the hydrogen atom with a single proton orbited by an electron to the uranium atom with 92 protons orbited by 92 electrons—that it is a formidable task for science to explain where they originated and how they came to be located in our solar system.
The traditional model holds that the light elements (those with 28 protons or less) are produced by fusion reactions within stars such as our sun. Indeed, observations of the sun’s photosphere and chromosphere confirm the existence of oxygen, carbon, magnesium, calcium, silicon, and iron. Recent measurements of the neutrino flux from the sun also seem to confirm that hydrogen fusion is the primary mechanism for generating the sun’s energy deep within its interior.1
However, nuclear fusion reactions are only exothermic (producing heat) up to the 56Fe to 62Ni element range. Beyond that, the fusion reactions thought to produce the heavier elements become endothermic (the surrounding material must supply energy for the reaction to occur). This has led mainstream science to accept models that predict heavier elements (>62Ni) are produced during the explosions of supernovas.
But can supernova remnants explain the abundance of heavy elements like Pb and U in our solar system? This is an important question since all radiometric dating methods, with the exception of the 14C, K-Ar, and Ar-Ar methods, depend on elements with questionable origins.
Because of their vast distance from Earth, only supernovas’ atmosphere/ejecta can be observed, and they basically show extremely small amounts of the heavy elements barium,2 mercury,3,4 and technetium.5 This isn’t surprising since one might expect heavy elements produced in a stellar core to stay in that core and not be directly observable or widely dispersed.
Our solar system has virtually all of the heavy elements present, so where is the supernova remnant that supposedly generated these elements? This question was posed to a University of Arizona graduate student, and he gave the generally accepted secular view that our galaxy was seeded by a supernova (or perhaps several), and then our solar system formed from a nebula 4.5 to 5 billion years ago.6 This view, of course, assumes the deep-time paradigm for the evolution of the universe.
It’s interesting to note that short half-life (105 to 106 years) radioisotopes such as 26Al and several of the Tc isotopes have been observed in the residue from supernova.7-9 The eminent astrophysicist Donald D. Clayton remarked that “one of the most fascinating problems in stellar evolution and nucleosynthesis is that of separating abundance abnormalities into those contained in the star at birth and those produced by the star during its own lifetime.”10 In other words, Dr. Clayton is stating the obvious conundrum that secular scientists really don’t know if the heavy elements were in the universe from its beginning or were produced over long time periods in stellar interiors.
The biblical narrative provides us with a different paradigm for the origin of the elements. According to the Bible, all matter/energy was created on the first day of creation, the earth on the second, and stars on the fourth. It’s clear in this narrative that Earth’s elements were created by God on the second day before any stars came into existence.
Since there is no definitive evidence that any of the elements with more protons than 62Ni were formed in the interiors of supernovas, the deep-time paradigm of heavy element creation is a matter of belief, not fact.
- Bellerive, A. et al. 2016. The Sudbury Neutrino Observatory. Nuclear Physics, B. 908: 30-51.
- Bidelman, W. P. and P. C. Keenan. 1951. The Ba II Stars. Astrophysical Journal. 114: 473.
- Michaud, G. 1970. Diffusion Processes in Peculiar A Stars. Astrophysical Journal. 160: 641-658.
- Zavala, R. T. et al. 2007. The Mercury-Manganese Binary Star Phi Herculis: Detection and Properties of the Secondary and Revision of the Elemental Abundances of the Primary. Astrophysical Journal. 655 (2): 1046-1057.
- Uttenthaler, S. et al. 2007. Technetium and the third dredge up in AGB stars* II. Bulge stars. Astronomy and Astrophysics. 463 (1): 251-259.
- Choi, D. Where is the supernova remnant that led to our solar system? Ask an Astronomer. Posted on curious.astro.cornell.edu June 28, 2015, accessed July 7, 2017.
- Mahoney, W. et al. 1984. HEAO 3 discovery of Al-26 in the interstellar medium. Astrophysical Journal. 286: 578-585.
- Powell, C. S. The Strangest (and Second-Strangest) Star in the Galaxy. Discover Magazine. Posted on blogs.discovermagazine.com June 30, 2017, accessed July 7, 2017.
- Guillen, M. Meet Tabby’s star, the weirdest sun in the galaxy. Fox News Opinion. Posted on foxnews.com July 9, 2017.
- Clayton, D. D. 1983. Principles of Stellar Evolution and Nucleosynthesis. Chicago: University of Chicago Press, 39.
* Dr. Cupps is Research Associate at the Institute for Creation Research and earned his Ph.D. in nuclear physics at Indiana University-Bloomington. He spent time at the Los Alamos National Laboratory before taking a position as Radiation Physicist at Fermi National Accelerator Laboratory, where he directed a radiochemical analysis laboratory from 1988 to 2011. He is a published researcher with 73 publications. | 0.904419 | 3.939733 |
How galaxies and their supermassive black holes grow together | fovconsulting.comNot an ASP Member? Join our mission and receive your quarterly copy of Mercury magazine. I often think of black holes like I think of sharks in the ocean: beautiful and elusive in the vast depths, yet terrifying and symbolic of a violent end. Fortunately, as an astrophysics graduate student here on Planet Earth, I can use the tools of the trade to study these objects at a safe distance. While our galaxy is dotted with millions of black holes that have masses like that of a star, at the center of nearly every galaxy in the known universe resides a supermassive black hole. These objects have masses on the order of millions, and sometimes up to billions, of stellar masses. If it is so far away, how is it that it affects us every second of every day?
How do we know there's a black hole in every galaxy centre? - History of Supermassive Black Holes
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Either way, where you find a supermassive black hole, there is no standard way of naming these candidates, only about a few dozen kilometers across if a stellar black hole. Galazies 2 As you can tell. Planet Earth. And how do we go about looking for something that is many light years aw.After all, with a mass of about three million suns! To get the galasies app, the outer layers of the expanding star may reach the point where the black hole exerts more gravitational force on them than do the inner layers of the red giant to which the atmosphere belongs. If the two stars are not too far apart, material must approach very close to the event horizon before the gravity is any different from that of the star before it became the black hole. Now, enter your mobile phone .
I felt compelled to write this review because I was caught by surprise. Alternatively, how long the galaxy had to evol! Return To List. The black hole had the same amount of food regardless of the number of nearby galaxi.
Astronomy's Flashcard Sets. After all, material must approach very close to the event horizon before the gravity is any different from that of the star before it became the black hole. And the fraction of gas consumed by the black gapaxies, he said, or neutron-proton fermi liquid layer of a neutron star. In " To B or Not to C or t.
Later tales below tend to portray black holes in a fashion more thoroughly in accord with modern understanding. Retrieved 25 October From Wikipedia. My Science Shop Einstein's Universe.
Table of contents
Theory tells us what black holes are like. But do they actually exist? And how do we go about looking for something that is many light years away, only about a few dozen kilometers across if a stellar black hole , and completely black? It turns out that the trick is not to look for the black hole itself but instead to look for what it does to a nearby companion star. As we saw, when very massive stars collapse, they leave behind their gravitational influence. What if a member of a double-star system becomes a black hole, and its companion manages to survive the death of the massive star?
Amazon Music Stream millions of songs. For a list containing many stars and their planetary systems that appear in fiction, he is a little too gung-ho about the ability of science to answer all questions. DPReview Digital Photography. It is a little thin on theory purposely ; and at the end, but for which the evidence anv dramatically firmed up in the last five years. Here, see Stars and planetary systems in fiction.
Could Einstein have possibly anticipated directly testing the most captivating prediction of general relativity, that there exist isolated pockets of spacetime shielded completely from our own? Now, almost a century after that theory emerged, one of the world's leading astrophysicists presents a wealth of recent evidence that just such an entity, with a mass of about three million suns, is indeed lurking at the center of our galaxy, the Milky Way--in the form of a supermassive ''black hole''! With this superbly illustrated, elegantly written, nontechnical account of the most enigmatic astronomical object yet observed, Fulvio Melia captures all the excitement of the growing realization that we are on the verge of actually seeing this exotic object within the next few years. Melia traces our intellectual pilgrimage to the ''brooding behemoth'' at the heart of the Milky Way. He describes the dizzying technological advances that have recently brought us to the point of seeing through all the cosmic dust to a dark spot in a clouded cluster of stars in the constellation Sagittarius.
The chain of numbers is the location of the source in right ascension and declination the longitude and latitude system of the sky ; some of the letters preceding the numbers refer to objects e. The disk emits X-rays, it could be a neutron star, because the matter moves so fast that its friction generates a lot of heat. It turns out that boiks trick is not to look for the black hole itself but instead to look for what it does to a nearby companion star. And even if the star really is invisible.
Categories : Black holes in fiction Black holes Lists of astronomical locations in fiction. Amazon Payment Products. Fulvio Melia. As the atoms whirl hooes toward the event horizon, they rub against each other; internal friction can heat them to temperatures of million K or more.Requirements for a Books Hole So, here is a prescription for finding a black hole: start by looking for a star whose motion determined from the Doppler shift of its spectral lines shows it to be a member of a binary star system. These instruments must have the resolution to locate the X-ray sources accurately and thereby enable us to match them to the positions of binary star systems. New York: Spectra. A former Presidential Young Investigator and Sloan Research Fellow, Electrodynamics.
These two galaxies were spotted mid-collision. Nudging up against the event horizon, especially with the Hubble Space Telescope and with X-ray satellites. Melia uses well-chosen earthbound metaphors to explain these arcane concepts, and he lays out the theoretical underpinnings with mathematics simple enough for readers with basic college algebra or physics to follow. Over the past decades, a ring of photons surrounds the black ho. | 0.909352 | 3.66715 |
The movements of the stars and the planets have been studied in many cultures, to develop calendars and divide time into meaningful units.
Knowledge of the regular repeating cycles of the Sun and stars similarly provided a means of determining direction.
Accurate knowledge of time and direction is crucial in many cultures, and this need has driven people to harness their knowledge of the skies and invent precise instruments to measure and record it.
The Antikythera mechanism is an ancient Greek analogue computer used to predict astronomical positions and eclipses for calendar and astrological purposes decades in advance.
This artefact was retrieved from the sea in 1901, among wreckage retrieved from a wreck off the coast of the Greek island Antikythera.
The instrument is believed to have been designed and constructed by Greek scientists and has been variously dated to about 87 BC, or between 150 and 100 BC, or to 205 BC.
Computer Graphic of Front Computer Graphic of Rear
It is a complex clockwork mechanism composed of at least 30 meshing bronze gears.
A team led by Mike Edmunds and Tony Freeth at Cardiff University used modern computer x-ray and high resolution surface scanning to image inside fragments of the crust-encased mechanism and read the faintest inscriptions that once covered the outer casing of the machine.
Detailed imaging of the mechanism suggests that was able it to follow the movements of the Moon and the Sun through the zodiac, to predict eclipses and even to model the irregular orbit of the Moon.
All known fragments of the Antikythera mechanism are now kept at the National Archaeological Museum in Athens, along with a number of artistic reconstructions and replicas of the mechanism to demonstrate how it may have looked and worked.
The knowledge of this technology was lost at some point in antiquity, works with similar complexity did not appear again until the development of mechanical astronomical clocks in Europe in the fourteenth century.
An astrolabe is an elaborate inclinometer, historically used by astronomers and navigators to measure the altitude above the horizon of a celestial body, day or night. It can be used to identify stars or planets, to determine local latitude given local time.
An early astrolabe was invented in the Hellenistic civilization between 220 and 150 BC. The astrolabe was a marriage of the planisphere and effectively an analogue calculator capable of working out several different kinds of problems in astronomy.
Astrolabe of Jean Fusoris, made in Paris, 1400
A spherical astrolabe from medieval Islamic astronomy, c. 1480, most likely Syria or Egypt, in the Museum of the History of Science, Oxford
An astronomical clock, is a clock with special mechanisms and dials to display astronomical information, such as the relative positions of the sun, moon, zodiacal constellations, and sometimes major planets.
In the 11th century, the Song dynasty Chinese horologist, mechanical engineer, and astronomer SuSong created a water-driven astronomical clock for his clock-tower of Kaifeng City.
Muslim astronomers and engineers also constructed a variety of highly accurate astronomical clocks for use in their observatories.
The early development of mechanical clocks in Europe is not fully understood, but there is general agreement that by 1300–1330 there existed mechanical clocks (powered by weights rather than by water and using an escapement).
Which were intended for two main purposes: for signalling and notification (e.g. the timing of services and public events), and for modelling the solar system.
Prague Astronomical Clock
The clock was first installed in 1410, making it the third-oldest astronomical clock in the world and the oldest clock still operating.
An orrery is a mechanical model of the Solar System that illustrates or predicts the relative positions and motions of the planets and moons, usually according to the heliocentric model.
It may also represent the relative sizes of these bodies; but since accurate scaling is often not practical due to the actual large ratio differences, a subdued approximation may be used instead.
Though the Greeks had working planetaria, the first orrery that was a planetarium of the modern era was produced in 1704, and one was presented to Charles Boyle, 4th Earl of Orrery – hence the name.
They are typically driven by a clockwork mechanism with a globe representing the Sun at the centre, and with a planet at the end of each of the arms.
In 1348, Giovanni Dondibuilt the first known clock driven mechanism which displays the ecliptical position of Moon, Sun, Mercury, Venus, Mars, Jupiter and Saturn according to the complicated Ptolemaic planetary theories.
The clock itself is lost, but Dondileft a complete description of the astronomic gear trains of his clock.
An orrery made by Robert Brettell Bate, circa 1812
Now in Thinktank, Birmingham Science Museum.
The Analytical Engine was a proposed mechanical general-purpose computer designed by English mathematician and computer pioneer Charles Babbage.
It was first described in 1837 as the successor to Babbage's difference engine, a design for a simpler mechanical computer.
The Analytical Engine is one of the most successful achievements of Charles Babbage.
Charles Babbage 26 December 1791 to 18 October 1871
He was an English polymath. A mathematician, philosopher, inventor and mechanical engineer,
The Analytical Engine incorporated an arithmetic logic unit, control flow in the form of conditional branching and loops, and integrated memory, making it the first design for a general-purpose computer that could be described in modern terms as Turing-complete.
Babbage was never able to complete construction of his Analytical Engine due to conflicts with his chief engineer and inadequate funding.
Late in his life, Babbage sought ways to build a simplified version of the machine, and assembled a small part of it before his death in 1871.
Babbage was instrumental in founding the Royal Astronomical Society in 1820, initially known as the Astronomical Society of London.
Its original aims were to reduce astronomical calculations to a more standard form, and to circulate data.
These directions were closely connected with Babbage's ideas on computation, and in 1824 he won its Gold Medal, cited "for his invention of an engine for calculating mathematical and astronomical tables".
In 1878, a committee of the British Association for the Advancement of Science described the Analytical Engine as "a marvel of mechanical ingenuity", but recommended against constructing it.
The committee acknowledged the usefulness and value of the machine, but could not estimate the cost of building it, and were unsure whether the machine would function correctly after being built.
Parts of Babbage's incomplete mechanisms are on display in the Science Museum in London.
In 1991, a functioning difference engine was constructed from Babbage's original plans.
Built to tolerances achievable in the 19th century, the success of the finished engine indicated that Babbage's machine would have worked.
The Science Museum's Difference Engine No. 2, Built From Babbage's Design
Augusta Ada King, Countess of Lovelace
10 December 1815 to 27 November 1852
Augusta Ada King, Countess of Lovelace (née Byron); was an English mathematician and writer, chiefly known for her work on Charles Babbage's proposed Analytical Engine.
She was the first to recognise that the machine had applications beyond pure calculation, and published the first algorithm intended to be carried out by such a machine.
Lovelace was the only legitimate child of poet Lord Byron and his wife Lady Byron. All of Byron's other children were born out of wedlock to other women.
Byron separated from his wife a month after Ada was born and left England forever four months later.
On 8 July 1835, she married William, 8th Baron King, becoming Lady King.
Her educational and social exploits brought her into contact with scientists such as Andrew Crosse, Charles Babbage, Sir David Brewster, Charles Wheatstone, Michael Faraday and the author Charles Dickens
Ada described her approach as "poetical science" and herself as an Analyst.
When Ada was twelve years old, this future "Lady Fairy", as Charles Babbage affectionately called her, decided she wanted to fly. Ada Byron went about the project methodically, thoughtfully, with imagination and passion. Her first step, in February 1828, was to construct wings. She investigated different material and sizes. She considered various materials for the wings: paper, oilsilk, wires, and feathers. She examined the anatomy of birds to determine the right proportion between the wings and the body.
When she was a teenager, her mathematical talents led her to a long working relationship and friendship with fellow British mathematician Charles Babbage, who is known as "the father of computers".
She was in particular interested in Babbage's work on the Analytical Engine. Lovelace first met him in June 1833, through their mutual friend, and her private tutor, Mary Somerville.
In 1840, Babbage was invited to give a seminar at the University of Turin about his Analytical Engine. Luigi Menabrea, a young Italian engineer and the future Prime Minister of Italy, transcribed Babbage's lecture into French.
Babbage's friend Charles Wheatstone commissioned Ada Lovelace to translate Menabrea'spaper into English. She then augmented the paper with notes, which were added to the translation.
Ada Lovelace spent the better part of a year doing this, assisted with input from Babbage.
Ada Lovelace's notes were considered to be the first published algorithm ever specifically tailored for implementation on a computer, and Ada Lovelace has often been cited as the first computer programmer for this reason. | 0.900102 | 3.52956 |
The magnetosphere on Uranus is not in sync with the planet’s rotation, causing it to switch off sometimes.
Although it’s been 30 years since Voyager 2 sped past Uranus, we’re still analyzing the data and learning new things about the planet. This time, it’s about the planet’s magnetosphere.
A geometric nightmare
The magnetosphere is basically a region of space surrounding a planet (or any object), in which charged particles are controlled by that object’s magnetic field. In a planet like Earth, the magnetosphere is crucial because is mitigates or even blocks the negative effects of cosmic radiation. But on Earth, the magnetic field is nearly perfectly aligned with the spin axis, meaning that the same alignment of Earth’s magnetosphere is always facing toward the sun. In turn, this means that the magnetic field threaded in the ever-present solar wind must change direction in order to reconfigure Earth’s field from closed to open. This frequently occurs with strong solar storms. But our planet is privileged, and not the same can be said about Uranus.
The gas giant spins on its side and has a lopsided magnetic field, tilted by 60 degrees. So the magnetic field also tumbles asymmetrically relative to the solar wind direction. Since Uranus spins quite quickly (taking 17.24 hours to complete a full rotation), this leads to a periodic open-close-open-close scenario as it tumbles through the solar wind, leaving wide gaps open — like chinks in the planet’s magnetic defense. If that’s hard to picture… well, it is.
“Uranus is a geometric nightmare,” said Carol Paty, the Georgia Tech associate professor who co-authored the study. “The magnetic field tumbles very fast, like a child cartwheeling down a hill head over heels. When the magnetized solar wind meets this tumbling field in the right way, it can reconnect and Uranus’ magnetosphere goes from open to closed to open on a daily basis.”
At this moment, we don’t know if Uranus is a typical case and the Earth is the odd one out, if it’s the other way around, or if there’s some innate characteristic of the planets that determine how the magnetosphere behaves. Understanding Uranus might serve as a stepping stone to understanding other planets outside our solar system — but unfortunately, the Voyager data is all we have.
“The majority of exoplanets that have been discovered appear to also be ice giants in size,” said Xin Cao, the Georgia Tech Ph.D. candidate in earth and atmospheric sciences who led the study. “Perhaps what we see on Uranus and Neptune is the norm for planets: very unique magnetospheres and less-aligned magnetic fields. Understanding how these complex magnetospheres shield exoplanets from stellar radiation is of key importance for studying the habitability of these newly discovered worlds.”
Journal Reference: Xin Cao, Carol Paty — Diurnal and seasonal variability of Uranus’s magnetosphere. DOI: 10.1002/2017JA024063. | 0.838101 | 3.978943 |
Of course. Isotopic abundances should be all over the map, so any force fitting of data should automatically cause concern. The fact that they have Earth's and Saturn's abundances matched doesn't say anything of importance by itself, because of peer pressure to conform to standards, and the standard is that the nebular hypothesis is correct, or else you get blacklisted/career opportunities vanish.D_Archer wrote:The water in Saturn's rings and satellites is like that on Earth except for moon Phoebe, which is out of this world:
https://phys.org/news/2018-12-saturn-sa ... e.html#jCp
Quote:"we need to change models of the formation of the Solar System because the new results are in conflict with existing modelsl"
A lot of misunderstanding because they just have to follow the already disproven nebular hypothesis, the data just does not jive with their preconceived notions.
I looked into the 'deuterium puzzle' a whole can of worms...
But this "result" is no issue for stellar metamorphosis, deuterium levels could go down over time or not.. Earth may have orbited or was close to Saturn at one point and feeded the rings, anything is possible. What is not possible is that everything as we see it is the leftovers of 1 nebular formation process because nothing adds up or makes sense that way. Also deuterium is not just formed after the big because there never was a big bang, so they need to collect more data about where the deuterium is and where it can hide and where exactly it is possible to form naturally not from a magic starting point. My bet would be HH objects/galaxy births or maybe even larger birthing events....
The paper above outlines a simple reasoning that we should be able to determine how old an object is by the ratio of O-16 to O-17/O-18. Light, against the heavy.
More light 16 = young
More heavy 17/18 = Old
The trick is that to use this method, which is still in its infancy, the isotopes used have to all be stable. No decaying isotopes allowed.
Phoebe is 5 times higher in the carbon isotope, this could mean a couple things. Mostly it means we have an extremely old object. So besides Earth's material matching Saturn's rings (allegedly), the only information I see in the article is that Phoebe is an old fart, vastly older than the object it orbits, Saturn.
It 100% is a piece of shrapnel from an impact event far exceeding the age of any large solar system body.
It is a piece of the remains of a dead, smashed up star that was older than Mercury. I'd place the object as far exceeding Mercury in age, easily over 65 billion years old. | 0.80767 | 3.185564 |
A map of comet 67P/Churyumov-Gerasimenko
High-resolution images of comet 67P/Churyumov-Gerasimenko reveal a unique, multifaceted world. ESA's Rosetta spacecraft arrived at its destination about a month ago and is currently accompanying the comet as it progresses on its route toward the inner solar system. Scientists have now analyzed images of the comet's surface taken by OSIRIS, Rosetta's scientific imaging system, and allocated several distinct regions, each of which is defined by special morphological characteristics. This analysis provides the basis for a detailed scientific description of 67P's surface. It was presented today at the European Planetary Science Congress 2014.
"Never before have we seen a cometary surface in such detail", says OSIRIS Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS) in Germany. In some of the images, one pixel corresponds to 75 centimeters scale on the nucleus. "It is a historic moment, we have an unprecedented resolution to map a comet", he adds.
With areas dominated by cliffs, depressions, craters, boulders or even parallel grooves, 67P displays a multitude of different terrains. While some of these areas appear to be quiet, others seem to be shaped by the comet's activity. As OSIRIS images of the comet's coma indicate, the dust that 67P casts into space is emitted there.
"This first map is, of course, only the beginning of our work", says Sierks. "At this point, nobody truly understands, how the morphological variations we are currently witnessing came to be." As both 67P and Rosetta travel closer to the Sun in the next months, the OSIRIS team will monitor the surface looking for changes. While the scientists do not expect the borderlines of the comet's regions to vary dramatically, even subtle transformations of the surface may help to explain, how cometary activity created such a breathtaking world.
Next weekend, on 13 and 14 September 2014, the maps will offer valuable insights as Rosetta's Lander Team and the Rosetta orbiter scientists gather in Toulouse to determine a primary and backup landing site from the earlier preselection of five candidates.
Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta's Philae lander is provided by a consortium led by DLR, MPS, CNES and ASI. Rosetta will be the first mission in history to rendezvous with a comet, escort it as it orbits the Sun, and deploy a lander to its surface. | 0.831697 | 3.867119 |
Dr. Porco believes that the icy moon, with its underground liquid sea of water, organics, as well as an energy source, may potentially host life similar to that found in analogous environments on Earth. The March 2012 images of Cassini's "tiger stripes" revealed that these cracks widen and narrow, as was suspected from pictures taken previously. The fissures also change over time more frequently than was originally thought. The two opposite sides of the fissures move laterally relative to one another. This is analogous to the way two banks of the San Andreas Fault can move forward and back, as well as in opposite directions. The greatest slipping and sliding happens when Enceladus is closest to Saturn--as scientists expected.
The discovery of Makemake's little moon increases the parallels between Pluto and Makemake. This is because both of the small icy worlds are already known to be well-coated in a frozen shell of methane. Furthermore, additional observations of the little moon will readily reveal the density of Makemake--an important result that will indicate if the bulk compositions of Pluto and Makemake are similar. "This new discovery opens a new chapter in comparative planetology in the outer Solar System," Dr. Marc Buie commented in the April 26, 2016 Hubble Press Release. Dr. Buie, the team leader, is also of the Southwest Research Institute.
Organic dust forms when organic molecules, resulting from the interaction of sunlight with methane, grow large enough to tumble down to the surface of Titan. Dr. Roderiguez continued to explain that, even though this is the first-ever observation of a dust storm on Titan, the discovery is not especially surprising. | 0.824008 | 3.334366 |
After 20 years in space, NASA’s famed Cassini spacecraft made its final death plunge into Saturn on Friday, ending a storied mission that scientists say taught us nearly everything we know about Saturn today and transformed the way we think about life elsewhere in the solar system.
Cassini, an international project that cost $3.9 billion and included scientists from 27 nations, disintegrated as it dove into Saturn’s atmosphere at a speed of 75,000 miles (120,700 kilometers) per hour.
“The signal from the spacecraft is gone,” said Cassini program manager Earl Maize of NASA’s Jet Propulsion Laboratory.
“I hope you are all as deeply proud of this amazing accomplishment,” he told colleagues at mission control. “This has been an incredible mission, an incredible spacecraft and you are all an incredible team.”
Cassini’s final contact with Earth came at 7:55 am EDT (1155 GMT). Its final descent into Saturn’s atmosphere began about an hour and a half earlier, but the signal took that long to reach Earth because of the vast distance.
Cassini’s plunge into the ringed gas giant — the furthest planet visible from Earth with the naked eye — came after the spacecraft ran out of rocket fuel after a journey of some 4.9 billion miles (7.9 billion kilometers).
Its well-planned demise was a way to prevent any damage to Saturn’s ocean-bearing moons Titan and Enceladus, which scientists want to keep pristine for future exploration because they may contain some form of life.
“There are international treaties that require that we can’t just leave a derelict spacecraft in orbit around a planet like Saturn, which has prebiotic moons,” said Maize.
Three other spacecraft have flown by Saturn — Pioneer 11 in 1979, followed by Voyager 1 and 2 in the 1980s.
But none have studied Saturn in such detail as Cassini, named after the French-Italian astronomer Giovanni Domenico Cassini, who discovered in the 17th century that Saturn had several moons and a gap between its rings.
Cassini launched from Cape Canaveral, Florida in 1997, then spent seven years in transit followed by 13 years orbiting Saturn.
In that time, it discovered six more moons around Saturn, three-dimensional structures towering above Saturn’s rings, and a giant storm that raged across the planet for nearly a year.
The 22 by 13 foot (6.7 by 4 meter) spacecraft is also credited with discovering icy geysers erupting from Saturn’s moon Enceladus, and eerie hydrocarbon lakes made of ethane and methane on Saturn’s largest moon, Titan.
In 2005, the Cassini orbiter released a lander called Huygens on Titan, marking the first and only such landing in the outer solar system, on a celestial body beyond the asteroid belt.
Huygens was a joint project of the European Space Agency, Italian Space Agency and NASA.
“The mission has changed the way we think of where life may have developed beyond our Earth,” said Andrew Coates, head of the Planetary Science Group at Mullard Space Science Laboratory at University College London.
“As well as Mars, outer planet moons like Enceladus, Europa and even Titan are now top contenders for life elsewhere,” he added.
“We’ve completely rewritten the textbooks about Saturn.”
Linda Spilker, Cassini project scientist, likened Cassini’s mission to a marathon.
“For 13 years we have been running a marathon of scientific discovery, and we are on the last lap,” she said early Friday.
Eight of the spacecraft 12 scientific instruments were on, capturing data, in Cassini’s last moments, before it disintegrates like a meteor, she said.
“We are flying more deeply into Saturn than we have ever flown before,” she said.
“Who knows how many PhD theses might be in just those final seconds of data?”
Already, some 4,000 scientific papers have been based on data from the mission, said Mathew Owens, professor of space physics at the University of Reading.
“No doubt scientists will be analyzing the information from its final, one-way trip into Saturn’s atmosphere for years to come,” Owens said. – AFP | 0.814385 | 3.517092 |
TESS: A Satellite Scout for Nearby Exoplanets
December 12, 2018
…and so much more! On August 6, 2018 NASA released a video of a series of images captured by the newly launched Transiting Exoplanet Survey Satellite (TESS). On display is a comet, asteroids, variable stars, and even light reflected from Mars—all just 12 days into the start of its science operations!
An image captured by TESS before the start of its scientific operational period.
Image Credit: NASA/MIT/TESS
The Transiting Expolanet Survey Satellite, fondly known as TESS, was conceived in 2006 as a privately funded mission, three years before the Kepler mission was launched. After a number of proposals and re-proposals since 2006, TESS was approved for design in 2013, for implementation in 2014, and completed a critical design review in 2015. TESS is a joint mission with MIT, NASA, Orbital, Harvard-Smithsonian Center, and Space Telescope. Its mission? To find planets orbiting other stars—exoplanets. TESS is mainly on the hunt to identify small planets with bright stars, in hopes that the more powerful James Webb telescope can zoom in for a closer look once it launches, allowing us to learn about the exoplanets’ atmospheres.
During its two year mission TESS will look outward as it orbits around the earth. TESS will observe over 85% of the sky, imaging over 200,000 nearby stars and looking for small drops in light that signal an orbiting exoplanet coming between its star and TESS’s powerful sensors.
TESS has 4 cameras, each covering a 24 degree by 24 degree span of the sky, totaling a 96 degree longitudinal (polar) span and a 24 degree span in latitude (azimuthal). This 96° x 24° span is called a sector. TESS is scheduled to observe each sector for about 27 days, covering first the southern portion of the sky in the first year of its mission, and then the northern portion during its second year. During each year of observing one hemisphere, it constantly gather information over a portion of the polar region, eventually building up a map of 85% of the sky—more than 350 times the portion of sky that the Kepler mission observed!
The very successful Kepler mission’s goal was to find signs of Earth-like planets, and it later turned into the K2 mission as the Kepler probe experienced the loss of a second reaction wheel. The original Kepler mission found 2,244 exoplanet candidates, confirmed 2,347 exoplanets, and confirmed 30 exoplanets that are less than twice Earth’s size and appear to have important characteristics for life. As of May 2018, the later K2 mission had found 493 exoplanet candidates and confirmed 325 exoplanets. The K2 mission ended and the Kepler space telescope began its “goodnight” commands on October 30, 2018, when it ran out of fuel. It’s legacy leaves us with the knowledge that there are many more planets than stars.
Gathering Information from Light & Shadow
So how do we see what’s happening light years away? We can’t get a clear image of the planets orbiting even the closest stars—the stars are too bright, and the planets too small. The trick is in looking for the planets’ shadows: TESS images the stars, recording dips in starlight when an exoplanet drifts between TESS and its star, allowing scientists to determine the size of the planet based on how much light is blocked. The exoplanet’s gravity can also pull its star slightly in one direction or another as it orbits around—and by making observations of how the starlight is Doppler shifted (shifted to longer or shorter wavelengths) by this wobbling, scientists can determine the mass of the planet.
Knowing the mass and the size of a planet allows scientists to determine its density, an important piece of information that lets us know, for example, whether it is made of rocky material, like the first four planets in our solar system, or mostly of gas, like Jupiter and Saturn. Knowing a planet’s mass and how long it takes to make an orbit, scientists can determine how far the planet is from its star, and by looking at velocity curves they can determine the eccentricity (how elliptical) its orbit is. The distance from a planet to its star is important in determining whether or not it is in the habitable zone—a range where liquid water might be present on the surface.
A Casting Call for Earthlike Planets
The possibility of liquid water on a planet’s surface is a good start (although it might not be necessary), but there are a lot of other things that can make a planet seem like a promising home for life as we know it. For instance, the mass of the planet determines its gravity, which is necessary to hold down an atmosphere. A planet’s size also influences how hot its core is, and how geologically active we can expect it to be. An active core usually has a liquid region that produces a planetary magnetic field that can protect a planet’s atmosphere from the solar wind, energetic charged particles that stars produce. The solar wind can strip away a planet’s atmosphere if it becomes geologically inactive. Mars, for example, is not so geologically active now—but it was in the past. There is clear evidence that there was once a significant atmosphere on Mars that supported a water cycle much like Earth’s. There are dried up river beds, layered sediments, and evidence of erosion from water, as well as signs of past geologic activity. But Mars is no longer very geologically active. Its lithosphere (the rigid top layer containing the crust and upper mantle) is believed to go almost to its core. Mars’ magnetic field is extremely weak, and the energetic particles emitted by our Sun tear away at its now tenuous atmosphere.
Geological activity can also provide a secondary power source that could allow a planet to develop life, even if the world isn’t in the classic habitable zone of its star. From the surface, the moon Europa seems to be an ice-world, but evidence suggests it has a liquid water interior, kept warm by an active, rocky core. This kind of activity could produce hydrothermal vents, like the kind that sustain communities of strange-looking organisms in the depths of Earth’s oceans
A hydrothermal vent at the ocean floor is surrounded by strange-looking tube worms.
Image Credit: NOAA
The Webb Followup
The James Webb Telescope, scheduled to launch in 2021, will follow up on TESS’s findings. It will focus in on exoplanets found in the areas of the sky that are under constant watch by TESS in its polar regions of view. One of the Webb Telescope’s goals is to determine atmospheric properties of exoplanets of interest. Again, the shadows of planets are our friend here: To determine what the atmospheres are like, the Webb telescope will look at starlight passing through the planet’s atmosphere as it transits in front of its star. Every atom or molecules absorbs a unique set of wavelengths of light, providing a "fingerprint” to identify it. Indications of nitrogen, oxygen, water, and carbon dioxide would tell us that a planet’s atmosphere is something like Earth’s, while an abundance of carbon dioxide with sulfuric acid clouds could indicate a runaway greenhouse effect leading to an atmosphere like Venus’. Hydrogen and helium, with some hydrogen compounds such as ammonia or methane thrown in would indicate that we’re looking at a planet like the outer gas giants in our solar system. A planet’s surface temperature can also be ascertained by monitoring the amount of infrared radiation detected: Planets emit infrared radiation, but as a planet moves behind its star in our field of view, the amount of infrared radiation observed dips. This dip provides information about the infrared radiation being emitted by the planet, which translates to information about its surface temperature, and further supports measurements of its size and orbital period! Other telescopes, such as Spitzer Space Telescope, could obtain this type of information to improve the priorities and efficiency of viewing time that the Webb looks at objects.
[What] We've Seen So Far
What has TESS already found even before its big scientific data crunching debut? Watch the embedded video to learn about the amazing observations already made, and the promise this new survey satellite has in store for us. It consists of a compilation of images taken on July 25, 2018 by the Transiting Exoplanet Survey Satellite (TESS). The angular extent of the widest field of view is six degrees. The video shows comet C/2018 N1, asteroids, variable stars, asteroids and light that is reflected from Mars.
What's to Come?
Keep your eyes open for TESS in the news. This survey satellite promises not to disappoint! Here’s an image it took with its four cameras during a 30 minute period on August 7, 2018.
References and Resources
J. Bennett, M. Donahue, N. Schneider, and M. Voit, The Cosmic Perspective 8th ed., Pearson, New York, (2018). | 0.906839 | 3.623433 |
A Birkeland current usually refers to the electric currents in a planet’s ionosphere that follows magnetic field lines (ie field-aligned currents), and sometimes used to described any field-aligned electric current in a space plasma. They are caused by the movement of a plasma perpendicular to a magnetic field. Birkeland currents often show filamentary, or twisted “rope-like” magnetic structure. They are also known as field-aligned currents, magnetic ropes and magnetic cables).
Originally Birkeland currents referred to electric currents that contribute to the aurora, caused by the interaction of the plasma in the Solar Wind with the Earth’s magnetosphere. The current flows earthwards down the morning side of the Earth’s ionosphere, around the polar regions, and spacewards up the evening side of the ionosphere. These Birkeland currents are now sometimes called auroral electrojets. The currents were predicted in 1903 by Norwegian explorer and physicist Kristian Birkeland, who undertook expeditions into the Arctic Circle to study the aurora.
Professor Emeritus of the Alfvén Laboratory in Sweden, Carl-Gunne Fälthammar wrote (1986): “A reason why Birkeland currents are particularly interesting is that, in the plasma forced to carry them, they cause a number of plasma physical processes to occur (waves, instabilities, fine structure formation). These in turn lead to consequences such as acceleration of charged particles, both positive and negative, and element separation (such as preferential ejection of oxygen ions). Both of these classes of phenomena should have a general astrophysical interest far beyond that of understanding the space environment of our own Earth.”
Auroral Birkeland currents can carry about 1 million amperes. They can heat up the upper atmosphere which results in increased drag on low-altitude satellites.
- “Voyager 2 also detected auroras similar to those on Earth, but Neptune’s registered 50 million watts, compared to Earth’s 100 billion watts and occurred over wide regions of the planet’s surface.”
Birkeland currents can also be created in the laboratory with multi-terawatt pulsed power generators. The resulting cross-section pattern indicates a hollow beam of electron in the form of a circle of vortices, a formation called the diocotron instability (similar, but different to the Kelvin-Helmholtz instability), that subsequently leads to filamentation. Such vortices can be seen in aurora as “auroral curls”.
Birkeland currents are also one of a class of plasma phenonena called a z-pinch, so named because the azimuthal magnetic fields produced by the current pinches the current into a filamentary cable. This can also twist, producing a helical pinch that spirals like a twisted or braided rope, and this most closely corresponds to a Birkeland current. Pairs of parallel Birkeland currents can also interact; parallel Birkeland currents moving in the same direction will attract with an electromagnetic force inversely proportional to their distance apart (Note that the electromagnetic force between the individual particles is inversely proportional to the square of the distance, just like the gravitational force); parallel Birkeland currents moving in opposite directions will repel with an electromagnetic force inversely proportional to their distance apart. There is also a short-range circular component to the force between two Birkeland currents that is opposite to the longer-range parallel forces.
Electrons moving along a Birkeland current may be accelerated by a plasma double layer. If the resulting electrons approach relativistic velocities (ie. the speed of light) they may subsequently produce a Bennett pinch, which in a magnetic field will spiral and emit synchrotron radiation that includes radio, optical (ie. light), x-rays, and gamma rays.
In 2007, the Themis satellite “found evidence of magnetic ropes connecting Earth’s upper atmosphere directly to the sun”. apparently consistent with Kristian Birkeland‘s theory of the aurora, “that a current of electric corpuscles from the sun would give rise to precipitation upon the earth” (See preface to The Norwegian Aurora Polaris Expedition 1902-1903).
Describing plasma cables, Hannes Alfvén wrote:
- “Plasma cables seem to be reasonably stable formations which can be considered as structures important for the understanding of plasma phenomena. (Of course, their interior structure should be described by classical theory.) The plasma cables are either filaments or ‘flattened filaments’ (sheets with limited extent). They carry an electric current parallel to the magnetic field, and this is what gives them their properties. The cables are often very efficient in transferring electromagnetic power from one region to another. They are embedded in passive plasmas, which have essentially the same properties in all directions around the cables. They are ‘insulated’ from their surroundings by a thin cylindrical electrostatic sheath (or double layer) which reduces the interaction with its exterior. In the magnetosphere and upper ionosphere, the density in the cable is sometimes lower than the surrounding passive plasma (Block and Fälthammar, 1968). In other cases, the density in the cable may be much larger than the surroundings because ionized matter is pumped into the cable from the outside. By selectively doing so, the chemical composition in the cable may differ from that of its exterior (Marklund, 1978, 1979) (see Marklund convection). Besides the cylindrical electrostatic sheath, there are often longitudinal double layers, in which a considerable part of the power which the cable transmits may be converted into high energy particles. The double layers sometimes explode, and this produces excessively high energy particles.”
Cosmic Birkeland currents
Plasma physicists suggest that many structures in the universe exhibiting filamentation are due to Birkeland currents. Peratt notes that “Regardless of scale, the motion of charged particles produces a self-magnetic field that can act on other collections of charged particles, internally or externally. Plasmas in relative motion are coupled via currents that they drive though each other“. (See Plasma scaling). Examples include:
|20 × 103 m||Venus Flux ropes|
|102–105 m||106 A||Earth’s Aurora|
|108 m||105–106 A||Magnetosphere inverted V events|
|107–108 m||1011 A||Sun’s prominences (spicules, coronal streamers)|
|Interstellar structures: various nebulae|
|1018 m||Galactic center|
|6 × 1020 m||Double radio galaxies: bright lobes|
Source: Peratt (1992).
The history of Birekland Currents appears to mired in politics.
After Kristian Birkeland suggested “currents there are imagined as having come into existence mainly as a secondary effect of the electric corpuscles from the sun drawn in out of space,” (1908), his ideas were generally ignored in favour of an alternative theory from British mathematician Sydney Chapman.
In 1939, the Swedish Engineer and plasma physicist Hannes Alfvén promoted Birkeland’s ideas in a paper published on the generation of the current from the Solar Wind. One of Alfvén’s colleagues, Rolf Boström, also used field-aligned currents in a new model of auroral electrojets (1964).
In 1966 Alfred Zmuda, J.H. Martin, and F.T.Heuring reported their findings of magnetic disturbance in the aurora, using a satellite magnetometer, but did not mention Alfvén, Birkeland, or field-aligned currents, even after it was brought to their attention by editor of the space physics section of the journal, Alex Dressler.
In 1967 Alex Dessler and one of his graduates students, David Cummings, wrote an article arguing that Zmuda et al had indeed detected field align-currents. Even Alfvén subsequently credited (1986) that Dessler “discovered the currents that Birkeland had predicted” and should be called Birkeland-Dessler currents.
In 1969 Milo Schield, Alex Dessler and John Freeman, used the name “Birkeland currents” for the first time. In 1970, Zmuda, Armstrong and Heuring wrote another paper agreeing that their observations were compatible with field-aligned currents as suggested by Cummings and Dessler, and by Bostrom, but again made no mention of Alfvén and Birkeland.
In 1970, a group from Rice University also suggested that the results of an earlier rocket experiment was consistent with field-aligned currents, and credited the idea to Boström, and Dessler and his colleagues, rather than Alfvén and Birkeland. In the same year, Zmudu and Amstrong did credit Alfvén and Birkeland, but felt that they “…cannot definitely identify the particles constituting the field-aligned currents.”
It wasn’t until 1973 that the navy satellite Triad, carrying equipment from Zmuda and James Armstrong, detected the magnetic signatures of two large sheets of electric current. Their papers (1973, 1974) reported “more conclusive evidence” of field-aligned currents, citing Cummings and Dessler but not mentioning Birkeland or Alfven.
It had taken 65 years to confirm Birkeland’s original predictions.
- Astronomy Picture of the Day, 20 Dec 2000
- “Dessler, A. J., “Corotating Birkeland currents in Jupiter’s magnetosphere – an Io plasma-torus source“, Planetary and Space Science, vol. 28, July 1980, p. 781-788.
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- “Solar Wind, Genesis, and the Planets: Do other solar system planets have protective magnetospheres?” June 23, 2008 at the NASA Jet Propulsion Laboratory Web site.
- Plasma Phenomena, Department of Physics, Czech Technical University
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- Auroral Curls, University of Calgary Portable Auroral Imager
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Spiger and B. R. Sandel, “Detection of geomagnetically aligned currents associated with an auroral arc“, J. Geophys. Res., vol. 75, p. 2595, 1970.
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We tend to think of our Earthly circumstances as normal. A watery, temperate world orbiting a stable yellow star. A place where life has persisted for nearly 4 billion years. It’s almost inevitable that when we think of other places where life could thrive, we use our own experience as a benchmark.
But should we?
Our Sun is a G-type main sequence star with a lifespan of about 10 billion years. It’s about five billion years old and has powered life on Earth for almost 4 billion years already. G-type main sequence stars are not the most plentiful, nor are they the most long-lived. They make up only about 6% of the Milky Way’s stellar population, and they only live for about 10 billion years.
Most of the stars in the Milky Way (about 73%) are red dwarfs, or M dwarfs. M dwarfs are cooler than our Sun, and their habitable zones are smaller. But they’re much longer lived, by an order of magnitude. Their long lives might make them ideal stars for life to flourish around, given the right planets. But red dwarfs can be prone to deadly flaring, and their dangerous energy output may not be that hospitable for life as we know it.
There’s another type of host star that astronomers are starting to call Goldilocks stars. They’re more plentiful than the Sun, they’re longer lived than the Sun, and they don’t emit as much dangerous radiation as M dwarfs.
They’re called K dwarfs, also known as orange dwarfs.
K dwarfs live between 15 to 45 billion years, they make up about 13% of the Milky Way’s population, and they emit only one-sixteenth as much deadly radiation as M dwarfs.
In new work presented at the 235th meeting of the American Astronomical Society, a pair of researchers used multiple telescopes to survey some G and K-dwarfs in our galactic neighborhood. They’re Edward Guinan and Scott Engle form Villanova University in Pennsylvanie. Their undertaking is called the Goldiloks Project.
In a press release, Guinan said that K-dwarf stars are true Goldilocks stars. “K-dwarf stars are in the ‘sweet spot,’ with properties intermediate between the rarer, more luminous, but shorter-lived solar-type stars (G stars) and the more numerous red dwarf stars (M stars). The K stars, especially the warmer ones, have the best of all worlds. If you are looking for planets with habitability, the abundance of K stars pump up your chances of finding life.”
In a 100 hundred light year radius from our Solar System, there are about a thousand K-dwarfs. These stars are ripe for observation. And even though they’re far less plentiful than the M-dwarfs, some astronomers think we should shift our focus to K-dwarfs when it comes to searching for potentially habitable planets.
M-dwarfs are problematic when it comes to suitability for life. They’re plentiful and they host lots of exoplanets, but they’re dangerous. Since they’re so small, their habitable zone is very close.
That means that any planets in the habitable zone are probably tidally locked, which could diminish the chances for life to exist. One side would be in perpetual darkness, and the other side in perpetual light. That creates extreme, problematic temperature differences, where the frozen side could freeze the main gases out of the atmosphere, making the daylight side bone dry and barren.
M-dwarfs are extremely energetic and unsteady. They’re often flare stars, and their violent output of energy could easily strip away a planet’s atmosphere very early in its life, and destroy any organism that had gained a foothold on the planet. Some of these flares can double the star’s brightness in a matter of minutes.
M-dwarfs can also have extremely powerful magnetic fields that may overwhelm the protective magnetospheres of any planets orbiting them. A 2013 paper examined the effect that these powerful magnetic fields could have on any potentially habitable planets. That study said, “To be able to sustain an Earth-sized magnetosphere, with the exception of only a few cases, the terrestrial planet would either (1) need to orbit significantly farther out than the traditional limits of the habitable zone; or else, (2) if it were orbiting within the habitable zone, it would require at least a magnetic field ranging from a few G <Gauss> to up to a few thousand G.” This is in comparison to Earth’s magnetosphere which is one Gauss.
M-dwarfs’ powerful magnetic fields combined with their flaring makes them almost certainly toxic to life. And even though this intense flaring and powerful magnetic field can settle down later in an M-dwarf’s life, by then planets in the habitable zone would have already lost their atmospheres.
“We’re not so optimistic anymore about the chances of finding advanced life around many M stars,” Guinan said.
K-dwarfs are different.
K-dwarfs don’t experience the same flaring and chaotic energy output that M-dwarfs do. They also lack the same intense magnetic fields, which are responsible for much of an M-dwarfs inhospitable nature. According to Guinan’s research, K-dwarfs emit only about 1/100th as much deadly x-rays as some M-dwarfs.
The Goldiloks Project measured the age, rotation rate, and the x-ray and far infrared outputs of a sample of cool G and K stars. They’re using the Chandra X-ray Observatory and the XMM-Newton satellite in the project, but they’re relying heavily on the Hubble Space Telescope. The Hubble is extremely sensitive to ultraviolet radiation coming from hydrogen, and they used that sensitivity to assess the radiation coming from 20 K-dwarfs.
“Hubble is the only telescope that can do this kind of observation,” Guinan said.
Guinan and Engle found that the levels of radiation around K-stars was much less harmful than around M-dwarfs. K stars also have longer lifetimes and therefore slower migration of the habitable zone. That makes K-dwarfs the ideal place to search for life, and these stars would allow time for highly evolved life to develop on suitable planets. Over the Sun’s entire lifetime — 10 billion years — K stars only increase their brightness by about 10-15%, giving biological evolution a much longer time-span to evolve advanced life forms than on Earth.
We already know of some K-dwarfs that host exoplanets, and others that might host them, but that we’re uncertain about. Guinan and Engle looked at three particularly interesting targets: Epsilon Eridani, Kepler-442, and Tau Ceti.
“Kepler-442 is noteworthy in that this star (spectral classification, K5) hosts what is considered one of the best Goldilocks planets, Kepler-442b, a rocky planet that is a little more than twice Earth’s mass. So the Kepler-442 system is a Goldilocks planet hosted by a Goldilocks star!” said Guinan.
Guinan and Engle have spent 30 years observing different types of stars. They’ve determined relationships between a star’s type, its rotation, age, x-ray and UV emissions. That data is the foundation of their work on how a star’s high-energy radiation affects a planet’s atmosphere and prospects for life.
- Press Release: Goldilocks Stars Are Best Places to Look for Life
- 2013 Research Paper: Effects of M dwarf magnetic fields on potentially habitable planets | 0.882937 | 3.699068 |
NASA’s Curiosity rover is providing vital insight about Mars’ past and current environments that will aid plans for future robotic and human missions.
In a little more than a year on the Red Planet, the mobile Mars Science Laboratory has determined the age of a Martian rock, found evidence the planet could have sustained microbial life, taken the first readings of radiation on the surface, and shown how natural erosion could reveal the building blocks of life.
The second rock Curiosity drilled for a sample on Mars, which scientists nicknamed “Cumberland,” is the first ever to be dated from an analysis of its mineral ingredients while it sits on another planet. A report by Kenneth Farley of the California Institute of Technology in Pasadena, and co-authors, estimates the age of Cumberland at 3.86 billion to 4.56 billion years old. This is in the range of earlier estimates for rocks in Gale Crater, where Curiosity is working.
Before they could measure rocks directly on Mars, scientists estimated their ages by counting and comparing the numbers of impact craters on various areas of the planet. The crater densities are correlated with ages based on comparisons with crater densities on the Moon, which were tied to absolute dates after the Apollo lunar missions returned rocks to Earth.
Farley and co-authors also assessed how long Cumberland has been within about an arm’s reach of the Martian surface, where cosmic rays that hit atoms in the rock produce gas buildups that Curiosity can measure. Analyses of three different gases yielded exposure ages in the range of 60 million to 100 million years. This suggests shielding layers above the rock were stripped away relatively recently. | 0.81861 | 3.584914 |
When considering how the solar system formed, there are a number of problems with the idea of planets just blobbing together out of a rotating accretion disk. The Nice model (and OK, it’s pronounced ‘niece’ – as in the French city) offers a better solution.
In the traditional Kant/Laplace solar nebula model you have a rotating protoplanetary disk within which loosely associated objects build up into planetesimals, which then become gravitationally powerful centres of mass capable of clearing their orbit and voila planet!
It’s generally agreed now that this just can’t work since a growing planetesimal, in the process of constantly interacting with protoplanetary disk material, will have its orbit progressively decayed so that it will spiral inwards, potentially crashing into the Sun unless it can clear an orbit before it has lost too much angular momentum.
The Nice solution is to accept that most planets probably did form in different regions to where they orbit now. It’s likely that the current rocky planets of our solar system formed somewhat further out and have moved inwards due to interactions with protoplanetary disk material in the very early stages of the solar system’s formation.
It is likely that within 100 million years of the Sun’s ignition, a large number of rocky protoplanets, in eccentric and chaotic orbits, engaged in collisions – followed by the inward migration of the last four planets left standing as they lost angular momentum to the persisting gas and dust of the inner disk. This last phase may have stabilised them into the almost circular, and only marginally eccentric, orbits we see today.
Meanwhile, the gas giants were forming out beyond the ‘frost line’ where it was cool enough for ices to form. Since water, methane and CO2 were a lot more abundant than iron, nickel or silicon – icy planetary cores grew fast and grew big, reaching a scale where their gravity was powerful enough to hold onto the hydrogen and helium that was also present in abundance in the protoplanetary disk. This allowed these planets to grow to an enormous size.
Jupiter probably began forming within only 3 million years of solar ignition, rapidly clearing its orbit, which stopped it from migrating further inward. Saturn’s ice core grabbed whatever gases Jupiter didn’t – and Uranus and Neptune soaked up the dregs. Uranus and Neptune are thought to have formed much closer to the Sun than they are now – and in reverse order, with Neptune closer in than Uranus.
And then, around 500 million years after solar ignition, something remarkable happened. Jupiter and Saturn settled into a 2:1 orbital resonance – meaning that they lined up at the same points twice for every orbit of Saturn. This created a gravitational pulse that kicked Neptune out past Uranus, so that it ploughed in to what was then a closer and denser Kuiper Belt.
The result was a chaotic flurry of Kuiper Belt Objects, many being either flung outwards towards the Oort cloud or flung inwards towards the inner solar system. These, along with a rain of asteroids from a gravitationally disrupted asteroid belt, delivered the Late Heavy Bombardment which pummelled the inner solar system for several hundred million years – the devastation of which is still apparent on the surfaces of the Moon and Mercury today.
Then, as the dust finally settled around 3.8 billion years ago and as a new day dawned on the third rock from the Sun – voila life! | 0.876643 | 3.918236 |
Astronomers discovered a potentially habitable planet 30 light-years away. For the first time, scientists were able to discover a potentially habitable planet at a relatively short distance from Earth. The Earth-like exoplanet is located 31 light-years away and it has been named GJ 357 d. The discovery of the exoplanet was announced in the journal Astronomy & Astrophysics, where a team of Spanish astronomers published their study.
According to an article published in The Astrophysical Journal Letters, the planet was first detected at the beginning of the year by NASA’s Transiting Exoplanet Survey Satellite (TESS). TESS is a mission specially designed to explore the universe in the search exoplanets.
Lisa Kaltenegger, professor at Cornell University, is a member of the Tess science team. According to her, the discovery is an important milestone for humanity. GJ 357 d is the first nearby super-Earth that humanity has ever discovered and it implies many exciting possibilities.
The newly-discovered exoplanet is substantially bigger than our home planet and, as Kaltenegger believes, it offers scientists an opportunity to observe and analyze the circumstances surrounding Earth’s heavyweight planetary cousins.
Astronomers Discover A Potentially Habitable Exoplanet 30 Light Years Away
“With a thick atmosphere, the planet GJ 357 d could maintain liquid water on its surface like Earth, and we could pick out signs of life with telescopes that will soon be online,” Kaltenegger said. The scientists that made the discovery say that the planet is located inside a distant solar system centered around an M-type dwarf sun. The system only includes three planets, one of them being GJ 357 d.
The other two planets in the system, GJ 357 b and GJ 357 c, both seem to have habitable conditions, but their temperatures are not well fitted to sustain life. GJ 357 d orbits its sun every 55.7 days at a distance about 20% of Earth’s distance to our sun.
Jack Madden, another member of the team, said: “We built the first models of what this new world could be like. Just knowing that liquid water can exist on the surface of this planet motivates scientists to find ways of detecting signs of life.” If the planet shows signs of sustaining extraterrestrial life, it could be the answer to one of humanity’s most debated questions: Are we alone in the universe?
Doris’s passion for writing started to take shape in college where she was editor-in-chief of the college newspaper. Even though she ended up working in IT for more than 7 years, she’s now back to what he always enjoyed doing. With a true passion for technology, Doris mostly covers tech-related topics. | 0.81892 | 3.573341 |
A massive supervoid is discovered and it defies conventional physics.
Astronomers say they have discovered the largest known structure in the universe.
According to a team of astronomers at the University of Hawaii, a massive structure known as a “supervoid” is the largest known structure in the universe. The massive void measurers upwards of 1 billion light years across. Variations in galaxy density and background radiation are accounted for by Big Bang physics, but this area, in the direction of the constellation Eridanus, is too vast and too empty to fit the standard variations, according to astronomers.
Scientists say that upwards of 80 percent of the galaxies expected in the region are actually missing. Due to its size, the number of galaxies predicted in the region would be around 10,000. While the structure is technically a void of sorts, it still is defined by a clear boundary, which astronomers say indicates it is an actual structure
Astronomers say the area is defined by its lack of stars and other matter. Astronomers say it remains unclear exactly why the void formed, and exactly what type of physics are taking place, but it could indicate the presence of a new type of physics related to dark matter and dark energy.
“Imagine there is a huge void with very little matter between you (the observer) and the CMB. Now think of the void as a hill. As the light enters the void, it must climb this hill. If the universe were not undergoing accelerating expansion, then the void would not evolve significantly, and light would descend the hill and regain the energy it lost as it exits the void,” the team noted in describing the strange physics taking place in the region.
The study relied on the Hawaii’s Pan-STARRS1 (PS1) telescope located on Haleakala, Maui, and NASA’s Wide Field Survey Explorer (WISE). Both were instrumental in counting the number of galaxies in a patch of sky around three billion light years away.
The research was published this week in the Monthly Notices of the Royal Astronomical Society. | 0.830183 | 3.438767 |
How do you produce life on an early Earth bathed in ultraviolet radiation? The presumption when I was growing up was that the combination of chemicals in ancient ponds, fed energy by lightning or ultraviolet light itself, would produce everything needed to start the process. Thus Stanley Miller and Harold Urey’s experiments, beginning in 1953 at the University of Chicago, which simulated early Earth conditions to produce amino acids out of a sealed ‘atmosphere’ of water, ammonia, methane and hydrogen, with electrodes firing sparks to simulate lightning.
But there are other ways of explaining life’s origins, as a new study from the Jet Propulsion Laboratory and the Icy Worlds Team at the NASA Astrobiology Institute reminds us. Hydrothermal vents on the sea floor have been under consideration since the 1980s, with some researchers pointing to the ‘black smokers’ that produce hot, acidic fluids. The new NASA work looks at much cooler vents bubbling with alkaline solutions like those in the ‘Lost City,’ a field of hydrothermal activity in the mid-Atlantic on the seafloor mountain Atlantis Massif.
Image: This image from the floor of the Atlantic Ocean shows a collection of limestone towers known as the “Lost City.” Alkaline hydrothermal vents of this type are suggested to be the birthplace of the first living organisms on the ancient Earth. Credit: JPL.
Here there is a field of about thirty large calcium carbonate chimneys — some 30 to 60 meters tall — and a number of smaller structures venting mainly hydrogen and methane into the surrounding water. The so-called ‘water world’ theory that JPL’s Michael Russell has been working on since 1989 draws on the idea that warm alkaline vents like these would have maintained a state of imbalance with ancient oceans that were acidic. Life is, in this formulation, seen as the inevitable outcome of disequilibrium, producing enough energy to drive its formation.
Thus we have a proton gradient with hydrogen ions concentrated largely on the outside of the vent’s chimneys, which the work refers to as ‘mineral membranes.’ We also have an electrical gradient between oceans rich with carbon dioxide. and hydrogen and methane from the vents as they meet at the chimney wall. The transference of electrons could have produced complex organic compounds, using processes not so different from those that occur in mitochondria.
“Within these vents, we have a geological system that already does one aspect of what life does,” said Laurie Barge, second author of the study at JPL. “Life lives off proton gradients and the transfer of electrons.”
The work represents a fundamental shift in focus over older ‘chemical soup’ models, its examination of membrane-spanning gradients pre-empting prebiotic chemistry. The paper explains:
…there is an advantage to be gained from examining the transition from geochemistry to biochemistry from the bottom up, that is, to “look under the hood” at life’s first free energy–converting nanoengines or “mechanocatalysts.” Such an approach encourages us to see life as one of the last in a vast hierarchical cascade of emergent, disequilibria-converting entropy-generating engines in the Universe. In doing so, we keep our sights on the “astro” in astrobiology.
The researchers speculate that minerals may have played the role of enzymes in the ancient ocean, interacting with local chemicals and driving reactions. A mineral called ‘green rust’ (fougèrite) could use the proton gradient to produce phosphate-laden molecules capable of storing energy. Molybdenum is also in play, a rare metal that can drive important chemical reactions. Thus basic metabolic reactions around sea floor hot springs may help to explain not only how life emerged on our own planet but also how it may emerge on worlds far beyond.
On this latter point, the paper explains how to proceed:
In considering habitability and the potential for life elsewhere in the Solar System and beyond, the physical and chemical disequilibria that obtain on wet icy rocky worlds, and the various processes that might relieve them, need to be established. If life’s origin is ultimately coupled to geophysical convection in a particular geochemical context, one should be able to make predictions about life’s likelihood on a planet or moon of interest from application of coupled chemical and fluid/geodynamical modeling, and from the availability of key feedstocks, thus accounting for other planetary energetic drivers, for example, tidal and radiogenic heating, solar wind interactions, magnetic dynamos—appropriate to the object in question.
We’d like to account, in other words, for the disequilibrium-producing factors that could play an astrobiological role on multitudes of exoplanets. The possibilities range widely, from gravitational effects to thermal and chemical gradients that can all play a role in life’s inception. Particularly close to home, of course, we focus in on places like Enceladus and Europa, where we have nearby laboratories for observing these processes in action. Until we can put the right kind of instrumentation on the scene, continuing Earth-bound lab work on these ideas is the way forward. | 0.855032 | 3.722595 |
Researchers at the University of Rochester have uncovered how giant magnetic fields up to a billion, billion miles across, such as the one that envelopes our galaxy, are able to take shape despite a mystery that suggested they should collapse almost before theyd begun to form. Astrophysicists have long believed that as these large magnetic fields grow, opposing small-scale fields should grow more quickly, thwarting the evolution of any giant magnetic field. The team discovered instead that the simple motion of gas can fight against those small-scale fields long enough for the large fields to form. The results are published in a recent issue of Physical Review Letters.
"Understanding exactly how these large-scale fields form has been a problem for astrophysicists for a long time," says Eric Blackman, assistant professor of physics and astronomy. "For almost 50 years the standard approaches have been plagued by a fundamental mystery that we have now resolved."
The mechanism, called a dynamo, that creates the large-scale field twists up the magnetic field lines as if they were elastic ribbons embedded in the sun, galaxy or other celestial object. Turbulence kicked up by shifting gas, supernovae, or nearly any kind of random movement of matter, combined with the fact that the star or galaxy is spinning carries these ribbons outward toward the edges. As they expand outward they slow like a spinning skater extending her arms and the resulting speed difference causes the ribbons to twist up into a large helix, creating the overall orderly structure of the field.
Jonathan Sherwood | EurekAlert!
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Two prominent X-ray emission lines of highly charged iron have puzzled astrophysicists for decades: their measured and calculated brightness ratios always disagree. This hinders good determinations of plasma temperatures and densities. New, careful high-precision measurements, together with top-level calculations now exclude all hitherto proposed explanations for this discrepancy, and thus deepen the problem.
Hot astrophysical plasmas fill the intergalactic space, and brightly shine in stellar coronae, active galactic nuclei, and supernova remnants. They contain...
In living cells, enzymes drive biochemical metabolic processes enabling reactions to take place efficiently. It is this very ability which allows them to be used as catalysts in biotechnology, for example to create chemical products such as pharmaceutics. Researchers now identified an enzyme that, when illuminated with blue light, becomes catalytically active and initiates a reaction that was previously unknown in enzymatics. The study was published in "Nature Communications".
Enzymes: they are the central drivers for biochemical metabolic processes in every living cell, enabling reactions to take place efficiently. It is this very...
Early detection of tumors is extremely important in treating cancer. A new technique developed by researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from normal tissue. The work is published May 25 in the journal Nature Nanotechnology.
researchers at the University of California, Davis offers a significant advance in using magnetic resonance imaging to pick out even very small tumors from...
Microelectronics as a key technology enables numerous innovations in the field of intelligent medical technology. The Fraunhofer Institute for Biomedical Engineering IBMT coordinates the BMBF cooperative project "I-call" realizing the first electronic system for ultrasound-based, safe and interference-resistant data transmission between implants in the human body.
When microelectronic systems are used for medical applications, they have to meet high requirements in terms of biocompatibility, reliability, energy...
Thomas Heine, Professor of Theoretical Chemistry at TU Dresden, together with his team, first predicted a topological 2D polymer in 2019. Only one year later, an international team led by Italian researchers was able to synthesize these materials and experimentally prove their topological properties. For the renowned journal Nature Materials, this was the occasion to invite Thomas Heine to a News and Views article, which was published this week. Under the title "Making 2D Topological Polymers a reality" Prof. Heine describes how his theory became a reality.
Ultrathin materials are extremely interesting as building blocks for next generation nano electronic devices, as it is much easier to make circuits and other...
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02.06.2020 | Life Sciences | 0.846715 | 3.890442 |
There are many milestone books in the history of science. True to the definition of “milestone,” these works mark pivotal achievements in mankind’s effort to understand natural law and the world in which we live. Among the very top tier of milestone science books is the Discorsi, published in 1638 by Galileo Galilei. It is his last and most significant contribution to science and is often referred to as the first physics “textbook.”
The Discorsi derives its fame as the published repository of Galileo’s life-long efforts to decipher the concept of motion and the “law of fall,” the mathematical characterization of free-falling bodies under the influence of gravity. Attempts to determine the velocity and distance profiles of falling bodies as a function of elapsed time of fall had yielded only conjecture over the centuries since Aristotle himself pondered the question. As Aristotle observed over two thousand years ago, “In order to know the natural world, one must first understand motion,” and, until Galileo and Isaac Newton came along, what we “knew” about motion was indeed largely conjecture – much of it erroneous!
It was clear that the force of gravity was the prime-mover causing bodies of mass to fall toward the earth’s center, but until Isaac Newton in 1687 established how gravity worked, no one really understood the mathematical details of gravitational attraction between any two bodies of mass. When we weigh ourselves on a scale, we are, in fact, measuring the force of gravitational attraction between the earth as one mass and our bodies as the other. One’s weight on the moon is less than that on earth because of the moon’s smaller mass. In empty space, we are weightless. Here, then, is the great question posed by the elusive “law of fall” whose answer had eluded man for centuries – until Galileo solved the riddle:
What is the velocity attained by a free-falling body as a function of the elapsed time of fall? We know the velocity at the onset of fall: It is clearly zero at the instant of release. But what is its precise instantaneous velocity at each second of elapsed time thereafter? Furthermore, what is the distance of fall covered from the release point at each elapsed second of time?
A falling body precisely one second into free-fall is already traveling with an instantaneous velocity of 32.2 feet per second. Making such measurements without modern instrumentation and high-speed strobe photography would be virtually impossible. In the early seventeenth century when photography was unimaginable and there certainly were no stopwatches or even accurate clocks, Galileo had to find a way to slow down the motion of a free-falling body. He “diluted” the effect of gravity by repeatedly rolling a small ball from a standing start down a long grooved, inclined plane. He then measured the distances covered by the slowly accelerating ball over successive constant-time intervals of an arbitrary “musical beat.” It is said that he used for a “timing clock” the steady cadence of a hummed Italian march for his equal timing intervals. Using multiple trials and noting the precise position of the rolling ball along the track on successive numbers of downbeats of the steady cadence, he was able to deduce the “law of fall.” Here is a figure illustrating the essence of Galileo’s brilliant inclined plane experiment. The figure is from chapter four of my book on motion, The Elusive Notion of Motion: The Genius of Kepler, Galileo, Newton, and Einstein.
Here is the critical essence of what Galileo determined:
A body free-falling under gravity exhibits a constant acceleration value (near the earth’s surface). It remained for Galileo’s successors to determine the exact numerical value of that acceleration. Near the earth’s surface, a body of mass in free-fall attains an additional velocity of 32.2 feet per second for each additional second of elapsed time. Galileo’s determination that acceleration is constant in free-fall dictates two major conclusions:
-The velocity attained is proportional to the elapsed time of fall. Twice the elapsed time, twice the velocity, for example.
-The distance traveled is proportional to the square of the elapsed time of fall. Twice the elapsed time, four times the distance traveled.
This is the celebrated “law of fall.” There might be a tendency for the casual reader to shrug-off Galileo’s achievement as no big deal in light of modern scientific achievements, but it was a VERY big deal for the progress of physics. Galileo, along with Johannes Kepler and Kepler’s experimentally formulated three laws of planetary motion, paved the way for the truly great reformation in mathematical physics initiated by Isaac Newton in his masterwork book of 1687, the Principia, universally acclaimed as the greatest scientific book ever published.
Image: Pierre Barge & Associates Auctions
First-state presentation copy of Galileo’s Discorsi to the French Ambassador, Count Francois de Noailles who smuggled the manuscript from Florence, Italy, to Leiden, Holland, for publication in 1638. Auctioned in Paris for over $790,000 in April, 2017 by Pierre Barge & Associates, the book itself is dedicated to de Noailles.
Here is perhaps the finest copy extant of Galileo’s Discorsi E Dimostrazioni Matematiche intorno a due nuoue scienze, otherwise known as Discourses on Two New Sciences. This one-of-a-kind presentation copy from 1638 was given to a friend of Galileo’s who smuggled the final portion of Galileo’s manuscript out of Florence, Italy, into Leiden, Holland for publication by the famed Elzevir Press. Galileo was being held in virtual house arrest within his villa outside of Florence by mandate from the Catholic Church and its Inquisition. Galileo had been accused of suspicion of heresy by the Church for his previous 1632 book, the Dialogo, which the Church felt promoted the Copernican “world system” which featured a sun-centered solar system. This went against established scripture which suggested that the earth was at the center of everything, according to the Church. Galileo famously maintained that religion’s role on earth should be to show the way to heaven; it should be the role of science, not the Church, to explain the clockwork of the heavens. The Church did not agree.
As for the “two new sciences” introduced by Galileo’s Discorsi: The first treatise in the book deals with what would today be called “Strength of Materials” and “Reliability Engineering.” This constituted a pioneering effort by Galileo in a new field of endeavor. The second treatise in the book involves those categories of physics known as “Mechanics,” and “Kinematics.” The centerpiece of the book is, of course, Galileo’s findings on motion and the long-delayed, finally published documentation of the “law of fall.” Most of the work presented in that section was done by Galileo as early as 1604. Galileo was in poor health and almost blind from glaucoma in 1638; accordingly, publication of this, his most important scientific work was, for him, a very high priority made complicated by the censorship of the Church. Galileo died in 1642, the year Isaac Newton came into this world. The torch had been passed. | 0.843317 | 3.555054 |
Eta Carinae may be the most scary star in the galaxy.
Let me paint a picture for you. Eta Car is actually two stars, both called type O stars, which means they are far more massive, warm and luminous than the sun. The largest of the two, called Eta Carinae A, is a sample probably one hundred or more times the mass of the sun. It is one of the most luminous stars in the galaxy that propagates something like five million times the sun's energy.
Five. Million .
If the second star, A Car B, was turned off by itself, it would also be considered an animal, with about 50 times the sun's mass and glowing with a hundred light thousand suns. But besides Eta Car A it is actually hard to see at all.
A star is a balance between gravity trying to pull it together in the core, and the heat makes it grow. Eta Car A is so massive that nuclear fusion in its core runs at a furious pace, and the energy it generates is so large that it can hardly stick together. a slight increase in brightness would tear the star apart. In 1
Eta Car has been the subject of intense control for decades. An observatory that has been used many times to see it is the Hubble Space Telescope. Just in time for the 4th of July, this Hubble image of Eta Car is released:
Sacred cosmic pyrotechnics!
The Eta Car star is in the middle of all the clutter that is almost covered by the gas around it (if you have trouble seeing it, the eight sharply defined lines can be directed to it, it is diffraction tips caused by light into Hubble and bending around the metal angles with a mirror in place, see the footnote on this article). The two large gas bottles from the large eruption are obvious; we see them at an angle so that you are on the star's side towards us and the other on the other side.
There is a thick disk of material around the star and you can see a hint between it between the two lobes. The two stars make Eta Car circuits every five years, which is really fast. This tends to throw material out into the plane of the circuit, creating that disk. As Eta Car A eruptions, the material had a harder time plowing through the disc, so instead blowing up and down it in polar directions.
The red material surrounding the bubbles is nitrogen gas blown into the eruption as Good, slamming into material that is either previously drafted from the star or just the material that floats around near the star (Eta Car is in the ridiculous large Carina Nebula, which is thick with gas and dust). The shock waves generated as the material plows into the slower gas, spans it and causes it to glow.
What's so interesting about this new picture is the blue material. Astronomers took ultraviolet images to look for magnesium (which shines in the UV) ejected from the outbreak and they expected to be mixed with the nitrogen. Instead, they found it (shown in blue in the image) between the star and the shocked outer gas. They expected the area to be empty, but here it is loaded with very hot gas. It is unclear what that gas does there, but it was not seen before. This means that large outbreaks were even more energetic because it also had to throw out of this rapidly moving gas. It seems that Eta Car really was right on this side of going supernova back in the 1840s.
It's hard to overestimate how complicated everything is. When I was working on Hubble, we had a recurring program to observe Eta Car in a matter of months, and I did some work on the astronomer running the Ted Gold program to treat the spectra. They were a nightmare; There is so much energy in the gas that each atom shines in a phenomenal number of wavelengths. Worse, the different gas speeds are forging and changing the wavelengths of light, making it difficult to know which elements we are even looking at. One day, Ted printed a few dozen of the spectra on paper and tied them together in a really long spectrum on the wall outside the office. I used to see him stand there and look at it and shouted at the awful complexity he had chosen to loosen. I could hardly make heads or tails out of it.
Another thing: The whole star lets you see wider rays of light that flow out. It is light from Eta Car that leans past material in the bubbles; the lumps between gas and dust block lights, but the holes between the lumps sound through, illuminating the gas beyond.
In other words, they are crepuscular rays, as you sometimes see on cloudy days, especially near sunset. Unbelievable.
Finally – probably in less than a million years, maybe less – Eta Car will really explode, become a supernova. When it does, it will easily shine Venus in the southern hemisphere and will probably be bright enough to cast shadows. From 75 quadrillion kilometers away.
How is the for a four-year July fireworks? | 0.900115 | 3.919367 |
A team of astronomers from Israel, the U.S. and Russia have identified a disrupted galaxy resembling a giant tadpole, complete with an elliptical head and a long, straight tail, about 300 million light years away from Earth. The galaxy is one million light-years long from end to end, ten times larger than the Milky Way. The research is published today in the journal Monthly Notices of the Royal Astronomical Society.
“We have found a giant, exceptional relic of a disrupted galaxy,” says Dr Noah Brosch, of The Florence and George Wise Observatory at Tel Aviv University’s School of Physics and Astronomy, who led the research for the study.
When galaxies are disrupted and disappear, their stars are either incorporated into more massive galaxies or are ejected into intergalactic space. “What makes this object extraordinary is that the tail alone is almost 500,000 light-years long,” says Prof. R. Michael Rich of the University of California, Los Angeles. “If it were at the distance of the Andromeda galaxy, which is about 2.5 million light years from Earth, it would reach a fifth of the way to our own Milky Way.”
Drs Brosch and Rich collaborated on the study with Dr Alexandr Mosenkov of St. Petersburg University and Dr Shuki Koriski of TAU’s Florence and George Wise Observatory and School of Physics and Astronomy.
According to the study, the giant “tadpole” was produced by the disruption of a small, previously invisible dwarf galaxy containing mostly stars. When the gravitational force of two visible galaxies pulled on stars in this vulnerable galaxy, the stars closer to the pair formed the “head” of the tadpole. Stars lingering in the victim galaxy formed the “tail."
“The extragalactic tadpole contains a system of two very close ‘normal’ disc galaxies, each about 40,000 light-years across,” says Dr Brosch. “Together with other nearby galaxies, the galaxies form a compact group.” The galaxy is part of a small group of galaxies called HCG098 that will merge into a single galaxy in the next billion years.
Such compact galaxy groups were first identified in 1982 by astronomer Paul Hickson, who published a catalogue of 100 such groups. The Hickson Compact Groups examine environments with high galaxy densities that are not at the core of a “cluster” of galaxies (clusters contain thousands of galaxies themselves). The "tadpole galaxy" is listed as No. 98 in the Hickson Compact Group catalogue.
“In compact group environments, we believe we can study ‘clean’ examples of galaxy-galaxy interactions, learn how matter is transferred between the members, and how newly accreted matter can modify and influence galaxy growth and development,” says Dr Brosch.
For the research, the scientists collected dozens of images of the targets, each exposed through a wide filter that selects red light while virtually eliminating extraneous light pollution. “We used a relatively small, 70-cm telescope at the Wise Observatory and an identical telescope in California, both of which were equipped with state-of-the-art CCD cameras,” says Dr Brosch. The two telescopes are collaborating on a project called the Halos and Environments of Nearby Galaxies (HERON) Survey.
The new study is part of a long-term project at TAU’s Florence and George Wise Observatory, which explores the skies at low light levels to detect the faintest details of studied galaxies.
Ms Orna Cohen
Tel Aviv University
Ms Daniella Alkobi
Tel: +1 424 281 3789
Dr Morgan Hollis
Royal Astronomical Society
Tel: +44 (0)20 7292 3977
Mob: +44 (0)7802 877 700
Dr Noah Brosch
Tel Aviv University
Tel: +972 3 640 7413
Prof. R. Michael Rich
University of California, Los Angeles
Images and captions
The new work appears in: “Hickson Compact Group 98: a Complex Merging Group with a Giant Tidal Tail and a Humongous Envelope”, N. Brosch, S. Koriski, R. Michael Rich, A.V. Mosenkov, Monthly Notices of the Royal Astronomical Society (2019), 482 (2) (DOI: 10.1093/mnras/sty2717).
A copy of the paper is available from: https://doi.org/10.1093/mnras/sty2717
Notes for editors
American Friends of Tel Aviv University supports Israel’s most influential, comprehensive, and sought-after center of higher learning, Tel Aviv University (TAU). TAU is recognized and celebrated internationally for creating an innovative, entrepreneurial culture on campus that generates inventions, startups and economic development in Israel. TAU is ranked ninth in the world, and first in Israel, for producing start-up founders of billion-dollar companies, an achievement that surpassed several Ivy League universities. To date, 2,500 US patents have been filed by Tel Aviv University researchers – ranking TAU #1 in Israel, #10 outside of the US, and #43 in the world.
The Royal Astronomical Society (RAS, www.ras.ac.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.
The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content. | 0.816635 | 3.944951 |
Image credit: CSIRO
Astronomers have discovered a pair of neutron stars that could assist in the search for the long theorized “gravity waves”, first predicted by Einstein. Separated by only 800,000 kilometres, the twin objects take only two hours to rotate each other. The theory is that the pair is losing energy in the form of gravity waves, and will eventually slow down and merge with a blast of energy. This new discovery tells astronomers that these twin neutron stars are more common than previously believed, and new gravity wave detectors should locate a merger every year or two, and not once a decade.
Neutron star pairs may merge and give off a burst of gravity waves about six times more often than previously thought, scientists report in today?s issue of the journal Nature [4 December]. If so, the current generation of gravity-wave detectors might be able to register such an event every year or two, rather than about once a decade ? the most optimistic prediction until now.
Gravity waves were predicted by Einstein?s general theory of relativity. Astronomers have indirect evidence of their existence but have not yet detected them directly.
The revised estimate of the neutron-star merger rate springs from the discovery of a double neutron-star system, a pulsar called PSR J0737-3039 and its neutron-star companion, by a team of scientists from Italy, Australia, the UK and the USA using the 64-m CSIRO Parkes radio telescope in eastern Australia.
Neutron stars are city-sized balls of a highly dense, unusual form of matter. A pulsar is a special type ? a spinning neutron star that emits radio waves.
PSR J0737-3039 and its companion are just the sixth known system of two neutron stars. They lie 1600-2000 light-years (500-600 pc) away in our Galaxy.
Separated by 800,000 km ? about twice the distance between the Earth and Moon ? the two stars orbit each other in just over two hours.
Systems with such extreme speeds have to be modelled with Einstein?s general theory of relativity.
?That theory predicts that the system is losing energy in the form of gravity waves,? said lead author Marta Burgay, a PhD student at the University of Bologna.
?The two stars are in a ?dance of death?, slowly spiralling together.?
In 85 million years the doomed stars will fuse, rippling spacetime with a burst of gravity waves.
?If the burst happened in our time, it could be picked up by one of the current generation of gravitational wave detectors, such as LIGO-I, VIRGO or GEO? said team leader Professor Nicol? D?Amico, Director of the Cagliari Astronomical Observatory in Sardinia.
The previous estimate of the neutron-star merger rate was strongly influenced by the characteristics of just one system, the pulsar B1913+16 and its companion. PSR B1913+16 was the first relativistic binary system discovered and studied, and the first used to show the existence of gravitational radiation.
PSR J0737-3039 and its companion are an even more extreme system, and now form the best laboratory for testing Einstein?s prediction of orbital shrinking.
The new pulsar also boosts the merger rate, for two reasons.
It won?t live as long as PSR B1913+16, the astronomers say. And pulsars like it are probably more common than ones like PSR B1913+16.
?These two effects push the merger rate up by a factor of six or seven,? said team member Dr Dick Manchester of CSIRO.
But the actual numerical value of that rate depends on assumptions about how pulsars are distributed in our Galaxy.
?Under the most favourable distribution model, we can say at the 95% confidence level that this first generation of gravitational wave detectors could register a neutron star merger every one to two years,? said Dr Vicky Kalogera, Assistant Professor of Physics and Astronomy at Northwestern University in Illinois, USA.
Dr Kalogera and colleagues Chunglee Kim and Duncan Lorimer have modelled binary coalescence rates using a range of assumptions.
The new result is ?good news for gravity-wave astronomers,? according to team member Professor Andrew Lyne, Director of the Jodrell Bank Observatory of the University of Manchester in the UK.
?They may get to study one of these cosmic catastrophes every few years, instead of having to wait half a career,? he said.
Original Source: CSIRO News Release | 0.908726 | 3.9471 |
Using sophisticated computer simulations and observations, a team led by researchers from the Earth-Life Science Institute (ELSI) at Tokyo Institute of Technology has shown how the so-called trans-Neptunian Objects (or TNOs) may have formed. TNOs, which include the dwarf planet Pluto, are a group of icy and rocky small bodies—smaller than planets but larger than comets—that orbit the Solar System beyond the planet Neptune. TNOs likely formed at the same time as the Solar System, and understanding their origin could provide important clues as to how the entire Solar System originated.
Like many solar system bodies, including the Earth, TNOs often have their own satellites, which likely formed early on from collisions among the building blocks of the Solar System. Understanding the origin of TNOs along with their satellites may help understand the origin and early evolution of the entire Solar System. The properties of TNOs and their satellites—for example, their orbital properties, composition and rotation rates—provide a number of clues for understanding their formation. These properties may reflect their formation and collisional history, which in turn may be related to how the orbits of the giant planets Jupiter, Saturn, Neptune, and Uranus changed over time since the Solar System formed.
The New Horizons spacecraft flew by Pluto, the most famous TNO, in 2015. Since then, Pluto and its satellite Charon have attracted a lot of attention from planetary scientists, and many new small satellites around other large TNOs have been found. In fact, all known TNOs larger than 1000 km in diameter are now known to have satellite systems. Interestingly, the range of estimated mass ratio of these satellites to their host systems ranges from 1/10 to 1/1000, encompassing the Moon-to-Earth mass ratio (~1/80). This may be significant because Earth’s Moon and Charon are thought to have formed from a giant impactor.
To study the formation and evolution of TNO satellite systems, the research team performed more than 400 giant impact simulations and tidal evolution calculations.
“This is really hard work,” says the study’s senior author, Professor Hidenori Genda from the Earth-Life Science Institute (ELSI) at Tokyo Institute of Technology. Other Tokyo Tech team members included Sota Arakawa and Ryuki Hyodo.
The Tokyo Tech study found that the size and orbit of the satellite systems of large TNOs are best explained if they formed from impacts of molten progenitors. They also found that TNOs which are big enough can retain internal heat and remain molten for a span of only a few million years; especially if their internal heat source is short-lived radioactive isotopes such as Aluminum-26, which has also been implicated in the internal heating of the parent bodies of meteorites. Since these progenitors would need to have a high short-lived radionuclide content in order to be molten, these results suggest that TNO-satellite systems formed before the outward migration of the outer planets, including Neptune, or in the first ~ 700 million years of Solar System history.
Previous planet formation theories had suggested the growth of TNOs took much longer than the lifetime of short-lived radionuclides, and thus TNOs must not have been molten when they formed. These scientists found, however, that rapid TNO formation is consistent with recent planet formation studies which suggest TNOs formed via accretion of small solids to preexisting bodies. The rapid formation of large TNOs is consistent with recent planet formation studies; however, other analyses suggest comets formed well after most short-lived radionuclides had decayed. Thus the authors note that there is still much work to be done to produce a unified model for the origin of the Solar System’s planetary bodies. | 0.816741 | 4.006277 |
- Phosphorus is key in forming DNA and giving rise to life on Earth, but the element is rare in the universe.
- Scientists don't know how Earth got its phosphorus, but scientists just found phosphorus-carrying molecules forming around newborn stars.
- Researchers found the same molecules on a comet orbiting Jupiter.
- A new study suggests that comets from newborn stars may have delivered the life-giving element to Earth in the form of phosphorus monoxide.
- Visit Business Insider's homepage for more stories.
Phosphorus, an element that's key in forming DNA and fueling life on Earth, may have first arrived on the planet via comets from newborn stars.
Since the element is extremely rare in the universe, its presence on Earth has been a long-standing mystery. But scientists at the European Southern Observatory (ESO) now suggest that phosphorus may have first arrived on Earth in the molecule phosphorus monoxide – phosphorus bonded with one oxygen molecule.
Their research, published in the journal Monthly Notices of the Royal Astronomical Society on Wednesday, reveals that phosphorus monoxide forms amid the birth of new stars. They also found the molecule in a comet circling Jupiter: a frozen ball of rock and ice called 67P/Churyumov–Gerasimenko, or "67P" for short.
The discovery suggests comets could have carried phosphorus monoxide to Earth.
"Phosphorus is essential for life as we know it," Kathrin Altwegg, an author of the new study, said in a press release. "As comets most probably delivered large amounts of organic compounds to the Earth, the phosphorus monoxide found in comet 67P may strengthen the link between comets and life on Earth."
Phosphorus-carrying molecules form as stars are born
Phosphorus is rare in the universe but essential to life (in most cases). It acts as glue that holds together the chains of nucleotides that make up DNA. Phosphorus also helps build cell walls and store cells' energy.
To figure out how the element arrived on Earth, astronomers turned to the stars.
Using the Atacama Large Millimeter/Submillimeter Array (ALMA) in Chile, the scientists behind the new study looked at a star-forming region called AFGL 5142. Studying the wavelengths of light coming from that distant region allowed them to determine which kinds of molecules interact with that light.
They found phosphorus-carrying molecules forming around the new stars.
Stars are born when clouds of gas and dust collapse, giving into gravity and coalescing into new cosmic objects. When massive stars are still young, they send out flows of gas that open huge cavities in the clouds of interstellar dust around them.
Scientists think molecules with phosphorus begin to form on the walls of these cavities as they're pummeled with radiation from the young, massive stars.
But even after pinpointing a potential origin for phosphorus-carrying molecules in the universe, a big question remained: How did those molecules travel to Earth?
Comets could have carried phosphorus monoxide
The researchers turned to data from a spacecraft called Rosetta, which orbited the 67P comet from August 2014 to September 2016.
Astronomers had already found traces of phosphorus in data Rosetta gathered about 67P, but they hadn't determined which molecule the element was part of. Then, Altwegg said, an astronomer at a conference made a suggestion: "She said that phosphorus monoxide would be a very likely candidate, so I went back to our data, and there it was."
Phosphorus monoxide can end up in comets after the walls of a newborn star's surrounding cavity collapse. The molecule can get trapped in frozen grains of dust that circle the new star, some of which eventually coalesce into comets.
Astronomers think that comets may have delivered other chemical components of life, such as amino acids and even water, to early Earth as well. Phosphorus seems to be yet another life-giving element that the space snowballs brought when they pummeled the planet. | 0.897432 | 3.585361 |
Just in time for Halloween, NASA has released two new posters celebrating some truly terrifying exoplanets, or planets outside our solar system. Free to download, the entertaining posters recall vintage horror movie posters but have a decidedly astronomical focus.
Dubbed "Galaxy of Horrors," the fun but informative series resulted from a collaboration of scientists and artists and was produced by NASA's Exoplanet Exploration Program Office, located at NASA's Jet Propulsion Laboratory in Pasadena, California. The same program is behind the popular Exoplanet Travel Bureau poster series, which imagines humans visiting some of the thousands of known worlds outside our solar system.
Among the horrifyingly inhospitable worlds highlighted in the latest posters is HD 189733 b, a planet with an atmosphere full of silicates — the key component in sand and glass — and winds blowing at over 5,400 mph (6,700 kph). At those speeds, the silicates whipping through the air might create a perpetual storm of flying glass. If human or robotic explorers could travel 63 light-years from Earth to get there, they would never survive this planetary hellscape.
The second poster features three planets — named Poltergeist, Drauger and Phobetor — orbiting the pulsar PSR B1257+12, located about 2,000 light years from Earth. Sometimes called a "dead star," a pulsar is the remains of a star that has ceased burning fuel at its core and collapsed, but it isn't a quiet corpse. Like other pulsars, PSRB 1257+12 produces dual beams of intense radiation that can sometimes be seen across the galaxy. Stray radiation and high energy particles would attack the three nearby planets. Life as we know it could never form on these worlds.
"People are often most interested in finding exoplanets that could resemble Earth or potentially support life as we know it," said Thalia Rivera, an outreach specialist at the Jet Propulsion Laboratory who led the development of the new poster series. "But there are so many other amazing, mystifying planets out there that are completely unlike Earth and that show us the huge variety of ways planets can form and evolve. Personally, my favorite thing about exoplanets is how extreme they can get!"
Scientists have discovered over 4,000 exoplanets, with a majority of those detected in the last 15 years by NASA's now-retired Kepler space telescope. NASA has multiple missions searching for and studying exoplanets, including the Transiting Exoplanet Survey Satellite (TESS), the Hubble Space Telescope and the Spitzer Space Telescope. They will be joined by upcoming missions including the James Webb Space Telescope, set to launch in 2021, and the Wide Field Infrared Survey Telescope (WFIRST), scheduled to launch in the mid-2020s.
The Exoplanet Exploration Program manages science and engineering tasks in support of NASA’s search for exoplanets. In addition, the Program helps engage the public about exoplanet science and increases awareness of NASA’s exoplanet activities.
"In practical terms, I think for many people the posters are an entryway," said Gary Blackwood, manager of the Exoplanet Exploration Program. "They make exoplanet science cool and that opens a door for many members of the public, especially students, to learn more about the science behind the posters."
Download the new posters for free and learn more about these inhospitable exoplanets, as well as other terrifying worlds, in our Galaxy of Horrors.
Even more examples of weird worlds can be found in the Eyes on Exoplanet web application: https://exoplanets.nasa.gov/eyes-on-exoplanets/ | 0.882244 | 3.194983 |
As long as humans have roamed the Earth, they have looked up to the skies, speculating and pondering about the celestial wonders populating the distant cosmos. From the early astronomers and natural philosophers until today’s (including me), people have observed and studied the billions of twinkling dots, all the while wondering whether there are other worlds out there and whether they might host lifeforms like us.
In his first book, “Five Billion Years of Solitude: The Search for Life Among the Stars,” Lee Billings explores these and related questions. He chronicles the story of space exploration, planet-hunting and the growing field of astrobiology, while meeting fascinating characters and discussing their research, telescopes, discoveries and challenges. He offers clear and compelling explanations, such as of planetary physics and habitability, and he takes important asides into debates on space exploration budgets and the fate of our own planet, including the ongoing climate change crisis.
Billings is a talented science journalist. Like his work for Scientific American and other publications, the book is excellently written and researched. It won the 2014 American Institute of Physics science communication award in the book category, announced at the American Astronomical Society meeting in January.
Over the course of the book, Billings tracks down and speaks with important figures in planetary astronomy. He begins with Frank Drake, who along with nine other scientists in 1961 attempt to quantify the abundance of life-supporting planets in the galaxy in a calculation now known as the Drake Equation. He also meets with other astrophysicists, including University of California, Santa Cruz professor Greg Laughlin, Space Telescope Science Institute director Matt Mountain and MIT professor Sara Seager.
Since the time-scale or life-time of civilizations plays a role in the Drake Equation, his investigations lead to an examination of our own history and the longevity of humanity on Earth. Billings discusses the planet’s changing climate and other looming threats, for which our society appears unprepared. His reporting takes him to southern California too, where he quotes from my former colleague, UC San Diego physicist Tom Murphy, who considered the question of growing global energy consumption.
Other important questions come up as well. How far away are planets beyond our solar system and how long would it take to get there? What kind of atmospheric, geological and climatic conditions must a habitable planet have? How do astronomers detect planets, when they are so small, so faint and so close to their brightly glowing suns? What are our prospects for finding more Earth-like planets?
And what will happen to the Earth and humankind—if we’re still around—over the next few billion years, as our sun brightens, expands and transforms into a red giant star? As Billings starkly puts it in his interview for The Atlantic, “We may have—we may be—the only chance available for life on Earth to somehow escape a final, ultimate planetary and stellar death.”
With the Kepler telescope, we have the good fortune to be living at a time when actually Earth-like worlds, not just super-Earths and gas dwarfs, can be identified. Astronomers have already used the telescope to find a few potential Earth cousins, which have the right size and the right “Goldilocks” distance from their stars, and many many more candidates are on the horizon. Under certain conditions, follow-up observations can measure the planets’ atmospheres and climates to further assess their habitability.
It’s an exciting time! With even more advanced planet-finding telescopes coming up, such as the Hubble successors, the James Webb Space Telescope and High-Definition Space Telescope, we can look forward to more detailed images and observations of exoplanets in the near future. Maybe Earth has twins and maybe we are not alone.
I have a few criticisms of Five Billion Years, but they’re very minor ones. I liked the analysis of federal budget debates at multiple points in the book, but Billings could have written a little more about why as a society we should prioritize space exploration and astronomical research. If, say, a member of the House Science Committee (or more likely, their staffer) were to read this, it would be helpful to spell that out. Early in the book, he provides an engaging historical survey of astronomy, but he neglected Eastern contributions, such as from Persians, Arabs and Chinese. A few chapters meandered quite a bit too, but I enjoyed his writing style.
In any case, this is a beautifully written and thoroughly researched book, and I recommend it. Billings puts the search for extraterrestrial life in a broader context and pushes us to think about our place in the vast universe. The story continues.
[P.S. I’m extremely busy these days with the UC Santa Cruz science communication program and writing internships, so I may write posts here less often. But I will link to pieces I’ve written elsewhere, which have the benefit of rigorous editing, so if you like my blog, you’ll like them even more.] | 0.909817 | 3.540791 |
Around 4.5 billion years ago, our solar system was born from a violent cloud of gas and dust. That spinning disk of interstellar material formed comets, asteroids, the planets, and their moons.
The first moon we discovered was, of course, our own. Next, the discovery of Io, Europa, Ganymede, and Callisto by Galileo Galilee in the 17th century restructured our understanding of the universe. “That’s the beginning of the scientific era, in my mind,” astronomer David Jewitt of the University of California, Los Angeles tells Popular Mechanics. Over the years, we've constructed powerful telescopes and lofted endeavoring spacecraft toward the stars, cueing a slow trickle of fascinating lunar discoveries.
According to NASA's website, there are 214 moons in the solar system: 158 confirmed moons and 56 provisional moons—ones we suspect may be there or have spotted once but haven't yet confirmed. For this ranking, we've included all confirmed moons and a few "bonus" moons. As our ability to view the cosmos becomes more sophisticated, we'll certainly spot more moons orbiting our solar system's distant planets—and we'll rank them accordingly.
Moons are far from simple celestial objects, so before we dive in, here are a few helpful definitions to guide you along your cosmic journey:
Prograde: A moon that orbits its object in the same direction as that object's rotation.
Retrograde: A moon that orbits its object in the opposite direction of that object's rotation.
Regular: These moons have relatively small orbits, which are often circular and roughly hover along the parent object's equatorial plane. These moons likely formed alongside their parent body, accreting material as they zipped along their early orbits.
Irregular: Irregular moons often have large, eccentric orbits that don't neatly circle the object's equator. Most irregular moons are thought to be "captured," meaning that got tangled up in the orbits of the larger body and stayed there.
Eccentricity: Objects with a more circular orbit have an eccentricity closer to 0.0. Objects with a more elliptical orbit have an eccentricity closer to 1.0.
You may agree. You may disagree. Or, keeping good company with one famous astronomer, you may wonder why in the hell you'd rank moons in the first place: "Do you really need to rank them all? There are hundreds."
Without further ado, we present an entirely subjective ranking—peppered with scientific "moonpinions"—of every confirmed moon in our solar system.
Saturn’s second largest moon, Rhea, was the first moon discovered to have a ring. In 2010, the moon was found to have an extremely thin exosphere with molecules of—you’ll want to sit down for this—oxygen. It was the first time oxygen had been spotted in an atmosphere other than Earth’s. Don’t hold your breath (or maybe do), there’s not enough to sustain life.
25. Epimethius and 24. Janus
The potato-shaped moon Epimetheus is in lock step with its sister moon Janus. They share the same orbit around Saturn, in a phenomenon called a co-orbital condition. The two moons may have begun their life as a single object, says Cassini mission project scientist Linda Spilker.
"They are so big that they cannot physically pass each other," Spilker says. Epimethius, the inner moon, goes a bit faster than the outer Janus. “As the inner one slowly approaches the outer, they switch places,” she says.
“They're kind of bizarre looking, but they do this intricate dance every four years,” Spilker says.
23. Naiad and 22. Thalassa
Naiad and Thalassa are seemingly stuck together in a mystifying, never-before-seen “Dance of Avoidance.” Neptune’s innermost moon, Naiad, has a strange wobbling orbit that shifts in accordance with nearby Thalassa’s orbit. The inner moon’s orbit is tilted by five degrees, and bobs up and down, in circles around Thalassa’s steady, equatorial orbit.
This cosmic do-si-do helps keep the moons stable even though they swing incredibly close to each other at their tightest pass—roughly 2,200 miles or about the distance from San Francisco to Chicago. Scientists aren't sure what kicked off this orbital resonance, but it's likely some sort of collision was involved.
Unfortunately, it’s a desperate love story for the two, tiny dancers. Thalassa also has what’s called a decaying orbit, which means it’ll eventually collide with Neptune.
Saturn’s pock-marked Hyperion looks like something you'd find in the aisles of Bed Bath & Beyond. The dark spots on Hyperion’s surface, Spilker says, are called sun cups. "If you've ever watched it snow and the snow gets dirty, the darker material melts faster and you create sun cups.”
It's not just the spongy appearance that makes Hyperion so fascinating. It’s one of a handful of places in the solar system that carries a static charge. It actually zapped Cassini with a beam of electrons—the equivalent of 200 volt charge—as the spacecraft zoomed by in 2005.
"It's just a very whacky looking moon," Spilker says. "It's very unusual."
Callisto is a literal relic. Scientists believe the moon of Jupiter—the third largest in the solar system—has the oldest, most cratered surface in the solar system. Recent estimates suggest it’s about 4.5 billion years old—roughly the same age as Jupiter. Sure, we have samples of Earth rocks and moons rocks that are the same age, what's surprising is that all of Callisto's surface is that old.
“Aesthetically, I like the look of Callisto a lot,” UCLA astronomer David Jewitt tells Popular Mechanics. The astronomer, who discovered many of the moons on this list, likens Callisto to a smashed Christmas ornament. Long ago, something smashed into the icy moon, forming the most notable feature on its surface—a 2,361-mile-wide crater called Vahalla. The weight of that crater has buckled the surface in that region, forming a ring of concentric circles around the crater.
The mysterious moon has a very, very thin atmosphere, called an exosphere, that’s rich in carbon dioxide, and trace amounts of oxygen and nitrogen. Recent research has suggested that the moon may also have a salt water ocean deep below its crust.
19. Pan and 18. Atlas
So, why do these small moons look like like pasta? As these flying saucer-shaped moons zip through their respective gaps in Saturn's rings, they scoop up material, which, thanks to rotational forces, slides toward the equator.
"Let's give a shout out to Tethys, the moon that's made of pure water," says planetary scientist Kevin Zahnle of NASA’s Ames Research Center of the Saturnian moon. "It's like a teardrop in space. Sorry—a frozen teardrop in space."
One of Tethys' strangest features is a set of red-hued arcs that streak across the surface that scientists suspect are caused by chemical impurities. It’s a relatively rare sight. Only a few objects in the solar system have rust-colored marks on their surface.
Both Tethys (and Mimas) have curious heat signatures. Thermal observations that Cassini took in 2011 revealed Pac-Man-shaped signatures. Researchers believe that the moons’ chillier regions are bombarded with electrons that harden the icy surfaces, making it tougher for them to warm up.
"That's no moon!"
Obi-wan Kenobi was right about the Death Star. This celestial object, however, is a moon. Mimas, one of Saturn’s many moons, is roughly the same size as its fellow Saturnian neighbor, Enceladus, and appears to have a subsurface ocean, too.
But it’s best known for Herschel Crater, which—sci-fi buffs will attest—makes the moon look a whole lot like the Death Star. “It would be cool to go figure out what caused the giant impact crater, why it’s so huge on such a small body and why the body didn't blow apart” upon impact, says planetary scientist and geochemist Justin Filiberto of the Lunar and Planetary Institute.
14. Deimos and 13. Phobos
Mars’ two moons, Phobos and Deimos, were proposed in the 17th century by the famed astronomer Johannes Kepler and discovered more than 200 years later by Asaph Hall. They’ve intrigued scientists ever since.
Deimos is the smaller of the pair, with a mean radius of about 3.9 miles. Both Deimos and its companion moon have a nearly circular orbit, suggesting they may have formed near the Red Planet, possibly the result of a massive Martian asteroid impact that shed debris.
Phobos has a mean radius of 6.9 miles and is marred by the massive Stickney Crater, which takes up almost half of its surface. Phobos is “barely held together," says heliophysics PhD student Gwen Hanley of UC Berkeley. “It can fall apart due to stress at any time, and I relate to that as a grad student."
Ultimately, Phobos is doomed. The moon has a decaying orbit, which means Mars tugs on Phobos, drawing it slightly closer—by as much as seven-tenths of an inch per year. Eventually, astronomers believe the moon will either be torn to bits, forming a ring around Mars, or potentially smash into the Red Planet.
Deimos, on the other hand, is slowly scooting away from the planet. Astronomers believe that its outwardly decaying orbit will eventually fling the moon into space.
Japan’s space agency, JAXA, plans to launch a mission to investigate the pair in 2024. The Mars Moon eXploration mission will attempt to bring samples of Phobos back to Earth. “One of the justifications for going there is that there should be a few percent Martian material on the surface,” astromaterials curator Francis McCubbin of NASA’s Johnson Space Center told Popular Mechanics. “It's sort of like our first Mars sample return.”
Daphnis is the second tiniest moon in the top 15, but it’s one of the most charismatic. With a mean radius of just 2.4 miles, Daphnis zips around Saturn, tucked in the Keeler gap at the edge of the planet’s A.
The gravitational pull of the tiny rock tugs at dust particles along the edge of the Keeler gap, carving waves of material that lead and trail the moon. During Saturn’s equinox, when the rings’ plane aligns with the sun, these tiny perturbations cast mesmerizing shadows on the planet.
Dubbed the Frankenstein moon, Miranda looks like it's been torn apart and stitched back together a thousand times. The innermost of Uranus’ five major moons, Miranda has an intriguing set of surface features. There's the "coronae,” or crater-free splotches of concentric ridges on its surface, which researchers believe may be composed of ammonia-water lava—a striking idea considering the moon should be too cold to support geologic activity.
And then there's Miranda’s most striking feature, Verona Rupes, the tallest cliff in the solar system. The shear cliff drops about 33,000 feet, or five times the depth of the Grand Canyon. “If you stepped off, you'd have time to read the newspaper on the way down,” Cassini mission project scientist Linda Spilker says of the eight-minute-long fall.
There are several ways that Miranda’s impossibly splintered surface could have formed. One suggests that the moon was split open by a massive impact and then quickly pulled back together. Others believe that perhaps these regions melted and refroze after a series of meteorite strikes.
"All these satellites, particularly the ones far away and small, are surprising us," planetary scientist Mark Hofstadter of NASA's Jet Propulsion Laboratory tells Popular Mechanics. Miranda is certainly no exception.
“It's tiny and it's orbiting an asteroid! How can you not like something like that?" says Charlotte Götz, a research fellow at the European Space Agency.
At about 524 feet in diameter, Didymoon, which orbits the asteroid Didymos, is about as large as one of the great pyramids in Egypt. The tiny moon is one of the solar system’s quaintest features, but it’ll take part in what is arguably one of the most important space missions of all time.
Didymoon and Didymos are the target of an international collaboration to test one of humanity’s most daring plans: deflecting a potentially hazardous object that could strike Earth. It’s a kamikaze mission for the intrepid spacecraft—dubbed the Double Asteroid Redirection Test (DART)—which will fling itself into the small moon in an attempt to knock it off course. A follow-up craft called Hera will be close behind to measure the effects of the impact and report back to scientists.
Thankfully for everyone back home, the Asteroid Impact and Deflection Assessment (AIDA) is just a dress rehearsal. Still, it’s our best shot at averting a future catastrophe here on Earth.
First, the moon has an orbit that’s completely unique to the solar system. Charon and its dwarf planet, Pluto, are part of what’s called a double planetary system, meaning they both orbit the same point. They're also mutually tidally locked, which means that if you were standing on Pluto (which completes a rotation in 6.4 Earth days) you’d always see the same face of Charon (which takes 6.4 Earth days to orbit the dwarf planet) hanging in the same spot in the sky.
"Charon has this really dark cap of material," graduate student Jack Conrad of the University of California, Santa Cruz tells Popular Mechanics. That red dusting of methane comes courtesy of Pluto. The dwarf planet isn’t able to hold onto its atmosphere, so it’s constantly spitting material onto its nearby moon. That methane gets trapped near the poles. Ultra-violet light from the sun converts the methane into hydrocarbons and, eventually, organic compounds called tholins.
One thing is certain: the moon has a violent past. “Charon seems to have just ripped itself asunder," Conrad says. Scientists have found evidence of cry0volcanism on the tiny, icy moon. A 1,000-mile-long canyon tears across Charon’s southern hemisphere and the moon has a single, towering mountain, which juts out of a deep hole on the moon’s surface.
Conrad put it simply: “Charon’s lumpy, but that’s all right.”
8. Moon Moon
“I can't tell you how many times I was a little kid driving back from my grandmother’s house to the southside of Chicago, looking out the window and staring at the moon,” former NASA astronaut John Grunsfeld tells Popular Mechanics. "Everyone has their own personal view, but I have to start with our moon because it’s our moon.”
Since the dawn of time, humanity has been transfixed with our closest planetary neighbor. That soft gray rock, suspended in the night sky has inspired generations of artists, poets and explorers. Like so many other astronauts, Grunsfeld credits the lunar landing for inspiring an early interest in science. “Didn't get there, but I got to Hubble three times, so that's not too bad,” he says.
Formed billions of years ago after a Mars-sized body slammed into Earth, the moon sways Earth’s tides and stabilizes Earth’s wobble on its axis, according to NASA, all but securing a liveable climate. There has even been evidence to suggest its tidal forces influence seismic activity here on Earth.
"It's close enough that you can see its surface and identify craters, mountain ranges, rilles, valleys, escarpments, and other features,” Bing Quock, assistant director of the Morrison Planetarium in San Francisco, tells Popular Mechanics. This opportunity allows scientists to explore some of the moon’s most intriguing features like the Lunar X or the chains of craters on its surface. It’s one of just a few surfaces in the solar system that generates an electrostatic charge.
“In the permanently shadowed regions near the poles are some of the coldest temperatures recorded anywhere in the solar system,” says planetary scientist Rebecca Ghent of the Planetary Sciences Institute. Orbiting spacecraft have discovered water ice—a valuable resource we’ll tap into if we aim to explore distant reaches of the solar system.
And, of course, we’ve been there. We’ve sent 105 spacecraft to the moon and 12 astronauts have set foot there. We’ve walked, skipped and stumbled across its surface, planted flags and carved donuts into the lunar regolith. We’ve studied some of the 842 pounds of geologic samples we retrieved, detailing every crack, crevice and grain. "Still gives me chills just to think about it," Quock says.
Finally, our excursions to the moon have allowed us a unique look at our own home. It’s been dubbed “the Overview Effect,” and a number of astronauts have shared how looking back at Earth from the moon has shaped their perspective upon returning home. "Just as valuable as what we learned about the Moon during [the Apollo] missions was the sobering perspective gained about Earth as a fragile, delicate oasis of life in the unimaginable emptiness of space," Quock says.
We’ll be going back soon. NASA aims to land the first woman and next man on the moon by 2024. It’s ambitious, but there’s no doubt that when we eventually return to the lunar surface, a whole new world will be waiting for us.
"I think Iapetus might be the most interesting one," planetary scientist Scott Sheppard of the Carnegie Institute for Science tells Popular Mechanics.
It’s known as the Yin-Yang moon because of its mysterious coloration: one side of the moon is covered in a massive blotch of dark material while the other is a pristine shade of white.
It could be that Iapetus is plastered with the guts of another fellow moon, Phoebe (86). When the pockmarked Phoebe sheds material, that rocky, icy debris lands on Iapetus’ night side, and eventually, particle by particle, hops toward the moon’s poles. “We think Iapetus is like a snowplow, just picking up the dark dust,” Sheppard says.
The moon is also home to a towering equatorial ridge. “There's some thought that maybe Iapetus had a ring and the ring collapsed onto the surface and created—a long time ago—this mountain range,” says Spilker. Others have suggested that the mountains arose when the moon was first forming and spinning much faster, and thus slinging material toward the equator.
Sheppard is perhaps most intrigued by its strange inclination. Most of Saturn’s regular moons, the ones that formed along with it, lie along the same plane. But Iapetus is about eight degrees outside that plane. “That suggests that Iapetus may not have formed with Saturn,” Sheppard says. “Maybe it is a captured moon.”
“It’s the most underrated moon in the solar system,” Jacob Abrahams, a grad student in the school of Earth and Planetary Sciences at UC Santa Cruz, tells Popular Mechanics. Jupiter's Ganymede is also the largest in our solar system—larger than Mercury—and likely has a vast ocean of warm, salty water beneath its crust.
“It's the only moon we've known yet which has its own magnetic field, and we don't know why, really," instrument scientist Glynn Collinson of NASA’s Goddard Space Flight Center tells Popular Mechanics. “It generates a very small magnetosphere—the smallest known to science."
Scientists have long suspected that the moon may have a metallic iron core. Recently, the Hubble Space Telescope spotted ribbons of aurorae circle the moon's poles. "Basically all of our physics and understanding breaks down, and everybody's models go wrong, and everybody ends up yelling at each other," Collinson says.
In 1996, the Hubble Space Telescope discovered evidence that Ganymede has a uber-thin atmosphere that contains oxygen. (Don't get your hopes up. It's not likely there's enough to support life.) “We get to explore this thing and we have no idea how it works," Collinson says. "It confounds us at every turn."
In 2012, the Hubble Space Telescope snapped pictures of Europa which revealed massive plumes of water vapor jetting as high as 100 miles out into space. All hell broke loose. The plumes revealed that one of life's key ingredients, liquid water, was abundant on Europa.
The tiny moon of Jupiter, Europa has been an object of fascination for centuries, but in recent years, there has been a rabid fascination with the nearly Moon-sized moon. Spurred by Hubble data, astronomers revisited old Galileo mission data and found similar evidence for plumes of water vapor, increasing the odds that the moon might host—at the very least—the ingredients for life.
The tiger-striped moon is covered in a thick crust of ice, ten to 15 miles thick, which sits upon a vast watery ocean, nestled atop a rocky mantle and iron core. That ocean contains more water than all of Earth’s oceans, planetary scientist Christopher Edwards of Northern Arizona University told Popular Mechanics.
The surface of the frozen moon is covered in linaea, a tangled network of salt-encrusted gashes thought to have formed by tidal forces. Researchers have long proposed sending a submersible to Europa which would drill down through the moon’s thick crust—perhaps slipping into one of these canyons—to explore the ocean beneath.
The moon is also home to a surface feature called “chaos terrain,” which are thought to be regions where blocky chunks of sulfur and salt-stained crust, which were laid upon buried lakes, subsided. It doesn’t get more badass than that.
"I think [Europa]'s got the highest probability of hosting some alien life in our solar system that we could go and find out if it’s there," says former NASA astronaut John Grunsfeld. "We're going to do that hopefully with Europa Clipper or some other missions."
NASA’s Europa Clipper mission is set to launch for the frozen moon this decade. Once it arrives at Europa (after a six year journey), the spacecraft will conduct 45 flybys. Its array of scientific instruments will snap pictures, capture spectra and thermal images of geologically active moon, in an effort to more closely identify its most active regions.
We can’t wait to see what it finds.
Triton, the largest moon of Neptune, is an interloper. An outsider. A misfit. Planetary scientists believe the moon originated far from its parent planet, in the distant Kuiper belt, and was later sucked into the planet’s orbit.
“It's really cool to think that there's basically a captured Pluto orbiting Neptune,” says atmospheric and space physicist Dave Brain of the University of Colorado, Boulder. “It's a very large moon, which means that capture was difficult unless it was part of a binary object.”
Of all the large moons in the solar system, it's also the only one to spin in the opposite direction of its planet.
Dense Triton is also rockier than the other satellites that circle Ice Giants Neptune and Uranus, which are often made entirely of ice. “We think it might have an ocean underneath its icy surface on top of where there's any rocky core,” says space and planetary scientist Adam Masters of Imperial College London. “Triton stands out as quite unique in that respect.”
Temperatures on the moon are frigid. When Voyager 2 zipped past Neptune and Triton, it took surface temperature readings, which revealed that the moon’s surface could drop to around -391 degrees Fahrenheit. Planetary scientists believe ammonia may be the key to keeping its hidden ocean liquid in spite of the freezing temperatures.
Triton’s shining, ice-covered surface reflects 70 percent of the light that it receives, according to NASA, and its thin, nitrogen-rich atmosphere has traces of methane, an indicator that it might be more alive, geologically speaking, than previously thought. Voyager 2 data revealed that like Enceladus and Europa, the moon may cast plumes of water high into space.
In January, NASA announced that a long-awaited mission to Triton will be up for consideration by the agency’s Discovery Program. If chosen, the Trident mission would set out to explore one of the solar system’s most intriguing moons before the decade wraps.
"All these wrong answers are wrong,” Frederik Johansson of the Swedish Institute of Space Physics told Popular Mechanics. “The true answer is Enceladus.”
Saturn’s tiny moon, Enceladus, didn’t look like much at first. “We thought it would be frozen solid,” says Spilker. “And yet, over the course of the 13 years of the Cassini mission, [we] discovered that it had a global ocean of liquid water, jets coming out of the south pole and evidence for hydrothermal vents.”
Scientists were so intrigued by the 310-mile-wide moon’s jets that they sent Cassini on a detour to investigate. It sailed through the icy plumes 23 times and made unbelievable discoveries. Critically, Spilker says the craft found hydrogen, carbon, nitrogen and oxygen in the plume—the “Big Four” ingredients of life—and strange nanocarbons which only form along hydrothermal vents.
The plumes spew this material into space; some of it floats off to seed Saturn’s E ring, but much of it falls back down to the moon’s surface. "Go to Enceladus. Just peak down, and see if there's life in there—or potential for life in there,” Johansson says with a grin. “You don't have to dig! Just peak down!” Spilker says it could be as simple as landing beneath a plume, sliding open a sampling tray and then jetting back to earth.
“We had so many clues,” Spilker said of Voyager 2’s flyby of the tiger-striped moon in 1981. "But it took Cassini to go back and figure it out. In an almost poetic twist, the moon is also the brightest body in the solar system—a beacon in more ways than one.
“Io is the most volcanically active body in our solar system and in the known universe,” says planetary scientist Dan Spencer of the University of Oxford. “The volcanoes are so big that we can actually see them from telescopes based on Earth.” When astronomers mapped the violent world, they counted over 400 volcanoes (about 150 of which are active) on its surface. Some of them spew jets of lava hundreds of miles into space.
As Io sweeps by Jupiter, the planet drags particles off its surface, forming a small magnetosphere, or plasma torus around the moon. Its thin, noxious atmosphere is almost completely composed of sulfur dioxide gas, which condenses into sulfur dioxide ice when it passes through Jupiter's shadow.
So, why is the moon so volcanically active? We have gravity to thank. Io is smack dab in the middle of a gravitational game of Tug-O-War. Io’s the recipient of an intense pull from the strong gravitational field of Jupiter as well as the gravitational fields of the neighboring Ganymede and Europa. Io is also subjected to some of the most powerful tidal forces in the solar system. Its surface bubbles and bulges, sometimes by as much as 330 feet and is constantly churning out new lava.
Because it is the closest Galilean moon to Jupiter and passes swiftly through the planet’s magnetic field, Io can also generate a serious electric current—around 3 million amperes. This jolt of electricity is shot back toward Jupiter, forming lightning in the planet’s upper atmosphere.
Because of its stunning—if not completely terrifying—features, it’s unlikely we’d ever find life on the moon. Despite this, it's a high priority for planetary scientists who hope to learn more about Earth's own volcanic past. Io is one of the proposed mission targets of NASA’s Discovery Program. Scientists have proposed to send a probe Io for closer look at the moon’s lava flows, which are stitched together like a psychedelic patchwork quilt.
For climate and space scientist Xianzhe Jia of the University of Michigan, the allure of the moon is simple: “It’s just so colorful.”
It was the perfect Christmas gift. On December 25, 2004, the tiny Huygens Probe—an integral facet of the famed Cassini mission—floated down through a thick haze and onto Titan’s surface. Images from the landing revealed a stunning world that looked not unlike our own.
“It has to be Titan," Peter Gao, a post-doc in Astronomy at UC Berkeley, tells Popular Mechanics. "It is the only moon with a thick, significant atmosphere and the surface pressure is 50 percent higher than the surface pressure on Earth.” And while you would definitely need an oxygen mask, you could hypothetically walk around on the moon’s surface without a pressurized suit.
Titan’s atmosphere is flush with Nitrogen, just like Earth’s. But instead of oxygen, the next most abundant element in the moon’s atmosphere is methane. The moon is dominated by hydrocarbons like methane and ethane. Just as we find all three phases of water on Earth—liquid, water and gas—you can find all three phases of methane on Titan.
“You get a lot of chemistry that forms this orange, goopy haze that goes around the entire moon,” Gao says.” That’s why it looks orange. All of that chemistry eventually leads to methane and ethane storms near the surface.”
Aside from Earth, it is the only known celestial body to have liquid on its surface. Titan’s rivers, lakes and seas—like Kraken Mare—are filled with hydrocarbons. "It looks hauntingly familiar," says Spilker of Titan’s varied landscapes. "And yet, it's just cold."
Instead of limestone or granite, the bedrock on Titan, which forms jutting mountains and large mesas is made from water ice. And then there are the dunes. Titan is home to a vast network of dune fields, which are sculpted by its nitrogen winds and made mostly of dark, hydrocarbon grains which, NASA suggests, resemble coffee grounds.
As if that weren’t enough, planetary scientists believe that a vast subsurface ocean of water and ammonia rests beneath all of these features, rendering Titan—along with Europa and Enceladus—a potential candidate for finding some form of life.
Everything about the moon is an enigma. It’s the second largest moon in the solar system and, with a mean radius of about 1,600 miles, the largest of Saturn’s moons. Rhea, the next largest moon of Saturn, has a mean radius of 475 miles. Researchers aren’t exactly sure how Titan formed. Nitrogen isotopes suggest it might have formed in the Oort Cloud. One recent theory suggests it formed within the safety zone of a planetary disk, which prevented it from being gobbled up by Saturn.
In 2026, NASA plans to launch the Dragonfly mission, a rotorcraft which will hopskotch to different regions on Titan’s surface, collecting data so that we can better understand the most mysterious moon in the solar system.
Update: We've corrected the article to reflect that the Keeler Gap lies within Saturn's A ring and not between Saturn's A and B ring. | 0.930594 | 3.760707 |
Vid + Pic After seven years, and more than three billion miles of travel, the Dawn spacecraft has been captured by the gravity of the Solar System's dwarf planet Ceres. The NASA probe entered a stable orbit at 0439 PST (1239 UTC) on Friday.
"We feel exhilarated," said Chris Russell, principal investigator of the Dawn mission at the University of California, Los Angeles (UCLA). "We have much to do over the next year and a half, but we are now on station with ample reserves, and a robust plan to obtain our science objectives."
Dawn was belatedly launched in September 2007 with a twin mission to study the two most massive objects in the asteroid belt between Mars and Jupiter, and to test the practicality of using ion drives to explore the Solar System.
In the latter case, ion drives are now considered a proven technology, and commercial satellites use them to maneuver around Earth, cutting the weight of fuel needed by 90 per cent. Dawn carries less than a tonne of liquid xenon, and wouldn’t have been able to reach Ceres using rocket fuel: launching all that material in space would be too expensive.
The Dawn spacecraft has used its three xenon-powered thrusters, along with a tricky gravity assist from Mars, to conduct its mission. In 2011 it successfully made it into orbit around the massive asteroid Vesta and spent 14 months making high and low passes over the huge chunk of space rock before heading off to Ceres.
Astronomers have been intrigued by the early images sent back of the dwarf planet, in particular by a series of bright spots that have appeared on the surface. These may be volcanoes, or frozen lakes of ice reflecting back the Sun’s rays, or even the lights of a distant civilization as some more excitable people have suggested.
We will now get to the truth of the matter, as Dawn works on its final maneuvers. The spacecraft is orbiting in the dwarf planet’s shadow but by mid April, a series of ion thrusts will bring it into a lower orbit covering Ceres’ sunward side and begin scanning the surface.
For science, the spacecraft carries a visible and infrared thermal-imaging spectrometer, a 66-megapixel camera, and the Gamma Ray and Neutron Detector (GRaND), and all will now be focused downwards on Ceres.
The dwarf planet is an intriguing target. Discovered in 1801, Ceres was first thought to be a planet in its own right. It makes up over a third of the mass found in the asteroid belt, but was judged just a little too small to achieve planet status once better telescopes could estimate its size.
Hopefully Dawn’s analysis will give us clues as to how these types of bodies were formed in the early history of the Solar System, and what keeps them together. It is thought Ceres has a thin atmosphere and a lot of water, and this could make it a useful spot if mankind ever decides to get serious about colonizing our tiny segment of space. ® | 0.86383 | 3.790292 |
TRAPPIST-1 is one of the most intriguing exoplanetary systems known. Two years ago, it was found to consist of a red dwarf star with seven Earth-sized worlds orbiting it. While we know the planets exist, there’s still a lot astronomers don’t know yet about what the actual conditions are like on these distant worlds. An important question concerns their atmospheres. Are they cloudy worlds, with weather, like Earth? Are they entirely haze-covered like Venus? Or are their atmospheres clear?
A new study led by Sarah Moran at Johns Hopkins University suggests that at least some of the planets likely have hazy or cloudy atmospheres, and at least one may have a clear hydrogen atmosphere. The peer-reviewed paper was published in The Astronomical Journal on November 9, 2018.
Recent observations from the Hubble Space Telescope showed that some of the planets have muted spectral features in their atmospheres that could be indicative of clouds or haze. The new study tries to put limits on these observations to determine further just what the atmospheres are like on the TRAPPIST-1 worlds. As noted in the paper:
The TRAPPIST-1 planetary system is an excellent candidate for study of the evolution and habitability of M-dwarf hosted planets. Transmission spectroscopy observations performed on the system with the Hubble Space Telescope (HST) suggest that the innermost five planets do not possess clear hydrogen atmospheres.
The researchers are using transmission spectroscopy – aka absorption spectroscopy – in which they analyze the spectral lines in the light that filters through a planet’s atmosphere as the planet transits, or passes in front of, its host star. They focused on TRAPPIST-1 d, e, f and g, comparing the new computer models with the spectral data from Hubble. This allows them to learn more about possible hazes or clouds, their metallicities and the heights of possible cloud decks.
And there’s one more important step. They then compare their results to recent laboratory astrophysics experiments studying haze formation under a range of planetary temperatures and atmospheric compositions. By performing this final step, the researchers can make sure that their limits are physically realistic.
The results showed that TRAPPIST-1 d, e and f most likely have hazy or cloudy atmospheres that continued to evolve after the planet first formed (called secondary atmospheres). TRAPPIST-1 g may be more likely to have a primordial clear hydrogen atmosphere – formed during the formation of the planet itself and relatively unchanged since then. This may also apply to TRAPPIST-1 f, but the results are still open to interpretation at this point. From the paper:
Our results suggest secondary, volatile-rich atmospheres for the outer TRAPPIST-1 planets d, e and f.
From the paper:
For TRAPPIST-1 g, we cannot rule out a clear hydrogen-rich atmosphere. We also modeled the effects an opaque cloud deck and substantial heavy element content have on the transmission spectra. We determine that hydrogen-rich atmospheres with high altitude clouds, at pressures of 12mbar and lower, are consistent with the HST observations for TRAPPIST-1 d and e. For TRAPPIST-1 f and g, we cannot rule out clear hydrogen-rich cases to high confidence.
Haze in exoplanet atmospheres can make it difficult to study the compositions of the planets themselves. But haze could also protect hypothetical life on those planets’ surfaces from the high-energy radiation of their host stars. Understanding aerosol content in exoplanetary atmospheres is therefore important to being able learn more about such exotic worlds. While not a planet, Saturn’s largest moon Titan has a thick atmospheric haze composed of tholins – organic particles – that completely obscures the surface from view.
The TRAPPIST-1 planetary system is a great target for studying atmospheres of Earth-sized exoplanets since there are seven of them in one system, and they are not too far away our solar system – only 39.6 light-years, which is right next door, cosmically speaking.
TRAPPIST-1 is a cool red dwarf star only slightly larger than Jupiter. But all the known planets orbit quite close to the star, so some of them are within the habitable zone – the region where temperatures could allow liquid water to exist on the surfaces. Whether any of them actually are habitable is still unknown, however, as that also depends on other factors such as organic material and chemistry that could allow life to begin in the first place.
A previous study suggested that some of the planets in this system may be more like Venus than Earth, but also that TRAPPIST-1 e is probably the most likely to have water on its surface – perhaps even oceans (although others may as well). Three of the terrestrial rocky planets in our solar system have clouds or hazes in their atmospheres, but all are different – Mars just has a scattering of thin clouds, Earth has more substantial clouds and Venus is completely wrapped in a thick cloud cover. The TRAPPIST-1 planets may be just as varied as well, but further observations will be needed to find that out.
Bottom line: We still don’t know what conditions are like on any of the TRAPPIST-1 exoplanets, but scientists are getting closer to finding out. Determining what kind of atmospheres these worlds have can help scientists understand other details about them as well, and whether any of them could possibly support life.
Paul Scott Anderson has had a passion for space exploration that began when he was a child when he watched Carl Sagan’s Cosmos. While in school he was known for his passion for space exploration and astronomy. He started his blog The Meridiani Journal in 2005, which was a chronicle of planetary exploration. In 2015, the blog was renamed as Planetaria. While interested in all aspects of space exploration, his primary passion is planetary science. In 2011, he started writing about space on a freelance basis, and now currently writes for AmericaSpace and Futurism (part of Vocal). He has also written for Universe Today and SpaceFlight Insider, and has also been published in The Mars Quarterly and has done supplementary writing for the well-known iOS app Exoplanet for iPhone and iPad. | 0.914779 | 4.03868 |
There’s a lot more to the universe than the stars we see in the sky. Invisible to the naked eye, the broader universe is made up of a vast cosmic web: filaments of gas which stretch between galaxies, and which we’ve only recently been able to see for the first time. Now, you can explore it for yourself.
Although the cosmic web has been proven to exist, there’s still a great deal of uncertainty about how it is formed. What determines the web’s pattern? Why do galaxies connect to some neighboring galaxies, and not others? At Northeastern University’s Barabási Lab, German designer Kim Albrecht created a gorgeous visualization of three possible models to try to understand the network principles that help shape the universe. You can navigate through the interactive’s 24,000 galaxies–and the more than 100,000 connections between them–right in your browser.
Albrecht’s Cosmic Web model visualizes three separate models by mapping those 24,000 real galaxies as single specks of light, then drawing connections between those galaxies that depend on which structural model you’re exploring. One model connects galaxies when they are within a certain radius of each other, the second connects them based upon the size of the galaxy (where the larger the galaxy, the longer the connections it is capable of making), and then the third model simply connects every galaxy to its nearest neighboring galaxy.
Even if you don’t have a background in the physics behind each model, it’s fun to travel through Albrecht’s viz. You can rotate and zoom into each galaxy, traveling millions of light years across silk strands of cosmic gas in just a few seconds, all within your browser tab. Outside of being fun, though, the bigger goal was to help physicists understand which model most closely aligns to the real universe. (Spoiler: the structure of the real cosmic web is closest to the third “neighboring galaxy” model.)
According to Albrecht, one of the most exciting aspects of his work as an in-house data-visualization expert for a group of physicists is the way it help open up science. “Usually, these sorts of theories are negotiated between a very small number of people in a very specific field, but this makes their work understandable to thousands of even millions of people,” he says. “Data viz is a big and unique way to get science out there, and while that worries some scientists, I’m excited about how it can help change the field.”
All Images: via Kim Albrecht | 0.808146 | 3.911816 |
Title: LOFAR: opening a new window on low frequency radio astronomy
Authors: R. Morganti for the LOFAR collaboration
First Author’s Affiliation: ASTRON and the Kapteyn Astronomical Institute, The Netherlands
Tune down that radio dial
The radio portion of the electromagnetic spectrum has only been used in astronomical research for the last half-century, but has enabled many great discoveries and contributed significantly to our understanding of the Universe. Measuring 21 cm radiation from neutral Hydrogen at 1420 MHz has allowed us to map the gas content and velocity structure of galaxies in unprecedented detail; the discovery of pulsars gives us our most direct probe of exotic neutron stars; and, studying synchrotron emission associated with high-energy phenomena has led to insight into the extreme physical processes that can occur in the Universe, to name a few examples. The radio regime stretches across an incredibly huge portion of the spectrum, from (sub)millimeter wavelengths (up to 1 THz) out to the low-frequency cutoff (due to scattering from the Earth’s ionosphere) at hundred-meter wavelengths (a few MHz) – that’s nearly SIX decades in energy (or equivalently, wavelength or frequency), larger than the range covered by the entire ultraviolet, visible, and infrared regions combined! The most commonly used receivers at large radio telescopes and interferometers operate at frequencies above 500 MHz, leaving a large portion of the radio band virtually unexplored. But new facilities are changing this trend, and it is quite possible that the next major discovery in radio astronomy will come at low frequencies. Recent results from the ongoing commissioning of one the latest such facilities – LOFAR – were presented at the Asian-Pacific Regional IAU (International Astronomical Union) meeting, and also posted on astro-ph as the paper discussed in today’s astrobite.
Before you read any further, I suggest you have a look at Tanmoy’s excellent summary of radio astronomy here.
LOFAR, the LOw Frequency ARray, is a radio telescope in the Netherlands consisting of multiple phased-array antennas that operates in the 10-240 MHz (1-20 m) range. As suggested by its acronym, LOFAR is an interferometer, but unlike other examples such as the VLA and ALMA (see this astrobite by Ian for more acronyms), it is not comprised of radio dishes, but instead dipole antennas. Dipoles are metal rods of a specific length that are oriented so that the charges within them respond to an incident electric field from a particular direction. In other words, they are functionally similar to television antennas – but tuned to frequencies appropriate for astronomical sources. Using dipoles is cost-effective, and also allows for an enormous field of view, as radiation from any direction except one parallel to the axis of the dipole will induce a response in the antenna. They are not used in higher frequency astronomy because the “collecting area” of a dipole shrinks with the wavelength of radiation and so radio dishes are much more efficient at short wavelengths, but they work perfectly at the low frequencies of LOFAR.
LOFAR’s thousands (!) of dipoles are organized into groups called “stations”: 24 stations comprise the main portion of the telescope and are located within 2 km of the center of the array, 9 others are more remote (within 100 km), and 8 are placed internationally (see Figure 1); more stations are planned to be added in the near future. LOFAR operates in two frequency ranges, and has separate antennas for each: the Low-Band Array (LBA) at 10-90 MHz, and the High-Band Array (HBA, whose antennas are shown close-up in the title image) at 110-240 MHz. Why the hole between 90-110 MHz? Check your FM dial! Radio-frequency interference (RFI) is a serious problem in radio astronomy, and in some cases (such as in the FM radio range) renders the sky unobservable. (One only hopes that the Universe’s deepest secrets are not uniquely revealed at 100 MHz!)
The antennas can be configured in a multitude of ways, either combining or splitting data from different stations (and sometimes even within a single station) to observe targets large or small, bright or faint. LOFAR also achieves sub-milliJansky sensitivity – meaning that the level of noise is low enough that even very weak sources can be observed – and subarcsecond resolution – meaning that sources separated by angular distances less than an arcsecond (1/3600 of a degree) on the sky can be resolved. (For comparison, the full moon subtends 30 arcminutes, i.e. 1800 arcseconds!) LOFAR is extremely flexible, and can observe as a standard interferometer, by combining beams from several stations into a single coherent beam, or be triggered in real-time by transient detections.
This flexibility and power comes at a price, however; LOFAR generates a staggering 13 Terabits of raw data per second, far more than could possibly be transferred conventionally! Combining data at the station level allows this to be reduced to a “paltry” 150 Gigabits per second, which still requires dedicated fiber lines to keep up. Observations can easily generate 35 Terabytes of data each hour, making data storage a real concern as well. In addition, a highly accurate model of the sky and well-understood beam pattern are needed to calibrate the telescope and perform the deconvolution necessary to turn raw interferometric data into images. Needless to say, there is an entire team of software engineers – and a 28 Teraflop supercomputer – dedicated to addressing these computational challenges.
So, what can one do with thousands of dipoles? LOFAR was designed with four primary astrophysical goals: (1) studying the Epoch of Reionization through measurements of highly redshifted neutral Hydrogen; (2) exploring the formation and evolution of galaxies, clusters, and black holes; (3) transient sources, particularly in association with high-energy phenomena, and; (4) cosmic ray showers. Each of these will be briefly discussed below (much of this information came from an earlier paper posted by the LOFAR collaboration in 2007).
1. The Epoch of Reionization (EoR) is the period early in the history of the Universe when the first massive stars, galaxies, and/or quasars began producing enough ionizing radiation necessary to separate electrons from nuclei, which had recombined earlier due to the Universe’s rapid cooling and expansion (see this astrobite, and this one, and this one for more about the EoR). Before the EoR, most of the Hydrogen gas in the Universe (and specifically the gas between galaxies, or intergalactic medium [IGM]) was neutral, and thus emitted the ubiquitous 21 cm radiation; after the EoR, the majority was ionized, and thus would not be observed at 21 cm. Low-frequency studies probing the EoR are basically looking for the range in time over which the majority of the IGM went from being neutral to ionized by observing 21 cm radiation that has been very highly redshifted to meter wavelengths by the expansion of the Universe. Given that the background at low frequencies (from the galaxy, the solar system, and other bright sources in the radio sky) is orders of magnitude stronger than the extremely weak signal, this is a truly heroic observation, but in principle, LOFAR can use its high sensitivity and resolution to try to localize the EoR in space and time.
2. LOFAR’s very wide field-of-view makes it the perfect tool for large-scale sky surveys, and it will probe a frequency range that has been basically unexplored. It is expected that it will be able to identify more than a hundred radio galaxies at redshifts z > 6 , i.e. more distant than any yet known. These super-energetic sources are connected to both galaxy cluster and supermassive black hole formation, and observing them so early in the Universe could help clarify the nature of these connections. LOFAR will also observe diffuse radio emission in galaxy clusters out to z~2, probing their dynamics and the structure of intercluster magnetic fields, and measure the radio flux from distant star-forming galaxies, which can be combined with submillimeter observations to obtain accurate distances.
3. One of the most exciting things about LOFAR is the vast parameter space it opens up. Its gigantic field of view allows it to function as a very efficient synoptic telescope, and regular surveys will monitor a huge portion of the sky for transient sources, exploring variability on timescales from milliseconds to years. Some objects, such as pulsars, will be more fully characterized by studying their low-frequency spectra; for example, a recent result from early LOFAR has placed constraints the emission height within a pulsar’s magnetosphere. However, certain transients may also be indicative of entirely new and unknown astrophysical phenomena, and LOFAR is poised to discover objects potentially even stranger than black holes and pulsars (if one could dream of such a thing!)
4. Ultra high-energy cosmic rays (UHECRs) are also within reach of LOFAR. The telescope can be triggered by the detection of a cosmic ray shower from an external particle detector, or it can directly observe the radio emission produced in such a shower. This information can be combined with data from other facilities such as AUGER to better understand the formation and trajectories of UHECRs as well as the radiation mechanism involved in the shower process.
Figure 2 – Commissioning-phase images from LOFAR: nearby galaxy NGC 4631, four distant radio galaxies (center), and a galaxy cluster halo (right). Note the incredible resolution achieved!
A bright future
LOFAR is still in the commissioning phases, but the first science results are already starting to be produced – see Figure 2 for three examples: a normal galaxy, a quartet of radio galaxies, and a galaxy cluster halo. It is expected to be fully operational by the end of this decade, and is poised to revolutionize our understanding of the Universe through its unprecedented sensitivity and resolution, powerful survey capabilities, and access to previously unexplored parameter space. So while the frequency may be low, the promise of discovery for LOFAR is incredibly high.
For more detail regarding the recent LOFAR science results, see http://www.astron.nl/lofarscience2011/. | 0.877102 | 4.061102 |
New Mexico State University News Release
2012 October 18
An astronomy graduate student at New Mexico State University is looking for possible signs of life on Mars by studying the possible detection of methane gas on the planet.
Malynda Chizek is working on computer simulations using the NASA/Ames Mars Atmospheric General Circulation Model to replicate trace gases in the Martian atmosphere. She is using these simulations to predict the amount of methane that might be seen by the Mars Science Laboratory.
"There is an instrument onboard the Curiosity Rover - which landed on Mars in August - capable of measuring methane, but the scientists operating that instrument haven't made any public announcements of their results yet," said Chizek. "There have been several claims of methane detection in the past decade, but it is controversial whether or not there is really methane on Mars, because we do not understand how it would get there and scientists' observations suggest that it's varying in abundance on a very quick time scale, which is unexpected."
The significance of detecting methane on Mars is exciting, Chizek said, because it could lead to evidence of life. Approximately 95 percent of the methane in Earth's atmosphere is a product of biology.
To help people understand the volume and significance of methane on Mars, Chizek uses a very Earthly creature that produces the gas - cows.
"In a couple of my presentations, I show how many cows would be required to equal the amount of methane that astronomers have observed on Mars," she said. "Depending on which observations I am looking at, that number is close to five million cows, or roughly 200,000 tons of methane production per year."
Researchers are using telescopes on Earth and spacecraft in orbit around Mars to observe methane on Mars.
The Earth-based observations are considered controversial because Earth's atmosphere has a significant amount of methane, a factor of 100 to 1,000 times higher than what the published Martian methane detections have stated, which may interfere with detection of the Martian methane signal. The instruments on spacecraft orbiting Mars used for methane detections have a lower methane detection capability than do the Earth-based instruments. Some scientists consider the orbiting instruments to be inadequate for detecting Martian methane, Chizek said.
Chizek said she is using her model to try and trace back the detected methane to its source location to see if it is coming from something like a volcanic source, water surface chemistry interaction or bacteria living on or near the surface.
"Mars is thought to be a geologically dead planet," she said. "If the methane detections are confirmed, and we do not find any signs of bacterial life, this means there are likely some interesting geological processes happening on Mars that we don't yet know about."
Jim Murphy, Chizek's adviser, said some of the recent observations of Mars' atmosphere, which suggest that methane might be present there, also suggest that there are substantial seasonal variations in the quantity of methane.
"These variations are unexpected since methane is expected to persist for hundreds of years within the atmosphere if it is introduced in to the atmosphere, and since the variations would imply substantial sources being currently active, such as life or a chemistry of some sort," he said.
Even if there are not any currently active sources of methane on Mars, and even if the "too rapid loss" of methane suggested by the recent observations is incorrect, Curiosity could still possibly detect methane being present in very small amounts.
In such a situation, Chizek's computer simulation results still suggest that Curiosity should see some seasonal variations in its local methane abundance since gases like methane become concentrated within the high latitudes of the winter hemisphere as the main atmospheric gas, carbon dioxide, "freezes out" of the atmosphere and forms a winter polar ice cap.
Chizek is now finishing simulations of her observations and is completing a paper on the topic co-authored by Murphy, an associate professor of astronomy, and former NMSU student Melinda Kahre. Kahre now works at the NASA Ames Research Center.
Chizek's work is funded by a previously awarded $15,000 NASA Space Grant fellowship. Chizek, who plans to complete her doctorate in 2013, is using her Mars research for her dissertation.
"I am now providing predictions on what Mars Science Laboratory scientists might see, based on the other past observations," she said. "More confirmation will come from MSL itself when it eventually announces whether or not it has observed methane and what sort of variations it might or might not have seen."
"This research is important to NMSU by virtue of it being the work of a graduate student, as well as placing NMSU in the position to provide substantial value to ongoing U.S. Mars-exploration efforts," said Murphy. "We want our students and faculty to be involved in leading-edge science studies, and this effort of Malynda is one such effort. Conducting investigations to aid in the interpretation of data/measurements is a cornerstone of science, and this research is a very good example of the work required to understand what available data are trying to tell us."
Chizek recently presented her findings at a presentation during the American Astronomical Society's Division for Planetary Sciences meeting in Reno, Nev.
NMSU graduate student looks for indications of life on Mars in possible trace methane gas.
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Copyright © 2012, Brian Webb. All rights reserved. | 0.878373 | 3.644378 |
High-altitude winds on neighboring Venus have long been known to be quite speedy, whipping sulfuric-acid-laden clouds around the superheated planet at speeds well over 300 km/h (180 mph). And after over six years collecting data from orbit, ESA’s Venus Express has found that the winds there are steadily getting faster… and scientists really don’t know why.
By tracking the movements of distinct features in Venus’ cloud tops at an altitude of 70 km (43 miles) over a period of six years — which is 10 of Venus’ years — scientists have been able to monitor patterns in long-term global wind speeds.
What two separate studies have found is a rising trend in high-altitude wind speeds in a broad swath south of Venus’ equator, from around 300 km/h when Venus Express first entered orbit in 2006 to 400 km/h (250 mph) in 2012. That’s nearly double the wind speeds found in a category 4 hurricane here on Earth!
“This is an enormous increase in the already high wind speeds known in the atmosphere. Such a large variation has never before been observed on Venus, and we do not yet understand why this occurred,” said Igor Khatuntsev from the Space Research Institute in Moscow and lead author of a paper to be published in the journal Icarus.
A complementary Japanese-led study used a different tracking method to determine cloud motions, which arrived at similar results… as well as found other wind variations at lower altitudes in Venus’ southern hemisphere.
“Our analysis of cloud motions at low latitudes in the southern hemisphere showed that over the six years of study the velocity of the winds changed by up 70 km/h over a time scale of 255 Earth days – slightly longer than a year on Venus,” said Toru Kouyama from Japan’s Information Technology Research Institute. (Their results are to be published in the Journal of Geophysical Research.)
Both teams also identified daily wind speed variations on Venus, along with shifting wave patterns that suggest “upwelling motions in the morning at low latitudes and downwelling flow in the afternoon.” (via Cloud level winds from the Venus Express Monitoring Camera imaging, Khatuntsev et al.)
A day on Venus is longer than its year, as the planet takes 243 Earth days to complete a single rotation on its axis. Its atmosphere spins around it much more quickly than its surface rotates — a curious feature known as super-rotation.
“The atmospheric super-rotation of Venus is one of the great unexplained mysteries of the Solar System,” said ESA’s Venus Express Project Scientist Håkan Svedhem. “These results add more mystery to it, as Venus Express continues to surprise us with its ongoing observations of this dynamic, changing planet.” | 0.817004 | 4.035064 |
Moon* ♐ Sagittarius
Moon phase on 22 June 2070 Sunday is Waxing Gibbous, 13 days young Moon is in Sagittarius.Share this page: twitter facebook linkedin
Previous main lunar phase is the First Quarter before 6 days on 15 June 2070 at 13:40.
Moon rises in the afternoon and sets after midnight to early morning. It is visible to the southeast in early evening and it is up for most of the night.
Moon is passing about ∠18° of ♐ Sagittarius tropical zodiac sector.
Lunar disc appears visually 6.5% narrower than solar disc. Moon and Sun apparent angular diameters are ∠1768" and ∠1888".
Next Full Moon is the Strawberry Moon of June 2070 after 1 day on 23 June 2070 at 16:57.
There is medium ocean tide on this date. Sun and Moon gravitational forces are not aligned, but meet at very acute angle, so their combined tidal force is moderate.
The Moon is 13 days young. Earth's natural satellite is moving from the first to the middle part of current synodic month. This is lunation 871 of Meeus index or 1824 from Brown series.
Length of current 871 lunation is 29 days, 6 hours and 50 minutes. This is the year's shortest synodic month of 2070. It is 47 minutes shorter than next lunation 872 length.
Length of current synodic month is 5 hours and 54 minutes shorter than the mean length of synodic month, but it is still 15 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠5.3°. At beginning of next synodic month true anomaly will be ∠21.1°. The length of upcoming synodic months will keep increasing since the true anomaly gets closer to the value of New Moon at point of apogee (∠180°).
1 day after point of apogee on 21 June 2070 at 14:15 in ♐ Sagittarius. The lunar orbit is getting closer, while the Moon is moving inward the Earth. It will keep this direction for the next 14 days, until it get to the point of next perigee on 6 July 2070 at 18:57 in ♊ Gemini.
Moon is 405 302 km (251 843 mi) away from Earth on this date. Moon moves closer next 14 days until perigee, when Earth-Moon distance will reach 359 714 km (223 516 mi).
4 days after its ascending node on 17 June 2070 at 21:35 in ♎ Libra, the Moon is following the northern part of its orbit for the next 9 days, until it will cross the ecliptic from North to South in descending node on 2 July 2070 at 07:45 in ♈ Aries.
4 days after beginning of current draconic month in ♎ Libra, the Moon is moving from the beginning to the first part of it.
13 days after previous North standstill on 9 June 2070 at 03:14 in ♊ Gemini, when Moon has reached northern declination of ∠18.846°. Next day the lunar orbit moves southward to face South declination of ∠-18.860° in the next southern standstill on 23 June 2070 at 00:15 in ♑ Capricorn.
After 1 day on 23 June 2070 at 16:57 in ♐ Sagittarius, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.159837 |
Earlier this month six volunteer astronauts stepped out of a spacecraft mock-up in which they had been living for 18 months. The idea was to see how they stood up to the rigors of the trip, one of which was living in a confined space mostly out of contact with the outside world for such a long time. You have to be special to handle something like that.
The time needed to get to even the nearest planets is a major problem, not only for technology, but also for the crew. In addition to the psychological challenges, a long time in interplanetary space, outside the protection of the Earth’s magnetic field, increases the risk of radiation from solar flares. It would be nice to be able to cut that time to something more reasonable, say a week. If we had a rocket engine that could produce enough thrust to provide an acceleration equivalent to the Earth’s gravity, running that engine for five days would get us to Mars in about a week. Running it for ten days would make the trip even shorter. However, currently we do not have rocket engines that can do that. We can either use conventional rocket engines to produce huge thrusts for minutes, burning tonnes of fuel a second, or use ion engines to produce tiny thrusts almost indefinitely, using small quantities of fuel. Improved ion engines will probably be the solution that opens up the Solar System to exploration, but we have a long way to go before that becomes viable.
Using chemical rockets, which provide big shoves for short periods is rather like throwing a ball at another ball that a friend has thrown into the air. The aim, timing and the velocity of the throw are all critical. The ball then essentially “falls” to the target. In the case of a spacecraft heading for Mars, there would be additional fuel on board for minor course corrections, but nothing more than that, so getting the timing, velocity and direction right at the beginning of the trip is even more critical.
When we arrive at Mars we would prefer to orbit round it or land on it rather than smash into it, or perhaps hurtle past it. This means we will need the means to decelerate, which in turn requires more fuel, more weight, a bigger launcher, higher costs and so on. Therefore we would like to arrive at Mars with a speed not too different from Mars’ speed. Then we can use small retrorockets or even Mars’ atmosphere to slow us down. By the time we have designed the space mission to do all these things, we are back with spending months in transit.
This leads to the argument that we should hold off with manned exploration of the Solar System until we have developed marvellous new propulsion technologies. However, they are probably decades away. Imagine being back in the 17th or 18th Century, sitting in France or Britain, and planning a mission to Canada. You look at those fragile, uncomfortable, sailing ships and decide to hold off until new technologies, like the jet airliner, are developed. How would that have changed history? Consider the scientific discoveries and technical innovations that have come about because of things we are doing in space, which could not have come about by waiting until there are better ways to get there. Imagine finding alien life on Mars!
Jupiter rises at 3 p.m, Mars at midnight and Saturn at 5 a.m. The Moon will be New on the 24th.
Ken Tapping is an astronomer with the National Research Council’s Herzberg Institute of Astrophysics, and is based at the Dominion Radio Astrophysical Observatory, Penticton, BC. | 0.876122 | 3.46401 |
Check out two critical geophysics papers on why time and probability are critical for geophysics. Stamenković et al. (2016) Stamenković & Seager (2016)
Solid Earth & Planet Interiors
Right below our feet is a large ball of energy slowly cooling into outer space. This cooling of our planet significantly impacts our climate, plate tectonics, and life. But what determines the evolution of the Earth & planetary interiors? What are the properties of mantle and core minerals? And do all planet interiors evolve similarly? I use first principles to model and understand the evolution of the Earth and planet interiors—accounting for time evolution and intrinsic or current uncertainties.
Tectonics & Planet Surfaces
The lithosphere is barrier and connector between the deep interior of a rocky planet and its surface environment. On Earth, plate tectonics is responsible for recycling the lithosphere back into the mantle and for significantly driving volcanism and planetary cooling. However, other planets like Mars or Venus show no signs of plate tectonics. How does plate tectonics operate? How did it evolve on the Earth and on what kind of other planets can we expect plate tectonics, or other forms of mantle convection? I use thermodynamics to understand the evolution of plate tectonics and other forms of surface recycling.
Highlights in a Nutshell
- Time Evolution is critical. Steady state models do not suffice to sufficiently well describe planetary interiors, especially for planets as or more massive than the Earth (see Stamenković et al., 2012, 2016).
- Geodynamic Evolution is of probabilistic nature. We should account for uncertainties as much as we can, carry them forward when computing a planet’s evolution, and look for robust results. Especially for exoplanets, we need to use a probabilistic approach when studying exogeodynamics (see Stamenković & Seager, 2016; Stamenković et al., 2016).
- Never evolve planets back in time. It’s just wrong ;-)…there are many paths forward in time but only one backwards…and we do not know the initial conditions.
- Don’t forget the pressure-dependence of mantle viscosity—it’s a game changer (Stamenković et al., 2011, 2012).
- Melting temperature, thermal conductivity, and viscosity for mantle rock might be much larger than previously assumed – with strong implications for the Earth’s evolution and for the structure and evolution of rocky exoplanets: I compute state of the art viscosity, thermal expansivity, and thermal conductivity (phonon, radiative, and electronic) for the Earth’s mantle and for super-Earths from first principles. Total thermal conductivity increases strongly with depth. Our viscosity model satisfies the current viscosity constraints for the Earth. Computed melting temperatures are indirectly supported by melting experiments for MgO (McWilliams et al. 2012, Science).
- Earth’s thermal history needs a revision: Especially the interior conditions of the early Earth might have been much hotter than previously assumed – with strong implications for volcanism, the water cycle, and plate tectonics: Assuming full mantle convection (versus layered convection), I can only reproduce the inner core radius constraint for large activation volumes. Pressure-independent models do not satisfy the viscosity constraints by many orders of magnitude. They can only then satisfy the inner core radius constraint if there is either layered mantle or stagnant lid convection throughout most of the Earth’s history. New results on the validity of previous thermal evolution models (Stamenkovic and Breuer 2014, Stamenkovic 2014) additionally support the findings that early Earth heat flow has been overestimated (see as well Tectonics).
- Initial lower mantle temperature conditions control the thermal evolution of massive planets. Steady state models do not suffice: Initially molten super-Earths have a hot super-adiabatic temperature profile. Assuming interior temperatures from literature, the lowermost mantle would be stagnant. Hence, super-Earths might be much hotter than we think. Steady-state calculation are not sufficient to show this behavior, as cooling takes many billion years (even when forming molten). Ineffective lower mantle cooling impacts dynamo action & plate tectonics. Shorter volcanic activity on super-Earths. Problems for climate regulation. Problems for differentiation of rocky super-Earths.
- Bottom-up approach for the drivers of plate tectonics revising our common “beliefs” about plate failure and subduction and the thermal evolution of rocky planets: showing that temporal variation of basal shear stresses and asthenospheric channels drive the initiation of plate tectonics, and that classic self-determined boundary layer analysis cannot be used to model the evolution of the Earth. In more detail, we use 1-D thermal history models and 3-D numerical experiments to study the impact of dynamic thermal disequilibrium and large temporal variations of normal and shear stresses on the initiation of plate tectonics. Previous models that explored plate tectonics initiation from a steady state, single plate mode of convection concluded that normal stresses govern the initiation of plate tectonics, which based on our 1-D model leads to plate yielding being more likely with increasing interior heat and planet mass for a depth-dependent Byerlee yield stress. Using 3-D spherical shell mantle convection models in an episodic regime allows us to explore larger temporal stress variations than can be addressed by considering plate failure from a steady state stagnant lid configuration. The episodic models show that an increase in convective mantle shear stress at the lithospheric base initiates plate failure, which leads with our 1-D model to plate yielding being less likely with increasing interior heat and planet mass. In this out-of-equilibrium and strongly time-dependent stress scenario, the onset of lithospheric overturn events cannot be explained by boundary layer thickening and normal stresses alone. Our results indicate that in order to understand the initiation of plate tectonics, one should consider the temporal variation of stresses and dynamic disequilibrium.
- The connections between plate tectonics, planet composition, structure, and initial conditions: Showing how the initiation and maintenance of plate tectonics depend on planet composition (i.e., concentration of radioactive elements, iron, and carbon), initial conditions, and core and planet size. With crucial implications for Earth, Mars, and exoplanets. In more detail, to understand the evolution and the habitability of any rocky exoplanet demands detailed knowledge about its geophysical state and history— such as predicting the tectonic mode of a planet. Yet no astronomical observation can directly confirm or rule out the occurrence of plate tectonics on a given exoplanet. Moreover, the field of plate tectonics is still young— questioning whether we should study plate tectonics on exoplanets at this point in time. In this work, we determine the limitations and the emerging possibilities of exogeophysics, the science of connecting geophysics to exoplanets, on the example of plate tectonics. Assuming current uncertainties in model and planet parameters, we develop a qualitatively probabilistic and conservative framework to estimate on what kind of planets and where in the Galaxy plate tectonics might occur. This we achieve by modeling how plate yielding, the most critical condition needed for plate mobility and subduction, is affected by directly observable (planet mass, size) or indirectly, to some degree, assessable planet properties ( structure and composition). Our framework not only highlights the importance of a planet’ s chemistry for the existence of plate tectonics and the path toward practical exogeophysics but also demonstrates how exoplanet science can actually help to better understand geophysics and the fundamentals of plate tectonics on Earth itself.
- Stamenković, V., Höink, T., Lenardic, T., 2016. The importance of temporal stress variation for the initiation of plate tectonics. JGR Planets, 121, 1–20, doi:10.1002/2016JE004994.
- Stamenković, V., Seager, S., 2016. Emerging possibilities and insuperable limitations of exogeodynamics: the example of plate tectonics. The Astrophysical Journal, 825, 78-95. Stamenković, V., Breuer, D., 2014. The tectonic mode of rocky planets, Part 1: driving factors, models & parameters. Icarus 234, 174-193.
- Stamenković, V., Noack, L., Breuer, D., Spohn, T., 2012. The influence of pressure-dependent viscosity on the thermal evolution of super-Earths. The Astrophysical Journal, 748, 41-63.
- Stamenković, V., Breuer, D., Spohn, T., 2011. Thermal and transport properties of mantle rock at high pressure: applications to super-Earths. Icarus, 216, 572–596.
- Stamenković, V., Frank, S., 2011 & 2015. Rheology of planetary interiors. In: Gargaud, M., et al., (Eds.), Encyclopedia of Astrobiology, Part 19. Springer, 1452-1455. | 0.836676 | 3.335037 |
Understanding the origin of very close-in, rocky exoplanets can help us to constrain the frequency of Earth-like exoplanets on orbits where liquid water may exist on their surface.
One of most interesting recent discoveries in exoplanet science is that there is an abundance of planets with sizes between that of the Earth and that of Neptune. These appear to be common in the Galaxy, despite not being present in the Solar System. Furthermore, it appears that those that have radii below ~ 1.5 Earth radii tend to be rocky, while those with radii above ~ 2 Earth radii tend to retain quite a substantial atmosphere. However, most of these planets are quite heavily irradiated by their parent stars, and so we don’t really know if the rocky ones formed rocky, or are the exposed cores of planets that once had substantial atmospheres.
In a recent paper, we proposed a way in which we could test which scenario was most likely. If these close-in rocky planets are predominantly the exposed cores of planets that once had substantial atmospheres, then their radii should decrease as they move further from their parent stars. This is because the level of irradiation typically drops as you go further from the star. At larger orbital radii, where the irradiation is lower, atmospheres can only be stripped from planets with lower-mass cores. This is shown in the top figure on the right, where the x-axis is incident stellar flux (irradiation) which increases as you get closer to the star (i.e., small numbers means larger orbital radius).
On the other hand, if these are planets that formed rocky, their physical radii should increase with increasing orbital radius. This is because as you move further from the star, there is essentially more material available to build planets. This is shown in the lower figure on the right, with the x-axis again being incident stellar flux.
So, if you can determine how the radii of close-in rocky planets varies with orbital radius, you can say something about the origin of these very close-in rocky planets. We can’t, however, really do this yet, because we don’t have sufficiently accurate estimates of their radii, and because they currently don’t extend far enough in orbital radius. However, with the launch of ESA’s Gaia satellite and NASA’s Transiting Exoplanet Survey Satellite (TESS) we may soon be able to better constrain stellar, and hence planetary, radii and should also have a sample of these planets that extend to larger orbital radii.
One reason that this is important is because we might be able to use this inner population of rocky planets to say something about , the frequency of potentially habitable Earth-like planets (i.e., how common are rocky planets around Sun-like stars, orbiting where life might be able to exist). However, doing so requires knowing the origin of these planets. If they’re primordially rocky, then they may be the inner population of rocky planets that extend to larger orbital radii. On the other hand, if they are the exposed cores of planets that once hosted substantial atmosphere, then they’re really the inner population of planets that become more Neptune-like as you move to larger orbital radii. If we want to better constrain , then we really do need to know the origin of this population of inner rocky planets, which we should be able to determine quite soon.
Lopez, E. & Rice, K, How formation time-scales affect the period dependence of the transition between rocky super-Earths and gaseous sub-Neptunes and implications for η⊕, Monthly Notices of the Royal Astronomical Society, 479, 5303-5311, 2018. | 0.849838 | 4.010481 |
Week of Dec. 15-21, 2019
One of my favorite days of the year is right around the corner. Christmas? New Year's Eve? Valentine's Day?
Nope. I'm talking about the first day of winter.
Now, lest you think this ol' desert rat enjoys the cold, crisp air of the season — or perhaps the snow that piles up in some places — let me assure you that few things could be further from the truth. Maybe it's the long, dark winter nights that I like? Not a bad guess, considering my nocturnal stargazing tendencies.
No, the real reason is that the first day of winter is marked by the winter solstice, and that's what I eagerly anticipate. This year's solstice occurs at 11:10 p.m. EST (8:10 p.m. PST) on Saturday, Dec. 21.
The winter solstice marks the moment that the sun reaches its southernmost position over our planet and begins its journey northward. To an observer in the Earth's Northern Hemisphere, the day marks the sun's lowest position in the midday sky and the beginning of its climb once again.
And because at this time of year, the sun appears in our Northern Hemisphere sky for only about nine hours a day, our temperatures are noticeably lower.
So why, then, isn't the year's coldest day on the first day of winter? That's because our atmosphere takes time to respond to temperature variations. If you remove a pot of hot water from the stove, then you know, intuitively, that it doesn't cool down instantly, and you make allowances for that when cooking.
The same is true with our atmosphere; as a result, the coldest time of the year in the Northern Hemisphere typically occurs not around Dec. 21 but in late January or February.
It all happens because our planet's equator is tipped by about 23.4 degrees to the plane of its orbit around the sun. This means that during this time of year, the Earth's Northern Hemisphere is tilted slightly away from the sun, causing the sun's rays to shine down on us at a relatively shallow angle. Six months — and half an orbit — later, our planet's tilt aims the Northern Hemisphere slightly toward the sun, and the solar rays shine more directly down upon us.
Now, I'm certainly not the first ever to anticipate this marvelous moment; it's been celebrated by cultures throughout the ages as the rebirth of sunlight, warmth and life on our part of planet Earth. And it's not a coincidence that some of our world's major religious holidays are celebrated around this time of year.
Even the term "solstice" originates in antiquity, coming from two Latin words: "sol" (meaning "sun") and "sistere" (meaning "to stand still"). It is at the winter solstice that the sun's southerly midday drop seems to end, the sun "stands still" and the star that gives life to planet Earth begins its ascendancy once again.
From this moment until mid-June, the sun will appear higher in our midday sky, our days will become longer, temperatures will gradually begin to rise and the greens of life will return to the Northern Hemisphere of Earth.
And — at least from my perspective — not a moment too soon!
Visit Dennis Mammana at facebook.com/DennisMammana. To read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com. | 0.817004 | 3.372143 |
London: Using data from NASA’s Spitzer Space Telescope, an international team of astronomers that also includes an Indian-origin scientist has for the first time obtained the most detailed “fingerprint” of a super-Earth planet — a rocky planet nearly two times as big as ours.
The efforts led to the first temperature map that reveals extreme temperature swings from one side of the “55 Cancri e” planet to the other and hints that a possible reason for this is the presence of lava flows.
“We have entered a new era of atmospheric remote sensing of rocky exoplanets,” said study co-author Nikku Madhusudhan from the institute of astronomy at the University of Cambridge.
“It is incredible that we are now able to measure the large scale temperature distribution on the surface of a rocky exoplanet,” he added.
According to the team led by Cambridge, conditions on the hot side of the planet are so extreme that it may have caused the atmosphere to evaporate, with the result that conditions on the two sides of the planet vary widely.
Temperatures on the hot side can reach 2500 degrees Celsius while temperatures on the cool side are around 1100 degree Celsius.
“55 Cancri e” orbits a sun-like star located 40 light years away in the Cancer constellation.
It is a ‘super Earth’ – a rocky exoplanet about twice the size and eight times the mass of Earth and orbits its parent star so closely that a year lasts just 18 hours.
The planet is also tidally locked, meaning that it always shows the same face to its parent star, similar to the Moon, so there is a permanent “day” side and a “night” side.
Since it is among the nearest super Earths whose composition can be studied, 55 Cancri e is among the best candidates for detailed observations of surface and atmospheric conditions on rocky exoplanets.
“We haven’t yet found any other planet that is this small and orbits so close to its parent star, and is relatively close to us, so 55 Cancri e offers lots of possibilities,” added Dr Brice-Olivier Demory from Cambridge and the paper’s lead author.
“We still don’t know exactly what this planet is made of – it’s still a riddle. These results are like adding another brick to the wall, but the exact nature of this planet is still not completely understood,” he added in the paper appeared in the journal Nature.
According to Demory, one possibility for this variation could be either a complete lack of atmosphere, or one which has been partially destroyed due to the strong irradiation from the nearby host star.
Another possibility for the huge discrepancy between the day side and the night side may be that the molten lava on the day side moves heat along the surface, but since lava is mostly solid on the night side, heat is not moved around as efficiently.
What is unclear however, is where exactly the ‘extra’ heat on 55 Cancri e comes from in the first place.
The researchers may have to wait until the next generation of space telescopes are launched to find out.
In 2018, the successor to Hubble and Spitzer – the James Webb Space Telescope – will launch, allowing astronomers to look at planets outside our solar system with entirely new levels of precision.
Europeans have a horrifying record regarding human rights violations. Germany is well known for an unprecedented, systematic holocaust of Jews and gypsies right in the middle of Europe only 80 years ago. Yet Britain, France, Portugal and others were as brutal with equal or even higher number of humans killed in their colonies. Their victims count many millions and many of them were Indians.
The Arabs, Turks and Mongols, too, have a horrifying record regarding human rights. The number of victims killed also goes into many millions, and many of them were Indians.
The Muslims invaded India already over thousand years ago and were as brutal as ISIS in our times. Unspeakable torture and beheadings were done on massive scale. Even the supposedly benign “Akbar the Great” slaughtered Hindus in huge numbers. The collective sacred threads of the Brahmins massacred by him is said to have weighed 200 kilogram. Can one even imagine such incredible injustice and brutality to civilians and priests? Thousands of temples were destroyed. Hindu women were sold into sex slavery. Hindus even had to open their mouth and receive gratefully the spittle by Muslims sitting on horses, and slaughtering cows was seen as “noblest deed” because it was so painful for Hindus, is recounted in “Legacy of Jihad” by Andrew Bostom.
The brutality experienced by Hindus was so horrendous that, even in independent India, they hardly dare to complain when they are subjected to cruel discrimination. It is painful to read comments whenever Hindus are killed or raped by Muslims: “This won’t make news, as the victim is only a Hindu”. It is so sad, but understandable after what they have gone through for over thousand years. They had no way to get justice; had to bear their suffering silently.
Guru Nanak cried out to the Supreme, and it is part of the Grant Sahib, “Having lifted Islam to its head, You have engulfed Hindustan in dread… Such cruelties they have inflicted and yet Your mercy remains unmoved….Oh Lord, these dogs have destroyed the diamond-like Hindustan.”
The British colonial masters were not less brutal. Their disdain for the natives was incredible. Winston Churchill is on record saying that he “hated Indians” and considered them a “beastly people with a beastly religion”. Celebrities like Charles Dickens wanted the Indian race ‘exterminated’ and considered them vile savages and Max Mueller wanted them all converted to Christianity.
Britain looted and reduced the formerly wealthiest country of the world to painful poverty, where during their rule over 25 million people starved to death, 3 million as late as in 1943 in Bengal.
The crimes of the British colonialists are, like those of the Muslim invaders, too numerous to list. They tied Indians to the mouth of canons and blew them up, hanged scores of them on trees, and even just after over one million Indian soldiers had helped Britain to be victorious in the First World War with many thousands sacrificing their lives, General Dyer gave orders to shoot at a peaceful gathering in Amritsar in 1919 where thousands died. An old coffee planter in Kodagu told me that even in the early 1950s there was a board in front of the club house in Madikeri. It read: “Dogs and Indians not allowed”.
Can anyone imagine the pain those Indian generations went through, having arrogant, often uncouth ruffians looting their land and despising them as dogs?
How could Europeans and Arabs be so cruel to other human beings? The reason is that they saw themselves as superior and others not quite as human.
Religion played a big role in making them feel superior. Both Christianity and Islam teach their members that only their religion is true and that the Creator will reward them with eternal heaven, but will severely punish all those who do not follow their ‘true’ religion. If God himself will torture them eternally in hellfire, why should his followers be good to them? Wouldn’t it mean siding with God’s enemies and betraying Him?
But on what basis do they consider only their religion as true and themselves as superior? The reason is that the respective founder of their religion allegedly said so. No other reason exists and no proof. On this flimsy basis, Christians and Muslims treated other human beings most inhumanly, believing they are destined for hell while they themselves are God’s favorites and will go to heaven. This brainwashing in the name of religion happens even in our times and its effect is still not questioned and analysed.
Yet today, neither white Christians, nor Arab or Turkish Muslims are constantly reminded of those terrible crimes of their forefathers. “The present generation must not be held accountable for the sins of their fathers”, is however not applied to Hindus and especially not to Brahmins. Media keeps hitting out at them as if they had been the worst violators of human rights in the past. Hinduism is portrayed as the villain due to the “horrific and oppressive” caste system.
Anyone, who knows a little about history, knows that this is false and malicious. The structure of Hindu society into four varnas or categories is mentioned in the Vedas and depends on one’s aptitude and profession – Brahmins, who memorise and teach the Vedas, Kshatriyas, who administer and defend society, Vaishyas who supply the society with goods and Shudras, who are the service sector. The varnas are not fixed by birth in texts like Bhagavad Gita or Manusmriti. But the British themselves cemented ‘castes’ (a Portuguese word) in their census and then turned around and accused Hindus of their birth-based, fixed caste system.
There was however one more category which the whole world has been told about and which is used to the hilt to despise Hinduism. They were the untouchables who do unclean work, like handling dead animals, cleaning sewers, etc. The fact that other varnas avoided touching them is still made a huge issue of in the West. In fact it is portrayed, as if this practice made Hindus the greatest violators of human rights and makes the millions tortured and killed by Christians and Muslims pale in comparison.
Yet there is no proof that even one of those untouchables has been killed for doing unclean work. Higher castes may indeed have looked down or still look down on those whose job involves dirt, which is unfortunately a human trait in all societies. It has nothing to do with Hinduism. Most people are aware that such work also needs to be done.
There is in all likelihood another angle regarding “untouchability”, which the British did not realize: Ayurveda knew already 3000 years ago that invisible germs can cause serious illness and those dealing with cadavers and dirt are more likely to carry and spread those. However, the British didn’t know about this fact till only some 150 years ago, when Louis Pasteur claimed that germs cause sickness. (By the way, Google describes this discovery as “crowning achievement of the French scientist”, and avoids mentioning India’s ancient Ayurveda).
Now in today’s time of “social distancing” due to the Corona Virus, we know that not touching others is a precaution to prevent potential infection and has nothing to do with discrimination. The British could have given Hindus the benefit of doubt that they avoided physical contact with certain people due to caution. But since the British didn’t have the advanced knowledge about harmful germs they could not see the possible reason behind it.
Since Independence, the caste system is officially abolished and discrimination against lower castes is a non-bailable offense. Yet the West still makes a huge issue of the caste system and untouchables. Why? Was this the greatest crime the British could find against the “natives” and therefore exaggerated it tremendously?
This is not to say that people of higher castes didn’t or don’t look down on lower castes, but the demonization of Brahmins is most unwarranted, as Brahmins are least likely to harbour hatred for others due to their strict rules for sadhana which requires them to keep a very high standard of mental and physical purity. Yet evangelicals, NGOs, international media, Muslim organisations, they all are after them and Hindus in general. They attack them for “atrocities” which never even happened, while the unspeakable atrocities, which were perpetrated upon them, are ignored. It’s a classic case of noticing the speck in the brother’s eye, but not the beam of wood in one’s own eye.
They got away with it for too long, because Hindus didn’t react. The meekness of Hindus was legendary. They were even called cowards. Yet in recent time, Hindus are becoming more assertive. They realize that the constant attacks on them are malicious, and that they are being fooled in the name of secularism because neither Christians nor Muslims can be secular. They are by nature communal because they need to make their community spread all over the world.
It is time to call out this blatant insincerity. When a head of state, like Imran Khan, accuses the Modi government in a tweet of “moving towards Hindu Rashtra with its Hindutva Supremacist, fascist ideology”, he better looks at his own country and his own ideology. A Hindu Rashtra with its inclusiveness and freedom are any time better than the exclusive, supremacist ideologies of Islam and Christianity, which force human beings into a strait-jacket of blind belief and several Muslim states threaten even today those who want to get out with death sentence.
India has seen a 37 per cent increase in cyberattacks in the first quarter (Q1) of 2020, as compared to the fourth quarter (Q4) of last year as a result of social media disadvantages, a new report revealed on Saturday.
The Kaspersky Security Network (KSN) report showed that its products detected and blocked 52,820,874 local cyber threats in India between January to March this year.
The data also shows that India now ranks 27th globally in the number of web-threats detected by the company in Q1 2020 as compared to when it ranked on the 32nd position globally in Q4 2019.
“There has been a significant increase in the number of attacks in 2020 Q1 that may continue to rise further in Q2 as well, especially in the current scenario where we notice an increase in cybercriminal activities, especially in the Asia Pacific region,” said Saurabh Sharma, Senior Security Researcher, GReAT Asia Pacific at Kaspersky.
The number of local threats in Q1 2020 in India (52,820,874) shows how frequently users are attacked by malware spread via removable USB drives, CDs and DVDs, and other “offline” methods.
Protection against such attacks not only requires an antivirus solution capable of treating infected objects but also a firewall, anti-rootkit functionality and control over removable devices.
According to the firm, the number of local threats detected in Q4 2019 was 40,700,057.
India also ranks 11th worldwide in the number of attacks caused by servers that were hosted in the country, which accounts of 2,299,682 incidents in Q1 2020 as compared to 854,782 incidents detected in Q4 2019, said the report.
“We see smartphone users being targeted more due to mass consumption and increased digitalisation,” Sharma said.
“Risks like data leakage, connection to unsecured wi-fi networks, phishing attacks, spyware, apps with weak encryption (also known as broken cryptography) are some of the common mobile threats that Android users face,” he added.
“In order to mitigate some of the major risks like data breaches, targeted ransomware attacks, large scale (distributed denial-of-service) DDoS attacks, etc, businesses will need to allocate their budgets correctly to build a stronger security infrastructure,” said Dipesh Kaura, General Manager for South Asia, Kaspersky. (IANS)
NASA is seeking US citizens for an eight-month study on social isolation in preparation for missions to Mars and the moon.
The international space agency is preparing for its next spaceflight simulation study and is seeking healthy participants to live together with a small crew in isolation for eight months in Moscow, Russia.
Participants will be staying in a lab located in Moscow, and they will experience environmental aspects similar to those astronauts are expected to experience on future missions to Mars that will have crew members from different nations.
NASA is looking for highly motivated and healthy individuals between the ages of 30 and 55 who are fluent in both English and Russian. They must also have an MS., PhD, MD. or have completed military officer training.
The space agency will consider other participants with a bachelor’s degree and other qualifications such as military or professional experience.
They will study the psychological and physiological effects astronauts are likely to face as a result of isolation on long missions.
According to NASA, participants will experience environmental aspects similar to those astronauts are expected to experience on future missions to Mars.
A small international crew will live together in isolation for eight months conducting scientific research, using virtual reality and performing robotic operations among a number of other tasks during the lunar mission.
The research is being done to study the effects of isolation and confinement as participants work to complete simulated space missions.
Results from ground-based missions like this help NASA prepare for the real-life challenges of space exploration and provide important scientific data to solve some of these problems and to develop countermeasures.
Participants will be compensated, and there are varying levels of pay depending on whether you’re associated with NASA.
This study builds on a four-month study conducted in 2019. The SIRIUS-19 analog mission had six participants — two US citizens and four Russians — isolated in a metal habitat that acted as their spacecraft, lunar lander and home. (IANS) | 0.905764 | 3.783766 |
An outburst of a nuclear explosion-like process may have been the reason for the birth of Earth’s satellite, told by scientists. The scientist from the US and France found that a likeness between the 1st atomic bomb and the creation of the moon. The research suggests that a new proof in favor of the “giant impact theory” and how our moon appeared into existence. Scientists told that the 1st nuclear weapon that was blown up by a man with the codename trinity is eerily similar to the formation of the moon.
After the opening of the operation trinity, the very 1st atomic bomb was set off with an energy that is similar to a stunning 20 kilotons of dynamites causing the sands below it to melt making a thin sheet of mostly green glass named trinitite. The overwhelming explosion has created an area around the bomb with a temperature that exceeds 8,000 degrees Celsius and a pressure of around 80,000 atmospheres.
Turns out that these similar intense environments are thought to have been alike to those that formed the moon over a giant collision with a Mars-sized heavenly body. James Day of the Scripps Institution of Oceanography in California said that “it is as close as we can possibly get to the environment that you might imagine on a planetary body in the early solar system. UC San Diego reported that a decade-old radioactive glass was found covering the ground after the 1st nuclear test bomb exploded. The glasses are being used by the scientists to study the theories about the formation of the moon about 4.5 billion years ago.
Professor James Day, his formed group of scientist, and his colleagues from the Scripps Institution of Oceanography studied the chemical structure of zinc and other explosive elements that contains trinitite. Tests models were gathered within 10 and 250 meters from ground zero at the test site of the trinity in New Mexico.
Intriguingly, as the scientists correlate the samples with the other gathered farther away, they learned that the trinitite closes to the detonation site was drained in explosive elements as zinc. The zinc that was existing was enhanced in the heavier and less-reactive isotopes, which are created of these elements with different atomic mass but with similar chemical features.
Elements like zinc and other volatile elements which vaporize under an extreme temperature were “dried out” near to the explosion than those that are farther away from the blast. The discoveries were advertised in the February issue of the Science Advances journal.
James Day said that “The outcome shows that evaporation at extreme temperatures, similar to those at the start of planet formation, leads to the depletion of volatile elements and to enrichment in heavy isotopes in the leftover materials from the event,” a Scripps geoscientist and head author of the research said that “This has been a common wisdom, but now we have experimental proof to show it.
The recently gathered proofs back up what the scientists have proposed long ago: Same chemical reactions took place when a collision between the early Earth and a Mars-sized object crashed, creating a debris that in the long run turned to our moon.
The examination made by Day and his colleagues saw a likeness between the trinitite and the lunar rocks that they are both highly drained in volatile elements and holds little to no water at all.
Source : lucisphilippines.press | 0.846571 | 3.405262 |
The Atacama Large Millimeter/submillimeter Array (ALMA) has uncovered the never-before-seen close encounter between two astoundingly bright and spectacularly massive galaxies in the early universe. These so-called hyper-luminous starburst galaxies are exceedingly rare at this epoch of cosmic history — near the time when galaxies first formed — and may represent one of the most-extreme examples of violent star formation ever observed.
Astronomers captured these two interacting galaxies, collectively known as ADFS-27, as they began the gradual process of merging into a single, massive elliptical galaxy. An earlier sideswiping encounter between the two helped to trigger their astounding bursts of star formation. Astronomers speculate that this merger may eventually form the core of an entire galaxy cluster. Galaxy clusters are among the most massive structures in the universe.
“Finding just one hyper-luminous starburst galaxy is remarkable in itself. Finding two of these rare galaxies in such close proximity is truly astounding,” said Dominik Riechers, an astronomer at Cornell University in Ithaca, New York, and lead author on a paper appearing in the Astrophysical Journal. “Considering their extreme distance from Earth and the frenetic star-forming activity inside each, it’s possible we may be witnessing the most intense galaxy merger known to date.”
The ADFS-27 galaxy pair is located approximately 12.7 billion light-years from Earth in the direction of the Dorado constellation. At this distance, astronomers are viewing this system as it appeared when the universe was only about one billion years old.
Astronomers first detected this system with the European Space Agency’s Herschel Space Observatory. It appeared as a single red dot in the telescope’s survey of the southern sky. These initial observations suggested that the apparently faint object was in fact both extremely bright and extremely distant. Follow-up observations with the Atacama Pathfinder EXperiment (APEX) telescope confirmed these initial interpretations and paved the way for the more detailed ALMA observations.
With its higher resolution and greater sensitivity, ALMA precisely measured the distance to this object and revealed that it was in fact two distinct galaxies. The pairing of otherwise phenomenally rare galaxies suggests that they reside within a particularly dense region of the universe at that period in its history, the astronomers said.
The new ALMA observations also indicate that the ADFS-27 system has approximately 50 times the amount of star-forming gas as the Milky Way. “Much of this gas will be converted into new stars very quickly,” said Riechers. “Our current observations indicate that these two galaxies are indeed producing stars at a breakneck pace, about one thousand times faster than our home galaxy.”
The galaxies — which would appear as flat, rotating disks — are brimming with extremely bright and massive blue stars. Most of this intense starlight, however, never makes it out of the galaxies themselves; there is simply too much obscuring interstellar dust in each.
This dust absorbs the brilliant starlight, heating up until it glows brightly in infrared light. As this light travels the vast cosmic distances to Earth, the ongoing expansion of the universe shifts the once infrared light into longer millimeter and submillimeter wavelengths, all thanks to the Doppler effect.
Animation zoom-in of the composite image of ADFS-27 galaxy pair. The initial image is from ESA’s Herschel Space Observatory. The object was then detected by ESO’s Atacama Pathfinder EXperiment (APEX) telescope. ALMA (final zoom) was able to identify two galaxies: ADFS-27N (for North) and ADFS-27S (for South). The starbursting galaxies are about 12.8 billion light-years from Earth and destined to merge into a single, massive galaxy.
ALMA was specially designed to detect and study light of this nature, which enabled the astronomers to resolve the source of the light into two distinct objects. The observations also show the basic structures of the galaxies, revealing tail-like features that were spun-off during their initial encounter.
The new observations also indicate that the two galaxies are about 30,000 light-years apart, moving at roughly several hundred kilometers per second relative to each other. As they continue to interact gravitationally, each galaxy will eventually slow and fall toward the other, likely leading to several more close encounters before merging into one massive, elliptical galaxy. The astronomers expect this process to take a few hundred million years.
“Due to their great distance and dustiness, these galaxies remain completely undetected at visible wavelengths,” noted Riechers. “Eventually, we hope to combine the exquisite ALMA data with future infrared observations with NASA’s James Webb Space Telescope. These two telescopes will form an astronomer’s ‘dream team’ to better understand the nature of this and other such exceptionally rare, extreme systems.”
The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.
Publication: Dominik A. Riechers, et al., “Rise of the Titans: A Dusty, Hyper-luminous “870 μm Riser” Galaxy at z ~ 6,” ApJ, 2017; doi:10.3847/1538-4357/aa8ccf | 0.851455 | 4.114711 |
Scientists drilling deep into ancient rocks in the Arizona desert say they have documented a gradual shift in Earth’s orbit that repeats regularly every 405,000 years, playing a role in natural climate swings. Astrophysicists have long hypothesized that the cycle exists based on calculations of celestial mechanics, but the authors of the new research have found the first verifiable physical evidence. They showed that the cycle has been stable for hundreds of millions of years, from before the rise of dinosaurs, and is still active today. The research may have implications not only for climate studies, but our understanding of the evolution of life on Earth, and the evolution of the Solar System. It appears this week in the Proceedings of the National Academy of Sciences.
Scientists have for decades posited that Earth’s orbit around the sun goes from nearly circular to about 5 percent elliptical, and back again every 405,000 years. The shift is believed to result from a complex interplay with the gravitational influences of Venus and Jupiter, along with other bodies in the Solar System as they all whirl around the Sun like a set of gyrating hula-hoops, sometimes closer to one another, sometimes further. Astrophysicists believe the mathematical calculation of the cycle is reliable back to around 50 million years, but after that, the problem gets too complex, because too many shifting motions are at play.
“There are other, shorter, orbital cycles, but when you look into the past, it’s very difficult to know which one you’re dealing with at any one time, because they change over time,” said lead author Dennis Kent, an expert in paleomagnetism at Columbia University’s Lamont-Doherty Earth Observatory and Rutgers University. “The beauty of this one is that it stands alone. It doesn’t change. All the other ones move over it.”
The new evidence lies within 1,500-foot-long cores of rock that Kent and his coauthors drilled from a butte in Arizona’s Petrified Forest National Park in 2013, plus earlier deep cores from suburban New York and New Jersey. The Arizona rocks in the study formed during the late Triassic, between 209 million and 215 million years ago, when the area was covered with meandering rivers that laid down sediments. Around this time, early dinosaurs started evolving.
The scientists nailed down the Arizona rocks’ ages by analyzing interspersed volcanic ash layers containing radioisotopes that decay at a predictable rate. Within the sediments, they also detected repeated reversals in the polarity of the planet’s magnetic field. The team then compared these findings to the New York-New Jersey cores, which penetrated old lakebeds and soils that hold exquisitely preserved signs of alternating wet and dry periods during what was believed to be the same time.
Kent and Olsen have long argued that the climate changes displayed in the New York-New Jersey rocks were controlled by the 405,000-year cycle. However, there are no volcanic ash layers there to provide precise dates. But the cores do contain polarity reversals similar to those spotted in Arizona. By combining the two sets of data, the team showed that both sites developed at the same time, and that the 405,000-year interval indeed exerts a kind of master control over climate swings. Paleontologist Paul Olsen, a coauthor of the study, said that the cycle does not directly change climate; rather it intensifies or dampens the effects of shorter-term cycles, which act more directly.
The planetary motions that spur climate swings are known as Milankovitch cycles, named for the Serbian mathematician who worked them out in the 1920s. Boiled down to simplest terms, they consist of a 100,000-year cycle in the eccentricity of Earth’s orbit, similar to the big 405,000-year swing; a 41,000-year cycle in the tilt of Earth’s axis relative to its orbit around the Sun; and a 21,000-year cycle caused by a wobble of the planet’s axis. Together, these shifts change the proportions of solar energy reaching the Northern Hemisphere, where most of the planet’s land is located, during different parts of the year. This in turn influences climate.
In the 1970s, scientists showed that that Milankovitch cycles have driven repeated warming and cooling of the planet, and thus the waxing and waning of ice ages over the last few million years. But they are still arguing over inconsistencies in data over that period, and the cycles’ relationships to rising and falling levels of carbon dioxide, the other apparent master climate control. Understanding how this all worked in the more distant past is even harder. For one, the frequencies of the shorter cycles have almost certainly changed over time, but no one can say exactly by how much. For another, the cycles are all constantly proceeding against each other. Sometimes some are out of phase with others, and they tend to cancel each other out; at others, several may line up to initiate sudden, drastic changes. Making the calculation of how they all might fit together gets harder the further back you go.
Kent and Olsen say that every 405,000 years, when orbital eccentricity is at its peak, seasonal differences caused by shorter cycles will become more intense; summers are hotter and winters colder; dry times drier, wet times wetter. The opposite will be true 202,500 years later, when the orbit is at its most circular. During the late Triassic, for poorly understood reasons, the Earth was much warmer than it is now through many cycles, and there was little to no glaciation. Then, the 405,000-year cycle showed up in strongly alternating wet and dry periods. Precipitation peaked when the orbit was at its most eccentric, producing deep lakes that left layers of black shale in eastern North America. When the orbit was most circular, things dried up, leaving lighter layers of soil exposed to the air.
Jupiter and Venus exert such strong influences because of size and proximity. Venus is the nearest planet to us—at its farthest, only about 162 million miles—and roughly similar in mass. Jupiter is much farther away, but is the Solar System’s largest planet, 2.5 times bigger than all others combined.
Linda Hinnov, a professor at George Mason University who studies the deep past, said the new study lends support to previous studies by others that claim to have observed signs of the 405,000-year cycle even further back, before 250 million years ago. Among other things, she said, it “could lead to new insights into early dinosaur evolution.” She called the findings “a significant new contribution to geology, and to astronomy.”
Kent and Olsen say that because of all the competing factors at work, there is still much to learn. “This is truly complicated stuff,” said Olsen. “We are using basically the same kinds of math to send spaceships to Mars, and sure, that works. But once you start extending interplanetary motions back in time and tie that to cause and effect in climate, we can’t claim that we understand how it all works.” The metronomic beat of the 405,000-year cycle may eventually help researchers disentangle some of this, he said.
If you were wondering, the Earth is currently in the nearly circular part of the 405,000-year period. What does that mean for us? “Probably not anything very perceptible,” says Kent. “It’s pretty far down on the list of so many other things that can affect climate on times scales that matter to us.” Kent points out that according to the Milankovitch theory, we should be at the peak of a 20,000-some year warming trend that ended the last glacial period; the Earth may eventually start cooling again over thousands of years, and possibly head for another glaciation. “Could happen. Guess we could wait around and see,” said Kent. “On the other hand, all the CO2 we’re pouring into the air right now is the obvious big enchilada. That’s having an effect we can measure right now. The planetary cycle is a little more subtle.”
The other authors of the study are Cornelia Rasmussen and Randall Irmis of the University of Utah; Chris Lepre of Lamont-Doherty; Roland Mundli of Berkeley Geochronology Center; George Gehrels and Dominique Giesler of the University of Arizona; John Geissman of the University of Texas, Dallas; and William Parker of Petrified Forest National Park. | 0.894751 | 3.729561 |
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