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The Leonids are a meteor shower that originates in the constellation of Leo (the lion) and occurs regularly. Every year in mid-November, Earth glides through a minefield of dust clouds. The source of the dust is Comet Tempel-Tuttle, and when Earth runs into a cloud we have a Leonid meteor shower. This year the Leonids are expected to peak on Nov. 19th around 2149 GMT (5:49 p.m. EST). At best, sky watchers will see one meteor per minute—nice, but not like the jaw-dropping displays of recent years, especially 1998 and 2001.
Aside from their occasional spectacular displays, the Leonids are important for understanding the origin of meteors and their relationship to comets. They play an important role in trying to predict meteor showers themselves. This year, a moderate display is predicted.
Meteors are the light trails we see when small dust grains or rocks enter the Earth's atmosphere. Most of the meteors are caused by dust particles no bigger than a grain of sand. Meteor showers occur when a lot of dust and rock enter our atmosphere close together. These associations of dust and rock are thought to be debris ejected from comets (more rarely from asteroids) and the Leonids are associated with comet 55P/Temple Tuttle.
The meteors appear to radiate out from a single spot in Leo (the radiant). However, the meteors in fact are moving along parallel paths. They appear to radiate from this spot in Leo for the same reason that parallel railway lines, or any other parallel lines on the ground, appear to originate from a point on the horizon.
Comet 55P/Temple Tuttle orbits the sun with an orbital period of 33.2 years. In line with the comet's return, every 33 years or so the Leonids give an outstanding display. The last big Leonid shower was in 1966, where the number of meteors ranged from 40 per hour to an estimated peak of 200 per second!
Accounts of the Leonid storms date back to 585 AD. Each one is different, because at the return of the comet every 33 years or so, the encounter with Earth's orbit varies due to the gravitational effects of planets on the comet's orbit. This magnificent comet passed close by the Sun again on February 28, 1998.
During a storm, Earth crosses the outer regimes of the dust trail of comet Tempel-Tuttle. When the meteoric matter hits the Earth's atmosphere, new molecules and solid particles are formed that are of interest to the origin of life, the interaction of Earth and Space, and the issue of ozone depletion.
More on the Science of the 2003 Leonid Storm
History of the Leonid Storm in Modern Times
Just before dawn on the night of November 12-13, 1833, the skies over eastern North America were lit up by thousands of meteors appearing
from the region of the constellation Leo. Many thousands of people saw the event. A scientist named Denison Olmsted gathered many accounts
of the meteor storm, and, together with accounts of of an abnormal display of meteors seen in Europe and the Middle East the prior year,
determined that the storm was caused by a discrete cloud of small particles orbiting the sun. That night marked the beginning of modern meteor
A repeat of the Leonid storm ocurred on November 13-14, 1866. Shortly before this, a scientist named Hubert Newton identified Leonid
showers as early as 585 AD, and he specified a period of about 33 years. In 1865 Comet Temple-Tuttle was discovered, and after its orbit had
been calculated, and that of the Leonid stream in 1867, astronomers made the connection between the two.
The Leonids failed to produce a storm in 1899. It was discovered that the stream had been perturbed in intervening years by encounters with
Jupiter and Saturn. A respectable display did occur in 1901, visible from the central and western United States.
A relatively weak display occurred in 1932, but enhanced activity was noted through 1939. The big event in 1966 was, however, on the way.
In 1965, the Leonids produced rates as high as 120 per hour. On the night of November 17th, 1966, observers all over the world settled in to
watch. Observers across the United States, particularly in the west, were rewarded by a true meteor storm. Observers in Arizona reported rates
as high as 2400 per hour. In Hawaii, observer Mike Morrow saw rates as high as 83 per minute, or about 5000 per hour!
approach the Earth nearly head on, and so appear very swift, often bright, with many leaving bright trails, known as trains, behind them. The
visible path of the meteor will generally be long near midnight and become a bit shorter as the radiant rises higher in the sky. | 0.844101 | 3.932964 |
Star BPM 37093 is now officially a girl’s bestest-estest. Friend. Evah. The Harvard-Smithsonian Center for Astrophysics has announced that this heavenly body, situated some fifty light years away as part of the constellation Centaurus, is in fact a mass of crystallised carbon. That is to say, BPM 37093 is now the biggest known diamond in the galaxy.
Scientists have renamed it ‘Lucy’ – after comedian Peter Cook’s daughter, of whom John Lennon’s son Julian painted a portrait, depicting her in the sky, with diamonds. Oh, the scientist would be citing the song that John Lennon wrote, inspired by that painting, ‘Lucy in the Sky with Diamonds’, located on the album Sgt Pepper’s Lonely Hearts Club Band, and long believed to be both tribute to and proof of Lennon’s experience with LSD (lysergic acid diethylamide). A substance, you may consider for just a moment, that may have also given rise to scientists believing there are huge gemstones in outer space. Perhaps Mars is a great big ruby, and Venus, a hunk of gold? (That’s just silly; everyone knows Venus and Mars are billiard balls!)
With an estimated diameter of 2500 miles (4000km), Lucy is thought to weigh around 10 billion trillion trillion carats – ie 10,000,000,000,000,000,000,000,000,000,000,000 carats – or some 2,000,000,000,000,000,000,000,000,000 tonnes, give-or-take. “You would need a jeweller’s loupe the size of the sun to grade this diamond,” said Travis Metcalfe, the astronomer from the Havard-Smithsonian Center for Astrophysics who led the team that discovered the interstellar gem. “Imagine trying to construct one – you’d most likely fall on your lens grinding machine and make a spectacle of yourself,” he might have added, had he been a Groucho Marx fan.
The diamond, naturally, is mostly carbon, coated by a thin layer of hydrogen and helium gases. It was formed by the crystallisation of a white dwarf – which itself is the hot core that remains of a star after it has used up all of its fuel (like the embers of a fire, I guess, except, since they don’t crystallise, once the fuel runs out, they become solid, unburnt carbon – more like graphite rather than diamond.)
Turns out astronomers have thought that the interiors of white dwarfs crystallised for more than four decades, but the ability to determine if this was the case only became possible recently. The white dwarf radiates not only light, but also sound, ringing “like a gigantic pulsating gong”, apparently. (So that’s what the constellation Orion is doing – it’s not the hunter at all, but a huge J. Arthur Rank gong-ringer!)
By measuring the pulsations, scientists were able to study the interior of the white dwarf in the same way geologists study the earth’s interior by measuring the pulses of earthquakes with a seismograph.
“We figured out that the carbon interior of this white dwarf has solidified to form the galaxy’s largest diamond,” says Metcalfe.
This raises some important issues – like should the Seven Dwarfs sign up for those space flights that have now become available? “Hi-ho, hi-ho, it’s into space we go” for the biggest diamond so far located in the known universe must make better sense than chipping away in the diamond mine day-in, day-out. Maybe they can get Mitsubishi to sponsor their trip (because ‘Mitsubishi’ means ‘three diamonds’).
And, if scientists have only just determined that there’s a star made entirely of diamond after four decades of suspicion, how did Jane Taylor know that a star could be exactly “like a diamond, in the sky” when she wrote the lyrics to ‘Twinkle, Twinkle, Little Star’ back in 1806?
What about our own nearest star, the sun? Why have we been lumbered with a so-called ‘mass of incandescent gas’ when other solar systems appear to be sporting bling? Fear not. Look forward to our own sun becoming a white dwarf when it dies. How long will that take? Astronomers reckon about 5 billion years. And a couple of billion years later, the core should crystallise to form a giant diamond. Until then, would Sir be interested in some cubic zirconia just beyond Pluto?
Meanwhile, the biggest problem facing the massive diamond in our galaxy is making the most of it. How the hell are we supposed to mount it onto one of those rings of Saturn? | 0.863643 | 3.258275 |
Supermassive black holes don’t really form dust ‘donuts’ — the structures surrounding these bodies are more akin to galactic matter fountains, new research reveals.
Computer simulations and new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) suggest that the gas accretion rings around supermassive black holes (SBH) aren’t ring-shaped at all. Instead, gas being expelled from the SBM interacts with infalling matter to create a complex circulation pattern — one which the authors liken to a fountain.
Jets of matter
Most galaxies revolve around a SBH. These objects can be millions, even billions of times as heavy as the Sun, and they knit together galaxies through sheer gravitational power. Some of these SBHs are actively consuming new material. So far, common wisdom held that instead of falling directly in, matter builds around an active black hole in a donut or ring-shaped structure.
It wasn’t far from the truth but, new research reveals, it wasn’t spot-on either. A study led by Takuma Izumi, a researcher at the National Astronomical Observatory of Japan (NAOJ), reports that this ‘donut’ is not actually a rigid structure, rather a complex collection of highly dynamic gaseous components.
The researchers used the ALMA telescope to observe the Circinus Galaxy and the SBH at its center — which is roughly 14 million light-years away from Earth. They then compared their observations to computer models of gas falling toward a black hole. These simulations were run using the Cray XC30 ATERUI supercomputer operated by NAOJ.
All in all, the team found that there’s a surprising level of interplay between the gases in this structure. Cold molecular gas first falls towards the black hole to form a disk near the plane of rotation. Being so close to a black hole heats up the gas until its atoms break apart into protons and electrons. Not all of these products go on to be swallowed by the black hole. Some are instead expelled above and below the disk but are then snagged by the SBH’s immense gravitational presence, falling back onto the disk.
These three components circulate continuously, the team explains. Their interaction creates three-dimensional flows of highly turbulent matter around the black hole.
“Previous theoretical models set a priori assumptions of rigid donuts,” explains co-author Keiichi Wada, a theoretician at Kagoshima University in Japan who lead the simulation study.
“Rather than starting from assumptions, our simulation started from the physical equations and showed for the first time that the gas circulation naturally forms a donut. Our simulation can also explain various observational features of the system.”
The team says their paper finally explains how donut-shaped structures form around active black holes and, according to Izumi, will “rewrite the astronomy textbooks.”
The paper ” Circumnuclear Multiphase Gas in the Circinus Galaxy. II. The Molecular and Atomic Obscuring Structures Revealed with ALMA” has been published in The Astrophysical Journal. | 0.888096 | 4.085282 |
Astronomers using European Southern Observatory’s Very Large Telescope (VLT) have captured the birth of a planet around a star 520 light-years away.
The image might not look like much at first glance. But among the swirling clouds of dust and gas is a little twist. That twist, astronomers hypothesize, is evidence of a planet forming as it rotates around its star.
The parent star of the developing planet is AB Aurigae, found in the constellation Auriga, a familiar constellation in the Northern Hemisphere. It is about one to five million years old, far younger than our 4.5 billion-year-old sun, and roughly four times more massive.
The spiral arms around the star were first detected five years ago using ESO’s Atacama Large Millimeter Array telescope in Chile, but it wasn’t able to observe this much detail. Using a special instrument on the VLT called SPHERE, astronomers were able to block out the star’s bright light and conduct extremely precise observations.
These types of spirals around young stars are indicative of newly forming planets and are created as these planets give the gas a “kick,” which in turn creates a disturbance of the swirling disc and forms a wave. The twists observed are in a kind of s-shape as gas swirls around the planet.
We do not see the planet yet, but we do see the material that is forming the planet, and we do see the mechanism at play for the formation of the planet.– Emmanuel Di Folco, astronomer and paper’s co-author
“These twists must be produced by a baby planet, which we don’t see directly, but we see the influence of the planet onto the spiral,” said Emmanuel Di Folco, co-author of the paper published in the journal Astronomy & Astrophysics and an astronomer at the Astrophysics Laboratory of Bordeaux in Bordeaux, France.
“We do not see the planet yet, but we do see the material that is forming the planet, and we do see the mechanism at play for the formation of the planet. And this was very exciting because the structure — the shape of this structure that we have detected — was exactly the shape that was predicted by theoretical models of planet formation.”
Astronomers hypothesize that stars and planets form after they’re given a different sort of kick, perhaps by a relatively nearby supernova explosion. Gas and dust first form the star and what remains forms the planets.
While more than 4,000 exoplanets — planets orbiting a distant star — have been discovered, it’s rare to see one so early on in its formation.
And Di Folco said that it’s likely this planet might have some company.
“In the [below] image on the right-hand panel there is a small red dot, which we believe is also a planet, and what you’re really seeing is that this planet is at the outer edge of what we call a cavity in this disc,” Di Folco said.
The cavity is a region where there is much less gas and dust, potentially created by another planet. It’s similar to the mechanism that creates gaps in Saturn’s rings.
“There may be other planets somewhere hidden behind the structure that we see here that we will detect later on, but we cannot yet interpret all the structure of that we see.”
The developing planet is roughly the same distance from its star as Neptune is from the sun, but it’s not Earth-like.
“It’s going to be a giant planet. It’s not going to be a terrestrial planet,” said Anthony Boccaletti, lead author and an astronomer at the Laboratory for Space Science and Astrophysical Instrumentation at the Paris Observatory in Meudon, France. “It’s really a massive one … probably something like Jupiter or even more massive than Jupiter.”
‘That would be amazing’
The image of this nascent planet is yet another step in better understanding how planetary systems form, including our own.
“This is part of our origin,” said Di Folco. “Here we have a snapshot of what could have been the formation of Neptune or or Saturn or Jupiter — our giant planets in the solar system.”
Di Folco said that they hope to conduct further observations, perhaps even capturing the suspected other planets in the system. But he’s also hoping that in the not-too-distant future, astronomers will be able to capture an image of an even younger planet.
“We are coming into a new era in astronomy where we’ll be able really to see — in a few years or maybe even 10 years from now — the direct formation of those planets around young stars,” Di Folco said.
“That would be amazing.” | 0.880361 | 4.011113 |
Boozy comet Lovejoy houses building blocks for life
Astronomers havediscovered large quantities of alcohol and sugar, as well as the presence ofcomplex organic molecules, on the comet Lovejoy. The observations,made by the 30 meter (98 ft) radio telescope at Pico Veleta, Spain,support the theory that comets may have played an important role inthe formation of life on Earth.
The vast majority ofcomets originate either in the Kuiper belt or the Oort cloud, however gravitational disturbances can manipulatethe orbits of these enigmatic bodies, causing them to pass relativelyclose to the Sun.
This inward trip fromthe far reaches of the solar system allows us to observe a comet'scomposition from afar, as increasing activity caused by closerproximity to the Sun causes a comet's coma to become much morepronounced.
Each comet essentially serves as a time capsule, allowing us to observe materials as theywere during the formative period of our solar system. The arrival ofRosetta and Philae around 67P/Churyumov–Gerasimenko (67P) in August2014 has revolutionized our understanding of the celestial wanderers,allowing scientists to take detailed readings of the nature andcomposition of a comet from orbit, and on the surface, for the firsttime in our history.
Whilst we lack arobotic presence on Lovejoy, telescopic observations of the comet arefurthering our knowledge of the remarkable, eclectic and variednature of the cosmic travellers. Recent studies have revealed thefirst recorded instance of ethyl alcohol present in a comet's coma,the same type of alcohol found in alcoholic beverages back on Earth.
"We found thatcomet Lovejoy was releasing as much alcohol as in at least 500bottles of wine every second during its peak activity," stateslead author of a paper on the findings Nicolas Biver, of the ParisObservatory, France. "The team found 21 different organicmolecules in gas from the comet, including ethyl alcohol andglycolaldehyde – a simple sugar."
Astronomers were ableto detect the signature of the alcohol and sugar by targeting Lovejoywith a large radio telescope, and observing for energized particlesglowing at specific microwave frequencies.
The presence of organicmolecules on Lovejoy further strengthens the theory thatancient comet impacts during the Late Heavy Bombardment played apivotal role in the emergence of life on Earth by delivering complexorganic molecules.
DominiqueBockelée-Morvan, co-author of the paper from Paris Observatory, concludes, "The next step is to see if the organic material beingfound in comets came from the primordial cloud that formed the solarsystem or if it was created later on, inside the protoplanetary diskthat surrounded the young sun."
A paper detailing thediscovery is available in the journal Science Advances. | 0.888876 | 3.921407 |
|Evenly spaced craters stand out in the Catena Davy crater chain (11.0°S; 6.2°W). From a mosaic of both the left and right hand frames of LROC Narrow Angle Camera observation M181208790, LRO orbit 11818, from 96.21 kilometers on January 14, 2012; illumination incidence angle 66.11° from the west, resolution over a field of view approximately 6 kilometers across (in the original) 0.98 meters per pixel [NASA/GSFC/Arizona State University].|
LROC News System
Many readers will remember the much publicized events of July 1994, when 21 ice fragments comprising Comet Shoemaker-Levy 9 impacted one after another with the atmosphere of Jupiter over a six-day period. Large, dark blotches were visible through backyard telescopes on the Jovian cloud tops for several months afterward. The largest impact produced energy estimated at six million megatons equivalent of trinitrotoluene (TNT).
What does comet Shoemaker-Levy 9 have to do with today's Featured Image?
|Shoemaker-Levi 9 on May 17, 1994, discovered a year before widely-viewed sequential impacts on the upper atmosphere of Jupiter|
|Very high resolution image of a 242 meter-wide part of the north wall and rim of one of the four small craters of Catena Davy, 1.87 km-wide "Delia," during LRO's low altitude maneuvers over the near side of the Moon in 2011; spacecraft orbit 9928, August 17, 2011 (LROC NAC M168245384R). At 42 cm per pixel, from only 27.58 km, block material can be seen continuing to be slowly shed from the crater's very degraded rim, testifying to great age [NASA/GSFC/Arizona State University].|
|Two thirds of 1.87 km Delia crater, of Catena Davy, in a highly resampled 5000 lines from M168245384R. The rectangle designates the area of the north wall and rim above [NASA/GSFC/Arizona State University].|
|Names for these member craters of the Catena Davy chain, adopted by the International Astronomical Union in 1976. Full-width reduction of the LROC NAC observation M181208790. In Russian Doll fashion, the rectangle approximates the field of view shown immediately above, though from a later observation and a different angle of incidence [NASA/GSFC/Arizona State University].|
|NASA Lunar Mapping and Modeling Program (LMMP) ILIADS application view shows the view from low orbit in the southwest over Catena Davy. The circle designates the four member craters in the LROC Featured Image [NASA/GSFC/Arizona State University].|
|Early LROC Wide Angle Camera (WAC) monochrome observation of a 48 km wide field of view, including Catena Davy. LROC WAC M119896473M, spacecraft orbit 2802, February 4, 2010; resolution 57 meters from 40.85 km [NASA/GSFC/Arizona State University].|
|The LROC Featured Image release contextual WAC mosaic showing Catena Davy in the context of a field of view about 120 km across [NASA/GSFC/Arizona State University].|
Comet Shoemaker-Levy 9 awakened world interest in the possibility for asteroid and comet impacts on Earth in modern times, the last significant example of which occurred on June 30, 1908 near the Podkamennaya Tunguska river in Northern Russia. That air-burst meteoroid encounter leveled more than 2,000 square kilometers of forest, but no human life was lost because no humans were present in this remote corner of planet Earth. The situation would be very different if such an event occurred over a metropolitan area. While these encounters are infrequent, they do constitute a natural hazard, and should be taken as seriously as other natural hazards (e.g. earthquakes, tsunamis, tornadoes, hurricanes, etc.).
Most of the impact hazard risk is associated with single asteroid bodies, not cometary strings. Astronomers are currently conducting sky surveys to identify as many of these objects as possible, determine their orbital parameters, and find out if any are currently on a collision course with Earth. As with all natural hazards, future incidents are indeed certain if such precautions are not taken. Click HERE to open the NAC mosaic for this feature. Additional discussion on crater chains can be found in our Mare Orientale post from March 2010, where the cause is likely to be from secondary, not primary, impacts. | 0.849488 | 3.627146 |
WHERE IN THE WORLD?
HOW ANCIENT MARINERS NAVIGATED
Sailing was important for trade and warfare in Ancient Greek times. However, in very early times, sailors did not have compasses or reliable maps. They had to use coastlines to help them find their way across the seas. Landforms gave them a guide to follow, and also meant that they could find their way to safety in case of storms. By the 2nd millennium BCE ancient people had learnt to use their knowledge of stars and constellations to help with navigation. As their knowledge of astronomy advanced, navigation became much easier. Sailors could easily work out latitude by measuring the angle of the North Star above the horizon. This angle, in degrees, would tell them the latitude of the ship. But there was still much ground (or sea) to cover. Sailors continued to develop new ways of navigating and mapping the seas throughout Ancient Greek times.
One simple instrument that was used to help with navigation was the use of sounding weights. These were used by sailors to work out the depth of the water in different places, by lowering the weights from their boat. This helped sailors to work out how far their ships were from land, since shallower water could suggest that land was nearby.
A more complicated invention by Ancient Greek navigators was called the Antikythera mechanism, which was discovered near the island of Antikythera. This was a mechanical tool with gears and wheels, which is believed to have been used to help sailors navigate during the 3rd or 2nd century BCE. It was probably used to predict eclipses and the positions of the stars at different times in the year, as the stars were one of the main guides for Ancient Greek navigators.
Another key invention used by Ancient Greek navigators was called the Astrolabe. The name of the device comes from the Greek astrolabos, meaning ‘star-taker’, since it was used to measure the positions of stars in the sky. The Astrolabe appeared during the 3rd century BCE, during the Hellenistic period. It is believed to have been invented by a man named Hipparchus, who was an astronomer and mathematician.
Jason & the Argonaut's Journey
This map shows the meandering journey made by Jason and his Argonauts. Jason and the Argonauts faced and defeated all kinds of enemies on the way to fetch the Golden Fleece. Harpies, giants and a king who was a little too into boxing- they all fell before the mighty Argonauts.
The tale of Jason and the Argonauts is one of the oldest examples of the 'heroes quest' which has become one of the most widely used and easily recognised story-lines which continue to be used in books, games and films to this day.
CARTOGRAPHY: THE ART OF MAP MAKING
In classical Greece, maps were made using both mathematics and information found by explorers. The first ancient Greek who is believed to have made a map of the world is Anaximander of Miletus, who lived in the 7th century BCE. He believed that the earth was a cylinder, which stayed still in space. According to his map, humans lived on the top of the cylinder, which was in the form of a big circle. Sadly, Anaximander’s map has not survived, and we rely on copies that were made later for information about this first map. One copy was made by Hecataeus of Miletus during the 6th century BCE, which follows the idea from Homer’s poems that the earth was a circle, surrounded by an ocean (like a moat). In this vision, Greece was literally thought to be the centre of the world.
Pythagoras of Samos (6th-5th century BCE) correctly suggested that the earth was a sphere, but other theories persisted: Anaximenes of Miletus from the 6th century BCE even believed that the earth was a rectangle!
An important stage in the Greeks’ understanding of geography was brought about by Herodotus, a historian who lived during the 5th century BCE. Herodotus did a lot of travelling and collected information as he went along. He recorded his findings in his Histories, in which he expands the number of continents to three (including Europe, Asia and Africa), where previous mapmakers thought there were only two (Europe and Asia). But Herodotus still made mistakes. He was convinced that Greece was at the centre of the earth and that the barbarians lived on the edges of the earth.
It was Aristotle (4th century BCE) who finally confirmed the theory that the earth was a sphere. He used three main observations to prove this: the lunar eclipse is always circular, ships seem to sink as they move away from view, and some stars can be seen only from certain points on earth.
Meanwhile, Dicaearchus, a geographer, was the first to start including coordinates on maps. This made it easier to find locations. Timosthenes later introduced the idea of using winds to indicate directions, which would help sailors on their sea voyages.
These advancements later helped Claudius Ptolemy (2nd Century CE) to write a textbook called 'Geographia' or ‘Geography’, which included thousands of accurate maps of the world. | 0.802187 | 3.103463 |
NASA scientists are closer to solving the mystery of how Mars’ moon Phobos formed.
In late November and early December 2015, NASA's Mars Atmosphere and Volatile Evolution (MAVEN) mission made a series of close approaches to the Martian moon Phobos, collecting data from within 300 miles (500 kilometers) of the moon.
Among the data returned were spectral images of Phobos in the ultraviolet. The images will allow MAVEN scientists to better assess the composition of this enigmatic object, whose origin is unknown.
Comparing MAVEN's images and spectra of the surface of Phobos to similar data from asteroids and meteorites will help planetary scientists understand the moon's origin – whether it is a captured asteroid or was formed in orbit around Mars. The MAVEN data, when fully analyzed, will also help scientists look for organic molecules on the surface. Evidence for such molecules has been reported by previous measurements from the ultraviolet spectrograph on the Mars Express spacecraft.
The observations were made by the Imaging Ultraviolet Spectrograph instrument aboard MAVEN.
MAVEN's principal investigator is based at the University of Colorado's Laboratory for Atmospheric and Space Physics, and NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the MAVEN project. Partner institutions include Lockheed Martin, the University of California at Berkeley, and NASA's Jet Propulsion Laboratory.
For more information on MAVEN, visit: http://www.nasa.gov/maven | 0.870254 | 3.207563 |
As long as it is 8 centimeters close to the sun, the earth will become the second Mars? Scientists decided not to hide2019-04-01 11:25:58 224 ℃
The Earth's ability to nurture life is largely attributed to the sun. If the sun does not continuously transmit energy to the earth, the earth will become a cold and lifeless scene. Scientists have predicted that if the sun suddenly disappears, the earth will fall into darkness in eight minutes, because it takes eight minutes for sunlight to reach the earth, and after eight minutes, the earth, including all living things on the earth, will feel bad.
Without the sun, the earth's temperature would drop to minus two Baidu, and no living thing could survive at such a temperature, which shows how important the sun is to the earth.
Besides the existence of the sun itself, the distance between the region and the sun is also the key. If the earth flow is too far from the sun, the energy obtained by the earth will decrease, but this does not mean that the closer the earth is to the sun, the better scientists have calculated. The distance between the sun and the earth can be said to be a perfect state, because as long as the earth is 8 cm closer to the sun's orbit, the whole area will be scorched, and the sea water will evaporate and cause the mass extinction of organisms.
Why do you say that? The sun's energy comes from its internal nuclear reactions rather than from the "burning" phenomenon we see. The core of the sun is less than 50 kilometers in diameter, but its temperature is as high as 15 million degrees, and it has great pressure. It has 250 billion atmospheric pressure.
In such a high temperature and pressure environment, every four hydrogen nuclei inside the sun combine to form a helium nucleus, while generating nuclear fusion, energy bursts to the surface in the form of flame magma, which is also the illusion of "burning in a bear". How much energy does the sun emit? According to scientists'calculations, the energy radiated by the sun to the earth's atmosphere is only one of 2.2 billion of its total radiation energy, up to 173,000 TW, but this radiation alone is enough to illuminate and warm the whole earth. If
and 173,000 TW is further converted, the energy irradiated to the earth per second is equivalent to 5 million tons of coal and 499,400,000,000 chars per second. It is precisely because the sun has such high energy that people can use solar energy to convert into a variety of energy, and convenient for human use.
According to the above calculation of solar energy, if the earth is close to the solar orbit, it may be really dangerous and not necessarily. The author believes that the earth is undoubtedly the "lucky man" in the solar system, because the distance between the earth and the sun is simply ingeniously designed. If the sun is too close or too far in the earth, it will have a negative impact on the life on the earth.
And if the Earth is near the sun, the end just needs to look at Mercury and Venus. Mercury is the closest planet to the sun, and its surface temperature is even higher than 400 degrees Celsius. For the current Earth, if it is closer to the sun, the Earth's temperature may rise to 50 degrees. At that time, the Earth may become The second barren Mars is not necessarily.
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- 20 moving pictures with feelings: these familiar things are produced in this way. | 0.843772 | 3.058661 |
The Gaia spacecraft was just launched in December, and while it hasn’t started gathering data yet, the project to support Gaia has already begun to discover new things about our galaxy. The purpose of the Gaia spacecraft is to map stars in our galaxy. It’s goal is to map a billion stars, including spectral analysis, which will tell us about their composition. This week a paper was submitted to Astronomy and Astrophysics that analyzes some project data to look at the metallicity of stars in the galaxy.1
Metallicity is a measure of how much metal (which in astronomy means everything not hydrogen or helium) a star contains. Since metals can only be formed in the cores of stars, the higher the metallicity the younger the star. For example, our Sun has a relatively high metallicity, which means it must have formed from the remnants of a few generations of stars.
We’ve known for a while that stars within the plane of our galaxy tend to be high metallicity, while those in the surrounding halo tend to have low metallicity. This new research looked at this distribution in more detail. Specifically it looked at levels of magnesium in different stars. The reason magnesium was chosen is that large quantities of it is produced in the cores of large, short lived stars. In the early history of our galaxy, these are the type of stars that would become supernovae first, so stars with higher levels of magnesium would have formed from the remnants of these early stars.
What the team found was that stars closer to the center of our galaxy than the Sun have higher levels of magnesium, while stars further away from the center than the Sun have lower levels of magnesium. This would seem to indicated that stars formed near the center of the galaxy first, with stars farther from the center forming later. A galaxy forming from the inside out, as it were.
Of course this paper hasn’t been peer reviewed, though I expect it will be soon. This is just the first chapter in what will likely be a very interesting story.
Bergemann, Maria, et al. “The Gaia-ESO Survey: radial metallicity gradients and age-metallicity relation of stars in the Milky Way disk.” Astronomy & Astrophysics 565 (2014): A89. ↩︎ | 0.827566 | 3.959898 |
The planet Neptune is the eighth and final planet orbiting the Sun every 164.8 years at a distance of around 30 AU (4.5 billion km). Seventeen Earths could fit inside of Neptune. Neptune is denser, but smaller in size than Uranus because its greater mass causes more gravitational compression of its atmosphere. Like Jupiter and Saturn, Neptune’s atmosphere is composed mostly of hydrogen, helium and “ices” such as water, ammonia, and methane. Neptune’s atmosphere also contains traces of hydrocarbons and potentially nitrogen.
Uranus and Neptune are dissimilar to Jupiter and Saturn in a distinct way. They are referred to as “ice giants” since have a more “icy” composition along with interiors primarily composed of ices and rock. Neptune’s bluish color is due to traces amounts of methane in the outermost regions of Neptune’s atmosphere. Neptune’s atmosphere is one of the most active in our Solar System, and it has some of the most robust, sustained wind systems of any planet. Wind speeds have been known to reach as high as 2,100 km/h (580 m/s; 1,300 mph). Neptune has had several unique storm formations in the past including the Great Dark Spot, the Scooter, and the Small Dark Spot.
Neptune is too far to be seen with the naked eye and was discovered using a mathematical prediction rather than by direct observation. During the 1700’s astronomer, Alexis Bouvard deduced that irregularities in the orbit of Uranus were the result of gravitational perturbations by a planet yet to be discovered. After that, Neptune was discovered on September 23, 1846, by Johann Galle. The world was within a degree of the position predicted by Urbain Le Verrier using Bouvard’s observations. Triton was discovered soon after. Neptune was named after the Roman god of the sea, and its moons were named after lesser sea gods in Roman mythology.
Neptune has been visited by one space probe, Voyager 2. Voyager 2 began photographing Neptune around May 1988 and officially began exploring the Neptunian system the next year around August 1989. Upon its last observation of Neptune, the probe ventured closer to Neptune than any other planet Voyager encountered on its mission, coming within 4,950 km (3,080 mi) above Neptune’s north pole.
Voyager 2 was able to send back unlimited data on Neptune’s atmosphere, rings, magnetosphere, Triton and newly moons! Voyager 2 was able to discover six new small satellites orbiting Neptune. These moons were Despina, Galatea, Larissa, Thalassa, Naiad, and Proteus. Six more moons were found later in 2002, 2003 and 2013 bringing Neptune’s total moons to 14. Voyager was able to photograph Proteus, Nereid, and Triton. Observations of Triton proved to be a huge success. The probe discovered Triton to be geologically active with nitrogen ice cryovolcanos or geysers active throughout its surface. Voyager 2 also found polar caps as well as a thin atmosphere of nitrogen ice particles.
Voyager 2 was able to gather data from Neptune’s intense weather patterns, including the storms mentioned above, the strong westward winds, and rapid cloud formations. Voyager 2 was sent back relevant data regarding Neptune’s magnetosphere. It found that Neptune’s magnetic field was found to be highly tilted and offset from the planet’s center with relatively weak auroras. Voyager 2’s radio instruments revealed that Neptune’s ring system consisted of four complete rings.
Just above Neptune’s surface or area in which there is a pressure of “0” lies the troposphere. The temperature in the troposphere decreases as altitude increases. The next layer is the stratosphere, in which temperatures increase with altitude. This elevated temperature is caused in part by the rotation of Neptune’s core against the grain of the stratosphere. The majority of Neptune’s storms, clouds, and extreme weather patterns are generated in the area in between the stratosphere and the troposphere. This area is known as the tropopause. The next layer is the thermosphere. The last and outer component of the Neptune’s atmosphere is known as the exosphere.
Neptune’s atmosphere forms up to 10% of its mass and extends to around 10% to 20% of the way toward the core, where it reaches pressures of about 100,000 times that of Earth’s atmosphere. Since Neptune’s has a similar methane composition as Uranus, scientists believe there is another unknown atmospheric element that contributes to Neptune’s bluish hue.
The mantle is rich in water, ammonia, and methane. This mixture is a hot, dense, and highly electrically conductive fluid sometimes referred too as a water–ammonia ocean. Scientists believe conditions may contribute to methane decomposes into diamond crystals that rain downwards like hailstones at a depths of 7,000 km. Sounds fun, right? The Lawrence Livermore National Laboratory has conducted high-pressure experiments to simulate conditions within Neptune’s mantle. These experiments suggest that the top of Neptune’s mantle may be a liquid carbon ocean with floating solid diamonds.
The core of Neptune consists of silicates and nickel-iron has a mass about 1.2 times that of Earth with a pressure of nearly twice as high as that at the center of Earth with temperatures as high as 5,400 K.
Neptune’s magnetic field is tilted relative to its planetary axis at 47° and offset at 13,500 km from the planet’s center. Neptune’s magnetopause begins to slow the solar wind at a distance of 34.9 times its radius. The magnetopause, where the pressure of Neptune’s magnetosphere counterbalances solar wind, lies at a distance of 23 to 27 times the radius of Neptune. The tail of the magnetosphere extends out to at least 72 times the radius of Neptune.
Moons of Neptune
Triton is the Neptune’s largest moon and the seventh-largest moon in the Solar System at 2,710 kilometers (1,680 mi) in diameter. Triton was discovered early October 1846, by English astronomer William Lassell. Triton is also the only large moon in the Solar System with a retrograde orbit around its planet. Scientists believe Triton’s retrograde orbit is an indicator that the moon may have been a dwarf planet captured from the Kuiper belt by Neptune’s gravity.
Triton’s composed of a frozen nitrogen surface, a water-ice crust, an icy mantle, and rocky core. The core makes up about two-thirds of its total mass. Triton’s density of 2.061 g/cm3, suggests a composition of around 15–35% water ice.
The most spectacular feature of Triton is its active cryovolcanic geysers. These geysers erupt in plumes up to 8 km high, steadily for nearly up to a year, driven by the sublimation of nitrogen ice. Sublimation is the transition of matter directly from the solid state of matter into the gaseous state of matter, without passing through the intermediate liquid phase. The only other geologically active moons within our Solar System are Io, Europa, Enceladus, and Titan. As a consequence of Triton’s geysers, its surface is relatively young, with few prominent impact craters. Well developed cryovolcanic and tectonic terrains suggest an extremely active geological history. Triton’s geysers are the source of its thin, nitrogen atmosphere, which has significantly less pressure than Earth’s atmosphere.
Neptune's Smaller Moons
Seven smaller moons with prograde orbits lie within Triton’s orbit. These moons are Naiad, Thalassa, Despina, Galatea, Larissa, Hippocamp, and Proteus. Hippocamp and Proteus are the only moons of this group that is tidally locked. Hippocamp is the smallest moon and the last moon to be discovered while Naiad is the closest moon to Neptune. Proteus is the largest regular moon and the second-largest moon of Neptune. Naiad, Thalassa, Despina, and Galatea orbit within Neptune’s rings and serve as shepherd moons, keeping the rings of Neptune together in one piece.
The largest of the inner moons is Proteus. They are believed to be re-accreted from the rubble disc generated after Triton’s capture after Triton’s orbit became circular. Neptune also has six smaller, irregular moons whose orbits are much farther from Neptune and highly inclined. Three of these moons have prograde orbits, while the remaining satellites have retrograde orbits.
Nereid, Halimede, Sao, Laomedeia, Psamathe, and Neso lie outside the orbit of Triton and are known as irregular moons. If you recall, an irregular moon is a natural satellite that follows a distant, inclined, and often eccentric and retrograde orbit around it’s primary, or in this case, planet. Their orbital behavior suggests that these moons did not form together with their world. They most likely were captured planetary bodies orbiting the Sun before the gravity of their planet captured them.
Triton and Nereid are the largest known irregular moons in our Solar System with Triton being significantly larger than all other irregular moons. Other orbital oddities including the eccentricity, inclination of their orbits make Triton and Nereid an unusual pair of irregular satellites. These consistencies with the Triton and Nereid give us a glimpse into the Neptunium system’s past. Triton was more than likely a plutoid body captured by Neptune. Upon its capture, Triton’s gravity disrupted the orbit of Nereid giving Nereid it’s highly eccentric, but low inclined orbit. The two outermost Neptunian irregular satellites, Psamathe and Neso, have the largest orbits of all moons in our Solar System. | 0.893991 | 3.654383 |
Until relatively recently, Mercury was one of the most poorly understood planets in the inner solar system. The MESSENGER mission to Mercury, is changing all of the that. New results from the Mercury Laser Altimeter (MLA) and gravity measurements are showing us that the planet closest to our sun is thin skinned and wrinkled, which is very different from what we originally thought.
The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft was launched back in 2004. It took a long time getting to its destination, completing 3 flybys of Mercury before finally entering orbit a little over a year ago. Currently, the spacecraft is in a highly eccentric polar orbit, approaching the planet much closer in the north than in the south. This allows the northern hemisphere to be probed and imaged at enviably high resolutions, but leaves the southern hemisphere poorly understood.
Even so, the data returned from MESSENGER is showing us some quite unanticipated findings. Two papers from the MESSENGER team, published in today’s issue of Science, are showing some surprising results from the laser altimeter and gravity experiments.
Using NASA’s Deep Space Network, Earth-based radio tracking of MESSENGER has allowed minute changes in the spacecraft’s orbit to be monitored and recorded. From this, Dr. Maria Zuber of MIT and her team calculated a model of Mercury’s gravity. Meanwhile, the on-board laser altimeter has provided invaluable topographic information. Combined together, these data have allowed the MESSENGER team to glean a great deal of information about the planet’s interior workings.
One of the most striking findings is that the iron-rich core of Mercury is very large. A combination of measurements and models suggest that the core has both a solid interior portion and a liquid outer portion. And while it is not certain how much of the core is solid and how much is liquid, it is clear that the total core has a radius of about 2030 km. This is a huge core, representing 83% of Mercury’s 2440 km radius!
Furthermore, these calculations suggest that the layer above the core is much denser than previously expected. Results from MESSENGER’s X-Ray spectrometer indicate that the crust, and by extension the mantle, are too low in iron to explain this high density. Dr. Zuber’s team think that the only way to explain this discrepancy is by the presence of a solid iron-sulfur layer just above the core. Such a layer could be anywhere from 20 to 200 km thick, leaving only a very thin crust and mantle at the top. This kind of interior structure is completely different from what was originally suggested for Mercury, and it is nothing like what we have seen in the other planets!
This striking fact may help explain some unexpected altimeter results, which show that Mercury’s topography has less variation than other planets. The total difference between the highest and lowest elevations on Mercury is only 9.85 km. Meanwhile, the Moon has a total difference of 19.9 km between its highest and lowest points, and on Mars this difference is 30 km. Dr. Zuber and her team speculate that the presence of the core so close to the surface could keep the mantle hot, allowing topographic features to relax. In such a scenario, the lithosphere under tall impact-formed mountains would sink down into a mushy mantle that cannot support their weight. Conversely, the thin lithosphere under impact basins would rebound upwards, taking part of the mobile mantle with it.
In fact, the gravity data shows evidence of exactly this kind of process, in the form of “mascons”. These mass concentrations form when large imacts make the local crust very thin, allowing denser mantle material to rise closer to the surface as the lithosphere rebounds from the impact event. Mascons are well known from studies on the Moon and Mars, and now MESSENGER’s gravity data has revealed three such mascons on Mercury, located in the Caloris, Sobkou, and Budh basins.
Interestingly enough, the mascons in Sobkou and Budh basins are not immediately obvious. They only show up when the effects of a regional topographic high are adjusted for. This topographic feature is a large quasi-linear rise that extends over half the circumference of Mercury in the mid-latitudes. The rise even passes through the northern part Caloris basin (which is large enough that its mascon is not overwhelmed by the rise). Studies of this rise by the MESSENGER team suggest that it is relatively young, having formed well after the formation of the basins, after the volcanic flooding of their interiors and exteriors, and even after some of the later impact craters that cover the flooded surfaces.
Dr. Zuber and her team also identified another young topographically elevated region, the Northern Rise, located in the lowlands surrounding the North Pole. They speculate that these young rises represent a buckling of the lithosphere, which happened when the planet’s interior cooled and contracted. This interpretation is supported by the presence of lobate scarps and ridges that can be seen around the planet, and which represent faulting of the crust when it was compressed.
So, it seems that Mercury is unlike the other planets of the Solar System. It appears to have a disproportionately large core that is covered by a thin skin of mantle and lithosphere. Furthermore, this skin seems to have wrinkled like a raisin’s when the huge core of the planet shrunk as it cooled.
Gravity Field and Internal Structure of Mercury from MESSENGER, Smith et al., Science V336 (6078), 214-217, April 13 2012, DOI:10.1126/science.1218809
Topography of the Northern Hemisphere of Mercury from MESSENGER Laser Altimetry, Zuber et al., Science V336 (6078), 217-220, April 13 2012, DOI:10.1126/science.1218805 | 0.829381 | 3.856919 |
Keywords:Jupiter, Ganymede, Satellite Exploration
JUICE is an ESA’s L-class mission to Explore Jupiter Icy Moons. JUICE was mission adopted in November 2014. It will be launched in 2022, arrive at Jupiter in 2030 and be inserted into Ganymede orbit in 2032. The science objectives of JUICE is to understand (1) emergence of habitable worlds around gas giants and (2) Jupiter system as an archetype for gas giants. Three Japanese groups were selected to provide part of the three science instruments RPWI, GALA, and PEP/JNA. Two Japanese groups were also selected as science Co-I of two instrument groups JANUS and J-MAG. JUICE is the first mission for ISAS/JAXA to participate to foreign large science mission as a junior partner who will provide part of the science instruments. JUICE will observe Jupiter system from Jupiter orbit in order to understand Jupiter system as an archetype for gas giants. JUICE will make observation of 3 of the 4 Galilean satellites, Europa, Ganymede, and Callisto in order to understand the emergence of habitable worlds around gas giants. JUICE will be launched by Arian-5. The Dry mass of JUICE is about 1800kg and the fuel is about 2900kg. The required Delta-V is about 2700m/s. JUICE is a three-axis stabilized spacecraft with solar cell paddle of about 70m2 that will generate approximately 700W power. The mass and power allocated to science instrument is 104kg and 150W, respectively. X band and Ka band are used for satellite-ground communications. After 7.5 years of interplanetary transfer and Earth-Venus-Earth-Earth gravity assists JUICE will be inserted into an orbit around Jupiter in January 2030. JUICE will make observation of all the three Jupiter icy Moons that potentially have subsurface ocean under the icy crust. After inserted into Ganymede orbit in 2032, JUICE will make detailed observation of the largest Icy Moon in the solar system. Taking into account all the data to be obtained by 5 instruments that JUICE-JAPAN will participate, Japanese team will be able to contribute to most of the major science objectives relating with planet Jupiter (JANUS), Jupiter magnetosphere (PEP/JNA, RPWI, and J-MAG), and Icy Moons (GALA, J-MAG, and JANUS). JUICE-JAPAN Working Group (WG) was established in September 2013. JUICE-JAPAN WG submitted a proposal for ISAS/JAXA small project in February 2014. JUICE-JAPAN WG passed the MDR in September 2014. JUICE-JAPAN is now preparing for the SRR. After SRR, SDR is scheduled in the end of 2015, PDR is scheduled in 2016 and CDR is scheduled in 2017. | 0.815235 | 3.445397 |
Data taken by Cassini of Saturn’s A-ring, B-ring, the Cassini Division, and Huygens gap, on May 25, 2017. Credit: NASA/JPL-Caltech/SSI/Sophia Nasr
Sometimes I find raw data from Cassini and think it really needs to be turned into a GIF. And when that data features Saturn’s rings, you know I’ll be on it! (As you will learn, I’m slightly obsessed with Saturn’s rings… but then, who isn’t?!)
The interesting thing about this data set is that the rings are so heavily sunlit here that Saturn’s B-ring is almost entirely washed out. May 25, 2017. What’s striking, however, is the detail we get in the Cassini Division—the gray area that stands out in this GIF. Further out, we get some detail in the A-ring, and then it’s washed out again. Just for reference, looking from the lower right to the upper left, we’re looking at Saturn’s B-ring, followed by the Huygens gap, followed by the stunning Cassini division, and finally, the A-ring. For more clarity, you can take a look at a high-definition Ring Scan featured on APOD. And, you’ll remember in my previous blog post that the B-ring is the spot for spokes!
Saturn’s rings are made up of mostly ice particles, ranging from the size of a grain of sand to several meters across, and trace amounts of rocky dust material as well. The ice particles are what make its rings so reflective, making Saturn the only planet with rings visible to the naked eye (and spectacular, at that). The width of Saturn’s main rings are about 300,000 km in extent, but some fainter rings extend far further—the E-ring a ring composed of ice particles only microns thin, extends out to the orbit of Titan! So wide they are indeed, but extremely thin—tens of meters thin!! Why are they thin? Well, the short answer to that is physics. The explanation is as follows: when a ring particle has an orbit that’s inclined to the plane, it has more orbital energy than do the ones in the ring. So when those with highly-inclined orbits collide with those in the rings, they lose orbital energy and are kind of forced back into the lower energy orbit, creating this flattened ring we see today. You can find good explanation and link to a detailed analysis of this mechanism given by my friend and astronomer Phil Plait.
Now, let’s talk about the rings (and gap) of interest in this GIF. Let’s start with the brightest, most massive ring of the Saturnian system—the B-ring! This stunning ring is about 25,500 km wide, and doesn’t seem to have any gaps in it. It does, however, appear to have moonlets—mini moons a few hundred kilometers across—in it.
Strange Things Afoot in the B Ring. Credit: NASA/JPL_Caltech/SSI
When you play the video above, you’ll notice a clump moving in orbit near the edge of Saturn’s B-ring. This is one of a couple such features in the B-ring; the mass, or moonlet, appears to be orbiting Saturn independently of the ring. And because of the moonlet’s mass, it exerts its gravitational force on the particles in the ring, flinging ice particles up while it moves! That creates that feature you see in the above video.
Saturn’s B-ring is even more complex than stated above. Oscillations in the ring material cause the waves and formations in the B-ring to move up and down, as you can see in this video. This behavior, along with embedded moonlets, causes these weird and beautiful vertical structures to form in the outer B-ring, as seen below:
Vertical structures in Saturn’s B-ring seen by Cassini in 2009. Credit: NASA/JPL-Caltech/SSI
With all this interesting stuff going on in the B-ring, scientists think it behaves the way a galaxy does. You can read more on this, and the oscillations described above, in an article written by science journalist Nancy Atkinson.
So the B-ring is a dense place with a mass nearly the same as Saturn’s moon Mimas (yup, our solar system’s very own death star). Let’s talk about something far less massive, but no less interesting—the Huygens Gap!
The Huygens Gap, found right in between the B-ring and the Cassini Division in the GIF above, is a gap formed by an orbital resonance with Saturn’s moon Mimas, where the resonance with Mimas is the location of the gap, and the Cassini Division (more on this next). The gap ranges to up to 400 km in width. An orbital resonance is caused by our favorite friend—gravity. Mimas exerts a force of gravity, and orbiting Saturn, it’s at just the right place to exert a gravitational pull in the Huygens Gap, pulling material out of it. So in that region, for every two orbits made, Mimas makes one, ie a 2:1 resonance. There’s also a ringlet in the gap (the thin white band just below the Cassini Division in the GIF). That ringlet has some irregularities in it, probably caused by the orbital resonance. Orbital resonances are all over the solar system! For example, three of Jupiter’s Galilean moons, Io, Europa, and Ganymede, have a 4:2:1 resonance. And Pluto is in orbital resonance with Neptune, a 2:3 resonance. So basically, the reason we get the Huygens Gap in Saturn’s rings is because gravity and orbital mechanics. And with all this talk of Mimas, our very own Death Star, I think it would be nice to show off an image of this beautiful moon:
A mosaic of 6 images of Mimas, taken by Cassini Feb 13, 2010. Credit: NASA/JPL-Caltech/SSI
Let’s move out to a really interesting spot, and the highlight (in my opinion) of the GIF: The Cassini Division. The Cassini Division, about 4700 km wide, lies between Saturn’s A-ring and B-ring. This is the “gap” you’ll see when you look at Saturn through a telescope, or images of Saturn taken through a telescope, but it’s no gap—there is ring material in there. Similar to the C-ring, the material here is made up of ice particles, but covered in a dark material that makes it harder to see. But there are gaps in this material, and it’s really sparse, because these particles are in orbital resonance with Mimas—2:1 (this resonance appears to mostly affect the inner portion of the Cassini Division, close to the Huygens Gap). The moon Mimas pulls on the material, forcing particles out of the Cassini Division. You can read more about this, and other resonances created by our very own Death Star, in an article by Matt Williams for Universe Today.
This brings us to the A-ring, a place of wonder, and soon, you’ll see why. Saturn’s A-ring is some 14,600 km in width. The A-ring hosts two gaps—the Encke Gap and the tinner Keeler Gap—and a bunch of propellers. Oh, also, the A-ring hosts some brilliant features caused by spiral density waves. So this is going to be a long section, but well worth your read!
Let’s start with the spiral density waves. I made a GIF of Cassini data taken on May 15, 2017, that features everything we’re going to discuss: spiral waves, the Encke Gap, the Keeler Gap, and a propeller! Here’s the GIF:
Data of Saturn’s A-ring, featuring the Encke Gap, Keeler Gap, and a propeller, taken by Cassini on May 15, 2017. Credit: NASA/JPL-Caltech/SSI/Sophia Nasr
This GIF features the Encke Gap, with one knotty ringlet clearly visible, the thinner Keeler Gap above, a propeller that swings by near the center, and spiral density waves! But the spiral density waves deserve a bit more attention. Here’s a nice close-up, which I got from planetary scientist Emily Lakdawalla’s blog:
Spiral waves seen in Saturn’s A-ring, taken by Cassini on Apr 8, 2008.
These strange and beautiful features are created by orbital resonances with Saturn’s outer moons. Emily Lakdawalla explains these really well in the link from which I got the cool image above.
Next, we move onto the Encke Gap. This gap, some 325 km wide, is cleared by the gravity of a special moon named Pan. Here’s an image of this weird space ravioli/pierogi moon, taken on March 7, 2017:
Saturn’s space pierogi moon Pan. Taken by Cassini on March 7, 2017.
This moon, with a mean radius of about 14 km, clears a gap in Saturn’s rings by kicking particles out with its gravity. You’ll also notice in the GIF, that just above the gap, you’ll see disturbances—these are also caused by Pan. They’re called spiraling wakes, and they’re caused because the particles closer to Pan move faster than those further away (just a statement of Kepler’s Laws), so Pan’s gravity creates these disturbances in the ring material. Pan shares this gap with a few ringlets, one visible in the GIF. You’ll notice it’s kinda knotty—this is probably due to Pan’s gravity as well.
Now let’s move onto the Keeler Gap—my favorite!! This gap is only about 42 km wide, and created by a lovely moon Daphnis, with a mean radius of about 4 km (but it’s shaped like a potato):
Saturn’s moon Daphnis, taken by Cassini on Jan 19, 2017.
Credit: NASA/JPL-Caltech/SSI/Matúš Motlo
Now, let’s get to the cool stuff. I processed an image that was really difficult to put together, because I had to rotationally align them—that is, Cassini’s perspective didn’t just change in an up-and-down direction between the red, green, and blue filter images, but it also changed in that it slightly rotated. The result is something I’m pretty happy with, because it shows a lot of what I’m about to discuss, and in color:
Daphnis making Waves in Saturn’s rings, taken by Cassini on Feb 6, 2017.
Credit: NASA/JPL-Caltech/SSI/Sophia Nasr
Okay so what are we seeing here?! Well, we’re seeing the gravitational effects of Daphnis on Saturn’s ring material in the Keeler Gap! But, why the waves, and material moving upwards?? Well, turns out Daphnis has an eccentric orbit, bringing it closer and farther from the material, depending on the point in its orbit. Because of this, Daphnis has a stronger gravitational pull on the material when it’s closer, which created waves. But its orbital inclination is what’s owed the credit for bringing material up or down from the ring plane. You can see in the image above that some material looks like it’s being pulled up below Daphnis, and down ahead of Daphnis. But wait, there’s more! Notice how below Daphnis, the waves only appear on the outer ring, and ahead of Daphnis, on the inner ring? That’s because of the orbital velocities of the particles in the rings—the particles in the inner ring move faster than Daphnis, and those in the outer ring move slower than Daphnis, which is why the leading waves are in those moving faster, and the trailing ones, in the ones moving slower. This is why the Keeler Gap and Daphnis are my favorite feature in Saturn’s rings!
Now, finally, we talk about the propeller you see in the GIF. It’s worth zooming in on one, the largest (known) propeller in Saturn’s rings, Bleriot (which I think is the same one you see in the GIF):
Bleriot Propeller in Saturn’s A-ring, taken by Cassini on Apr 12, 2017.
So, what is this thing, and how many are there? Well, to answer the second question, Saturn’s rings are full of propellers—they’re all over the place!! How are they formed? Now this is where it gets interesting. First, these propellers are formed by moonlets—mini moons only a couple of hundred meters across. These moonlets are trying to do what Daphnis and Pan do—clear a gap in Saturn’s rings. But they’re small, so the gravity they exert is smaller as well. So they fail to clear a gap throughout Saturn’s ring, but they succeed in clearing one within their vicinity. They actually can kick up material 0.5 km above/below the ring plane! But it’s even more interesting because of the shape. Why a propeller? Well, orbital mechanics and gravity are yet again responsible! We basically have a gravitational tug-of-war going on between the moonlet and Saturn. Let’s start with the ring material that’s ahead of the moonlet. These particles have an associated with them some orbital angular momentum; now, the moonlet uses its gravity to pull these particles towards it, causing those particles lose some of their momentum, and they fall inward due to Saturn’s gravity, and then go merrily along in their path, slightly inward from the moonlet. This happens throughout the moonlet’s orbit, creating the forward propeller. Now, those particles behind the moonlet are pulled in, which gives them a boost in orbital energy, causing them to fling ourward. Occuring throughout the moonlet’s orbit, you get the rear end of the propeller. Phil Plait explains this much better, here. And voila! You have a propeller in the ring!
In summary, a lot of the cool stuff we see in Saturn’s rings is owed to gravity and orbital mechanics. Physics, my friends, is why you see stuff that’s this cool. | 0.836014 | 3.916277 |
While Pluto deservedly stole the headlines last week, Chris Russell’s Dawn update at the Exploration Science Forum at NASA Ames reminded us that the other dwarf planets are also sharing their secrets with eager scientists. As an eager scientist unaffiliated with the Dawn mission, I’m happy to share what I heard!
Russell’s update began with some relatively mundane results: Ceres’ North Pole is pointing in a different direction than ground-based measurements suggested, leading to slightly different lighting conditions than they were anticipating. Ceres is also a bit smaller than they were expecting, which leads to a slightly larger density. Again, nothing terribly newsworthy.
However, Russell then began to discuss the surface features on Ceres, and things rapidly became much less mundane. He suggested that the distribution of bright spots on Ceres didn’t look like they were consistent with impacts. This was a bit hard to understand, particularly since I was still trying to work through the North Pole results, but I took it to mean that while there were many bright spots across the surface, the relative numbers of large versus small ones don’t look like what we’d expect if they were all simply craters. However, it may also have been a statement about the distribution of these bright spots across the surface in terms of latitude or longitude.
NASA / JPL / UCLA / MPS / DLR / IDA / Emily Lakdawalla
Ceres global view: White spots aplenty
This image of Ceres is part of a sequence taken by Dawn on May 7, 2015, from a distance of 13,600 kilometers.
He then focused on the most famous complex of bright spots, in Occator crater. This group is also known as “Spot 5” from earlier Hubble Space Telescope observations. Russell said that a “haze” was visible in this crater at certain times of day, and that it was seen more than once. A follow-up question, the only one there was time for, established that the haze was confined to the crater itself.
NASA / JPL / UCLA / MPS / DLR / IDA
Occator crater, a bright spot on a dark world
A cluster of mysterious bright spots on dwarf planet Ceres can be seen in this image, taken by Dawn from an altitude of 4,400 kilometers. The image, with a resolution of 410 meters per pixel, was taken on June 9, 2015.
There are a lot of exciting possibilities as to what this means, though the Dawn project itself will need to clarify exactly what was observed. One could easily interpret the bright spots as ice (as many have done in past months), and imagine that what was seen can be associated with the water vapor signature seen by the Herschel spacecraft. However, “haze” usually implies a particulate component, and the team itself seemed to be favoring a non-ice composition for the bright spots in recent weeks. A “haze” rather than a “plume” or “jet” also suggests material is sticking around, which is difficult to imagine (though Ceres’ relatively large gravity may help in that regard).
Finally, I’ll note a possible connection to a similar claim made by the Framing Camera team at this past LPSC: They saw Spot 5 from beyond the limb of Ceres, which they argued meant it was elevated. However, I haven’t heard this claim again and it’s possible that an updated shape model would show a sight line to the surface.
Given the importance of Russell’s announcement of what amounts to a transient, localized atmosphere on Ceres, I would expect a more official account to emerge before long! | 0.800044 | 3.640496 |
‘We’re here!’: Curiosity rover arrives at Mount Sharp on Mars
After a long, and at times risky two-year journey, the Mars Science Laboratory rover Curiosity has reached the base of the lower slopes of Mount Sharp, the primary destination since its landing back in 2012. Mount Sharp is about the same height as Mount Rainier on Earth and sits in the middle of the expansive Gale crater. The arrival was announced on Thursday, Sept. 11 at a NASA telecon which discussed Curiosity’s achievements so far and what else now awaits at the mountain.
“It has been a long but historic journey to this Martian mountain,” said Curiosity Project Scientist John Grotzinger of the California Institute of Technology in Pasadena. “The nature of the terrain at Pahrump Hills and just beyond it is a better place than Murray Buttes to learn about the significance of this contact. The exposures at the contact are better due to greater topographic relief.”
As Jim Green, director of NASA’s Planetary Science Division at NASA Headquarters in Washington, also noted, “Curiosity now will begin a new chapter from an already outstanding introduction to the world. After a historic and innovative landing along with its successful science discoveries, the scientific sequel is upon us.”
The arrival is actually a little earlier than previously estimated, due to a detour that the rover has taken. The original plan was to continue a bit farther west from where it is now, to an area of outcrops called Murray Buttes, before turning and starting to go up the lower slopes of the mountain. In the new traverse route now however, Curiosity will head to another outcrop called Pahrump Hills just a short distance away where it will do more drilling before taking a much shorter route up the slopes. Both Pahrump Hills and Murray Buttes lie at the edge of the boundary between the lower slopes of Mount Sharp and the crater floor.
The route will also take Curiosity past some of the very dark sand dunes around the base of Mount Sharp, another interesting target of study. As the rover continues up the lower slopes of the mountain, it will get into areas of the larger mesas and buttes which are 60 feet (18 meters) tall or more, which should provide some spectacular scenery. This region as a whole is very reminiscent of the desert southwest in the United States.
Last month, Curiosity attempted to drill at an outcrop called Bonanza King, but the rock proved to be too unstable to continue drilling safely, as it moved too much during drilling tests. Other analysis from the Alpha Particle X-ray Spectrometer (APXS) instrument however, did show an unusually high amount of silicon in the outcrop. The rover science team now hopes to find other similar outcrops at Pahrump Hills or elsewhere, as the silicon finding could provide more evidence as to how wet this region used to be a long time ago. Other discoveries have already shown that there was a lakebed and rivers here billions of years ago.
The rover’s journey has not been without difficulties however. The outer aluminum casings on Curiosity’s wheels have taken quite a beating from sharp rocks, although the main wheel structure itself is fine. This has caused some concern of course, but the new driving route and more emphasis on stopping for science investigations may help with this issue as well. According to Jennifer Trosper, Curiosity Deputy Project Manager at NASA’s Jet Propulsion Laboratory in Pasadena, California:
“The wheels issue contributed to taking the rover farther south sooner than planned, but it is not a factor in the science-driven decision to start ascending here rather than continuing to Murray Buttes first. We have been driving hard for many months to reach the entry point to Mount Sharp.” She added, “Now that we’ve made it, we’ll be adjusting the operations style from a priority on driving to a priority on conducting the investigations needed at each layer of the mountain.”
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. Then, in 2005 he began to detail his passion for the skies in his own online journal. While interested in all aspects of space exploration, his primary passion is planetary science. In 2011, he started writing on a freelance basis, and currently writes for Examiner.com. He has also done supplementary writing for the well-known iOS app Exoplanet. | 0.842609 | 3.194309 |
A red dwarf is the smallest and coolest kind of star on the main sequence. Red dwarfs are by far the most common type of star in the Milky Way, at least in the neighborhood of the Sun, but because of their low luminosity, individual red dwarfs cannot be easily observed. From Earth, not one that fits the stricter definitions of a red dwarf is visible to the naked eye. Proxima Centauri, the nearest star to the Sun, is a red dwarf, as are fifty of the sixty nearest stars. According to some estimates, red dwarfs make up three-quarters of the stars in the Milky Way.
The coolest red dwarfs near the Sun have a surface temperature of ~2,000 K and the smallest have radii of ~9% that of the Sun, with masses about ~7.5% that of the Sun. These red dwarfs have spectral classes of L0 to L2. There is some overlap with the properties of brown dwarfs, since the most massive brown dwarfs at lower metallicity can be as hot as 3,600 K and have late M spectral types.
Definitions and usage of the term "red dwarf" vary on how inclusive they are on the hotter and more massive end. One definition is synonymous with stellar M dwarfs (M-type main sequence stars), yielding a maximum temperature of 3,900 K and 0.6 M☉. One includes all stellar M-type main-sequence and all K-type main-sequence stars (K dwarf), yielding a maximum temperature of 5,200 K and 0.8 M☉. Some definitions include any stellar M dwarf and part of the K dwarf classification. Other definitions are also in use (see definition). Many of the coolest, lowest mass M dwarfs are expected to be brown dwarfs, not true stars, and so those would be excluded from any definition of red dwarf.
Stellar models indicate that red dwarfs less than 0.35 M☉ are fully convective. Hence the helium produced by the thermonuclear fusion of hydrogen is constantly remixed throughout the star, avoiding helium buildup at the core, thereby prolonging the period of fusion. Low-mass red dwarfs therefore develop very slowly, maintaining a constant luminosity and spectral type for trillions of years, until their fuel is depleted. Because of the comparatively short age of the universe, no red dwarfs exist at advanced stages of evolution.
The term "red dwarf" when used to refer to a star does not have a strict definition. One of the earliest uses of the term was in 1915, used simply to contrast "red" dwarf stars from hotter "blue" dwarf stars. It became established use, although the definition remained vague. In terms of which spectral types qualify as red dwarfs, different researchers picked different limits, for example K8–M5 or "later than K5". Dwarf M star, abbreviated dM, was also used, but sometimes it also included stars of spectral type K.
In modern usage, the definition of a red dwarf still varies. When explicitly defined, it typically includes late K- and early to mid-M-class stars, but in many cases it is restricted just to M-class stars. In some cases all K stars are included as red dwarfs, and occasionally even earlier stars.
The most recent surveys place the coolest true main-sequence stars into spectral types L2 or L3. At the same time, many objects cooler than about M6 or M7 are brown dwarfs, insufficiently massive to sustain hydrogen-1 fusion. This gives a significant overlap in spectral types for red and brown dwarfs. Objects in that spectral range can be difficult to categorize.
Description and characteristics
Red dwarfs are very-low-mass stars. As a result, they have relatively low pressures, a low fusion rate, and hence, a low temperature. The energy generated is the product of nuclear fusion of hydrogen into helium by way of the proton–proton (PP) chain mechanism. Hence, these stars emit relatively little light, sometimes as little as 1⁄10,000 that of the Sun, although this would still imply a power output on the order of 1022 watts (10 trillion gigawatts). Even the largest red dwarfs (for example HD 179930, HIP 12961 and Lacaille 8760) have only about 10% of the Sun's luminosity. In general, red dwarfs less than 0.35 M☉ transport energy from the core to the surface by convection. Convection occurs because of opacity of the interior, which has a high density compared to the temperature. As a result, energy transfer by radiation is decreased, and instead convection is the main form of energy transport to the surface of the star. Above this mass, a red dwarf will have a region around its core where convection does not occur.
Because low-mass red dwarfs are fully convective, helium does not accumulate at the core, and compared to larger stars such as the Sun, they can burn a larger proportion of their hydrogen before leaving the main sequence. As a result, red dwarfs have estimated lifespans far longer than the present age of the universe, and stars less than 0.8 M☉ have not had time to leave the main sequence. The lower the mass of a red dwarf, the longer the lifespan. It is believed that the lifespan of these stars exceeds the expected 10-billion-year lifespan of our Sun by the third or fourth power of the ratio of the solar mass to their masses; thus, a 0.1 M☉ red dwarf may continue burning for 10 trillion years. As the proportion of hydrogen in a red dwarf is consumed, the rate of fusion declines and the core starts to contract. The gravitational energy released by this size reduction is converted into heat, which is carried throughout the star by convection.
According to computer simulations, the minimum mass a red dwarf must have to eventually evolve into a red giant is 0.25 M☉; less massive objects, as they age, would increase their surface temperatures and luminosities becoming blue dwarfs and finally white dwarfs.
The less massive the star, the longer this evolutionary process takes. It has been calculated that a 0.16 M☉ red dwarf (approximately the mass of the nearby Barnard's Star) would stay on the main sequence for 2.5 trillion years, followed by five billion years as a blue dwarf, during which the star would have one third of the Sun's luminosity (L☉) and a surface temperature of 6,500–8,500 kelvins.
The fact that red dwarfs and other low-mass stars still remain on the main sequence when more massive stars have moved off the main sequence allows the age of star clusters to be estimated by finding the mass at which the stars move off the main sequence. This provides a lower limit to the age of the Universe and also allows formation timescales to be placed upon the structures within the Milky Way, such as the Galactic halo and Galactic disk.
All observed red dwarfs contain "metals", which in astronomy are elements heavier than hydrogen and helium. The Big Bang model predicts that the first generation of stars should have only hydrogen, helium, and trace amounts of lithium, and hence would be of low metallicity. With their extreme lifespans, any red dwarfs that were a part of that first generation (population III stars) should still exist today. Low-metallicity red dwarfs, however, are rare. The accepted model for the chemical evolution of the universe anticipates such a scarcity of metal-poor dwarf stars because only giant stars are thought to have formed in the metal-poor environment of the early universe. As giant stars end their short lives in supernova explosions, they spew out the heavier elements needed to form smaller stars. Therefore, dwarfs became more common as the universe aged and became enriched in metals. While the basic scarcity of ancient metal-poor red dwarfs is expected, observations have detected even fewer than predicted. The sheer difficulty of detecting objects as dim as red dwarfs was thought to account for this discrepancy, but improved detection methods have only confirmed the discrepancy.
The boundary between the least massive red dwarfs and the most massive brown dwarfs depends strongly on the metallicity. At solar metallicity the boundary occurs at about 0.07 M☉, while at zero metallicity the boundary is around 0.09 M☉. At solar metallicity, the least massive red dwarfs theoretically have temperatures around 1,700 K, while measurements of red dwarfs in the solar neighbourhood suggest the coolest stars have temperatures of about 2,075 K and spectral classes of about L2. Theory predicts that the coolest red dwarfs at zero metallicity would have temperatures of about 3,600 K. The least massive red dwarfs have radii of about 0.09 R☉, while both more massive red dwarfs and less massive brown dwarfs are larger.
Spectral standard stars
The spectral standards for M-type stars have changed slightly over the years, but settled down somewhat since the early 1990s. Part of this is due to the fact that even the nearest red dwarfs are fairly faint, and the study of mid- to late-M dwarfs has progressed only in the past few decades due to evolution of astronomical techniques, from photographic plates to charged-couple devices (CCDs) to infrared-sensitive arrays.
The revised Yerkes Atlas system (Johnson & Morgan 1953) listed only 2 M-type spectral standard stars: HD 147379 (M0 V) and HD 95735/Lalande 21185 (M2 V). While HD 147379 was not considered a standard by expert classifiers in later compendia of standards, Lalande 21185 is still a primary standard for M2 V. Robert Garrison does not list any "anchor" standards among the red dwarfs, but Lalande 21185 has survived as a M2 V standard through many compendia. The review on MK classification by Morgan & Keenan (1973) did not contain red dwarf standards. In the mid-1970s, red dwarf standard stars were published by Keenan & McNeil (1976) and Boeshaar (1976), but unfortunately there was little agreement among the standards. As later cooler stars were identified through the 1980s, it was clear that an overhaul of the red dwarf standards was needed. Building primarily upon the Boeshaar standards, a group at Steward Observatory (Kirkpatrick, Henry, & McCarthy 1991) filled in the spectral sequence from K5 V to M9 V. It is these M-type dwarf standard stars which have largely survived as the main standards to the modern day. There have been negligible changes in the red dwarf spectral sequence since 1991. Additional red dwarf standards were compiled by Henry et al. (2002), and D. Kirkpatrick has recently reviewed the classification of red dwarfs and standard stars in Gray & Corbally's 2009 monograph. The M-dwarf primary spectral standards are: GJ 270 (M0 V), GJ 229A (M1 V), Lalande 21185 (M2 V), Gliese 581 (M3 V), Gliese 402 (M4 V), GJ 51 (M5 V), Wolf 359 (M6 V), Van Biesbroeck 8 (M7 V), VB 10 (M8 V), LHS 2924 (M9 V).
Many red dwarfs are orbited by exoplanets, but large Jupiter-sized planets are comparatively rare. Doppler surveys of a wide variety of stars indicate about 1 in 6 stars with twice the mass of the Sun are orbited by one or more Jupiter-sized planets, versus 1 in 16 for Sun-like stars and only 1 in 50 for red dwarfs. On the other hand, microlensing surveys indicate that long-orbital-period Neptune-mass planets are found around one in three red dwarfs. Observations with HARPS further indicate 40% of red dwarfs have a "super-Earth" class planet orbiting in the habitable zone where liquid water can exist on the surface. Computer simulations of the formation of planets around low mass stars predict that Earth-sized planets are most abundant, but more than 90% of the simulated planets are at least 10% water by mass, suggesting that many Earth-sized planets orbiting red dwarf stars are covered in deep oceans.
At least four and possibly up to six exoplanets were discovered orbiting within the Gliese 581 planetary system between 2005 and 2010. One planet has about the mass of Neptune, or 16 Earth masses (M⊕). It orbits just 6 million kilometers (0.04 AU) from its star, and is estimated to have a surface temperature of 150 °C, despite the dimness of its star. In 2006, an even smaller exoplanet (only 5.5 M⊕) was found orbiting the red dwarf OGLE-2005-BLG-390L; it lies 390 million km (2.6 AU) from the star and its surface temperature is −220 °C (53 K).
In 2007, a new, potentially habitable exoplanet, Gliese 581c, was found, orbiting Gliese 581. The minimum mass estimated by its discoverers (a team led by Stephane Udry) is 5.36 M⊕. The discoverers estimate its radius to be 1.5 times that of Earth (R⊕). Since then Gliese 581d, which is also potentially habitable, was discovered.
Gliese 581c and d are within the habitable zone of the host star, and are two of the most likely candidates for habitability of any exoplanets discovered so far. Gliese 581g, detected September 2010, has a near-circular orbit in the middle of the star's habitable zone. However, the planet's existence is contested.
On 23 February 2017 NASA announced the discovery of seven Earth-sized planets orbiting the red dwarf star TRAPPIST-1 approximately 39 light-years away in the constellation Aquarius. The planets were discovered through the transit method, meaning we have mass and radius information for all of them. TRAPPIST-1e, f and g appear to be within the habitable zone and may have liquid water on the surface.
Planetary habitability of red dwarf systems is subject to some debate. In spite of their great numbers and long lifespans, there are several factors which may make life difficult on planets around a red dwarf. First, planets in the habitable zone of a red dwarf would be so close to the parent star that they would likely be tidally locked. This would mean that one side would be in perpetual daylight and the other in eternal night. This could create enormous temperature variations from one side of the planet to the other. Such conditions would appear to make it difficult for forms of life similar to those on Earth to evolve. And it appears there is a great problem with the atmosphere of such tidally locked planets: the perpetual night zone would be cold enough to freeze the main gases of their atmospheres, leaving the daylight zone bare and dry. On the other hand, recent theories propose that either a thick atmosphere or planetary ocean could potentially circulate heat around such a planet.
Variability in stellar energy output may also have negative impacts on the development of life. Red dwarfs are often flare stars, which can emit gigantic flares, doubling their brightness in minutes. This variability may also make it difficult for life to develop and persist near a red dwarf. It may be possible for a planet orbiting close to a red dwarf to keep its atmosphere even if the star flares. However, more-recent research suggests that these stars may be the source of constant high-energy flares and very large magnetic fields, diminishing the possibility of life as we know it. Whether this is a peculiarity of the star under examination or a feature of the entire class remains to be determined.
- List of red dwarfs – Wikipedia list article
- Aurelia and Blue Moon – Hypothetical examples of a planet and a moon supporting extraterrestrial life
- Cataclysmic variable star – Stars which irregularly increase in brightness by a large factor, then drop back down to a quiescent state
- M-type star – Classification of stars based on their spectral characteristics
- Habitability of red dwarf systems
- Hertzsprung–Russell diagram – A scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities versus their stellar classifications
- Flare star – Type of variable star that can undergo unpredictable dramatic increases in brightness for a few minutes
- Nemesis (hypothetical star) – Hypothetical star orbiting the Sun, responsible for extinction events
- Red giant – Large cool stars that have exhausted their core hydrogen
- Star count
- Stellar evolution – Changes to a star over its lifespan
- White dwarf – Type of stellar remnant composed mostly of electron-degenerate matter
- Kapteyn's Star
- Yerkes luminosity classification
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- Neptune-Size Planet Orbiting Common Star Hints at Many More
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- Variable stars AAVSO
- Stellar Flares Publications about Flares by the Stellar Activity Group (UCM)
- Red Dwarfs Jumk.de
- Red Star Rising : Small, cool stars may be hot spots for life – Scientific American (November 2005) | 0.913191 | 3.997425 |
Recently, the scientists received the latest data from Jupiter and Saturn that has challenged a lot of current theories about the planets in our solar system. The Juno and Cassini spacecraft sent the detailed magnetic and gravity data from the giant gas planets.
David Stevenson from Caltech terms the recent data as “invaluable but also confounding.” He is also participating in the 2019 March Meeting of American Physical Society which will be held in Boston. In the meeting, he will also present an update on both of the missions.
Besides this, he will present the work done so far in a press conference. The audience can watch the press conference and ask questions from him remotely by logging in to the link provided by them.
According to Stevenson, the recent data received from the gas planets is like puzzles that need to be explained yet. However, it has also clarified some of the theories about how planets were formed and how they developed magnetic fields.
The Cassini spacecraft orbited Saturn for 13 years before it dived into the interior of the planet in 2017. While Juno spacecraft has been orbiting Jupiter for 2.5 years. The successful mission of Juno is a tribute to innovative design. It consists of instruments that are powered by solar energy and protected to withstand the fierce radiation environment.
In the current mission, the scientists included a microwave sensor on Juno. It was an unconventional choice but this allowed them to figure out the deep atmosphere using microwaves. The data received showed that the atmosphere deep inside the planet is evenly mixed. This phenomenon was a new concept compared to the conventional theories.
The researchers are further exploring weather events that could be related to possible explanations of such phenomenon. These include significant amounts of gas, liquids, and ice in different parts of the atmosphere. But they think that any explanation to this will be unorthodox.
The scientists also received perplexing data from other instruments on Juno including gravity and magnetic sensors. The gravity data confirmed the presence of heavier elements in the midst of Jupiter. As we know that, at least 90% of the mass of the gas planet consists of hydrogen and helium. The heavier elements are mixed with the hydrogen in the core. Most of them are in the form of metallic liquid amounting to more than 10 times the mass of Earth.
The magnetic field data consisted of spots indicating the regions of the anomalously low and high magnetic field. Moreover, there’s also a distinct difference between the northern and southern hemispheres.
This new data has provided rich information about the outer parts of both planets. The presence of heavier elements in abundance in these regions is still uncertain. However, the outer layers play a greater role in the generation of the magnetic fields of the two planets. The scientists are further working on experiments mimicking the pressures and temperatures on the gas planets to understand the processes that are going on. | 0.841243 | 3.659684 |
A NASA spacecraft 4 billion miles from Earth yielded its first close-up pictures Wednesday of the most distant celestial object ever explored, depicting what looks like a reddish snowman.
Ultima Thule, as the small, icy object has been dubbed, was found to consist of two fused-together spheres, one of them three times bigger than the other, extending about 21 miles (33 kilometres) in length.
NASA’s New Horizons, the spacecraft that sent back pictures of Pluto 3 1/2 years ago, swept past the ancient, mysterious object early on New Year’s Day. It is 1 billion miles (1.6 billion kilometres) beyond Pluto.
On Tuesday, based on early, fuzzy images taken the day before, scientists said Ultima Thule resembled a bowling pin. But when better, closer pictures arrived, a new consensus emerged Wednesday.
“The bowling pin is gone. It’s a snowman!” lead scientist Alan Stern informed the world from Johns Hopkins University’s Applied Physics Laboratory , home to Mission Control in Laurel. The bowling pin image is “so 2018,” joked Stern, who is with the Southwest Research Institute.
The celestial body was nicknamed Ultima Thule — meaning “beyond the known world” — before scientists could say for sure whether it was one object or two. With the arrival of the photos, they are now calling the bigger sphere Ultima and the smaller one Thule.
Thule is estimated to be 9 miles (14 kilometres) across, while Ultima is thought to be 12 miles (19 kilometres).
Scientist Jeff Moore of NASA’s Ames Research Center said the two spheres formed when icy, pebble-size pieces coalesced in space billions of years ago. Then the spheres spiraled closer to each other until they gently touched — as slowly as parking a car here on Earth at just a mile or two per hour — and stuck together.
Despite the slender connection point, the two lobes are “soundly bound” together, according to Moore.
Scientists have ascertained that the object takes about 15 hours to make a full rotation. If it were spinning fast — say, one rotation every three or four hours — the two spheres would rip apart.
Stern noted that the team has received less than 1 per cent of all the data stored aboard New Horizons. It will take nearly two years to get it all.
The two-lobed object is what is known as a “contact binary.” It is the first contact binary NASA has ever explored. Having formed 4.5 billion years ago, when the solar system taking shape, it is also the most primitive object seen up close like this.
About the size of a city, Ultima Thule has a mottled appearance and is the colour of dull brick, probably because of the effects of radiation bombarding the icy surface, with brighter and darker regions.
Both spheres are similar in colour, while the barely perceptible neck connecting the two lobes is noticeably less red, probably because of particles falling down the steep slopes into that area.
So far, no moons or rings have been detected, and there were no obvious impact craters in the latest photos, though there were a few apparent “divots” and suggestions of hills and ridges, scientists said. Better images should yield definitive answers in the days and weeks ahead.
Clues about the surface composition of Ultima Thule should start rolling in by Thursday. Scientists believe the icy exterior is probably a mix of water, methane and nitrogen, among other things.
The snowman picture was taken a half-hour before the spacecraft’s closest approach early Tuesday, from a distance of about 18,000 miles (28,000 kilometres).
Scientists consider Ultima Thule an exquisite time machine that should provide clues to the origins of our solar system.
It’s neither a comet nor an asteroid, according to Stern, but rather “a primordial planetesimal.” Unlike comets and other objects that have been altered by the sun over time, Ultima Thule is in its pure, original state: It’s been in the deep-freeze Kuiper Belt on the fringes of our solar system from the beginning.
“This thing was born somewhere between 99 per cent and 99.9 per cent of the way back to T-zero (liftoff) in our solar system, really amazing,” Stern said. He added: “We’ve never seen anything like this before. It’s not fish or fowl. It’s something that’s completely different.”
Still, he said, when all the data comes in, “there are going to be mysteries of Ultima Thule that we can’t figure out.”
Marcia Dunn, The Associated Press | 0.897243 | 3.380899 |
All right, maybe not blinking like a flashlight (or a beacon on the tippity-top of a communication tower—don’t even start that speculation up) but the now-famous “bright spots” on the dwarf planet Ceres have been observed to detectably increase and decrease in brightness, if ever-so-slightly.
And what’s particularly interesting is that these observations were made not by NASA’s Dawn spacecraft, currently in orbit around Ceres, but from a telescope right here on Earth.
Researchers using the High Accuracy Radial velocity Planet Searcher (HARPS) instrument on ESO’s 3.6-meter telescope at La Silla detected “unexpected” changes in the brightness of Ceres during observations in July and August of 2015. Variations in line with Ceres’ 9-hour rotational period—specifically a Doppler effect in spectral wavelength created by the motion of the bright spots toward or away from Earth—were expected, but other fluctuations in brightness were also detected.
“The result was a surprise,” said Antonino Lanza from the INAF–Catania Astrophysical Observatory, co-author of the study. “We did find the expected changes to the spectrum from the rotation of Ceres, but with considerable other variations from night to night.”
Watch a video below illustrating the rotation of Ceres and how reflected light from the bright spots within Occator crater are alternately blue- and red-shifted according to the motion relative to Earth.
First observed with Hubble in December 2003, Ceres’ curious bright spots were resolved by Dawn’s cameras to be a cluster of separate regions clustered inside the 60-mile (90-km) -wide Occator crater. Based on Dawn data they are composed of some type of highly-reflective materials like salt and ice, although the exact composition or method of formation isn’t yet known.
Since they are made of such volatile materials though, interaction with solar radiation is likely the cause of the observed daily brightening. As the deposits heat up during the course of the 4.5-hour Ceres daytime they may create hazes and plumes of reflective particles.
“It has been noted that the spots appear bright at dawn on Ceres while they seem to fade by dusk,” noted study lead author Paolo Molaro in the team’s paper. “That could mean that sunlight plays an important role, for instance by heating up ice just beneath the surface and causing it to blast off some kind of plume or other feature.”
Once day turns to night these hazes will re-freeze, depositing the particles back down to the surface—although never in exactly the same way. These slight differences in evaporation and condensation could explain the random variation in daily brightening observed with HARPS.
These findings have been published the journal Monthly Notices of the Royal Astronomical Society (full text on arXiv here.) | 0.866042 | 4.01122 |
Show notes for Episode 189, March 17th 2014
Hosts: Paul, Julie, Hugh
Title: Julie: YorkUniverse`s Expansion!
Introducing Julie Tome: words from Julie about her background from York U to Science North to the OSC and the ROM.
This week in space/astronomy history:
1. March 16, 1750 Birth of Caroline Herschel, sister of William Herschel and astronomer in her own right. She discovered several comets including the periodic comet 35P/Herschel-Rigollet. She received many awards for her contributions to science.
2. March 13, 1781 William Herschel discovered Uranus. Uranus came from Greek mythology and the God of the Sky (Ouranos). Observed constantly in earlier times (eg Flamsteed catalogued Uranus in 1690 as 34 Tauri), Herschel tried naming the new planet (thought to be a comet initially) Georgium Sidus (after King George III) but following Bode’s suggestion, Uranius became the aame of choice universally from 1850.
3. Vanguard 1 launched March 17 1958 (56 years in space!). First solar powered satellite (4th launched) and oldest satellite to still be in orbit. Last contact in May 1964. 1.5 kg in mass, 16.5 cm diameter sphere, the primary mission was to collect geodetic data (Earth shape) and to measure atmospheric drag (eccentric orbit of 133 minutes).
1. Big announcement from Harvard-Smithsonian centre for astrophysics, BICEP2 found B-mode polarization in the CMB which is a smoking gun for gravitational waves caused by the rapid inflation of the universe immediately following the big bang. The major point of it is that this is the first ever direct observation of gravitational waves: B-mode fluctuations (polarized light that swirls and curls around itself) are predicted to result from gravitational waves caused by rapid inflation of the universe, and BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) has for the first time detected those exact B-mode fluctuations. The challenge in identifying these fluctuations is that they are incredibly faint, and that your data may be skewed by E-mode fluctuations that have been distorted by gravitational lensing to look like B-mode fluctuations. The takeaway message is this: if the observations are confirmed then gravitational waves predicted by inflation have been discovered, which in turn lends immense credibility to the theory of inflation, explains why spacetime is flat and implies that our universe is in fact infinite and always will be infinite. The next question: what drove inflation? Suggested reading: Space.com article High level summary from Bad Astronomer http://bicepkeck.org/
2. New Hypergiant star 1300x Sun diameter. The stats for the star are impressive indeed: dubbed HR 5171 A, the binary system weighs in at a combined 39 solar masses, has a radius of over 1,300 times that of our Sun, and is a million times as luminous. Located 3,600 parsecs or over 11,700 light years distant, the star is 50% larger than the famous red giant Betelgeuse. Binary star (about 10 AU apart) but surfaces only 2.9 AU! 1300 day orbital period for this contact eclipsing binary. Amateurs and professional astronomers combined to unravel this system dating back over 60 years.
Read more: http://www.universetoday.com/110205/astronomers-identify-the-largest-yellow-hypergiant-star-known/#ixzz2wGoaPuna (Suggested Reading: Universe Today article, ESO Press Release, arXiv preprint)
3. Contest via NASA to find potentially harmful NEO. NASA and Planetary Resources (the asteroid miners!) have conspired with topcoder.com a crowd sourced algorithm development platform, to identify potentially harmful asteroids from data sets consisting of 4 images seperated by about 10 minutes each. The winning algorithm will be able to correctly identify errors and artifacts in the data and will receive $35,000 in prize money, so if you think you have what it takes then head on over to topcoder and give it a shot! (Suggested Reading: IFLS article, Contest Details)
4. Mars Reconnaissance Orbiter went into safe mode March 9 after an unexpected switch from one main computer to another. NASA scientists are working on the problem and hope to have the spacecraft back online in a few days. This happens somewhat regularly, this is the 5th time in MRO’s lifetime, the last time was November 2011. MRO is the link between Opportunity and Curiosity rovers and Earth. Mars Odyssey can handle the science operations while MRO is being repaired.
(Suggested Reading: Space.com article) Curiosity Rover tweeted March 13 that MRO is back online. (Suggested Reading: JPL press release)
5. The IAU has released a statement against the practice of organizations letting members of the public name features on Mars (and other places) for a fee. The statement is not explicit about which organization they are criticizing but the target would appear to be Uwingu. The Uwingu team “consists of nationally and internationally accomplished scientists, educators, NASA vets, and business people, who are passionate about astronomy, space exploration, and space education.” It uses its naming projects to raise money to fund science and education. (Suggested reading Space.com article, Uwingu web site)
6. Yutu Rover: The little jade rabbit that could survives its third lunar night, to enter its fourth lunar day! Given that it was designed to be a 3 month mission that means that as of March 14th the little Jade bunny has met its mission design requirements. Its instruments are for the most part still working, although it’s not able to maneuver its solar panels nor is it able to move around on the surface, but I’m happy to hear that it has survived! As an interesting side note, it’s always interesting to me the sense of personal and emotional attachment you end up feeling towards these little rovers as we follow along with their lonely journeys across other worlds (perhaps its the effect of watching WALL-E too many times!).
7. COSMOS episode last night: Episode 2. The big element to me last night was the discussion and explanation of Natural and Artificial Selection. I thought this was done very well. Agreed, I also particularly liked the segment on how our eyes aren’t well adapted to life on land, we often forget that evolution is a bit of a one way street (hence, compound eyes!). We could possibly talk about Titan?
8. Arecibo observatory is back in action following a 6.4 magnitude Earthquake on January 13th this year that damaged one of the cables which moves the hanging detector around the area above the dish. I for one am glad to hear this not only because the Arecibo observatory has historically and presumably will continue to produce some great science (first evidence for neutron stars in 69, first binary pulsar in 74, first millisecond pulsar in 82, first extra solar planet in 94), but I am also glad to hear this because I think the Arecibo observatory is just one of the coolest telescopes out there. Our viewers will recognize it as the large 300m concrete dish in Puerto Rico that is used for radio astronomy and was featured in the films Goldeneye and Contact (along with many others I’m sure). The cable that was damaged was one of 18 cables that holds up the 900 ton focal platform, and interestingly this cable was already known to be a structural weak point: during the original construction of the facility one of the cables that was delivered was too short, so it was spliced together with another section of cable in order to span the appropriate distance–this structural weakpoint was exposed when the earthquake caused the cable to break.
Major Topics Discussed:
Topic: Where stars transition to Brown Dwarfs on the HR diagram
The Hertzsprung-Russell (HR) diagram Main Sequence (MS) has a lower temperature limit. New observations by Dieterich & Henry suggest that the lower temperature limit of the MS (core hydrogen burning) appears to be around 2075K. They examined 62 objects with spectral types M6V to L4, determining their temperatures and distances (and thus their luminosities) to plot the lower end of the MS.
When stars reach the MS they are in thermal equilibrium (hydrostatic equilibrium having been established by coire H fusion). Brown Dwarfs however never reach such a stage as they are continually cooling. Low mass, cool stars on the MS can be potentially very old whereas the Brown Dwarfs are relatively young. Further, lower mass stars have lower radii whereas higher mass Brown Dwarfs have smaller radii (as they are held up by electron degeneracy rather than radiation pressure).
Suggested Reading: NOAO newsletter
Thanks for listening!
YorkUniverse is a co-production of Astronomy.FM and the York University Astronomical Observatory. For more information on us, check out the following links:
AFM page: astronomy.fm/yorkuniverse
Observatory webpage: www.yorkobservatory.com
Observatory twitter: @YorkObservatory | 0.940609 | 3.57539 |
When you’re a comet, there are some thing you just shouldn’t do if you plan to live a long, icy life. Number one on the list: Don’t fly into the sun.
But comets aren’t sentient beings that can distinguish what will save them and what will kill them. Comets can’t read and have therefore never learned the lessons bestowed upon us by the Greek myth of Icarus and the sun. And that’s why one unwitting ball of ice and rock that got too close to the sun managed to feel the brunt ferocity of the center of our solar system.
Between August 3 and 4, the Solar and Heliospheric Observatory — jointly run by NASA and the European Space Agency — managed to capture the sight of a bright Kreutz (sungrazing) comet zooming carelessly into our sun. As happens with pretty much anything that gets close to the sun, the comet disintegrated due to the high amount of heat emanating from the star, as well as the immense gravitational forces that cause Earth and the seven other main planets of the solar system to orbit around it.
Comets commonly orbit the sun at elliptical orbits. When they whip around the sun (this guy was cruising at a sweet 1.3 million mph), they tend to lose a lot of material. In this instance, the comet didn’t simply shoot straight into the sun, but rather was torn apart as it veered too closely.
This new observation comes at a perfect time: NASA is currently doing status assessments for its heliophysics missions in the next couple of years, and the new instruments that will be sent into space are sure to pick up crazier things than this. | 0.904538 | 3.207306 |
Antarctica: Scientists find 200-year-old skull that could potentially shed light on first arrivals on frozen continent
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NASA: Agency reprocesses images of Jupiter's moon Europa in preparation for upcoming alien search mission
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An exoplanet within arm’s reach: the Earth
Exobiology is an exciting discipline. It is based simultaneously on the latest data from astrophysics, planetary geology and the origins of life on Earth, all of which are evolving as we continue to study them. It could be said that exobiology is essentially Earth-oriented, as it’s based primarily on knowledge learned here that we try to apply to other possible or observed situations.
As revealed through the study of geology, the biology of evolution allows us to understand how life forms came to populate our planet, and also to anticipate its future (an aspect that is unfortunately underdeveloped at present). Indeed, these disciplines are based on the assumption that the physicochemical and biological rules that are exerted on the Earth since it was formed are essentially the same elsewhere in the universe (all this in the absence of proof – yet – that life exists elsewhere).
Reading the future from the past
The study of the fossil record often upsets our preconceptions and constantly raises questions, almost as if we are regularly discovering a “new” planet. Indeed, whether it is at the beginning of the birth of life on Earth or in the great episodes of the evolution of the Paleozoic (the Primary Era) and the Mesozoic (the Secondary Era), many forms of life very different from those we know today emerged, developed and had their time of glory.
Alongside these successes are many extinct communities and lineages – trial runs, as it were. Some were present at the origin of life as we know it, others are known only by fossils. It’s as if each great stratum of life corresponded to different planetary conditions, with their particular procession of living creatures. How many more of these “exotic” forms of life are waiting for us to be discovered in the Earth’s archives?
The Ediacaran fauna in Australia (-575 Ma), the Burgess faunas in Canada (-625 Ma) and Chengjiang fauna (-530 Ma) in China testify to the complex lifeforms that arose early in the history of our planet that are now extinct. Recently the beautiful discovery of an enigmatic fossil in Gabon has pushed the beginnings of multicellular life to more than 2 billion years.
Much closer to us in time is amber, from the middle of the Cretaceous (99 million years), tree resin in which plants, insects and even small animals became trapped and that subsequently fossilised. They’re an extraordinary record of life on earth, including a fragment of tail of a dinosaur – with feathers.
For scientists, these previously unknown families, orders and forms suggest that the territories in which they developed were isolated, almost like planets themselves – ancient islands with unique fauna, the evolutionary hotspots of the past…
What does the sci-fi say?
The series Terra Nova. dvdbash.com
Science fiction tends to look at the fate of humanity in the future, or of time travellers as they search for resources on a long-ago Earth. They may seek to escape from the destruction of our planet (as in the series Terra Nova) or be caught up in unearthly mysteries (Fringe.
Indeed if the search for a habitable exoplanet could serve humanity (something central to the series The Expanse), reaching back to our planet’s “origins” is logical… if we could solve the problem of travel time and its associated paradoxes. If we change the past, what will be the impact on the “future” in which we now live? Fiction has extensively looked at multiverse hypotheses, including Men in Black and The Man in the High Castle.
In the same way that we need to fully understand the Earth’s current biodiversity, the paleodiversity of our planet is full of information on the processes of evolution and functioning our planet, and even the discovery of new resources and, in a sense, “lost worlds” – Lake Vostok under the Antarctic ice sheet, the glacial valleys of Greenland revealed by melting ice…
Preserve the archives of the Earth
While understanding the past functioning of our planet is crucial, paleosciences aren’t yet in the spotlight in the academic world. The only exception is when they concern the “near” past and allow us to understand better the variations of the climate and the development and lives of the first humans.
There is currently a lack of will to preserve the fossil record of our ancient rocks and sediments that is the Earth’s archives. Every day and everywhere on our planet, unpublished information is destroyed, crushed, ground, paved over, polluted, damaged. How many unique fossil biota have been yet destroyed ?. As with archaeology, we can’t keep everything from the past, but “preventive paleontology” is essential if we are to understand the origin of our planet and the life forms that have lived here.
Thankfully, there is an enthusiasm among the general public for these sciences of the past, from museum expositions to local initiatives. Investments in research and the preservation of our paleontological heritage can even be a source of geotourism. A leading example is South Africa, which as palaeontology a national cause or public enthusiasm in Argentina (https://palaeo-electronica.org/content/2014/1003-comment-paleontology-in-argentina) and provides substantial resources. Compensating for the lack sufficient resources in the paleosciences, the work of citizen scientists also helps us to reach back into the Earth’s archives – and allow us to better understand its future. | 0.832904 | 3.001516 |
Chibis-M Microsatellite Mission
Chibis-M (Chibis means a “lapwing” in Russian, it is the name of a bird of the Vanellus family, the “M” stands for Molniya=Thunderstorm) is a low-cost microsatellite mission of IKI-RAS (Space Research Institute-Russian Academy of Sciences), Moscow, Russia. The partner institutions of the science mission are: SINP (D. V. Skobeltsyn Institute of Nuclear Physics) of the Lomonosov Moscow State University (MSU), Moscow; SRG (Space Research Group) of Eötvös University, Budapest, & BL-Electronics Kft., Solymar, Hungary; and LC-ISR (Lviv Centre-Institute for Space Research) of NANU-NKAU, Lviv, Ukraine. The PI of the Chibis project is Lev Zeleny of IKI.
The objective of the mission is to study the interrelation of the transient plasma-wave processes connected with the manifestation in the ionosphere of solar-magnetosphere-ionosphere-atmosphere connections and the parameters of space weather. The fundamental goal is the search for universal laws governing transformation and dissipation of plasma-wave energy in the magnetosphere-ionosphere system. 1) 2) 3) 4) 5) 6) 7)
Event monitoring of the ULF/VLF spectrum is required to register the EMR (Electromagnetic Radiation) occurring with various types of lightning events and space weather phenomena. In particular, the VLF emissions are closely connected with lightning discharges. The science goals will be achieved with the following coordinated studies:
1) In situ study of the fluctuations of electrical and magnetic fields, the parameters of thermal and epithermal plasma in the ionosphere near the F layer during different helio- and geomagnetic conditions. Identify the generation mechanisms for TLEs (Transient Luminous Events) and TGFs (Terrestrial Gamma-ray Flashes) and advance the physical understanding of the links between TLEs and TGFs.
2) Parallel observations of the geomagnetic and geophysical parameters at ground-based observatories with the time event scales from 10-1 to 10-3 s.
3) Study of the EMR phenomena (spectra of ULF/VLF waves) in different regions of near-earth space by means of the comparative analysis of the EMR measurements carried out simultaneously by different spacecrafts and ground geophysical stations.
It is important to note that the signals recorded by the on-board magnetic-wave complex in KNA “Groza” can be transmitted via telemetry also as waveforms, which makes it possible to conduct precise a posteriori spectral - temporal processing on the Earth. The most efficient methods for their analysis are the simultaneous measurements of the SCD (Spatial Current Density) and the magnetic field fluctuations arising during a wave process.
Recently, a number of fascinating physical effects have been discovered which have changed fundamentally our notions about the lightning discharges in the atmosphere. The satellites COMPTON and RHESSI detected powerful impulses of gamma rays (1017-1018 quanta with energies > 100 keV) coming from the Earth. These impulses were found to be generated 2-3 µs before the main lightning stroke. The short (~1 µs) single discharges resulting in the generation of high-power radio-impulses (> 100 GW) were found in high-altitude (13-20 km) thunderclouds. A wideband electromagnetic emission from these discharges were detected on the ground at distances up to a few thousand km. Ground observations revealed gamma bursts related to the jumps of an electric field typical for the step-wise propagation of the lightning leader.
All these observational effects are possibly caused by a new physical phenomenon known as “runaway electron breakthrough” which was theoretically predicted by Gurevich & Zybin in 2001. Emerging during the breakthrough an avalanche of runaway electrons accelerated up to the relativistic energies produces gamma emission. This type of electric discharge can occur under rather low magnitudes of the atmospheric electric field, but its initiation requires seeding high-energy particles. The seeding high-energy electron can be produced by the cosmic rays. The accelerated motion of lower energy electrons in the thunderstorm electric field produces a powerful burst of radio emissions. Thus, the high altitude discharges in the atmosphere are to be accompanied by powerful splashes of radio, UV, X-ray and gamma ray emissions.
The microsatellite Chibis-M will be equipped with two payload instruments: “Thunderstorm” and “Wave Package”. A special synergy of this project is expected -- because not only the direct observation of lightning, but also the synchronized study of the wave processes which are triggered by the lightning will be carried out in parallel onboard the satellite and at ground support stations. This will give an unprecedented opportunity to monitor the development of the lightning mechanism from its generation until the relaxation in the form of electromagnetic (EM) waves.
Special attention is paid at the ULF-VLF frequency range. These waves play a major role in the interactions in the system “magnetosphere-ionosphere-atmosphere-lithosphere” and their study is essential to monitor them.
Figure 1: Artist's rendition of various TLE types in the upper atmosphere (image credit: AGU, S. Nielson, et al.)
Figure 2: Artist's view of the deployed microsatellite Chibis-M (image credit: IKI, Ref. 7)
The Chibis-M spacecraft has been developed by IKI of Moscow. It is of Kolibri-2000 heritage, an educational program with a launch of the Kolibri microsatellite on Nov. 26, 2001 on the Russian transport cargo vehicle Progress M1-7 service flight to the ISS.
• Actuation: Electromagnetic coils, flywheels motors
• Attitude sensing: rate sensors, digital solar sensors, magnetometer.
Several operating modes are being offered by the system. The ACS may be used for orbit inclinations in the range of 45-98.6º for altitude ranges of 400-700 km.
Figure 3: Photo of the ACS (image credit: ScanEx RDC)
ADCS (Attitude Determination and Control Subsystem): Attitude sensing is provided by 5 digital sun sensors, a Honeywell magnetometer (HMR 2300R)and three single-axis angular velocity sensors (ADIS 16130). Actuation is provided by three mutually orthogonal magnetorquers and six reaction wheels. The magnetorquers are used to induce a controllable dipole magnetic moment. The reaction wheels are based on a brushless DC electric motor. The motor forces the wheel to accelerate or stop its rotation which results in the control torque. The torque value may be finely tuned according to the on-board computer commands, the torque direction is controlled by the proper distribution of the wheels rotation rates. The ADCS control unit is the main body of the system, linking sensors and actuators together and providing a feedback for the external control devices. The main tasks for the unit are the information collection and an analysis using attitude determination algorithms; processing attitude information to construct necessary control actions and passing all required information to the actuators in order to implement a torque. The pointing accuracy of the spacecraft is ±0.1-0.2º, while the angular velocity estimated error is 0.05º/s.. 10)
A combined GPS/GLONASS receiver provides the orbit and timing for the spacecraft. In addition, there is a gravity gradient boom for passive stabilization; however, the gravity boom is currently in stowed position, it will be used only as a backup passive stabilization system in case of a fly wheel failure.
Table 1: Overview of some spacecraft parameters
RF communications: The TT&C data link (referred to as engineering channel) uses the VHF-band (145 MHz) in the uplink and the UHF-band (435 MHz) in the downlink at data rates of 9.6 kbit/s. The S-band (2.2 GHz) is used for the downlink of the payload data at rates of 128 kbit/s (1.2 Mbit/s max). The CCSDS packet telemetry protocol is being used. The on-board storage capacity is 50 Gbit. A volume of ~ 50 MByte/day of science data are being downlinked.
Launch: On Nov. 2, 2011, the Chibis microsatellite arrived at the ISS (International Space Station). It was part of the payload carried by the cargo service vehicle Progress M-13M (Russian ID, or Progress 45 (NASA ID). The Progress M-13M spacecraft lifted off from the Baikonur Cosmodrome in Kazakhstan on Oct. 30, 2011, starting with the 45th unmanned Russian space station resupply mission. The docking of Progress 45 marked the fully successful return of Progress operations to ISS after the loss of Progress 44 in August 2011. Progress 45 delivered 2800 kg of food, fuel and supplies to the space station, including the Chibis-M microsatellite.
The Chibis spacecraft is to be released and deployed on the return flight of Progress into a higher orbit than the one of ISS. After this event, the Progress vehicle will be directed to its predefined destination, namely the Pacific Ocean (Ref.15).
Final orbit of Chibis: Near-circular orbit (not sun-synchronous), altitude = 480 km, inclination = 52º.
• The Chibis-M mission is operating nominally in February 2014. The Chibis-M microsatellite is on orbit as a free-flyer since January 25, 2012. During this time, about 2000 contacts were made with the spacecraft; approximately 300 contact periods were used to download the data of the Groza equipment, totaling ~30 GB. 11)
The map of Figure 4 is derived from data of the RFA (Radio Frequency Analyzer) device onboard the microsatellite "Chibis-M". The points marked on the map represent instrument response characteristic radio emissions of lightning events in the 26-48 MHz range. The highlighted areas with the highest number of events, which are in good agreement with the known regions of high lightning activity, occur primarily in the equatorial latitudes.
Figure 4: “Picture of the month: Map Chibis-M,” IKI, December 16, 2013 (Space Research Institute)
The RFA device data provide not only scientific information, but are also being used as a "trigger" for the other instruments on board the microsatellite: a signal received from the RFA switch in the data recording process from the instruments operating in other range of the electromagnetic radiation. Together, they represent the "bulk" image atmospheric lightning discharge in the visible, ultraviolet, X-ray and gamma-ray and ultra-low frequency range where the manifest magnetic ripple effects of electrical activity in the ionosphere.
• The Chibis-M mission is operating nominally in 2013. 12)
• In the summer of 2012, the Chibis-M is in nominal flight operations.
• Mission operations of the Chibis-M microsatellite are planned to be started in March 2012, after all systems have been tested (Ref. 15).
• On January 25, 2012 ,the microsatellite Chibis (lapwing) was successfully deployed from the transportation vehicle Progress M-13M and started its own mission.
• The new orbit parameters are: perigee = 497 km, apogee = 513 km, inclination = 51.6°, period = 94.55 minutes. The telemetry information confirmed that all onboard systems are working. The size of the microsatellite with open solar panels and antenna is 1.2 m x 1 m. 13)
• On January 24, 2012, the Progress M-13M space freighter with the Chibis-M microsatellite undocked from the ISS Pirs docking module as scheduled, in an automated mode. Thereafter, Russian controllers started the propulsion engines and brought Progress M-13M into an orbit of ~ 500 km altitude (including two orbit corrections). The Chibis-M microsatellite was deployed on January 25, 2012 from the space freighter and will remain in orbit for at least four years studying lightnings and thunderstorms in the Earth's atmosphere. 14)
• Progress M-13M is planned to remain docked to the Space Station for nearly three months. It will undock from the Pirs Nadir port in late January 2012 and will raise the Chibis microsatellite to the pre-designed near-circular orbit of 480 km altitude, inclination ~52º. Then Chibis-M will be deployed and will begin its own mission in space. 15)
Sensor complement: (Groza, KNA Groza)
Table 2: Overview of scientific instruments
Figure 5: Schematic view of ionospheric perturbations (image credit: LC-ISR)
Scientific payload Groza:
The scientific payload of the Chibis-M, designed for the study of new physical processes at high-altitude atmospheric lightning discharges, includes: 16)
• RGD (X-ray and Gamma-ray Detector) with a 0.02-1.0 MeV energy band
• DUF (Ultraviolet Detector) of radiation with wavelengths from the UV (180-400 nm) to IR (650-800 nm)
• RFA (Radio Frequency Analyzer) in the frequency range 26 - 48 MHz
• CFK (Digital Camera) with a spatial resolution of 300 m and the exposure time of 15 frames/s
• MWC Magnetic Wave Complex) in the frequency range of 1 - 40,000 Hz
• BND (Data Acquisition Unit).
Each instrument of Groza has a ring memory (RM) with a fixed size sufficient to record a few events. The total size of the memory of the instrument is determined by the maximum duration of the event, which is set for each instrument by the PI of the experiment. The duration of the record can be controlled by ground commands. For example, the RFA can provide registration time 50 ms, RGD - 20 ms, DUF - 100 ms. Other digitization parameters also can be set by command from the Earth: the period of sampling (sampling time), the criterion of "event" or trigger of the instrument (Ti), the size of saved memory "before" and "after" the event. Due to the accidental nature of the events, the project is interested in the record in the RM which is connected to the on-board time forming the identity array of the event (header, number, etc.), Figure 6. Only the records matching the Ti criterion are stored in RM. If no event was identified, the next loop of recording is carried out.
Figure 6: Example of production of the trigger complex Tc by the BND instrument (image credit: Chibis-M collaboration)
The logic of the Groza operation is illustrated below in the example of the RGD instrument intended to record sporadic outbursts (bursts) of the hard X-ray and gamma-ray at high-altitude atmospheric discharges. Four gamma-ray scintillators are used, which are based on crystals of NaI(Tl) with a diameter of 5 cm and a thickness of 1.0 and 2.0 cm. In the course of the experiment, the permanent recording of the RGD readings is carried out. The output of the detectors providing the time profile of the burst is digitized with a resolution of less than 100 ns and recorded during a time interval that is set by the internal RM resources (not less than 20 ms) and is further overwritten with the subsequent set of readings. Thus, the RM always keeps the current sequence of digitized detector readings of the last 20 ms. Along with the recording of the digitized signals from each of the 4 detectors, the number of counts (with a signal amplitude exceeding a threshold corresponding to the energy release in the detector 25 keV) is accumulated over the interval of 3 ms and over the interval of 1 s (optionally) prior to the interval of 3 ms. By summing up the counts at each detector channel during 1 s interval prior to 3 ms, one can determine the background level. The excess of counts summed over 3 ms over the background level for a certain number of "sigma" in a predefined number of detectors (the number of "sigma" and the number of detectors are set by ground command, the default value - 3σ for at least two detectors) is a sign of the event.
The Scientific Committee of the project has acknowledged that the best option for lightning strikes registration at the first stage would be such when the Tc is initiated with the Ti of RFA, the latter being the highest sampling speed instrument that measures the intensity of radio emissions in a typical lightning range of 26-48 MHz. The instrument includes a spectrum analyzer with five broadband filters, evenly spaced over the operating range. At the output of each filter a set of threshold elements and the majority scheme of signal enrollment (precision of trigger binding to the board time is 1 µs) are mounted. After the Ti receiving a radio signal over a time period, defined by a ground command, is recorded in the RM, Figure 7. In this case, the moment of the Ti receiving is in the middle of the selected time interval. The Ti can be used by other MS instruments to record likely lightning discharge at the same moment as the RFA in the ultraviolet, infrared, gamma radiation and ELF frequency ranges.
During its operation, the RFA has identified areas of the most intense man-made interference and most promising areas for the registration of lightning activity. The RFA operation schedule is planned now with taking these zones into account. For the past eight months of satellite operation in 2012 several hundred triggers were recorded with more than a hundred of them associated with short and powerful lightning. Figure 7 demonstrates examples of the RFA waveform recordings of lightning discharges possessing different appearances. They show gradual increase of electromagnetic activity ending by a single powerful short radio pulse and subsequent decay of the field, or multiple short discharges, following with an intervals of 50-100 µs during about 1 ms, or increased storm activity during 400 µs without discharges at all.
Figure 7: Examples of different waveforms recorded with the RFA in the equatorial region. The duration of each recording is 3ms (image credit: Chibis-M collaboration)
Chibis-M is able to effectively monitor electromagnetic environment of the Earth at ionospheric altitudes producing simultaneous measurements of electromagnetic emissions in a very broad frequency band from VLF and VHF to X- and gamma-rays. Special technique of trigger formation makes it possible to prevent uncontrollable expanding of the amount of data stored. Recordings of VLF electromagnetic fields conducted by Chibis-M are believed to be relevant to natural processes in the ionosphere and the magnetosphere of Earth, in the first place to lightning activity what was proved with primary analysis of received data (Ref. 16).
KNA Groza (Wave Probe):
The objective of KNA Groza is the study of the process of the development of the stepped leader of high-altitude lightning in high electric fields.
The Wave Probe (WP) device is a combination of three sensors in one module: SLP (Split Langmuir Probe), search-coil magnetometer, and electric probe. The Wave Probe instrument was already successfully tested in the spatial experiment VARIANT onboard the Ukrainian SICH-1M satellite (launch Dec. 4, 2004).
Table 3: Specification of the WP assembly
Figure 8: Overview of ULF/VLF Wave Probe components (image credit: LC-ISR)
Figure 9: Schematic view of the ULF/VLF sensor configuration (image credit: LC-ISR)
Figure 10: Schematic view of the Wave Probe construction (image credit: LC-ISR)
Figure 11: Photo of WP (Wave Probe, left), protection and testing cover (TC, middle), WP with TC (right), image credit: IKI
The PSA (Programmable Signal Analyzer) provides event processing of the payload strobe for the fixation at lightning discharge occurrence of EM radiation generation in the UHF/VLF (2 x 104 to 10-2 Hz) range. The EMR generated in the basic phase of the lightning discharge, called whistles, are recorded in the VLF frequency range. The main task is the measurement of the EM fluctuations in the range of frequencies 0.1Hz - 40 kHz.
Table 4: Overview of PSA-SAS3 (Spectral Analyzer and Sampler- version 3) input signals
Figure 12: Photo of the PSA instrument (image credit: LC-ISR, SRG, IKI)
Figure 13: Block diagram of PSA-SAS3 (image credit: LC-ISR, IKI, SRG)
The magnetic - wave experiment is aimed also at the study of the interrelation of plasma - wave processes in the ionosphere, which take place during the sun - magnetosphere - ionosphere - atmosphere interactions and is of great interest for studying the parameters of space weather. It is expected that the systematic study of these connections will make it possible to find the universal laws, which regulate conversion and dissipation of plasma - wave energy in the magnetosphere - ionosphere system.
The FM (Fluxgate Magnetometer) will be included in the WP. This is a newly developed low mass and low-power but highly sensitive device, especially designed for micro- and nanosatellites. Its parameters are (parameters are specified for all three analogue outputs):
Table 5: Parameters of the FM device LEMI-012M
Figure 14: Photo of the FM device (image credit: LC-ISR, IKI)
Table 6: Parameters of the IM (Induction Magnetometer) LEMI-127
Figure 15: Photo of the IM device, LEMI-127 (image credit: IKI)
Table 7: Parameters of the Wave Probe LEMI-603
Figure 16: Photo of the Wave Probe LEMI-603 (image credit: LC-ISR)
The project uses a few ground stations in Russia. The main station is located in Tarusa (Russia). It provides facilities for both engineering and scientific channels. The spare station for engineering channel is provided in Kaluga (Russia), and a spare station for science data is located in Panska Ves (Czech Republic). 17) 18)
Figure 17: Illustration of the communication links and ground stations in Russia (image credit: IKI)
The nature of the low-cost mission requires that all nodes of the ground segment (stations, processing centers, operations centers, workstations of investigators) are being linked by public internet facilities.
The main node of the ground system is located at IKI of Moscow, providing the functions of MOC (Mission Operations Center) and DPDC (Data Processing and Distribution Center). Other organizations such as telemetry stations, SINP MSU (Skobeltsyn Institute of Nuclear Physics of Moscow State University) and LPI RAN (Lebedev Physical Institute of the Russian Academy of Sciences) interconnect through the main node.
Figure 18: Inter-node communications between the various entities of the mission (image credit: IKI)
Figure 19: The main nodes of the ground segment for the Chibis-M mission (image credit: IKI) 19)
Ground-based observations coordinated with the Chibis-M mission are to be performed by institutions in the following countries:
• Russia (Caucasus observatory, Yakutsk Lightning Monitoring System)
• Europe (Eurosprite network - France, Spain, Hungary, Greece)
• Israel (Tel Aviv University)
• USA (Stanford University, Duke University)
• Brazil (Instituto Nacional de Pesquisas Espacias)
• New Zealand (WWLLN Network)
• India (Institute of Geomagnetism)
• Japan (Hokkaido University)
Theoretical and modeling efforts in support of the data analysis are to be provided by:
• European centers (Eindhoven University, )
• Russian centers (Lebedev Institute of Physics, Institute of the Physics of the Earth, N. Novgorod University).
1) Stanislav Klimov, Denis Novikov, Valeriy Korepanov, Andriy Marussenkov, Csaba Ferencz, Janos Lichtenberger, Laszlo Bodnar, “The Study of Electromagnetic Parameters of Space Weather. Micro-Satellite Chibis-M,” Proceedings of the 7th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, May 4-7, 2009
2) V. N. Angarov, G. K. Garipov, V. M.Gotlib, A V.; Gurevich, S. I. Klimov, V. G. Rodin, S. I. Svertilov, L. M. Zelenyi, “Investigation of new physical phenomena in the atmospheric lightning discharges: Micro-satellite CHIBIS-M,” Proceedings of the 7th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, May 4-7, 2009, IAA-B7-0214P
3) S. I. Klimov, L. M. Zelenyi, D. I. Novikov, Cs. Ferencz, J. Lichtenberger, L. Bodnar, V. E. Korepanov, A. A. Marusenkov, “Electromagnetic Parameters Study for Space Weather Research (Microsatellite “Chibis-M”),” Proceedings of the AGU Chapman Conference on the Effects of Thunderstorms and Lightning in the Upper Atmosphere, Penn State, College Park, PA, USA, May 10-14, 2009
4) L. M. Zelenyi, V. G. Rodin, V. N. Angarov, T. K Breus, M. B. Dobriyan, S. I. Klimov, O. I. Korablev, V. E. Korepanov, V. M. Linkin, E. A. Loupian, N. N. Ivanov, L. E. Lopatento, O. Yu. Sedykh, “Micro-satellite “Chibis” – universal platform for development of methods of space monitoring of potentially dangerous and catastrophic phenomena.,” Proceedings of the 5th International Symposium of the International Academy of Astronautics (IAA), Berlin, Germany, April 4-8, 2005, URL: http://www.dlr.de/iaa.symp/Portaldata/49/Resources/dokumente/archiv5/1502_Klimov.pdf
5) V. Korepanov, A. Marusenkov, S. Belyayev, S. Klimov, L. Zelenyi, D. Novikov, Cs. Ferencz, J. Lichtenberger, L. Bodnar, “Earth Observation Microsatellite Chibis,” Proceedings of the 60th IAC (International Astronautical Congress), Daejeon, Korea, Oct. 12-16, 2009, IAC-09.B1.1.11
6) V. Pilipenko, “New physical phenomena in the atmospheric lightning discharges: observations from microsatellites and ground,” FP7-SPACE-2010-1, URL: http://www.kpk.gov.pl/.../Pilipenko_New_physical_phenomena_in_the_atmospheric_lightning_discharges.pdf
7) L. M.Zelenyi, S. I.Klimov, A. A.Petrukovich, “International experiments of the Russian Academy of Sciences in the frame of the Space Weather Program,” The Scientific & Technical Subcommittee of the COPUOS (Committee on the Peaceful Uses of Outer Space) 2010, 47th session, Vienna, Austria, February 8-19, 2010, URL: http://www.oosa.unvienna.org/pdf/pres/stsc2010/tech-11.pdf
8) “Microsatellite attitude control system,” ScanEx RDC, URL: http://www.scanex.ru/en/acs/default.asp?submenu=orientation&id=idescription
9) Information provided by Stanislav Karpenko of Sputnix LLC, Moscow, Russia
10) M. Yu. Ovchinnikov, D. S. Ivanov, N. A. Ivlev, S. O. Karpenko, D. S. Roldugin, S. S. Tkachev, “Chibis-M Microsatellite ACS Development, Complex Investigation, Laboratory and Flight Testing,” Proceedings of the 9th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 8-12, 2013, paper: IAA-B9-1216P
11) The information was provided by Stanislav I. Klimov of IKI (Space Research Institute), Moscow.
13) Information letter N2 “Project Chibis” received on January 26, 2012 from Viacheslav Pilipenko of IKI (Space Research Institute), Moscow, URL: http://chibis.cosmos.ru/index.php?id=1671&tx_ttnews[tt_news]=2667&cHash=b5453ccfa30964a8230f766622b7f79d
14) “Progress Space Freighter Undocks from ISS,” Space Travel, Jan. 25. 2012, URL: http://www.space-travel.com/reports/Progress_Space_Freighter_Undocks_from_ISS_999.html
15) Information letter “Project Chibis” received on January 17, 2012 from Viacheslav Pilipenko of IKI (Space Research Institute), Moscow
16) S. I. Klimov, V. M. Gotlib., L. M. Zelenyi, V. N. Karedin, V. M. Kozlov, I. V. Kozlov, D. I. Vavilov, M. S. Dolgonosov, G. K. Garipov, S. I. Svertilov, V. V. Bogomolov, I. V. Yashin, V. E. Korepanov, L.Bodnar, Cs. Ferenz, “Algorithm of the formation of high altitude atmospheric lightning trigger testing -Academic microsatellite Chibis-M," Proceedings of the 9th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 8-12, 2013, paper:IAA-B9.0501
17) V. Nazarov, R. Nazirov, V. Gotlib, O. Batanov, N. Eismont, V. Karedin, F. Korotkov, A. Ledkov, Ya. Markov, A. Melnik, A. Tretiyakov, A. Popkov, S. Svertilov, “Low-cost ground segment for Russian Academia-University science space missions,” Proceedings of SpaceOps 2012, The 12th International Conference on Space Operations, Stockholm, Sweden, June 11-15, 2012, URL: http://www.spaceops2012.org/proceedings/documents/id1293615-Paper-003.pdf
18) V. Angarov, N. Eismont, V. Gotlib, V. Kozlov, V. Nazarov, R. Nazirov, V. Rodin, “Ground segment of low budget satellite Chibis,” Proceedings of the 7th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, May 4-7, 2009, IAA-B7-0215P
19) V.Nazarov, R.Nazirov, L.Zelenyi, V.Angarov, O.Batanov, L.Bodnar, N.Eismont, V.Gotlib, V.Karedin, S.Klimov, F.Korotkov, I.Kozlov, A.Ledkov, A.Melnik, A.Papkov, V.Rodin, A.Ryabova, Ya.Shmelauer, A.Tretiakov, “Ground segment and operations for microsatellite Chibis-M: learned lessons, current status and prospective evolutions,” Proceedings of the 9th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 8-12, 2013, paper: IAA-B9-0802
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates. | 0.833552 | 3.100577 |
Thanks to NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to Mars, you may soon never need to fiddle with the tuning dial on a car radio again.
When we listen to songs on the radio, the sound travels via radio waves that are given out by a transmitter and then received by a receiver — in the case of a car, the car's antenna is the receiver.
Radio waves travel in the form of electromagnetic radiation from one antenna to the other. The journey, however, isn't always perfect.
Sometimes, there is a sudden spike in the amount of hot gas in the upper layer of Earth's atmosphere which causes interference in radio communications. If you are tuned into a favorite station, that could result in static, or for one radio station to be replaced by another.
This phenomenon, known as sporadic E layer, is difficult to study on Earth because that part of the planet's atmosphere is hard to reach with satellites. As a result, scientists can't predict when they will occur — leaving us to fiddle with dials.
But thanks to MAVEN, a spacecraft traveling 300 million miles away from our planet, we could finally have the solution.
MAVEN detected sporadic E layer in Mars’ upper atmosphere, and scientists are hoping to be able to use the Red Planet as an off-Earth laboratory to study the phenomenon up close. Already, the data have provided new insights into the cause of radio static, which also affects communications with aircrafts and military radars.
"What we learn on Mars is directly applicable to Earth.”
The findings are detailed in a new study published Monday in the journal Nature Astronomy.
MAVEN discovered the unusual ripples by pure accident.
The mission was launched in November, 2013 and has been orbiting the Red planet ever since to find out how Mars lost its atmosphere and became the desolate world it is today.
Armed with tools to measure Mars’ upper atmosphere, MAVEN’s static instrument picked up on weird “wiggles” in the data.
“As she’s flying through the upper atmosphere, [the spacecraft] kept seeing these flips,” Glyn Collinson a researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of the study, tells Inverse.
These flips were spikes in the concentration of plasma, or the gas that is located in the ionized atmosphere of a planet. Sporadic E layer has never been detected on any other planet before, so the researchers didn't initially realize what they were seeing.
Joseph Grebowsky, who is a co-author of the new study and member of the MAVEN team, happens to also be an expert on the sporadic E layer phenomenon on Earth — he was able to recognize it on Mars.
Here on Earth, sporadic E layers are — as the name suggests — unusual occurrences. Spikes in plasma can come out of nowhere — cutting out your favorite tune, or essential military radio communications, without warning.
But on Mars, the weird phenomenon is long-lived and constantly forming. That means it is stable enough to study in detail.
“The physics is universal,” Collinson says. “Although there are slight differences in the details, what we learn on Mars is directly applicable to Earth.”
Revealing radio waves
Aside from their unpredictability, plasma spikes occur in the Earth’s ionosphere, the upper-most region of the atmosphere. This area is too thin for aircrafts to fly through, but too thick for satellites to orbit. As a result, scientists have known about sporadic E layer events for 80 years, but have never been able to fully understand or observe it at close hand.
Mars’ ionosphere, on the other hand, is totally accessible for spacecraft, enabling scientists to directly observe the phenomenon in action for the first time.
“Sure they’re interesting on Mars, but why they’re really exciting is that we can use it to better understand this phenomenon on Earth,” Collinson says.
Already, MAVEN is revealing intriguing details of how these weird interference events work. In its initial observations, the spacecraft also discovered a "rift" — or a mirror opposite of sporadic E layer. Just as there can be an increase of the amount of plasma in Mars' ionosphere, there can also be a depletion, where the amount of hot gas decreases.
A rift has never been observed before, Collinson says. But it makes sense for there to be an opposite of the spike, he says, since it's logical for plasma to decrease after experiencing a spike.
The team of researchers does not know whether the rifts also take place on Earth, or if they only occur on Mars. An answer may be difficult to get: They are short-lived, which means they could be over too quickly to detect.
Mars: The ideal lab
Mars is at the top of the list for space exploration missions this decade. Scientists hope to answer the ultimate question about the Red Planet: Is it capable of hosting life? NASA is sending another rover to the planet in July, paving the way for a human-led mission to Mars. NASA hopes to launch astronauts to the Red Planet in the next decade.
For now, scientists can depend on remote craft like MAVEN to help solve this rather common, disruptive phenomenon on Earth.
“For me, what’s so exciting about this is here’s something that’s super common that happens over our heads all the time,” Collinson says. “It turns out, Mars is a good place to go to help study these things.”
MAVEN can help collect further data about sporadic E layer events, but the researchers hope to send a new mission to Mars designed specifically to study this phenomenon. That will provide a clearer picture of these unusual spikes — and how they function on our own planet.
"On Earth, they come and they mess with our radio systems without any warning and then they sort of fade," Collinson says. "But on Mars, they're right there!"
Abstract: Understanding and predicting processes that perturb planetary ionospheres is of paramount importance for long-distance radio communication. Perhaps the oldest known ionospheric disturbances are ‘sporadic E layers’1: unpredictable and short-lived concentrations of plasma2, which can bounce radio signals over the horizon for thousands of kilometres3. Consequentially, local radio broadcasts can become jammed by more distant transmissions, and thus sporadic E layers are a potentially serious complication for commercial radio, aviation, shipping or the military. According to the current theory of their formation, we should also expect an equal proportion of localized ionospheric density depletions to develop. However, no such ‘sporadic E rifts’ have been detected in over 85 years of ionospheric research. In addition, despite being common at Earth, no sporadic E layers have yet been reported at other planets. Here we report the detection of sporadic E-like phenomena in the ionosphere of Mars by NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, providing a physical explanation for previous unexplained observations at Mars4,5,6,7. We observe enhanced-density layers that can be explained through the presence of a sporadic E-like mechanism, and we establish the existence of sporadic E rifts in nature. We find that, unlike the case at Earth, Martian sporadic E features are trapped in a near-perpetual state of dynamic formation and may form at predictable locations. Also unlike the case at Earth, Martian sporadic E features are readily accessible to satellites, and indeed MAVEN has already encountered more of the phenomena at Mars than have ever been explored in situ at Earth with suborbital rockets. | 0.850285 | 3.803747 |
Hubble sees a supermassive and super-hungry galaxy
This NASA/ESA Hubble Space Telescope image shows the spiral galaxy NGC 4845, located over 65 million light-years away in the constellation of Virgo (The Virgin). The galaxy's orientation clearly reveals the galaxy's striking spiral structure: a flat and dust-mottled disk surrounding a bright galactic bulge.
NGC 4845's glowing center hosts a gigantic version of a black hole, known as a supermassive black hole. The presence of a black hole in a distant galaxy like NGC 4845 can be inferred from its effect on the galaxy's innermost stars; these stars experience a strong gravitational pull from the black hole and whizz around the galaxy's center much faster than otherwise.
From investigating the motion of these central stars, astronomers can estimate the mass of the central black hole—for NGC 4845 this is estimated to be hundreds of thousands times heavier than the sun. This same technique was also used to discover the supermassive black hole at the center of our own Milky Way—Sagittarius A*—which hits some four million times the mass of the sun.
The galactic core of NGC 4845 is not just supermassive, but also super-hungry. In 2013 researchers were observing another galaxy when they noticed a violent flare at the center of NGC 4845. The flare came from the central black hole tearing up and feeding off an object many times more massive than Jupiter. A brown dwarf or a large planet simply strayed too close and was devoured by the hungry core of NGC 4845. | 0.811443 | 3.733366 |
Each year, 1,000 students come to NASA's Jet Propulsion Laboratory for internships at the place where space robots are born and science is made. Their projects span the STEM spectrum, from engineering the next Mars rover to designing virtual-reality interfaces to studying storms on Jupiter and the possibility of life on other planets. But the opportunity for students to "dare mighty things" at JPL wouldn't exist without the people who bring them to the Laboratory in the first place – the people known as mentors.
A community of about 500 scientists, engineers, technologists and others serve as mentors to students annually as part of the internship programs managed by the JPL Education Office. Their title as mentors speaks to the expansiveness of their role, which isn't just about generating opportunities for students, but also guiding and shaping their careers.
"Mentors are at the core of JPL's mission, pushing the frontiers of space exploration while also guiding the next generation of explorers," says Adrian Ponce, who leads the team that manages JPL's internship programs. "They are an essential part of the career pipeline for future innovators who will inspire and enable JPL missions and science."
Planetary scientist Glenn Orton has been bringing students to JPL for internships studying the atmospheres of planets like Jupiter and Saturn since 1985. He keeps a list of their names and the year they interned with him pinned to his office wall in case he's contacted as a reference. The single-spaced names take up 10 sheets of paper, and he hasn't even added the names of the students he's brought in since just last year.
It makes one wonder what he could need that many students to do – until he takes out another paper listing the 11 projects in which he's involved.
"I think I probably have the record for the largest number of [projects] at JPL," says Orton, who divides his time between observing Jupiter with various ground- and space-based telescopes, comparing his observations with the ones made by NASA's Juno spacecraft, contributing to a database where all of the above is tracked and producing science papers about the team's discoveries.
"Often, you get to be the first person in the world who will know about something," says Orton. "That's probably the best thing in the world. The most exciting moment you have in this job is when you discover something."
Over the years, Orton's interns have been authors on science papers and have even taken part in investigating unexpected stellar phenomena – like the time when a mysterious object sliced into Jupiter's atmosphere, sparking an urgent whodunnit that had Orton and his team of interns on the case.
Orton says his passion for mentoring students comes from the lack of mentorship he received as a first-generation college student. At the same time, he acknowledges the vast opportunities he was given and says he wants students to have them, too.
"As a graduate student, it was close to my first experience doing guided research, so I had no idea how research was communicated or conducted," says Orton of his time at Caltech, when he often worried that his classmates and professors would discover he wasn't "Nobel material." "I want to be able to work with students, which I sincerely enjoy, to instruct them on setting down a research goal, determining an approach, modifying it when things inevitably hit a bump, as well as communicating results and evaluating next steps."
For Alexandra Holloway and Krys Blackwood, the chance to provide new opportunities isn't just what drives them to be mentors, but also something they look for when choosing interns.
"I look for underdogs, students who are not representing themselves well on paper," says Holloway. "Folks from underrepresented backgrounds are less likely to have somebody guide them through, 'Here's how you make your résumé. Here's how you apply.' The most important thing is their enthusiasm for learning something new or trying something new."
It's for this reason that Holloway and Blackwood have become evangelists for JPL's small group of high-school interns, who come to the Laboratory through a competitive program sponsored by select local school districts. While less experienced than college students, high-school interns more than make up for it with perseverance and passion, says Blackwood.
"[High-school interns] compete to get a spot in the program, so they are highly motivated kids," she says. "Your results may vary on their level of skill when they come in, but they work so hard and they put out such great work."
Meet JPL Interns
Read stories from interns pushing the boundaries of space exploration and science at the leading center for robotic exploration of the solar system.
Holloway and Blackwood met while working on the team that designs the systems people use to operate spacecraft and other robotic technology at JPL – that is, the human side of robotics. Holloway has since migrated back to robots as the lead software engineer for NASA's next Mars rover. But the two still often work together as mentors for the students they bring in to design prototypes or develop software used to operate rovers and the antennas that communicate with spacecraft across the solar system.
It's important to them that students get a window into different career possibilities so they can discover the path that speaks to them most. The pair say they've seen several students surprised by the career revelation that came at the end of their internships.
"For all of our interns, we tailor the project to the intern, the intern's abilities, their desires and which way they want to grow," says Holloway. "This is such a nice place where you can stretch for just a little bit of time, try something new and decide whether it's for you or not. We've had interns who did design tasks for us and at the end of the internship, they were like, 'You know what? I've realized that this is not for me.' And we were like, 'Awesome! You just saved yourself five years.'"
The revelations of students who intern with Parag Vaishampayan in JPL's Planetary Protection group come from something much smaller in scale – microscopic, even.
Vaishampayan's team studies some of the most extreme forms of life on Earth. The group is trying to learn whether similar kinds of tough microbes could survive on other worlds – and prevent those on Earth from hitching a ride to other planets on NASA spacecraft. An internship in Planetary Protection means students may have a chance to study these microbes, collect samples of bacteria inside the clean room where engineers are building the latest spacecraft or, for a lucky few, name bacteria.
"Any researcher who finds a new kind of bacteria gets a chance to name it," says Vaishampayan. "So we always give our students a chance to name any bacterium they discover after whoever they want. People have named bacteria after their professors, astronauts, famous scientists and so forth. We just published a paper where we named a bacterium after Carl Sagan."
The Planetary Protection group hosts about 10 students a year, and Vaishampayan says he's probably used every JPL internship program to bring them in. Recently, he's become a superuser of one designed for international students and another that partners with historically black colleges and universities, or HBCUs, to attract students from diverse backgrounds and set them on a pathway to a career at the Laboratory.
"I can talk for hours and hours about JPL internships. I think they are the soul of the active research we are doing here," says Vaishampayan. "Had we not had these programs, we would not have been able to do so much research work." In the years ahead, the programs might become even more essential for Vaishampayan as he takes on a new project analyzing 6,000 bacteria samples collected from spacecraft built in JPL's clean rooms since 1975.
With interns making up more than 15 percent of the Laboratory population each year, Vaishampayan is certainly not alone in his affection for JPL's internship programs. And JPL is equally appreciative of those willing to lend time and support to mentoring the next generation of explorers.
Says Adrian Ponce of those who take on the mentorship role through the programs his team manages, "Especially with this being National Mentoring Month, it's a great time to highlight the work of our thriving mentor community. I'd like to thank JPL mentors for their tremendous efforts and time commitment as they provide quality, hands-on experiences to students that support NASA missions and science, and foster a diverse and talented future workforce."
Explore JPL’s summer and year-round internship programs and apply at: jpl.nasa.gov/intern
Career opportunities in STEM and beyond can be found at: jpl.jobs
The laboratory’s STEM internship and fellowship programs are managed by the JPL Education Office. Extending the NASA Office of STEM Engagement’s reach, JPL Education seeks to create the next generation of scientists, engineers, technologists and space explorers by supporting educators and bringing the excitement of NASA missions and science to learners of all ages. | 0.885811 | 3.159743 |
It’s sometimes hard to grasp the length of time involved in events in the Universe. But the Universe is huge and it has been around for a very long time – 13.7 billion years! That’s about three times older than Earth, and it’s hard to imagine a time before our planet existed!
These big time scales mean that astronomers can’t study something like the lifetime of a star by studying one star, as that would take millions or billions of years! Instead they observe different stars at different stages of their lives.
Sometimes, though, things that are far away in deep space change in the night sky during our lifetime. Take this new space photo, for example. It shows a cloud of glowing gas that is left over from the explosive death of a massive star about 11,000 years ago. Astronomers call an explosion like this a ‘supernova’.
The cloud is travelling very fast in space, at a speed of about 650,000 kilometres per hour. Remarkably, even though it is very far away from Earth, it is travelling so quickly that it will change its position in the night sky within a human lifetime. The stars that it appears to be next to in the night sky will be different when you are elderly than the ones it seems to be close to now.
Even after 11,000 years, the supernova explosion is still changing the face of the night sky!
Get involved: Many astronomers keep diaries or logs of their observations. These are great records to refer back to and see if something has changed in the Universe. Why don’t you start your own observing log? Even if you don’t have a telescope you can make sketches of things that you can see, like the Moon, and special objects, like the occasional comet.
This Space Scoop is based on an ESO Press Release. | 0.841872 | 3.007327 |
- TRAPPIST-1, a red dwarf star 39-light-years away from us, has seven Earth-size planets orbiting it.
- It's likely that all of these worlds are rocky and may possibly harbor liquid water.
- Red dwarf stars are the most abundant type of star in the Milky Way galaxy.
- In the future, telescopes might be able to detect light that passes through the planets' atmospheres — and possibly signal the presence or absence of alien life.
Less than a year ago, astronomers announced an astounding discovery: They'd found three Earth-size planets orbiting a small, dim red star.
But as it turns out, their first observations missed a whole bunch of worlds.
The astronomers now think seven rocky planets similar to our own may circle the star, called TRAPPIST-1 — an "ultra-cool" red dwarf located about 39 light-years away in the constellation Aquarius. Thirty researchers from around the world announced the new discovery Tuesday in the journal Nature.
The team's surprise didn't end with an increased world count, though.
Each planet orbits TRAPPIST-1 in the star's Goldilocks-like habitable zone — a region where there's enough starlight to permit the existence of liquid water. Four of the seven worlds may even be candidates for hosting alien life, team members said Tuesday during a press teleconference call.
"This is really the first time we have seven planets that we can say are in the terrestrial zone, and it's really, really surprising," said Michaël Gillon, a study co-author and astronomer at the Université de Liège in Belgium.
The discovery of the new worlds, each within 10-20% of the size of Earth, may have profound implications for the search for extraterrestrial life beyond the solar system.
"We've made a giant, accelerated leap forward in the search for habitable worlds," Sara Seager, a planetary scientist at MIT who wasn't involved in the research, said during a NASA press conference on Wednesday. "In this system, it's like Goldilocks has many sisters."
An alien, yet possibly common, solar system
The dwarf star and its system of seven known planets — called TRAPPIST-1b, 1c, 1d, 1e, 1f, 1g, and 1h — is relatively small compared to our own.
In fact, one "year" on the innermost planet, 1b, lasts only about 1.5 Earth-days. The outermost planet, 1h (which scientists have caught only a fleeting glimpse of), may take about 20 Earth-days to orbit the star.
"If we put the TRAPPIST-1 star [in] the place of the sun, we'd have all seven planets inside the orbit of Mercury," Emmanuël Jehin, another co-author at the Université de Liège, said on the call.
But that isn't a deal-breaker for the possibility of life.
TRAPPIST-1's surface temperature is about half that of the sun's, making it "ultra-cool" as stars go. However, if a planet orbits closely enough, it can receive the same amount of solar energy as the Earth receives from the sun at 93 million miles away. All of TRAPPIST-1's worlds appear to be "temperate" and not close enough to get roasted.
The team said it's "very hard to know" if they just got lucky with their unprecedented discovery of seven Earth-size planets around a single star, or if such an abundance of worlds is common, said Amaury Triaud, fellow co-author and astronomer at the Institute of Astronomy in Cambridge, UK.
Either way, the bounty of worlds may vastly improve the chances that humans aren't alone in the Milky Way galaxy, let alone the universe at large.
That's because red dwarf stars comprise "30 to 50%" of our galaxy's 100 to 400 billion stars, Triaud said, which makes them the most abundant and long-lived type of star around. (Sun-like solar systems represent only about 10% of those discovered thus far, the researchers said.)
"I think we've made a crucial step toward finding life out there," Triaud told Business Insider during the call.
"I don't think we've had the right planets to look at," he said. "If life managed to thrive and release gases similar to those here on Earth, then we will know. We have the right targets."
Another target could also be Proxima Centauri, a red dwarf just 4.24 light-years away — many times closer than TRAPPIST-1. In 2016, astronomers learned this star system may harbor an Earth-like planet called Proxima b.
NASA's upcoming James Webb Space Telescope (JWST) might be able to study the probable world's alien atmosphere for signs of life. A Russian billionaire is also backing an ambitious mission called Starshot to laser-propel a fleet of tiny spacecraft toward Proxima Centauri and its close neighbor Alpha Centauri to directly study and photograph any worlds around the stars.
Why there could be life around TRAPPIST-1
Since astronomers verified the discovery of the first exoplanet 25 years ago, scientists have gradually come around to the idea that life is probably common in the universe. (Whether or not it's intelligent, angry, friendly, or indifferent, however, is a different matter.)
The transit method, where a planet passes in front of a star and dims its light ever-so-slightly, showed humanity that perhaps trillions of planets may exist in our galaxy alone.
Gillon and his colleagues used the same method to discover the seven new worlds. They found the first three in previous years using a ground-based telescope named TRAPPIST. They detected the four additional worlds featured in the new study by staring down TRAPPIST-1 for 20 consecutive days with NASA's Spitzer Space Telescope.
And, as previously mentioned, more-abundant stars that are much cooler than the sun can warm up rocky planets enough to melt water; that is, if they have enough insulating gases in their atmospheres.
"It's possible their atmospheres are very similar to the Earth, or Venus, or something completely different," Gillon said.
The study suggests that the diameters and masses of each planet, estimated based on the amount of starlight dimming they cause, match up with that of rocky worlds, and possibly those that harbor water as ice or liquid oceans.
That's not to say life is guaranteed around TRAPPIST-1.
Dangerous space weather, including solar flares and coronal mass ejections, could endanger any aliens by blasting them with dangerous high-energy particles. And unfortunately, red dwarf stars — more than most other types of stars — are known for such temper tantrums.
The planets also seem to orbit in "resonance," which could mean that they may be tidally locked and always facing the star with the same side, much like Jupiter's largest moons.
But neither of these necessarily mean doom for any life that may exist there, the researchers said.
For one, Gillon said, TRAPPIST-1 "is a very quiet star" as far as giant balls of fusing plasma go.
Gillon also says orbital resonances and tidal locking may actually be an advantage.
"This could lead to a huge tidal heating in the cores of the planets," he said, by kneading them with gravitational strain.
Such warmth could melt ice into liquid, belch insulating gases into the planet's atmosphere through volcanism, and generally stir up the ingredients for life.
What's next for the TRAPPIST-1 system
Gillon said the team's discovery of TRAPPIST-1's seven planets "is just the beginning."
Direct photographs of the planets may not be possible, the researchers said. But within the next 5 years, they hope to use telescopes like JWST — scheduled to launch in 2018 — to peek at starlight that passes through the atmospheres of the planets.
The technique could help them measure how much oxygen, ozone, and other gases the worlds might contain.
"For instance, oxygen can be produced by photolysis of water on a water-rich planet," Gillon said. "It's really the molecules and their relative abundances that enable us to give the plausible or restricted extent of life. We'll see."
The Search for Extraterrestrial Intelligence, or SETI, has already tuned in and listened to the system and found no unusual signals, Gillion said during NASA's press conference on Wednesday.
And even if TRAPPIST-1 seems to be a dead or sterile planetary system now, that still doesn't mean it's an unlikely place to seek out aliens in the future.
"Could any of the planets harbour life? We simply do not know," Ignas A.G. Snellen, a researcher at Leiden University who wasn't part of the research team but reviewed the study for Nature, wrote in an accompanying editorial.
"But one thing is certain: in a few billion years, when the Sun has run out of fuel and the Solar System has ceased to exist, TRAPPIST-1 will still be only an infant star. It burns hydrogen so slowly that it will live for another 10 trillion years" Snellen wrote, adding that's "more than 700 times longer than the Universe has existed so far, which is arguably enough time for life to evolve." | 0.92622 | 3.778408 |
Over 100 new minor planets found at edge of solar system
Reidar Hahn, Fermilab/University of Pennsylvania
Astronomers have discovered more than 100 new trans-Neptunian objects (TNOs), minor planets located in the far reaches of the solar system.
For the study, published in The Astrophysical Journal Supplement Series, the researchers used data from Dark Energy Survey (DES), an international collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of our universe.
The study also describes a new approach for finding similar types of objects and could aid future searches for the hypothetical Planet Nine and other undiscovered planets.
"The number of TNOs you can find depends on how much of the sky you look at and what's the faintest thing you can find," said Gary Bernstein, Professor at the University of Pennsylvania in the US.
Using the first four years of DES data, Pedro Bernardinelli from the University of Pennsylvania started with a dataset of seven billion "dots," all of the possible objects detected by the software that were above the image's background levels.
He then removed any objects that were present on multiple nights - things like stars, galaxies, and supernova - to build a "transient" list of 22 million objects before commencing a massive game of "connect the dots," looking for nearby pairs or triplets of detected objects to help determine where the object would appear on subsequent nights.
With the seven billion dots whittled down to a list of around 400 candidates that were seen over at least six nights of observation, the researchers then had to verify their results.
"We have this list of candidates, and then we have to make sure that our candidates are actually real things," Bernardinelli said.
To filter their list of candidates down to actual TNOs, the researchers went back to the original dataset to see if they could find more images of the object in question.
Bernardinelli developed a way to stack multiple images to create a sharper view, which helped confirm whether a detected object was a real trans-Neptunian object.
They also verified that their method was able to spot known trans-Neptunian objects in the areas of the sky being studied and that they were able to spot fake objects that were injected into the analysis.
After many months of method-development and analysis, the researchers found 316 TNOs, including 245 discoveries made by DES and 139 new objects that were not previously published.
Two new planets 8-times the size of Earth could support life — and they're right next-door
Habitable earth-sized planet discovered but its Sun doesn't set for over two weeks
NASA's planet-hunter uncovers its first world with two stars 1,300 light-years away
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- Infosys reportedly plans to reduce the number of managers— the CEO and COO got over 25% salary raise in FY20 | 0.847285 | 3.788239 |
Like other giant planets, Uranus has a set of rings and more than a dozen moons that make it resemble a miniature solar system unto itself. But unlike its king-sized neighbors (and the rest of the planets for that matter) the ice giant system turns on its side, rolling rather than spinning. Now, a new simulation of the planet’s early years buttresses a theory developed to explain the weird orientation by showing that it can produce the planet’s moons too.
The bizarre planet demands an origin story unusual enough to match its oddball nature. Earth, Jupiter, and most of our cosmic crew spin “vertically” like tops, their north poles all pointing out into the universe in the same direction as the north pole of the sun. But not Uranus. It alone rolls on its side, its rings and moons swinging “up” and “down” out of the solar system’s plane as they orbit.
So what tipped the Uranus system over? It could have tilted of its own accord from an initial twist in the dusty disk that spun it into being, but many planetary scientists assume that the young planet—when it was just a few hundred million years into its billions of years of life—suffered a cataclysmic collision. Back then, the early solar system swirled with more planets than the canonical eight(ish), so run-ins were unavoidable. A Mars-sized rock dubbed Theia may have liquidated much of the Earth to create the moon. Similarly, baby Uranus may have taken a crushing, off-center blow from a roaming ice ball perhaps a few times Earth’s size that knocked both bodies for a loop. When the dust settled, what was left of the two would have merged into a single rolling world.
Researchers first put the theory to the test in the early 1990s with a computer simulation. They broke up the proto-Uranus and its antagonist into thousands of digital pieces, each representing roughly a tenth the mass of Earth’s moon. By smashing the two particle-clouds together over and over at various speeds and angles, they concluded that the double Armageddon would have lasted just days, after which the resulting amalgamation did indeed acquire the characteristic roll.
Two years ago a team including Don Korycansky of the University of California, Santa Cruz, and Chris Fryer of Los Alamos National Laboratory pushed the idea even farther. Harnessing three decades of computing advances, they simulated a range of collisions between two planets each made up of millions of pieces. “It’s like going from a monitor with 200 [pixels] on a side to a 2000 by 2000 [pixel] image,” Korycansky says. “You can see lots of details that can be further investigated.” The planet-tipping theory withstood their high definition scrutiny.
Now research from Ida and his colleagues picks up where the previous simulations left off. “They take it to the next level,” Fryer says. “It’s getting quite exciting.”
Wrecking two worlds makes a mess, and the earlier models suggested that tons of debris would have ended up orbiting the freshly minted globe—but the planet-wide simulations weren’t sharp enough to nail down the shape the detritus would have taken. Ida’s results, which appeared last week in Nature Astronomy, tackle the problem by zooming in on the disk itself and breaking the system’s history into two distinct eras.
Starting from the mass of the disk predicted by past simulations, they first analyzed the immediate aftermath of the collision. Assuming the initial planets had been mostly ice balls, the impact’s violence would have vaporized some of their bulk. The team treated the debris as a cloud of water vapor mixed with hydrogen and helium gas, and analyzed how the disk cooled and thinned as it orbited and fell onto the planet. They found that after thousands of years, it eventually condensed into ice particles, which in turn clumped into miles-long ice chunks—the seeds of Uranus’s future moons.
When the wreckage transitioned from a cloud to a chunky collection of objects, Ida’s team switched tactics. They set up a digital Uranus with a swarm of 10,000 icy moonlets (with properties fixed by the results of their first simulation) and let them fly. When the inevitable game of bumper cars settled down, about a dozen large survivors remained. Their assorted sizes and locations matched those of Uranus’s observed moons. The largest four were a particularly close fit to reality.
The result resolves a number of challenges in other models, according to Ida, making more complicated theories unnecessary. “Our study shows that the simple impact scenario beautifully reproduces the Uranus satellite system if the disk evolution is properly taken into account,” he says.
Other impact researchers say that the work doesn’t substantially change their understanding of how the system formed, but that it does give the theory twice the explanatory power it had before. “Not only does the collision model easily explain the tilt,” Fryer says, “but it also answers the question, ‘how did Uranus form its satellites?’”
Earlier studies remained relatively agnostic about what the incoming planet might have been made of—rock or ice. But only ice appears sticky enough to glom together into moonlets properly, according to the new work, so future models may be able to focus on fleshing out the icier scenarios. Ida says that precisely accounting for the relative amounts of ice and rock in the system’s moons is a major direction for future research.
But the planetary science community can learn only so much by looking backwards. Building computer programs that generate “right answers” matching Uranus’s real moons is a great step forward, researchers say, but the real smoking gun would be a genuine prediction of a currently unknown feature. Fryer, for instance, is currently developing new simulations that forecast what substances might have been forged in the heat of the collision (as opposed to less dramatic formation scenarios, in which the planet would have stayed cooler). To confirm such a theory, a future spacecraft would have to go out and check exactly what Uranus is made of.
Fryer hopes that theoretical studies like his and Ida’s will turn up a variety of potential signs that only an impact could have produced. And since any mission to the outer planets will take decades to plan and execute, they’ll have plenty of time to calculate. | 0.903281 | 3.891086 |
Scientists from NASA and three universities have presented new discoveries about the way heat and energy move and manifest in the ionosphere, a region of Earth’s atmosphere that reacts to changes from both space above and Earth below.
Far above Earth’s surface, within the tenuous upper atmosphere, is a sea of particles that have been split into positive and negative ions by the Sun’s harsh ultraviolet radiation. Called the ionosphere, this is Earth’s interface to space, the area where Earth’s neutral atmosphere and terrestrial weather give way to the space environment that dominates most of the rest of the universe – an environment that hosts charged particles and a complex system of electric and magnetic fields. The ionosphere is both shaped by waves from the atmosphere below and uniquely responsive to the changing conditions in space, conveying such space weather into observable, Earth-effective phenomena creating the aurora, disrupting communications signals, and sometimes causing satellite problems.
Many of these effects are not well-understood, leaving the ionosphere, for the most part, a region of mystery. Scientists from NASA’s Goddard Space Flight Center in Greenbelt, Maryland, the Catholic University of America in Washington, D.C., the University of Colorado Boulder, and the University of California, Berkeley, presented new results on the ionosphere at the fall meeting of the American Geophysical Union on Dec. 14, 2016, in San Francisco.
One researcher explained how the interaction between the ionosphere and another layer in the atmosphere, the thermosphere, counteract heating in the thermosphere – heating that leads to expansion of the upper atmosphere, which can cause premature orbital decay. Another researcher described how energy outside the ionosphere accumulates until it discharges – not unlike lightning – offering an explanation for how energy from space weather crosses over into the ionosphere. A third scientist discussed two upcoming NASA missions that will provide key observations of this region, helping us better understand how the ionosphere reacts both to space weather and to terrestrial weather.
Changes in the ionosphere are primarily driven by the Sun’s activity. Though it may appear unchanging to us on the ground, our Sun is, in fact, a very dynamic, active star. Watching the Sun in ultraviolet wavelengths of light from space – above our UV light-blocking atmosphere – reveals constant activity, including bursts of light, particles, and magnetic fields.
Occasionally, the Sun releases huge clouds of particles and magnetic fields that explode out from the Sun at more than a million miles per hour. These are called coronal mass ejections, or CMEs. When a CME reaches Earth, its embedded magnetic fields can interact with Earth’s natural magnetic field – called the magnetosphere – sometimes compressing it or even causing parts of it to realign.
It is this realignment that transfers energy into Earth’s atmospheric system, by setting off a chain reaction of shifting electric and magnetic fields that can send the particles already trapped near Earth skittering in all directions. These particles can then create one of the most recognizable and awe-inspiring space weather events – the aurora, otherwise known as the Northern Lights.
But the transfer of energy into the atmosphere isn’t always so innocuous. It can also heat the upper atmosphere – where low-Earth satellites orbit – causing it to expand like a hot-air balloon.
“This swelling means there’s more stuff at higher altitudes than we would otherwise expect,” said Delores Knipp, a space scientist at the University of Colorado Boulder. “That extra stuff can drag on satellites, disrupting their orbits and making them harder to track.”
This phenomenon is called satellite drag. New research shows that this understanding of the upper atmosphere’s response to solar storms – and the resulting satellite drag – may not always hold true.
“Our basic understanding has been that geomagnetic storms put energy into the Earth system, which leads to swelling of the thermosphere, which can pull satellites down into lower orbits,” said Knipp, lead researcher on these new results. “But that isn’t always the case.”
Sometimes, the energy from solar storms can trigger a chemical reaction that produces a compound called nitric oxide in the upper atmosphere. Nitric oxide acts as a cooling agent at very high altitudes, promoting energy loss to space, so a significant increase in this compound can cause a phenomenon called overcooling.
“Overcooling causes the atmosphere to quickly shed energy from the geomagnetic storm much quicker than anticipated,” said Knipp. “It’s like the thermostat for the upper atmosphere got stuck on the ‘cool’ setting.”
That quick loss of energy counteracts the previous expansion, causing the upper atmosphere to collapse back down – sometimes to an even smaller state than it started in, leaving satellites traveling through lower-density regions than anticipated.
A new analysis by Knipp and her team classifies the types of storms that are likely to lead to this overcooling and rapid upper atmosphere collapse. By comparing over a decade of measurements from Department of Defense satellites and NASA’s Thermosphere, Ionosphere, Mesosphere Energetics and Dynamics, or TIMED, mission, the researchers were able to spot patterns in energy moving throughout the upper atmosphere.
“Overcooling is most likely to happen when very fast and magnetically-organized ejecta from the Sun rattle Earth’s magnetic field,” said Knipp. “Slow clouds or poorly-organized clouds just don’t have the same effect.”
This means that, counterintuitively, the most energetic solar storms are likely to provide a net cooling and shrinking effect on the upper atmosphere, rather than heating and expanding it as had been previously understood.
Competing with this cooling process is the heating that caused by solar storm energy making its way into Earth’s atmosphere. Though scientists have known that solar wind energy eventually reaches the ionosphere, they have understood little about where, when and how this transfer takes place. New observations show that the process is localized and impulsive, and partly dependent on the state of the ionosphere itself.
Traditionally, scientists have thought that the way energy moves throughout Earth’s magnetosphere and atmosphere is determined by the characteristics of the incoming particles and magnetic fields of the solar wind – for instance, a long, steady stream of solar particles would produce different effects than a faster, less consistent stream. However, new data shows that the way energy moves is much more closely tied to the mechanisms by which the magnetosphere and ionosphere are linked.
“The energy transfer process turns out to be very similar to the way lightning forms during a thunderstorm,” said Bob Robinson, a space scientist at NASA Goddard and the Catholic University of America.
During a thunderstorm, a buildup of electric potential difference – called voltage – between a cloud and the ground leads to a sudden, violent discharge of that electric energy in the form of lightning. This discharge can only happen if there’s an electrically conducting pathway between the cloud and the ground, called a leader.
Similarly, the solar wind striking the magnetosphere can build up a voltage difference between different regions of the ionosphere and the magnetosphere. Electric currents can form between these regions, creating the conducting pathway needed for that built-up electric energy to discharge into the ionosphere as a kind of lightning.
“Terrestrial lightning takes several milliseconds to occur, while this magnetosphere-ionosphere ‘lightning’ lasts for several hours – and the amount of energy transferred is hundreds to thousands of times greater,” said Robinson, lead researcher on these new results. These results are based on data from the global Iridium satellite communications constellation.
Because solar storms enhance the electric currents that let this magnetosphere-ionosphere lightning take place, this type of energy transfer is much more likely when Earth’s magnetic field is jostled by a solar event.
The huge energy transfer from this magnetosphere-ionosphere lightning is associated with heating of the ionosphere and upper atmosphere, as well as increased aurora.
Though scientists are making progress in understanding the key processes that drive changes in the ionosphere and, in turn, on Earth, there is still much to be understood. In 2017, NASA is launching two missions to investigate this dynamic region: the Ionospheric Connection Explorer, or ICON, and Global Observations of the Limb and Disk, or GOLD.
“The ionosphere doesn’t only react to energy input by solar storms,” said Scott England, a space scientist at the University of California, Berkeley, who works on both the ICON and GOLD missions. “Terrestrial weather, like hurricanes and wind patterns, can shape the atmosphere and ionosphere, changing how they react to space weather.”
ICON will simultaneously measure the characteristics of charged particles in the ionosphere and neutral particles in the atmosphere – including those shaped by terrestrial weather – to understand how they interact. GOLD will take many of the same measurements, but from geostationary orbit, which gives a global view of how the ionosphere changes.
Both ICON and GOLD will take advantage of a phenomenon called airglow – the light emitted by gas that is excited or ionized by solar radiation – to study the ionosphere. By measuring the light from airglow, scientists can track the changing composition, density, and even temperature of particles in the ionosphere and neutral atmosphere.
ICON’s position 350 miles above Earth will enable it to study the atmosphere in profile, giving scientists an unprecedented look at the state of the ionosphere at a range of altitudes. Meanwhile, GOLD’s position 22,000 miles above Earth will give it the chance to track changes in the ionosphere as they move across the globe, similar to how a weather satellite tracks a storm.
“We will be using these two missions together to understand how dynamic weather systems are reflected in the upper atmosphere, and how these changes impact the ionosphere,” said England. | 0.802368 | 4.057106 |
A team of researchers has identified a record-breaking faint dwarf galaxy neighboring our very own Milky Way. Named Virgo 1 for the constellation Virgo, in whose direction it lies, it resides in a class of hard-to-find dwarf satellite galaxies virtually undetectable prior to the introduction of new, larger-diameter telescopes.
The new results, published Monday in the Astrophysical Journal, show that Virgo 1 exhibits an optical waveband magnitude of -0.8, making it the faintest satellite galaxy ever detected, and could play an important role in helping astrophysicists find and characterize dark matter. The new discovery also stokes hopes that there are other faint and ultra-faint satellite galaxies residing close by to the Milky Way that would further aid our understanding of the structure of our neck of the cosmic woods.
The term ‘satellite galaxy’ maybe a bit confusing, but what scientists are referring to is simply a smaller aggregation of gas and energy that’s orbiting the Milky Way on the outskirts. We’ve already identified about 50 faint dwarf galaxies in the Milky Way’s halo, most of which are quite faint. But the Hilo, Hawaii-based Subaru Telescope — which has a diameter of nearly 27 feet, as opposed to the earlier telescopes with diameters between approximately eight to 13 feet — is rapidly stringing together new discoveries of so-called ‘ultra-faint galaxies’.
“This discovery implies hundreds of faint dwarf satellites waiting to be discovered in the halo of the Milky Way, project leader Masashi Chiba, of Japan’s Tohoku University, told the Subaru Telescope Facility. How many satellites are indeed there and what properties they have, will give us an important clue of understanding how the Milky Way formed and how dark matter contributed to it.”
Dark matter is a slippery field of study, but the edges of galaxies — like in the Milky Way halo, where Virgo 1 site — are where we tend to look to observe it and hopefully better understand. The more faint satellites in these locations we can identify, the more we can infer about the process by which dark matter itself assembles in the same regions, and ultimately how dark matter contributed to the formation of the Milky Way itself.
Virgo 1 itself has a radius of 124 light-years, meaning it’s simply too big to anything else with a comparable luminosity, like a globular cluster. The previous record-holder for faintest satellite galaxy was called Segue 1, which weighed in at a -1.5 magnitude on the optical waveband to Virgo 1’s -0.8. A third find called Cetus II actually has a mag of 0.0, but hasn’t been officially confirmed as a galaxy — it’s too compact, and at 280,000 light-years away is too distant to be able to say for sure.
The project behind the discovery is called the Hyper Suprime-Cam Subaru Strategic Survey, and has been active since March 2014. It has a few different goals, but much of its job is surveying extremely large cross-sections of sky for entities that could tell us more about galaxy formation, galactic structure, and the assemblage of dark matter — including dwarf satellites like Virgo 1. The project will be active until at least 2019, so hopefully this is far from the last faint galaxy we stumble upon. | 0.815785 | 3.979396 |
Several robotic space missions are on the anvil in the decade of the 2020s. The National Aeronautics and Space Administration (NASA) is likely to reexamine two Venus mission proposals – an atmosphere probe, named Davinci, and an orbiter with a radar payload, called Veritas – which it had initially rejected earlier this year. The Russian space agency, Roscosmos, is considering a proposal to revisit Venus with a new mission, Venera-D, which too will carry a radar payload. The Indian Space Research Organisation (ISRO) could also orbit around Venus around the same time, its first visit to the planet.
What has occasioned all this academic curiosity in a planet that is plain inhospitable – its atmosphere consists of sulfuric acid, and a shroud of heavy metal frost, with average surface temperatures reaching as high as 460 degrees Celsius, the hottest in the solar system. Recent studies suggest that once upon a time, Venus had oceans and balmy temperatures: scientists are keen to find out how this changed.
The space race has its own reasons and offers immediate scope for one-upmanship, but the interest in Venus holds implications for a wide range of high-technologies.
Most missions to Venus so far have fallen short of success because the technologies in use lacked the ability to penetrate the planet’s extremely thick and opaque atmosphere and map its surface. For example, in the 1960s, only the military establishments of the U.S. and Soviet Union owned satellite-based, visually penetrating geospatial intelligence (GEOINT) technology. The space-defense industrial complex of these two nations undertook to rapidly incorporate this technology for use in military reconnaissance and thereafter transfer some of it to civilian space agencies.
In 1964, Washington’s National Reconnaissance Office (NRO), an agency within the U.S. Department of Defense, launched the world’s first radar satellite, OPS 3762, also known as Quill, which could observe the Earth’s surface at night through clouds and atmospheric obscurations. The success of Quill yielded to the NRO the highly classified ground-penetrating Lacrosse series of radar GEOINT satellites (1988), whose presence was kept clandestine for decades.
Moscow was not far behind in this either. Since the 1960s, its NII-17 design bureau was developing high-resolution radars for the nuclear-powered Radar Ocean Reconnaissance Satellite (RORSAT) series of GEOINT satellites, which could identify small destroyers and cruisers under favourable weather conditions, and large aircraft carriers in inclement weather.
As for mapping the surface of Venus, nobody could attempt this until satellite-based radars could be discharged for civilian purposes. Immediately after Quill, Washington’s civilian space agency, NASA, launched the SeaSat satellite (1978) that, for the first time, carried a synthetic aperture radar (SAR), which was able to observe the structure of the Earth’s ocean floor at a very high resolution. The same year NASA carried a surface radar mapper payload on its Venus-bound Pioneer Venus Orbiter (1978). The Russian Venera-15 and Venera-16 (1983) also carried SAR payloads that were able to map Venus’ surface.
Radars have been able to provide a cloud-penetrating view of the surface of Venus. But the major challenge remains an extensive and sustained exploration of the surface by landers and rovers. One major reason for this is silicon’s limitations as a semi conductor. The search is on for suitable alternatives, such as silicon carbide, graphene and silicene, owing to these materials’ ability to operate at higher voltages, frequencies, temperatures, and energy efficiency levels, besides being of lighter mass . The silicon-based electronic circuits of the Venera and Pioneer landers lasted only an hour.
The next-generation Venus landers will be constructed, using more robust high-temperature electronic circuits . Their fitness to operate on Venus could pave the way for their utilisation in other high-temperature and demanding environments, such as very deep-Earth oil and gas exploration, nuclear reactor monitoring, space missions to the Sun, and in lighter and more efficient military electronics.
The ISRO recently invited scientific research and development (R&D) laboratories across India to contribute to a future Venusian Orbiter Mission. It has not chosen the payload for this mission yet, but it must try and accommodate a probe, made of electronics and mechanical components, that will descend through the atmosphere, analysing the chemical composition in real time and also withstand the harsh climatic conditions. India possesses vibrant defense, oil and gas, and civilian-nuclear industrial sectors. The competencies of novel electronics and components, if proved on Venus, can provide a breakthrough for these sectors and India’s greater scientific-industrial complex too.
The ISRO currently has indigenous capabilities as well as international alliances for the R&D of space-based radar technologies. The Radar Imaging Satellite-2 (RISAT-2), jointly operated by it and the Indian Air Force, received an advanced X-band SAR from the Israeli Aerospace Industries.
New Delhi is also jointly developing with Washington the NASA-ISRO Synthetic Aperture Radar (NISAR) mission for launch in the 2020-21 time frame. NISAR will provide unprecedented dual-frequency observations of complex terrestrial geological and anthropogenic processes, like ecosystem shifts, forest- and land-usage, earthquakes, tsunamis, volcanic eruptions, glacial monitoring, and landslides.
Aggregating its experience with the RISAT and NISAR, New Delhi must carry a SAR payload for its Venus Orbiter Mission, and future Mars and Moon missions as well. Both Moon and Mars terrain and sub-terrain need radar mapping before India can lead any initiative on human habitation or extraterrestrial resource extraction and utilisation. An apt selection of payloads has the ability to attract the international scientific community, and New Delhi can use this as a means to advance its ‘space diplomacy.’
The exceptionality of each planetary object in the solar system should be taken as a crucible for developing newer types of high-end technologies. New Delhi must create policies that enable this. It must not gratify itself by merely orbiting or landing on a celestial object, using the ‘technology-demonstrator’ and ‘low-cost’ yardsticks to brush the outcomes of a space mission under the carpet. The planetary exploration programme has the potential equally to cater to India’s academic, diplomatic, and strategic interests. New Delhi has not tested it to the fullest.
Dr. Chaitanya Giri is Adjunct Fellow, Space Studies, Gateway House. He is also a ELSI Origins Network Scientist at the Earth-Life Science Institute, Tokyo Institute of Technology, Japan.
This article was exclusively written for Gateway House: Indian Council on Global Relations. You can read more exclusive content here.
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Indian Space Research Organisation, Department of Space, Government of India, Announcement of Opportunity (AO) for Space Based Experiments to Study Venus, (New Delhi: Indian Space Research Organisation), <http://www.isro.gov.in/announcement-of-opportunity-ao-space-based-experiments-to-study-venus>
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Missions to Venus galvanised the research and development (R&D) of high-technologies during the Cold War. In the 1950s, military radar technologies were making great forays into the civilian-scientific domain in the fom of a novel technique, called ‘planetary radar astronomy.’ Venus, due to its proximity to the Earth, was the first planet to be located by this technique.
As the Cold War spilled over into the civilian-scientific domain in the form of the Space Race, measuring the precise distance between the Earth and Venus and seeking Venus’ measurements and images became part of its agenda and was practiced through radar astronomy. This ‘Venusian astronomy contest’ resulted in numerous space missions. The first successful space missions to Venus – the Mariner-2 flyby mission of the United States (1962) and Venera-5 atmospheric probe by the Soviet Union (1969) – happened in the course of a decade.
Len Scott, Stephen Twigge, Planning Armageddon: Britain, the United States and the Command of Western Nuclear Forces, 1945-1964, Routledge Studies in the History of Science, Technology and Medicine, Edition 1, ISBN-10: 1138002305
Asif Siddiqi, Staring at the sea: The Soviet RORSAT and EORSAT programmes, Journal of the British Interplanetary Society, 52, 397-416, (1999).
Hangseok Choi, Overview of Silicon Carbide power devices, Retrieved from the Fairchild Semiconductor website <https://www.fairchildsemi.co.kr/Assets/zSystem/documents-archive/collateral/technicalArticle/Overview-of-Silicon-Carbide-Power-Devices.pdf>
Patrick Vogt, Paola De Padova, Claudio Quaresima, Jose Avila, Emmanouil Frantzeskakis, Maria Asensio, Andrea Resta, Benedicte Ealet, Guy Le Lay, Silicene: Compelling experimental evidence for graphenelike two-dimensional silicon, Physical Review Letters, 108, 155501, (2012).
A.H. Monica, D.M. Deglau, D. Maier, E. Kohn, N.R. Izenberg, S.J. Papadakis, High-temperature electronics for future Venus exploration, USRA Venus Lab and Technology Workshop (2015), Retrieved from the website <https://www.hou.usra.edu/meetings/venustech2015/pdf/4032.pdf>
Philip Neudeck, Roger Meredith, Liangyu Chen, David Spry, Leah Nakley, Gary Hunter, Prolonged silicon carbide integrated circuit operation in Venus surface atmospheric conditions, AIP Advances, 6, 125119, (2016), Retrieved from the website <http://aip.scitation.org/doi/10.1063/1.4973429> | 0.831265 | 3.53054 |
A new planet-hunting algorithm suggests that at least 9 percent of nearby stars could host planets orbiting out of sight — and the stars’ chemistry could help find the worlds.
Planetary astrophysicist Natalie Hinkel of the Southwest Research Institute in San Antonio and colleagues trained a machine-learning algorithm on a catalog of thousands of stars and their chemical compositions (SN: 5/11/19, p. 34). In the dataset of stars located within about 500 light-years of the sun, 290 were known to host giant planets, while more than 4,200 didn’t — or so astronomers thought.
First, the algorithm analyzed the chemistry of the planet-hosting stars. Then, based on what it learned about those celestial objects, the program estimated the probability that each of the stars in the other group actually does host planets.
It works similarly to how online TV streaming companies like Netflix choose which TV shows to recommend to viewers, Hinkel says. “If I watch a bunch of movies, Netflix learns that I like science fiction, martial arts movies and British period movies,” she says. The program then uses that knowledge to identify other shows she might like — that is, the stars with planets not yet detected.
The new algorithm identified 368 additional stars — or about 9 percent of the stars thought to be lacking planets — that had a more than 90 percent probability of hosting a giant exoplanet, Hinkel will report June 26 in Seattle at the Astrobiology Science Conference. “That was way more than I was expecting,” she says.
The stellar elements that best predicted a potential planet’s presence were iron, carbon, oxygen and sodium. But the ratios of those elements to each other seemed to matter more than just having a lot of each one. The way the elements interact in a planet-forming disk around a star probably shapes planet formation, similar to how baking ingredients interact to make a cake rise, Hinkel says (SN: 5/12/18, p. 28). | 0.840617 | 3.507108 |
Recently astronomers announced the discovery of the youngest black hole yet found, which we see as an object that’s roughly 30 years old. But the news created a bit of a stir, because the black hole lies in a galaxy that’s about 50 million light-years away.
Understanding the controversy means knowing the definition of a light-year. From Merriam-Webster:
Main Entry: light-year
: a unit of length in interstellar astronomy equal to the distance that light travels in one year in a vacuum, or 5,878,000,000,000 miles
In other words, a light-year isn’t a unit of time, but a unit of distance that’s based on light having a speed limit.
Seeing across the light-years: The Hubble Ultra Deep Field
—Image courtesy NASA, ESA, and R. Thompson (Univ. Arizona)
Scientists had been debating whether light has a finite speed since the time of the ancient Greeks. But it wasn’t until 1676 that Danish physicist Ole Christensen Rømer was able to prove it.
Rømer figured it out by watching Jupiter and measuring how long it took for the moon Io to reappear after its orbit took it behind the planet.
Because of the two planets’ relative distances from the sun, Earth and Jupiter orbit at different speeds, which is part of the reason the distance between the two planets varies over time.
Several years of data showed Rømer that Io reappeared faster when Earth was closer to Jupiter and took longer to reappear when Earth was farther away.
—Image courtesy NASA/JPL
Jupiter’s size wasn’t changing, though, so why would this be?
French astronomer Jean-Dominique Cassini, to whom Rømer was an assistant, suggested the effect might be due to the time it takes light to travel from the Jovian system to Earth.
Running with that hypothesis, Rømer used his data to calculate that light takes 22 minutes to travel a distance equal to the width of Earth’s orbit.
In truth Rømer was slightly off, because Earth’s orbital width wasn’t accurately known at the time. But if you combine modern data for Earth’s orbit with Rømer’s Jupiter data, you get pretty close to the currently accepted value for the speed of light.
Fast forward 162 years to the work of German astronomer Friedrich Wilhelm Bessel.
He was the first person to calculate the distance between Earth and a star other than the sun, 61 Cygni, using parallax, or the apparent change in position of an object when it’s seen from two different points along a baseline.
That’s a wonky way of putting it, I know, so try this: Sit at a desk and place a small cup about arm’s length in front of you. While sitting in place, focus on the cup and close one eye, then the other.
It’s subtle, but you should notice that the cup seems to jump from one position to another on the table—even though nothing is actually moving.
If you could calculate how much the cup “shifts” and combine that with the distance between your eyes, you’d be able to figure out the distance between you and the cup.
For objects as far away as stars, astronomers use Earth’s position along its orbit in place of two eyes, with the width of the orbit as a baseline.
Take a star’s position on dates separated by half a year, and you get the widest possible baseline. Even then, stars appear to shift by miniscule amounts, so this is a tricky calculation.
But Bessel managed it in 1838, calculating the distance to 61 Cygni as 10.3 light-years. By some accounts, he was also the first to use the term “light-year” as a unit of measurement in astronomy.
Today, no matter how we calculate distance in astronomy, the figures are often expressed in light-years, because it’s a great way to think about things on such huge scales.
Confusion sets in when we start talking about age.
The speed of light is really fast, so on Earth-scale distances, you can be pretty sure that when you meet a 30-year-old person, he or she appeared on this planet 30 years ago.
That 30-year-old black hole, meanwhile, is 50 million light-years away.
That means the light from the black hole (technically, the light from superheated material falling into the black hole) left its point of origin about 50 million years ago.
What we see from Earth is the way the black hole looked about 30 years after it formed, which is great for scientists who want to study how young black holes grow and evolve.
But if we could instantly transport to the black hole, the object we’d see would be about 50,000,030 years old.
Baby or senior citizen?
—Image courtesy NASA/CXC/SAO/D.Patnaude et al; ESO/VLT; NASA/JPL/Caltech
This makes things tricky when talking about objects from the early universe. These objects may be 13 billion years old, give or take, but we’re seeing them as they existed shortly after the big bang.
Depending on how you want to think about it, galaxies in pictures from Hubble’s deep observations, for example, are either among the youngest or the oldest objects yet seen.
Another interesting effect of this light-year business is that some of the structures we see today may, in fact, no longer exist—we just haven’t seen their destruction yet.
Add all this to the fact that the universe is expanding, and that expansion is accelerating. This means there may be some galaxies that started out so far away from Earth their light hasn’t reached us yet.
Since we’re moving away from these galaxies, we may be going fast enough that their light will never reach us, effectively meaning there are galaxies that we’ll never be able to see. | 0.905096 | 3.856255 |
50-foot ice spikes may dot Europa's surface
Jupiter's moon Europa is one of the most fascinating worlds in our solar system, with its slushy subsurface ocean a promising place to look for extraterrestrial life. While NASA has plans to possibly send a lander to the moon in the coming years, a new discovery might make touchdown tricky – there's a chance that large swathes of Europa's surface are covered in ice spikes almost 50 ft (15 m) high.
The new study, led by researchers at Cardiff University, investigated some of the smaller-scale features that might make up the surface of Europa. The team calculated that the conditions on the moon might be perfect for creating structures called penitentes – tall, jagged blades of ice.
Penitentes form through the process of sublimation, where ice skips the liquid water phase and turns straight from a solid into gaseous water vapor. For that to happen, you need sustained sunlight and cold, dry air, so here on Earth they form in high-altitude tropical areas like the Andes in South America. There's even evidence of a penitentes presence on Pluto.
And Europa, with its icy surface and consistent sunlight, might be paradise for them. The researchers used observational data to determine how fast sublimation might occur across different parts of the surface, and then used that to estimate where any potential penitentes might form and how big they could get.
The team found that these spiky icicles could get as tall as 49.2 ft (15 m), which is about three times the size of Earthly penitentes. They'd likely be spaced about 24.6 ft (7.5 m) apart, and would tend to cluster around Europa's equator.
"The unique conditions of Europa present both exciting exploratory possibilities and potentially treacherous danger," says Daniel Hobley, lead author of the study.
But why haven't these penitentes been spotted directly? Europa has been fairly well-studied over the decades, from afar by telescopes like Hubble and from relatively close-up by Voyager in the 1970s and Galileo in the 1990s. Those observations have helped scientists find evidence of an underground ocean and plumes spraying the liquid water into space.
But, the team says, the resolution of these images hasn't been high enough to see surface features down to the scale of a few meters. Given the thermal conditions there, penitentes could therefore be hiding on Europa's surface, but that's far from confirmed at this point. Other scientists suggest that Europan ice has a very different composition to Earth's, which might affect its sublimation.
Either way, with NASA's Europa Clipper due for a flyby within the next decade, a much higher-resolution peek at the moon's icy surface should bring some answers.
The research was published in the journal Nature Geoscience.
Source: Cardiff University | 0.838456 | 3.902969 |
There are millions of people who want to become astronomers, to look up at the night sky and try to discover what might be lurking in the cosmos.
But for those who want to do more than just look up at the night sky and play around with a telescope, there are ways to take steps to become a true amateur astronomer. From joining groups to getting the right equipment to choosing the right location, these tips will master the chances of being able to see the night sky.
The American Association of Amateur Astronomers
This quadruple “A” group has been an online haven of resources and guidance since 1996, offering news on the space industry. Their store also offers journals to help observers read up on what exactly they could be looking at when they peer through the telescopes.
They also offer a kit for beginner astronomers, filled with star charts, kits, binoculars, and even predicted dates for comets and meteor showers. Other programs also include a list of significant things that all amateur astronomers should observe in their lifetime, with tips to ensure that they all get to be observed.
The right type of gear
Believe it or not, having the highest powered telescope isn’t the way to get started in astronomy. The best way to get started is to simply look up. By training the eyes to look into stars and by mapping out the constellations, it can then lead to research to figure out what exactly is being watched.
Then there are different types of telescopes. Some are particularly good for getting a glance at the sky and zooming in and out, while others are practically mobile computers that can pinpoint exactly where in the world the telescope is looking and at what star or planetary body it is gazing at.
Some telescopes can even work in your mobile device and can be run from a tablet or phone with no trouble. Still, whichever one ends up being chosen, it’s important to ensure that it is durable and able to get a good view of the skies’ beauty.
The right place
Not all places are created equal, and this is especially apparent when it comes to stargazing. While backyards and small towns are very good for amateur stargazing, most people will eventually want to graduate and put their powerful technology for a test drive.
Several national parks, such as Big Bend, are often good choices for stargazers as these places have been untouched by nature and by artificial light. Spending an evening under those stars will show the power of the night sky like nothing else.
Observatories that are open to the public are also great places to see the stars up close and even observe planets with some real high powered machinery.
While stress about having the right gear and supplies for this hobby shouldn’t be a part of the stargazing experience, being knowledgeable about the right toys and places to practice astronomy will only make it more fun.
How Astronomy Outreach is Reaching the World
Astronomy outreach is needed now more than ever, in order to get the public and young people interested in astronomy… | 0.81114 | 3.461715 |
This study is a close exploration of the radical theory that the planet Saturn was once a sun, supported by the vast collection of ancient literary sources and comparative mythology between the greatest astronomically skilled cultures in history. This theory, popularized by 20th-century scholar Velikovsky, examines a possible cosmic event that may have inspired the original institutions of sun worship, along with its rippling evolution through time, all conspicuously aligned with the Biblical accounts.
In Mesopotamia and other ancient civilizations, descriptions of the Sun and the planets portray them in orbits and positions that would seem impossible according to our modern understanding. Sumerian hymns stored in the Louvre literary catalogue also tell of the planet-goddess Inanna (Venus) and her ability to eclipse the sun: “She darkens the bright daylight, turns the midday light into darkness.” Another such invocational hymn to Nergal (Mars) defies our entire understanding of cosmology as he is said to rise from the East: “You are horrifying like a flood, rising on the mountain where the sun rises.” Many more accounts likes these likewise show a radical inconsistency with the contemporary heavens, but are, however, consistent with the history of the respective planets in the polar configuration reconstructed by David Talbott, a long-time advocate of the concept’s modern progenitor, Immanuel Velikovsky. Many scholars have scratched their heads over the numerous analogous accounts of the ancients, who seem to have been inspired by a common view of the celestials, hinting at how the skies of their time might have looked much different than the skies of today.
Another curious text is found in the Popol Vuh, a mytho-historical corpus containing some of the oldest extant narratives of the Mayan people, which makes a bold assertion that the ancient world saw a different sun than the one we see now: “Like a man was the sun when it showed itself… It showed itself when it was born and remained fixed in the sky like a mirror. Certainly it was not the same sun which we see, it is said in their old tales.”
In the ancient world, there were seven classical planets, known as the “asteres planetai”, that is, the “wandering stars”. These seven luminaries were the Moon, Mercury, Venus, the Sun, Mars, Jupiter, and Saturn, placed in this order according to the Ptolemaic system, which determined their distance from the earth. The Romans used these seven to name each of the seven days of the week. They were the same seven recognized by the Babylonians, since these seven were the only major celestial bodies visible to the naked eye. In alchemy, each of them is associated with one of the seven metals known to the classical world—the Moon is silver, Mercury is mercury, Venus is copper, the Sun is gold, Mars is iron, Jupiter is tin, and Saturn is lead.
The curious things is, the Babylonians called the planet Saturn “Ninib”, an older rendering of “Ninurta”, who is in early commentaries a solar deity. In fact, Greek historian Diodorus of Sicily (90 BC – 30 BC) reported that the Chaldeans, renowned astronomers who ruled Babylon in the 6th century BC, called Kronos (Saturn) by the name “Helios”, which means “sun”, explaining that it was the most conspicuous star in the sky. Latin author Gaius Julius Hyginus (64 BC – AD 17) also noted that Saturn was referred to as “Sol”, also meaning “sun”. Roman Stoic Philosopher Seneca (4 BC – AD 65) wrote that Greek astrologer Epigenes of Byzantium (approx. 200 BC) “estimates that the planet Saturn exerts the greatest influence upon all the movements of celestial bodies.” The Greeks also called Saturn “Phaenon”, which means “the shinging one”—odd, considering that Saturn’s remoteness made it appear darkest of the seven asteres planetai.
Ancient Babylonian literary sources say: “We learn from the notes written by the astrologers that by the word ‘sun’ we must understand the ‘star of the sun,’ i.e., Saturn” (No. 176 in archive of ancient astrological reports). The text is “Mul (il) Šamaš šu-u”. The word “Šamaš” (Shamash) is the name of the Babylonian sun god. In a more accurate rendering of this text, seeing as there is a division mark between “Mul” and “Šamaš”, it should read “Planet Saturn (as a) star is Shamash” or “Saturn is the sun-star”. We also know that the original scribe’s reference to Saturn is not mistaking it for the Sun, but rather, it tells us that what was once called the sun is the same astral body that we presently call Saturn. Consider the text “(Mul) Lu-Bat Sag-Uš ina tarbas Sin izzaz”, which translates to “Saturn stands in the halo of the moon”. This cannot refer to the present Sun, because the effect of a moon’s halo only occurs at night. It therefore acknowledges that Saturn is indeed a nighttime star, yet the claim is that it used to be the Sun.
Since the planet Saturn has an entirely gaseous atmosphere in constant motion, just like the Sun, it’s plausible that it used to be a solar body itself. Its decline in luminosity can be explained by a nova. If a sudden influx of matter generates instability in a star, its approach towards another astral body can cause a violent stellar explosion in a mutual disturbance between the two atmospheres. The only other planetary body capable of causing such an event is Jupiter, the “king planet”, which is also the planet closest in proximity to Saturn for the majority of its orbit. Saturn and Jupiter are both densely covered with gaseous atmospheres, lending further credence to the possibility of this historical scenario, and the mass of Jupiter itself indicates that it is the only planet that would have been capable of causing this effect on Saturn. If this occurred in ancient history, then these planets, and the entire view of the heavens, would have appeared much different at one time. This theory is not only possible, but probable, considering what we know about Saturn and Jupiter’s thermal properties and remarkably star-like composition.
The Russian-Jewish scholar Immanuel Velikovsky developed this theory in his own independent research, reasoning that, being almost ten times farther away from the Sun than the Earth, the average temperature of Saturn had to be around -155 degrees Celsius. This proved true, and was considerably hotter than previous estimates, explained by Velikovsky as being the “residual heat of the catastrophe in which Saturn was derailed from its orbit.” He also calculated that “the radioactivity that resulted from the catastrophe must still be pronounced on Saturn.” Astronomer Kenneth I. Kellerman’s observations and measurements at a wavelength of 21.3 centimeters revealed a temperature of 90 degrees Fahrenheit for the planet’s inner atmospheric layers. Textbooks such as Fred Whipple’s “Earth, Moon and Planets” were revised after these findings, speaking of a “room temperature” on Saturn, which had been recorded on the 21-centimeter band. Measurements at radio wavelengths of 50 and 100 centimeters respectively found temperatures of 240 degrees F. and 520 degrees F., which was considered “unusually high”. In Are the Jovian Planet’s ‘Failed’ Stars?, author D. McNally wrote, “Thus it appears that Saturn, like Jupiter, is not the entirely frozen wasteland it was once thought to be.” It was eventually accepted that an internal energy source must be inside of Saturn, and that it was, in fact, more like a star than a planet in many aspects. It does, however, still lack the sufficient mass to function as an actual star. In the textbook Icarus 31, page 315, the stated measurements show how the far-infrared and submillimeter ranges indicate that the internal energy source on Saturn lies “within the range of 2.3 to 3.2 times the absorbed solar flux”, which means that Saturn gives off about three times the amount of energy it receives from the Sun. In 1980, the measurements retrieved by NASA’s Pioneer 11 space probe during its flight past Saturn revealed that the planet’s interior has a temperature exceeding 10,000 degrees Kelvin, which is much hotter than the Sun’s internal temperature of less than 6,000 degrees Kelvin.
This theory is greatly supported by classical mythology. Consider the Greco-Roman stories of Saturn/Kronos being overthrown by his son Jupiter/Zeus, a symbolic representation of the planet Jupiter vanishing the Sun’s light and displacing its heavenly position.
In Egyptian mythology, Osiris was equated to the Roman Saturn, and he descended into the underworld when the throne was taken over by his son Horus, who is in all sources equated with Jupiter. Said by Diodorus and Macrobius to have been a sun god who descended into the underworld, Osiris was invariably depicted with shadowy skin—either dark green or pitch black—which represented his dominion in the underworld. Again, this lore tells the same account of the Sun diminishing from its heavenly station to become the darkest of the seven classical planets.
This is fascinating because researchers of comparative mythology know that the Egyptians’ religion stemmed from the Babylonians, and the Greeks’ religion stemmed from the Egyptians, and the Romans’ religion stemmed from the Greeks. All of these myths throughout history depict the same pantheon, which is probably the symbolic portrayal of a real cosmic event that took place, a celestial drama retold as the story of these mythical gods.
Ancient Babylon fits the same pattern through ancient hymns that equate the god Tammuz with the sun-god Shamash. Professor Stephen Langdon, a 20th-century American Assyriologist, notes that Tammuz is called either “Damu” or “Dumuzi”, who was in mythology drowned beneath the river Euphrates. The ancient hymns plead for his resurrection, “O Damu, from the river arise…” This is why Ezekiel 8:14 mentions the age-old female ritual of “weeping for Tammuz”. Other Babylonian hymns say of him “O my exalted one, who is like Shamash? Thou art like Shamash” (See Ch. 11, p. 343 of Mythology of All Races V). More ancient liturgical texts reveal, “The flood has taken Tammuz” (See Ch. 15 of Tammuz and Ishtar).
So, in the Babylonian hymns, we see an illustration of a sun-god being drowned by a flood. This is an important clue as to the possible timing of Saturn’s decline from solar status.
In Greek mythology, the Golden Age was the first of the ages. It was said to have been ruled over by the god Pan, who is the same as the later identified Kronos, or Saturn. In fact, Pan was a type of he-goat called a “satyr”, which derives from the same root word as “Saturnus”, and “Kronos” comes from the ancient Semitic word “qrn”, which means “horn”, effectively making Kronos/Saturn the “horned god” (think of words like Capricorn, tricorn, unicorn, etc…). It was said that the end of the Golden Age was marked by the death of Pan. This is, in fact, the only pagan deity whose death is recorded, recounted in Plutarch’s “The Obsolescence of Oracles”.
If Pan, Kronos, Saturn, Osiris and Tammuz are indeed one in the same, personifications of the ancient sun, then the end of the Golden Age as marked by his death again portrays the planet Saturn’s decline from solar status. And, the ancient Babylonian hymns tell us that it was “the flood” that drowned Tammuz. This strongly indicates that this cosmic event occurred at the time of the Biblical Deluge; furthermore, this cosmic shift in our solar system is likely what caused the disturbances that precipitated this globally destructive disaster. Remember, the Flood is spoken of in the ancient lore of over 250 cultures worldwide. The Book of Genesis tells us that people used to live hundreds of years before being reduced to only 120 years near the end of Noah’s life (Genesis 6:3). This is interesting because a study conducted by the Norwegian University of Science and Technology revealed that being born during a period of heightened solar activity can shorten a person’s life span. If the Sun truly has such a pivotal effect on the human life span, then it is probable that the shift between the former Sun (Saturn) and our present Sun is the cause for the subsequent shortening of mankind’s life span.
Now we know why it was called the “Golden Age”. The base metal gold has always represented the Sun, and it was the former Sun that ruled the pre-Flood time known as the antediluvian era. The Golden Age ended because the sun of that time literally faded to darkness and became a mere planet, Saturn, a story told in every major mythological account throughout classical antiquity.
In ancient Rome, the original date for the festival of Saturnalia was on December 17th, the first day of the astrological sign of Capricorn, relating Saturn to his role as the horned he-goat Pan from the Golden Age. Originally, the idea was that Saturnalia should be 16 days before the calends of the year. This was the dedication anniversary—”dies natalis”—of the Temple to Saturn in the Roman Forum in 497 BC. In ancient Babylon, this is the same time that Tammuz was said to be reborn, as the Sun began to return the fullness of its light subsequent to winter solstice. December 25th, now called “Christmas”, was referred to by ancient Mithraic cults as “Solis Invicti”, which means “Birthday of the Unconquered Sun”—hopefully, you can see that this was not Christ’s actual birthday, and that celebrating it as such accomplishes quite the opposite intention. Saturnalia’s close proximity to the winter solstice celebration just a few days afterwards related Saturn to the sun-god, a sequence possibly demonstrating how, chronologically, the fallen Saturn came before the more victorious sun that we see today.
The Roman Catholic symbol used in portraits to distinguish saints has always been a golden halo, an invention suspiciously absent from the Biblical scriptures. If the planet Saturn was once the sun of the ancient world, having its notably unique rings, it might have appeared as a shining ring of light. Via gnostic occultism, lingering remnants of Rome’s paganism probably continued to manifest within Roman Catholicism, and so, it isn’t farfetched to conceive that the early Catholic Church was still falsely attributing Christianity to ancient sun worship. The halo’s interchangeability with the golden disc supports the idea that this symbol is representative of the sun.
It should also be observed that, the idea of the former Sun becoming the planet Saturn is a perfect portrayal of the Judeo-Christian concept of Lucifer becoming Satan. The brightest of the heavenly stars became the darkest, just as the most luminous of the angels fell from Heaven and became the epitome of evil, from one extreme to the other. Ezekiel 28 tells us that Lucifer was “anointed as a guardian cherub”, “the signet of perfection, full of wisdom and perfect in beauty”. The name “Lucifer” itself, given in Isaiah 14:12, means “light-bearer”, from the Hebrew “Helel”, which can be translated as “bright star”, or “star of the morning”, as in the star that presides over daytime—the Sun. The prophet Isaiah wrote, “How you are fallen from heaven, O Lucifer, son of the morning!” This is perfectly describing the cosmic decline of solar Saturn—the brightest star that once ruled the morning was stripped of its light and cast off to become the most distant of the seven classical planets, and thus, the darkest. Light became darkness. Good became evil.
Isaiah 14:13 reads, “For you have said in your heart: ‘I will ascend into heaven, I will exalt my throne above the stars of God…”
Kronos/Saturn has also been called “Typhon”, from which comes his other title “Baal-Zephon”. The word “Zephon”, as in the Hebrew “Tsaphon”, can also mean “hidden”. “Saturn” comes from the word “סָתַר” (in English, “STR”), which means “to hide or conceal”. This name literally signifies how Saturn as a shining sun disappeared from the heavens for a period of time and reemerged as a tiny, distant star, which was portrayed in mythology as Osiris’ descent into the underworld, as well as Kronos/Saturn being imprisoned in Tartarus (the underworld) after being defeated by Zeus/Jupiter in the great war known as the Titanomachy. When Saturn reappeared as a distant star only a fraction of its former size, the ancients were still able to recognize it as their former Sun, as demonstrated by the Babylonian astrological records, and it was this very reemergence that told the story of the god’s death and rebirth, hence the Greek phoenix, based on the Egyptian Bennu, both cyclically rebirthing birds being directly related to the Sun in their mythology. Both Osiris and Kronos/Saturn are linked to the underworld by their chthonic nature, just as the planet Saturn was forevermore transformed into the darkest of the seven stars.
Acts 7:43 makes a reference of Amos 5:26 by mentioning a long-worshipped Ammonite deity known as “Moloch”, or “Remphan”, to whom infants were sacrificed alive as burnt offerings: “Yea, ye took up the tabernacle of Moloch, and the star of your god Remphan, figures which ye made to worship them…” The name “Remphan“, from the Greek Septuagint’s “Raiphan“, is taken from the Hebrew “Kewan“, stemming from the old Babylonian “Kayawanu“, which is the name for the planet Saturn. This is what is meant by “the star of your god”.
A small symbol can be seen in the illustration above on the right-hand side, along the hillside at the base of the idol. This symbol is called the “Sigil of Saturn”. It is a magical symbol dating back to medieval times, drawn from the “magic square” of Saturn, an ancient table of numbers believed to contain the magical essence of the planet. The sigil is drawn by tracing the numbers within the magic square in order. It is also a disguised hexagram—six-pointed star—also known as the “Seal of Solomon”. In ancient Babylon, the priests used to wear an amulet called “Sigilla Solis” (the Sun Seal), which contained numbers from 1 to 36, since their astrologers divided the stars of heaven into 36 constellations. If you add the numbers of any column either horizontally, vertically, or diagonally, the total is always 111. The sum of all six columns, horizontally or vertically, is therefore 666, a number visually represented by the hexagram symbol. This directly relates the hexagram to Babylonian sun-worship, thereby equating the two sigils of Saturn and the Sun. It’s also obvious that the magic square of Saturn is based on the Sun Seal’s similar square table of numbers.
This Sigil of Saturn is also the basis for the “Square and Compasses” emblem of Freemasonry.
Saturn has always been equated with the base metal lead, because Saturn is now the furthest from the Sun, therefore being as dark as lead, just like the shadowy skin of Osiris. This correlation to Osiris makes sense in terms of his diabolical characteristics, since the satyr god Pan, who was Kronos/Saturn/Osiris, is where we derive our modern image of Satan as having horns and goat-like features.
In the Bible, purely by analyzing the stars, the three magi knew that a king of all kings had been born in Bethlehem, which is how they found the cradle of the infant Jesus Christ. This denotes how the cosmic events depict what’s actually taking place in history, a sort of reflection of reality that we can see in the heavens to help us understand the story of life, which also means that history must have been predetermined before it began. In Genesis 1:14, the first listed purpose for the creation of the “lights in the firmament of the heaven” is that they are to be for “signs”, to “mark sacred appointments”.
Genesis 6:5 says that God sent the Flood because evil filled the earth: “Then the Lord saw that the wickedness of man was great in the earth, and that every intent of the thoughts of his heart was only evil continually.” If this antediluvian era was the same as the fabled Golden Age, then its dominion under the sun-god Saturn/Lucifer is precisely why it was considered so evil.
The Bible often refers to Satan as being “the ruler of this world” (John 12:31). It could be asserted that the decline of solar Saturn via Jupiter was the celestial depiction of Jesus Christ usurping Satan’s seat of authority over the earth, since the planet that overthrew Saturn was Jupiter, known as the “king planet”. Remember, Christ is called “the King of Kings”, and the Bible prophesies of Christ’s sovereign rule over the earth during the final millennial reign that follows His second-coming. The sign of Saturn’s darkening illustrates Lucifer’s descent into becoming Satan, after which Christ strips him of his temporal earthly authority.
In alchemy, the much sought-after Philosopher’s Stone was said to be the key material needed to transform lead into gold—lead representing Saturn, and gold representing the Sun. To transform one into the other is to depict darkness turning into light, that is, the triumph of Satan’s campaign to revive his former glory as Lucifer. In Virgil’s Fourth Eclogue, the Cumaean Sibyl, an ancient Apollonian priestess, is said to have spoken about a revived Golden Age: “Now the last age by Cumae’s Sibyl sung has come and gone, and the majestic roll of circling centuries begins anew: Astraea (Justice) returns, returns old Saturn’s reign.” This pagan prophecy of Saturn, who ruled the first Golden Age, speaks about him returning to rule the last age also. Interestingly, Luke 17:26 tells us that, at the time that Christ returns to the earth, it will be “just as it was in the days of Noah”. The days of Noah refers to the antediluvian era, the so-called Golden Age, thus the Sibyl’s prophecy signifies that this final period in history will be a revived age of Saturn-ruled paganism. Of course, the Bible prophesies of its failure, a quickly delivered terminus at the second-coming of Christ, but the idea clearly falls in line with the age-old endeavor to transform lead into gold, which is to transform Saturn back into the Sun, and Satan back into Lucifer—the fallen Devil’s futile aspiration to justify himself.
There is a circulating claim that Jesus Christ was yet another reincarnation or myth of this same Osirian/Saturnian sun-god, based on a few vague similarities; however, as historical scholars and theologians analyze in detail the many records of Christ’s life and teachings, it is quickly revealed that He was not only different than this preceding pagan deity, but in fact, He vehemently opposed this deity, regarding the Babylonian/Egyptian religion as the Devil’s own handiwork, as did the entire Old Testament to which He was entirely enmeshed. The theory is absurd and premature, and it denies that, whereas Christ was a real person historically recorded in both apostolic and Roman accounts, the gods of the pagan pantheon were but mere personifications of the stars, whose legends were symbolic of ancient cosmic events.
Archive of Ancient Astrological Reports: http://archive.org/stream/reportsofmagicia07thomuoft/reportsofmagicia07thomuoft_djvu.txt
Archive of Prof. Stephen Langdon’s “Mythology of All Races V”: http://archive.org/stream/MythologyOfAllRacesVolume5/MAR05_djvu.txt
Archive of Prof. Stephen Langdon’s “Tammuz and Ishtar”: http://archive.org/stream/cu31924029165914/cu31924029165914_djvu.txt
Bibliography and Other Sources:
[#2 p.163] Hyginus, Astronomica (ed. Bunte), II, 42, 6-10.
Diodorus, Bibl. Hist., II, 30, 3-4
Ev Cochrane, Martian Metamorphoses | 0.878058 | 3.10367 |
The sparkle from the stars in this newly discovered galaxy took about 13 billion years to be seen on Earth.
The cluster of stars, dust and gas – codenamed z8-GND-5296 – is the most distant ever to be seen in space.
Astronomers were able to calculate how many light years away it is from Earth using a special telescope in Hawaii.
Project leader Dr Steven Finkelstein, of Texas University, said: “We’re learning something about the distant universe. There are way more regions of very high star formation than we thought.”
The galaxy’s red colour implies it is rich in metal and churns out over 300 stars a year compared to the Milky Way’s two or three a year.
It is so distant, it is being seen at around 700 million years after the Big Bang, which occurred about 13.7 billion years ago.
Professor Bahram Mobasher, of California University, said: “By observing a galaxy that far back in time we can study the earliest formation of galaxies.”
He is hopeful of further finds by 2020 after more powerful telescopes in Hawaii and Chile and the James Webb space telescope become operational. | 0.808237 | 3.153426 |
The constellation Phoenix was created by Flemish astronomer Petrus Plancius in the 16th century, based upon the observations of Dutch explorers Pieter Dirkszoon Keyser and Frederick de Houtman who mapped the southern sky that century. It is named after the fabulous sacred bird from mythology, with the constellation’s brightest stellar object, an orange giant star called Ankaa, found 77 light years from Earth, and shining with an apparent magnitude of 2.37.
Located in the southern celestial hemisphere, Phoenix is the 37th largest constellation in the night sky and can be seen by observers situated between +32° and -80° of latitude. Its nearest neighboring constellations include Eridanus, Grus, Fornax, Hydrus, Sculptor and Tucana.
Johann Bayer Constellation Family
Phoenix is a member of the Johann Bayer family of constellations, together with Apus, Chamaeleon, Dorado, Grus, Hydrus, Indus, Musca, Pavo, Tucana and Volans.
The Phoenix is a mythical creature that is known as the sacred firebird throughout a number of ancient mythologies, including those of the Arabs, Chinese, Egyptians, Greeks, Persians, Romans, Indians, and Turks. Said to be as large as an eagle, the Phoenix had plumage that corresponds to the colors of fire, complete with red, gold and purple feathers and a scarlet and gold tail. This sacred firebird was also said to live anywhere from 500 to 1,400 years before reaching the end of its life span, after which it would create a nest for itself in a palm tree with cinnamon bark and incense before combusting the nest and perishing in the flames. From there, according to legend, a new firebird would be born from its predecessor’s ashes, with the whole process taken to symbolize rebirth and immortality.
– Ankaa (Alpha Phoenicis), the constellation’s brightest star, is an orange giant (K0.5 IIIb) located 77 light years from our solar system that shines with an apparent visual magnitude of 2.37. It is in actual fact a binary system in which its component stars orbit each other once every 10.5 years. Its name originates from the Arabic word al-‘anqa, meaning “Phoenix”, although the star is also sometimes known as Nair al-Zaurak, which means “the bright star of the skiff.”
– Beta Phoenicis, the second brightest star in the constellation Phoenix, is a binary star system found 198 light years away, and consisting of two yellow giants of apparent magnitudes 4.0 and 4.1 which orbit each other once every 168 years. They are given the spectral class G8IIIvar, and together shine with a combined visual magnitude measuring 3.32.
– Gamma Phoenicis is assigned the spectral class M0IIIa, meaning that it is a red giant star. It is located about 234 light years away, and possesses a visual magnitude of 3.41, although it is actually a variable star whose magnitude varies from between 3.39 and 3.49.
Other stars of interest in Grus includes the white subgiants Kappa Phoenicis and Eta Phoenicis; the white dwarfs Iota Phoenicis and Lambda-1 Phoenicis; the yellow-white dwarf Nu Phoenicis; the orange giant Epsilon Phoenicis; the yellow giants Delta Phoenicis and Mu Phoenicis; the red giant Psi Phoenicis; and the binary system Zeta Phoenicis.
Notable Deep Sky Objects
The constellation does not contain any Messier objects, but it does have a number of notable deep-sky objects.
– The Phoenix Cluster, located 5.7 billion light-years away, is one of the largest-known galaxy clusters, and is believed to contain around 3 trillion stars inside its 7.3 million light years wide expanse. It forms around 740 stars annually, representing the highest rate ever documented inside a galaxy cluster, and also emits more x-rays than any other galaxy cluster observed. The galaxy at its center contains huge amounts of hot gas, and there is a supermassive black hole located in the center of the system that has 20 billion times the mass of our Sun, and is expanding at a rate of about 60 solar masses a year.
– Robert’s Quartet is a small group of galaxies found about 160 million light years away from the Sun that have a combined visual magnitude that nears 13. These four galaxies (NGC 92, NGC 89, NCG 88 and NGC 87) span a total area of 75,000 light years, and are currently in the process of colliding and merging with each other. They were first discovered by the English astronomer John Herschel in the 1830s.
– NGC 625 is a barred spiral galaxy that is around 12.7 million light years away, and has a visual magnitude of 11.7. It is a member of the Sculptor Group found near the south galactic pole.
There are two meteor showers associated with the constellation Phoenix, the most prolific of which is called the Phoenicids, having been named after the location of their radiant. The Phoenicids are associated with the comet D/1819 W1, and are best seen in the Southern Hemisphere from 29th November to 9th December, with the shower peaking around 5/6th December when anything upwards of 5 meteors per hour can be observed.
The other minor meteor shower associated with the Phoenix constellation is called the July Phoenicid, whose peak on July 14th only results in around one meteor per hour. | 0.846246 | 3.596607 |
Venus’ lack of water
The Runaway Greenhouse
Earth’s gain of O2
Evolution according to the geological record
Titan’s dwindling CH4
What’s happening here.
Venus formed closer to the Sun, where H2O was
depleted compared to the building blocks of Earth.
Venus was warm enough to catastrophically loose all
it’s water in a Runaway Greenhouse event.*
* This further suggests that there is a tipping point for which
atmospheres can irreversibly reach an entirely different state.
Convection involves the rise of hot air, which is more buoyant than the overlying air.
This occurs fast enough that little heat is exchanged and the process is adiabatic.
Assume ideal gas: (1)
Include (2): (3)
First law of thermodynamics:
For adiabatic motion (dq=0):
And hydrostatic equilibrium:
(radiative equilibrium) Optical depth due to vapor alone
Dry lapse rate
Flux not conserved
Assume hydrostatic equilibrium:
Write condensable mass density:
Assume grey atmosphere:
H is the humidity, Ps the saturation pressure, Pv is the
partial pressure of the vapor , k the absorption
coefficient, mv and m the mean molecular weights of the
vapor and the atmosphere, and g the gravity
Optical depth at Trc
Consider: K= 0.1 cm2/g (appropriate for 8-20 um window
H = 100%
m = 29 g (N2) and mv = 18 g (H2O)
g = 10 m/s
Po = 8 mm Hg
Fmax = 0.63 cal cm-2 min-1
T = 260 K
Average incident sunlight on Earth is 0.5 cal cm-2 min-1
Average incident sunlight on Earth is 0.9 cal cm-2 min-1
But the albedos of Earth is 0.3 and for Venus is 0.78
So… both Venus and Earth absorb 0.3
They are subcritical.
But what if Venus was not as cloudy as in the past
Note: runaway greenhouses grow from below
Atmosphere is transparent at short wavelengths
This prohibits vast cloud cover above the Trc level
Surface has a large condensable reservoir
When vaporized the condensable is optically thick at
However, this study indicates that an atmosphere can reach a tipping point,
beyond which a planet irreversibly ends up in a radically different state.
Titan Ganymede Callisto
R=2575 km R=2631 km R=2410 km
d=1.88 gm/cm3 d=1.93 gm/cm3 d=1.83 gm/cm3
Formed from different ices, perhaps with more carbon?
Acquired an atmosphere but lost it through impacts. (Griffith & Zahnle 1995)
How can a molecule or atom transition between 2 states?
LTE: the occupation is set by collisions and follows a Boltzmann distribution
Non-LTE: spontaneous and stimulated emission can depopulate states
Lunine, Stevenson and Yung 1982, Sagan & Dermott 1982
The atmosphere has the equivalent of 5 m of methane. It is close to saturation.
Just running out of methane after billions of years
Idea: CH4 outgassed early on, heated e.g. by accretion
Consequence: the surface has 0.5 km of organics*
Has a recent bout of geological activity & outgassing
Idea: Titan’s interior is freezing now, which circularizes the orbit
Advantage: Explains Titan’s non-circular orbit
Consequence: there are not a lot of organics coating the surface
Is in some sort of equilibrium with subsurface CH4
Idea: Subsurface aquifers or methanogens balance CH4 loss
Consequence: There’s more than meets the eye.
* The byproducts of CH4 & N2 photolysis
PCA analysis of Cassini Data
Griffith, in preparation
Composition of abundant elements likely established by
thermochemical equilibrium because hot and “surfaceless”
Secondary molecules affected by photochemistry
Complications: magnetospheric effects on atmospheric structure
and chemistry, disentangling host star & planet signals, and effects
of clouds on measurements of gas abundances and temporature
If hot, potentially somewhat in thermochemical equilibrium, but
surface interaction/effects are inevitable.
Complicated non-equilibrium effects inevitable and perhaps most
In situ measurements of V, E, M, J, A, T
Surface, Atmosphere, Magnetosphere, Ionosphere,
Spatially resolved observations (e.g. 1 meter by HiRISE)
Detailed information of the Sun’s attributes too
Greater breadth of conditions to test processes
E.g. The C/O ratio in giant planets
More photons (TMT)
More spectral coverage (JWST)
But not spatially resolved, nor in situ… or not…
A = Asteroid (Bennu, a carbonaceous asteroid) Mission: OSIRIS-Rex (University of Arizona)
The StarChip can be mass-produced at the cost of an iPhone and be sent on
missions in large numbers to provide redundancy and coverage
Light beam to propel gram-scale ‘nanocrafts’ to 20% speed of light could reach
Alpha Centauri (4.37 light years) within about 20 years of its launch.
StarChip: cameras, photon thrusters, power supply, navigation and communication
equipment, and constituting a fully functional space probe.
Lightsail: Advances in nanotechnology are producing increasingly thin and light-
weight metamaterials, promising to enable the fabrication of meter-scale sails no
more than a few hundred atoms thick and at gram-scale mass.
2. Light Beamer
The rising power and falling cost of lasers, consistent with Moore’s law, lead to
significant advances in light beaming technology. Meanwhile, phased arrays of
lasers (the ‘light beamer’) could potentially be scaled up to the 100 gigawatt level.
To be lead by Pete Worden, the former director of NASA AMES Research Center | 0.814568 | 3.754925 |
Cancer represents the crab that, in Greek mythology, was crushed underfoot by Hercules during his battle with the multiheaded Hydra. It lies between Gemini and Leo and is the faintest constellation of the Zodiac; its brightest star, Beta Cancri, is of magnitude 3.5. The Sun is within Cancer's boundaries from July 20th until August 10th.
Points of Interest
A multiple star. Through a small telescope, it is seen to consist of two stars, of magnitude 5.1 and 6.2. A telescope with an aperture larger than about 6 in (150 mm) will show that the brighter component has a much closer companion, of magnitude 6.1, which orbits it every 60 years.
An open cluster, also known as the Beehive cluster or the Manger. (Praesepe is Latin, meaning both manger and hive) It appears as a cloudy patch at the limit of naked-eye visibility - its brightest are of 6th magnitude, and it was known to the ancient Greeks - but binoculars show it as a field of stars more than three times the apparent width of the full Moon. It lies about 520 light-years away. To the north and south of the cluster are the stars Gamma Cancri (magnitude 4.7) and Delta Cancri (magnitude 3.9). In ancient times, these were visualized as donkeys feeding at the manger, hence they are known as the aselli, or asses.
M67 (Open Cluster)
An open cluster. It contains more stars than M44 (Praesepe), but it is farther away from us (about 2,600 light-years) and so appears fainter and smaller. | 0.817785 | 3.110769 |
This is a plan for a star party with some constraints:
- Bright lighting (expected to be used at community events, at places such as school with property lights on)
- Young observers (Scout or school audiences)
- July (summer objects)
- Early evening (twilight ends between 8:30 and 9:00). I expect to use this on evenings when the Moon does not rise till later. On nights when the Moon is up you could add that; it’s a good target for kids. Because the other targets in this plan are bright, they should work acceptably in moonlight.
- Bright objects, easy to find and mostly also visible to the kids’ naked eyes
- Examples of the major categories of sky objects
- Fun, large, colorful objects that kids tend to appreciate more than small faint fuzzies
Plan by type of object
Different planets are visible in the evening from year to year. You will need to look up what is visible when you use this plan. The bright, easy-to-see planets that might be in the sky in the evening are:
- Mercury (but it is always difficult to find low on the horizon
Everybody has heard of Mars, but it usually appears as only a pale orange dot. It is exciting when you know what it is, or if you can see surface features at high magnification, but Mars is usually not a successful choice for an easy target with youth.
Only occasionally does a bright comet appear in the sky. If you hear of an opportunity to show one, take advantage of it.
The best nebulas are easy to see in other parts of the year.
The Milky Way contains many dust lanes, best seen now.
- Trifid Nebula M20 in Sagittarius.
- The Milky Way is high, spanning most of the sky in the summer..
- The Whirlpool Galaxy M51 in Canes Venatici. A faint fuzzy, and so not a great target for kids, unless high magnification can make the spiral structure visible.
- M81 and M82 in Ursa Major. Faint fuzzies, but the close association may give a feeling for how common galaxies are.
- The Big Dipper in Ursa Major, though it is so spread out it does not impress kids as a cluster. All but two of its stars are in the Ursa Major Moving Group. Technically, it has spread out more than groups we typically call clusters.
- Coma Berenices Cluster Mellotte 110 in Coma Berenices, high between Ursa Major’s handle and Virgo. Technically the entire constallation is not a cluster, but the Coma Berenices Cluster dominates the constellation.
All globulars look like small faint fuzzies to kids. But summer features two that illustrate what a globular is:
- The Great Hercules Cluster M13 in Hercules. Best example.
- M3 globular cluster in Canes Venatici. Difficult to find. Right ascension 13h 42m 11.62s, Declination +28° 22′ 38.2″, halfway along a line from Arcturus to Cor Caroli.
- Dumbell Nebula M27 in Vulpecula, between Cygnus and Delphinius. Rises late at night in the spring, easier to find in the summer. Among the brightest planetary nebulas. Right ascension 19h 59m 36.340s Declination +22° 43′ 16.09″
- Arcturus in Bootes (red giant, some class it as yellow)
- Antares in Scorpius (red giant)
- Regulus in Leo (blue giant)
- ρ (rho) Cassiopeiae is a yellow hypergiant, a very rare type of star. 23h 54m 23.0s +57° 29′ 58″. Below the line of Cassiopea formed by α (alpha) and β (beta).
- La Superba Y Canum Venaticorum, red carbon star in Canes Venatici. 12h 45m 24.2s +45° 24′ 49″.
- Albireo, beta Cygni in Cygnus. Many consider this the most beautiful double star in the sky.
- Mizar and Alcor in Ursa Major
- ι (iota) Cassiopeiae in Cassiopea
- Polaris (you will need high magnification to split the double)
- Cor Caroli carbon star in Canes Venatici, high, under the handle of the Big Dipper
- Ursa Major, with asterism Big Dipper upside down
- Ursa Minor, with asterism Little Dipper
- Canes Venatici
- Corona Borealis
- Coma Berenices
- Zodiacal constellations:
- Summer Triangle, an asterism composed of
- Vega in Lyra
- Deneb in Cygnus
- Altair in Aquilla
Plan in target order
story of King Charles and the hunting dogs
High, beneath the handle of the Big Dipper.
Y Canum Venaticorum, red carbon star. 12h 45m 24.2s +45d 24′ 49″
α (alpha) Canum Venaticorum, double star
belongs to the story of Andromeda and Perseus
ι (iota) Cassiopeiae
story of creation of constellation, Rotating Man and Woman
Mizar and Alcor
Most likely an optical double, though uncertainty in the measurements is an interesting science lesson. Mizar is a 4-star system.
double star (now known to be a triple, the third member only recently seen for the first time)
Story of a Star Life
- Sagittarius Star Cloud
- Birthplace of stars.
- A main sequence star.
- Example of planet formation. Rings are common.
- Albiereo in Cygnus
- Many stars are found in pairs.
- Coma Berenices
- Open cluster. Stars are often born together, and are found in clusters after their creation.
- Great Hercules Globular Cluster M13
- A larger grouping of stars.
- Milky Way Galaxy
- An even larger grouping of stars. Galaxies are important structures in the larger universe.
- A blue giant. A large star may become this instead of a main sequence star.
- A red giant. A main sequence star in old age may become this.
- Dumbell Nebula M27 in Vulpecula
- A planetary nebula. An older star sheds its outer layer to make a nebula. This is the brightest summer candidate.
- Polaris B
- A white dwarf is the core remnant after a giant loses mass. We probably won’t be able to distinguish the white dwarf
- Crab Nebula M1
- A supernova remnant. A supernova is another possible end of star life. This is not easy to see. A supernova might leave behind a white dwarf, a neutron star, or a black hole.
- Sagittarius A*
- A black hole. You can’t actually see it, but you can point out the location of the black hole at the center of our own galaxy. A black hole is another possible end of star life. | 0.844528 | 3.30359 |
Herschel, an ESA space observatory equipped with science instruments provided by European-led Principal Investigator consortia with important participation from NASA, was launched on 14 May 2009. With its 3.5m diameter primary mirror, Herschel is the largest space telescope ever launched into space, and carries onboard three science instruments, whose focal plane units are cryogenically cooled inside a superfluid helium cryostat. The PACS and SPIRE instruments provide broadband imaging photometry in six bands centred at 75, 100, 160, 250, 350, and 500 microns and imaging spectroscopy over the range 55–672 microns. The HIFI instrument provides very high-resolution heterodyne spectroscopy over the ranges 157–212 and 240–625 microns. The results obtained already in the first year and a half of routine science operations demonstrate that Herschel will have strong impact on all research fields, from Solar System studies to the area of Cosmology, from the analysis of star formation to the mysteries of galaxy formation. In this talk I will review the Herschel highlights in the area of evolved stars in general and of planetary nebulae more in particular, resulting from observations performed with the three instruments onboard Herschel since launch. This will be exemplified by a few observational results, just the tip of the iceberg of what is yet to come in the remaining year and a half of science operations. | 0.890706 | 3.0612 |
Kathryn Volk (U. British Columbia)
Kepler revealed the common existence of tightly-packed planetary systems around solar-type stars, existing entirely on orbits with periods shorter than ~200 days. Those systems must have survived for the ages of their host stars (~5 Gyr), so their formation mechanism must provide inter-planet spacings that permit long-term stability. If one postulates that most planetary systems form with tightly-packed inner planets, their current absence in some systems could be explained by the collisional destruction of the inner system after a period of meta-stability. The signatures of such intense collisional environments may have been observed around stars in the form of rapidly varying debris disks; in these observed disks, collisional products are being disposed of via drag down onto the star or grinding to the nearly instantaneous dust blow-out limit. We use the orbital spacings and planet masses of the observed Kepler multi-planet systems to investigate the stability and long-term behavior of the systems. We find that many of our Kepler system analogs are unstable on 100 Myr timescales, even for initially small eccentricities (0-0.05); the instability timescales in these systems are distributed such that equal fractions of the systems experience planetary collisions in each decade in time. We discuss the likely outcomes of collisions in these systems based on the typical collision speeds from our numerical integrations and what implications this has for interpreting the observed Kepler multi-planet systems. The possible implications for our Solar System are discussed in a companion abstract (Gladman and Volk).
- Architectures of close-in (closely packed) planetary systems (from Kepler)
- Fabrycky 2014
- ~5-10% ofFGK field stars
- These systems must be stable on Gyr timescales
- Are all stars formed tightly packed?
- Modeled 13 such Kepler systems
- Preserved $a$ and masses, orbital angles randomized
- Allowed $e_0$ to vary $0 < e_0 < 0.05$
- Sudden onset of instability in 11 of these 13 after tens to ~100 Myr
- [why is she surprised?]
- These eccentricities are in range of observed values
- Decay rates consistent with e.g. Holman & Wisdom (1992 AJ)
- Why sudden onset?
- History is very sensitive to ICs [duh]
- Consolidation (low-speed collisions) vs. Destruction (high-speed collisions)
- First collision is often near the accretion/erosion boundary — i.e., low-speed
- Masses in 4-5 planet systems tend to be lower, while individual masses in ~3-planet systems are higher: mergers?
- Tracked collision speeds during integrations.
- Second collision often goes into erosion regime (i.e., high-speed)
- Observing debris should be rare (but see Meng et al. 2012)
- Ergodicity allows large variety of outcomes
- $\Rightarrow$ tightly packed systems could be ubiquitous initially
- Young stars should show higher fraction
- The remaining ~95% should be 0-2 planet systems | 0.831524 | 4.069983 |
Mechanical failures interrupted Kepler’s original mission, but the telescope is still hunting exoplanets. From http://www.nature.com/news/three-super-earth-exoplanets-seen-orbiting-nearby-star-1.16740.
Discussed a brilliant paper today in journal club from Ian Crossfield and collaborators, in which they announce the discovery of a three-planet system around a nearby M-dwarf star.
The team found the new system in data from the re-incarnated Kepler mission called K2. This system is only the second discovered by the mission (the first was announced a few months ago).
This new system is especially exciting because, as the authors point out, it is observable by other available facilities, allowing astronomers to characterize the planets and star in detail.
The outermost planet in the system, with an orbital period of 45 days, is very near the inner edge of the system’s habitable zone and has a temperature of about 310 K (100 F), making it plausibly habitable. Combined with the fact that we can probably characterize the planet in detail, there’ll probably be a flurry of exciting studies of the system very soon.
Journal club was attended by Jennifer Briggs, Trent Garrett, Nathan Grigsby, Emily Jensen, Liz Kandziolka, and Brenton Peck.
Three planets in the Kepler-11 system as they simultaneously transit their star as imagined by by a NASA artist (Image credit: NASA). From http://ciera.northwestern.edu/Research/highlights/research_highlights.php#ForeignWorlds.
Great finish to the meeting, and thankfully no big disasters at my special session.
Lots of excellent talks, but the talk that stood out for me was Sarah Ballard’s, in which she addressed an impressively simple but compelling question: Is there a difference between planetary systems where we’ve only found one planet and systems where we’ve found more than one?
This question is important because such a difference could point to different formation and/or evolutionary processes in these systems, and so comparison of these systems could elucidate subtle but significant aspects of planet formation.
In fact, Ballard did find the two types of planetary system are different, and that, for some reason, about half of M-dwarf stars that host planets have only one.
She also found modest but intriguing differences in the stars that host single planet: their features suggest they may be older than stars with multi-planet systems. Does that mean that single-planet stars used to have multiple planets but enough time has passed that the system became dynamically unstable, leaving behind a single planet?
Blue glacial ice. From http://upload.wikimedia.org/wikipedia/commons/1/10/JoekullsarlonBlueBlockOfIce.jpg.
I really enjoyed Aomawa Shields‘s dissertation talk in the “Extrasolar Planets: Host Stars and Interactions” session, in which she discussed how different stellar types could influence the climates of putative Earth-like planets.
She highlighted how the ice-albedo feedback would operate differently on planets orbiting M-dwarfs as compared to those orbiting F-stars. Since they are so cool, M-dwarfs shine primarily in infrared (IR) wavelengths, while F-stars are much hotter and emit in the visible and ultraviolet (UV). At the same time, water ice primarily absorbs IR but reflects visible light.
Therefore, around an M-dwarf, the ice on an Earth-like planet’s surface would absorb a lot of the stellar insolation, heating the planet, while around an F-star, the ice would reflect it, keeping the planet cool. As a consequence, Shields argued that M-dwarf planets have climates more stable against global ice ages than F-star planets. So although there may be other challenges to life on an M-dwarf planet, climate stability is probably not one of them.
The radial velocity method to detect exoplanet is based on the detection of variations in the velocity of the central star, due to the changing direction of the gravitational pull from an (unseen) exoplanet as it orbits the star. From http://en.wikipedia.org/wiki/Doppler_spectroscopy#mediaviewer/File:ESO_-_The_Radial_Velocity_Method_%28by%29.jpg.
Another great day at the AAS meeting. One talk that stuck out for me was the dissertation talk from Ben Nelson (PSU). I was amazed at how much he was able to squeeze into his 15 minutes and still not lose the audience.
Among the things he covered was his new MCMC code, RUNDMC, specially suited to analyze radial velocity (RV) observations of planetary systems and thoroughly but quickly sample the sprawling parameter space associated with these systems. He applied his code to several systems to understand how robustly different planetary configurations could be detected in those systems, including whether the RV data favored additional planets in a system or other kinds of variability.
Lots of amazing presentations today, running the gamut from transmission spectroscopy of hot Neptune-like planets to the detailed and puzzling architectures of multi-planet systems. But two talks really stuck out for me.
The first one, by Prof. Dan Baker at U Colorado, covered recent developments in the study of the Van Allen radiation belts (which Van Allen preferred to call “zones” — when asked by a reporter what was the function of Van Allen belts, he said they hold up Van Allen’s pants). As a member of the Radiation Belt Storm Probe mission, Baker explained what we understand and what remains mysterious about these powerful celestial phenomena suspended above our heads, including a bizarre “glass wall” that keeps charged particles at bay.
The European Space Agency’s Rosetta spacecraft captured these photos of the Philae lander descending toward, and then bouncing off, the surface of Comet 67P/Churyumov–Gerasimenko during its historic touchdown on Nov. 12, 2014. Credit: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/ID — http://www.space.com/27788-philae-comet-landing-bounce-photos.html
In the afternoon, Dr. Paul Weissman gave the most recent updates on the Rosetta mission, still in orbit around Comet Churyumov-Gerasimenko (which Weissman called “comet CG”). Following up on the more-exciting-than-expected landing of the Philae spacecraft, Weissman explained that the lander struck a surprisingly hard sub-surface layer (comparable in strength to solid ice), which probably contributed to the lander’s unplanned ballistic trajectory around the comet. Lots of other interesting science, including more evidence about the origin of Earth’s water.
Day 2 of the workshop was just as great as day 1. Lots of great resources, but the one that really stood out for me was the seaborn plotting module for matplotlib — just produces some amazing plots, have a look.
Onto the rest of the conference!
The new year finds me in Seattle two days before the AAS 225 meeting officially begins to attend the Software Carpentry workshop. This workshop is put on by a volunteer organization that teaches scientists how to write and maintain robust code.
On the first day, we covered some shell scripting, basic python, and the ipython notebook. Just the first few lessons are already hugely useful for me, and the teachers are doing a great job explaining things clearly. They are also using a variety of tools to record and document the workshop. I’ve pasted links to those records below.
Very much looking forward to Day 2.
Useful links and particularly useful notes: | 0.944361 | 3.608991 |
Watch earth satellites transit our vernal equinox sky
The Sun climbs northwards at its fastest for the year in March and crosses the sky’s equator at 21:58 on the 20th, the time of our vernal or spring equinox. As the days lengthen rapidly, the stars in the evening sky appear to drift sharply westwards so that Orion, which is astride the meridian as the night begins on the 1st, stands 45° over in the south-west by nightfall on the 31st.
Another consequence of the Sun’s motion is that the Earth’s shadow, on the night side of the planet, is tilting increasingly southwards so that it no longer reaches so far above Scotland at midnight. Indeed, by the end of March the shadow is shallow enough that satellites passing a few hundred kilometres above our heads may be illuminated by the Sun at any time of night. This allows them to appear as moving points of light against the stars as they take a few minutes to cross the sky. Some are steady in brightness while others pulsate or flash as they tumble or spin in orbit.
Dozens of satellites are naked-eye-visible every night, while many times this number may be glimpsed through binoculars. Predictions of when and where to look, including plots of their tracks against the stars, may be obtained online for free, or example from heavens-above.com, or via smartphone apps. Of particular interest are the so-called Iridium satellites which can outshine every other object in the sky, bar the Sun and Moon, during brief flares when their orientation to the Sun and the observer is just right. Although online predictions also include these, Iridium flares are falling rapidly in frequency since the satellites responsible are being deorbited as they are replaced by 2nd generation (and non-flaring) craft.
The most obvious steadily-shining satellite is, of course, the International Space Station which can outshine Sirius as it transits up to 40° high from west to east across Edinburgh’s southern sky. As it orbits the Earth every 93 minutes at a height near 405 km, it is visible before dawn until about the 15th and begins a series of evening passes a week later.
Sunrise/sunset times for Edinburgh change from 07:05/17:46 GMT on the 1st to 05:47/18:48 GMT (06:47/19:48 BST) on the 31st which is the day that we set our clocks to British Summer Time.
The Moon is new on the 6th and spectacular over the following days as its brightly earthlit crescent stands higher each evening in the west-south-west. Catch the Moon 12° below Mars on the 10th and 6° below and left of the planet on the 11th. Mars itself stands around 30° high in the west-south-west at nightfall and is well to the north of west when it sets before midnight. This month it dims from magnitude 1.2 to 1.4 as it speeds more than 20° north-eastwards from Aries into Taurus to end the period only 3° below-left of the Pleiades.
Mercury has been enjoying its best spell of evening visibility this year, but is now fading rapidly and may be lost from view by the 7th. Binoculars show it shining at magnitude 0.1 on the 1st as it stands 10° directly above the sunset position forty minutes after sunset.
The Moon and planets never stray far from the ecliptic, the line around the sky that traces the apparent path of the Sun during our Earth’s orbit. The ecliptic slants steeply across our south-west at nightfall towards the Sun’s most northerly point which it reaches to the north of Orion at our summer solstice in June.
Given a clear dark evening, this is the best time of year to spy a broad cone of light stretching along the ecliptic from the last of the fading twilight. Dubbed the zodiacal light, this glow comes from sunlight scattering from interplanetary dust particles and was the subject on which Brian May, the lead guitarist of Queen, gained his doctorate.
As the Moon continues around the sky, it reaches first quarter on the 14th and passes just north of the star Regulus in Leo on the night of the 18/19th. Regulus, 45° high on Edinburgh’s meridian at our map times, lies less than a Moon’s breadth above the ecliptic and marks the handle of the Sickle of Leo.
Algieba in the Sickle is a splendid binary whose contrasting orange and yellow component stars lie 4.7 arcseconds apart and may be separated telescopically as they orbit each other every 510 years or so. The larger of the pair has at least one companion which may be a planet much larger than Jupiter or, perhaps, a brown dwarf star.
Between full moon on the 21st and last quarter on the 28th, the Moon passes very close to the conspicuous planet Jupiter on the 27th. The giant planet rises in the south-east in the small hours and is unmistakable at magnitude -2.0 to -2.2 low in the south before dawn where it is creeping eastwards against the stars of southern Ophiuchus.
The red supergiant star Antares in Scorpius lies some 13° to the right of Jupiter while Saturn, fainter at magnitude 0.6, is twice this distance to Jupiter’s left and lower in the twilight. Look for Saturn to the Moon’s left on the 1st and just above the Moon on the 29th.
Venus is brilliant (magnitude -4.1) but becoming hard to spot very low down in our morning twilight. More than 10° to the left of Saturn as the month begins and rushing further away, it rises in the south-east 81 minutes before sunrise tomorrow and only 39 minutes before on the 31st.
Diary for 2019 March
1st 18h Moon 0.3° N of Saturn
2nd 21h Moon 1.2° S of Venus
6th 16h New moon
7th 01h Neptune in conjunction with Sun
11th 12h Moon 6° S of Mars
13th 11h Moon 1.9° N of Aldebaran
14th 10h First quarter
15th 02h Mercury in inferior conjunction
17th 13h Moon 0.1° S of Praesepe
19th 00h Moon 2.6° N of Regulus
20th 21:58 Vernal equinox
21st 02h Full moon
27th 02h Moon 1.9° N of Jupiter
28th 04h Last quarter
29th 05h Moon 0.1° S of Saturn
30th 10h Mars 3° S of Pleiades
31st 01h GMT = 02h BST Start of British Summer Time
This is a slightly revised version, with added diary, of Alan’s article published in The Scotsman on February 28th 2019, with thanks to the newspaper for permission to republish here.
The mysterious noctilucent clouds of summer
If we are prepared to do battle with June’s night-long twilight, and provided the weather improves at last, there is plenty of interest in our June sky. Saturn is the pick of the planets while the bright star Vega in Lyra leads the onslaught as the constellations of summer invade from the east at our star map times. We also need to be alert for noctilucent clouds as they make their seasonal appearance low in our northern sky.
The Sun is furthest north at 11:51 BST on the 21st, the instant of our summer solstice. On that day, the Sun dips only 10.6° below Edinburgh’s northern horizon in the middle of the night, so that our sky remains bathed in twilight throughout the night while from further north in Scotland the sky is brighter still. This obviously impedes our ability to see the dimmer stars and “faint fuzzies” such as galaxies and nebulae. On the other hand, it means that satellites remain sunlit whenever they pass overhead. Indeed, the International Space Station is conspicuous two or three times each night until 10 June as it transits from west to east across Scotland’s southern sky – visit heavens-above.com for predictions customised for your location.
The Sun’s shallow sweep below our northern horizon overnight also allows us occasional views of noctilucent or “night-shining” clouds. Composed of tiny ice crystals in a thin layer at a height near 82 km, they catch the sunlight long after our usual low-level clouds are in darkness and can appear like chaotic banks of electric-blue cirrus, sometimes in a herringbone pattern. Their preferred direction follows the Sun around the horizon, so they are more commonly seen low in the north-west after nightfall and towards the north-east before dawn. They occur from mid-May to mid-August but why they are more frequent than they were a century ago remains a mystery. Could the rise be due to global warming, increased industrial pollution or even particles from rocket launches?
Sunrise/sunset times for Edinburgh change from 04:35/21:47 BST on the 1st to 04:26/22:03 on the 21st and 04:31/22:02 on the 30th. The Moon is at first quarter on the 5th, full on the 13th, at last quarter on the 19th and new on the 27th.
At magnitude -1.9, our brightest evening planet continues to be Jupiter, but we must look lower into the west to catch it below Pollux in Gemini as the twilight fades. Shining at magnitude -1.9, it stands 9° above-right of the Moon on the 1st. Jupiter sinks to set in the north-west almost three hours after the Sun as June begins but by the 30th it is only 6° high at sunset and may already be lost from view.
Mercury lies 18° below and to the right of Jupiter on the 1st but is one twentieth as bright at magnitude 1.4 and fading rapidly as it moves to pass through inferior conjunction between the Sun and Earth on the 19th.
The bright star Arcturus in Bootes stands high on the meridian at nightfall but has moved to the middle of our south-western sky by the map times. This leaves our high southern sky devoid of bright stars until we come to Vega in Lyra high in the east-south-east. Directly below Vega is Altair in Aquila while Deneb in Cygnus, almost due east, completes the Summer Triangle. The arc from Vega to Arcturus cuts through Hercules and Corona Borealis, the pretty semi-circular Northern Crown whose main star has the dual names of Alphecca or, perhaps more appropriately, Gemma.
Mars fades from magnitude -0.5 to 0.0 as it tracks eastwards in Virgo towards Spica. It also recedes from 119 million to 148 million km during the month as its small disk contracts from 12 to 9 arcseconds if viewed through a telescope. Look for its reddish light about 26° high in the south-west at nightfall and catch it above the Moon on the 7th. Our maps show it sinking towards the west where it sets two hours later.
Saturn, magnitude 0.2 to 0.4, stands almost 20° high in the south at nightfall at present and continues to creep westwards in Libra almost 4° above-left of the double star Zubenelgenubi. After standing close to Spica on the 8th, the Moon lies near Saturn on the 10th when the planet appears 18 arcseconds wide, its disk set within rings that span 41 arcseconds and have their north face inclined 21° towards us. Don’t miss an opportunity to observe it this month for it will soon be following Mars lower into the south-west at nightfall, and it stands even further south in our summer sky during every year until 2022.
Continuing as a brilliant morning star of magnitude -4.0 to -3.9, Venus rises above Edinburgh’s east-north-eastern horizon 61 minutes before the Sun tomorrow and in the north-east 102 minutes before sunrise on the 30th. Before dawn on the 24th, it lies 5° left of the slender waning Moon and 6° below the Pleiades in Taurus.
Last month, I reported the prediction that the Earth would slice through streams of particles from Comet 209P/LINEAR on the morning on 24 May and that the resulting meteor shower might be spectacular. In fact, it appears that the encounter occurred as forecast, but that the resulting display was disappointing with only a few bright meteors, even for observers in the Americas for whom the timing of the outburst was ideal. Radar studies suggest that the vast majority of meteoroids were unusually small and their meteors too dim to be seen by the unaided eye. | 0.86764 | 3.520664 |
Crescent ♉ Taurus
Moon phase on 20 March 2007 Tuesday is Waxing Crescent, 2 days young Moon is in Aries.Share this page: twitter facebook linkedin
Previous main lunar phase is the New Moon before 1 day on 19 March 2007 at 02:43.
Moon rises in the morning and sets in the evening. It is visible toward the southwest in early evening.
Moon is passing about ∠19° of ♈ Aries tropical zodiac sector.
Lunar disc appears visually 2.4% wider than solar disc. Moon and Sun apparent angular diameters are ∠1973" and ∠1927".
Next Full Moon is the Pink Moon of April 2007 after 13 days on 2 April 2007 at 17:15.
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 2 days young. Earth's natural satellite is moving from the beginning to the first part of current synodic month. This is lunation 89 of Meeus index or 1042 from Brown series.
Length of current 89 lunation is 29 days, 8 hours and 53 minutes. It is 1 hour and 2 minutes longer than next lunation 90 length.
Length of current synodic month is 3 hours and 51 minutes shorter than the mean length of synodic month, but it is still 2 hours and 18 minutes longer, compared to 21st century shortest.
This New Moon true anomaly is ∠348.7°. At beginning of next synodic month true anomaly will be ∠4°. 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 perigee on 19 March 2007 at 18:39 in ♈ Aries. The lunar orbit is getting wider, while the Moon is moving outward the Earth. It will keep this direction for the next 13 days, until it get to the point of next apogee on 3 April 2007 at 08:38 in ♎ Libra.
Moon is 363 305 km (225 747 mi) away from Earth on this date. Moon moves farther next 13 days until apogee, when Earth-Moon distance will reach 406 327 km (252 480 mi).
2 days after its ascending node on 18 March 2007 at 07:40 in ♓ Pisces, the Moon is following the northern part of its orbit for the next 10 days, until it will cross the ecliptic from North to South in descending node on 31 March 2007 at 11:41 in ♍ Virgo.
2 days after beginning of current draconic month in ♓ Pisces, the Moon is moving from the beginning to the first part of it.
7 days after previous South standstill on 12 March 2007 at 16:11 in ♐ Sagittarius, when Moon has reached southern declination of ∠-28.608°. Next 4 days the lunar orbit moves northward to face North declination of ∠28.582° in the next northern standstill on 25 March 2007 at 05:37 in ♊ Gemini.
After 13 days on 2 April 2007 at 17:15 in ♎ Libra, the Moon will be in Full Moon geocentric opposition with the Sun and this alignment forms next Sun-Earth-Moon syzygy. | 0.848363 | 3.230513 |
The mystery, which took place 100 years ago, on June 30, 1908, not far from the Tunguska River in Russia’s Siberia, still remains unraveled. Many compare the power of the Tunguska catastrophe with the nuclear explosion of Hiroshima and Nagasaki, although there were not so many casualties, since the meteorite or whatever it was fell down in the uninhabited area.
Science has not been able to explain the mysterious Tunguska phenomenon yet. Scientists and pseudo-scientists consider several versions which include antimatter, a miniature black hole and even an alien spaceship.
First researchers appeared on the site of the Tunguska disaster in more than ten years after the event occurred. Regular studies were launched only in the 1920s. Eyewitnesses told researchers that they had seen a huge pillar of fire in the sky and could feel the earthquake. The people living very far from the site of the catastrophe said that they could feel the heat in the air.
In 1930, astrophysicist Harlow Shapley found the biggest problem, which deprived scientists of sleep for decades: there was no crater on the site where the space body supposedly hit the Earth. The scientist put forward another version in an attempt to explain the mystery. Shapley believed that the Tunguska meteorite was not a meteorite but a comet or its fragments.
In 1940, Vladimir Royansky from the US-based Union College in Schenectady presumed that the Tunguska meteorite was made of antimatter. In 1941, Lincoln La Paz from the Ohio University in Columbus published two articles on this subject in Popular Astronomy magazine and substantiated the hypothesis. Afterwards, he sent a letter to the Academy of Sciences of the USSR suggesting to search for anomalous isotopes on the site of the impact to prove the presence of antimatter.
The idea was developed further by three prominent US scientists with Nobel Prize winners Willard Libby and Clyde Cowan (a discoverer of the neutrino) among them. Libby, the creator of the renowned radiocarbon dating (a process which revolutionized archeology), concluded that the space body of antimatter had not reached the Earth, but annihilated as a result of entering dense layers of the Earth’s atmosphere. However, gamma-ray detectors installed on first artificial satellites did not show any incidents of antimatter annihilation in near space.
In 1973, two physicists from the University of Texas presumed that the Tunguska meteorite was a miniature black hole which went through the Earth. Physicist Stephen Hawking believed that miniature black holes appeared after the Big Bang. However, there was no information about the miniature black home coming out of the planet at another end of the globe and thus producing an explosion similar to the Tunguska disaster.
There is also a simple version to explain the Tunguska mystery. It was said that the disaster was caused with an earthquake which triggered the discharged and the subsequent explosion of a huge amount of natural gas – up to ten million tons. In this case gas could form the pillar of fire rising up to the sky and spread a massive wave of heat.
Chris Chyba, Kevin Zahnle and Paul Thomas unraveled the biggest mystery of the Tunguska meteorite in 1993. With the help of computer models they showed that the meteorite exploded in the atmosphere into thousands of fragments and thus left no crater on the site of the impact.
Various UFO aficionados have claimed that the Tunguska event was the result of an exploding alien spaceship or even an alien weapon going off to "save the Earth from an imminent threat". These claims appear to originate from a science fiction story penned by Soviet engineer Alexander Kazantsev in 1946, in which a nuclear-powered Martian spaceship, seeking fresh water from Lake Baikal, blew up in mid-air. This story was inspired by Kazantsev's visit to Hiroshima in late 1945.
Many events in Kazantsev's tale were subsequently confused with the actual occurrences at Tunguska. The nuclear-powered UFO hypothesis was adopted by TV drama critics Thomas Atkins and John Baxter in their book The Fire Came By (1976). The 1998 television series The Secret KGB UFO Files (Phenomenon: The Lost Archives), broadcast on Turner Network Television, referred to the Tunguska event as "the Russian Roswell" and claimed that crashed UFO debris had been recovered from the site. In 2004, a group from the Tunguska Space Phenomenon Public State Fund claimed to have found the wreckage of an alien spacecraft at the site.
The proponents of the UFO hypothesis have never been able to provide any significant evidence for their claims. It should be noted that the Tunguska site is downrange from the Baikonur Cosmodrome and has been contaminated repeatedly by Russian space debris, most notably by the failed launch of the fifth Vostok test flight on December 22, 1960. The payload landed close to the Tunguska impact site, and a team of engineers was dispatched there to recover the capsule and its two canine passengers (who survived).
According to unnamed sources, doctors believe that Kadyrov contracted the infection about two or three weeks ago | 0.878599 | 3.703344 |
The climate of the planet Venus could have been stable and temperate for almost three billion years, which would have allowed life to develop, say American planetologists.
A mysterious planetary event reshaped 80% of its surface, show climatic models created by the astrophysicist Michael Way and his colleagues from NASA’s Goddard Institute for Space Studies.
Could the planet next to Earth have been able to shelter life? Most likely, based on the simulations of the American team, which suggest that temperatures of 20 to 50 degrees Celsius would have prevailed on the second planet of the solar system for about three billion years.
Today, it is considered the hottest planet in the system, with an average surface temperature of around 460 ° C.
The American Pioneer Venus probes 1 and 2 detected in the 1970s the first clues that the planet may have already had a shallow ocean.
According to the researchers, a temperate climate would still be observed today if the cataclysmic event 700 or 750 million years ago did not cause a massive release of carbon dioxide into the atmosphere. This gas was hitherto imprisoned in the rocks of the planet.
A volcanic planet
The explanation could well be related to the intense volcanic activity of the planet. It is quite possible that large quantities of magma accumulated there, releasing into the atmosphere a huge amount of carbon dioxide that would not have been reabsorbed over time for some unknown reason.
This massive influx of CO2 into the atmosphere would have triggered an intense greenhouse effect that would have caused temperatures to rise.
If life could have existed in the past, it would have disappeared as a result of the event. Nowadays, Venus remains an unlikely world for the presence of life, not only because of the high temperature, but also because of the pressure on its surface.
Some volcanoes are still active on the planet.
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Feigelson et al.: X-Ray Properties of Young Stars and Stellar Clusters 313 X-Ray Properties of Young Stars and Stellar Clusters Eric Feigelson and Leisa Townsley Pennsylvania State University Manuel Güdel Paul Scherrer Institute Keivan Stassun Vanderbilt University Although the environments of star and planet formation are thermodynamically cold, substantial X-ray emission from 10–100 MK plasmas is present. In low-mass pre-main-sequence stars, X-rays are produced by violent magnetic reconnection flares. In high-mass O stars, they are produced by wind shocks on both stellar and parsec scales. The recent Chandra Orion Ultradeep Project, XMM-Newton Extended Survey of Taurus, and Chandra studies of more distant high-mass star-forming regions reveal a wealth of X-ray phenomenology and astrophysics. Xray flares mostly resemble solar-like magnetic activity from multipolar surface fields, although extreme flares may arise in field lines extending to the protoplanetary disk. Accretion plays a secondary role. Fluorescent iron line emission and absorption in inclined disks demonstrate that X-rays can efficiently illuminate disk material. The consequent ionization of disk gas and irradiation of disk solids addresses a variety of important astrophysical issues of disk dynamics, planet formation, and meteoritics. New observations of massive star-forming environments such as M 17, the Carina Nebula, and 30 Doradus show remarkably complex X-ray morphologies including the low-mass stellar population, diffuse X-ray flows from blister HII regions, and inhomogeneous superbubbles. X-ray astronomy is thus providing qualitatively new insights into star and planet formation. 1. INTRODUCTION Star and planet formation is generally viewed as a hydrodynamic process involving gravitational collapse of interstellar material at low temperatures, 10–100 K in molecular cloud cores and 100–1500 K in protoplanetary disks. If thermodynamical equilibrium holds, this material should be neutral except in localized HII regions where the bolometric ultraviolet emission from massive O-star photoionization is present. However, stars have turned out to be sources of intense X-rays at almost every stage of early formation and evolution, from low-mass brown dwarfs to massive O stars, to an extent that the stellar environment is ionized and heated (beyond effects due to ultraviolet radiation) out to considerable distances and thus made accessible to magnetic fields. X-ray observations reveal the presence of highly ionized plasma with temperatures of 107–108 K. In lower-mass stars, the X-ray emission is reminiscent of X-rays observed on the Sun, particularly the plasma explosively heated and confined in magnetic loops following magnetic reconnection events. X-ray flares with luminosities orders of magnitude more powerful than seen in the contemporary Sun are frequently seen in young stars. Evidence for an impulsive phase is seen in radio bursts and in U-band enhancements preceding X-ray flares, thought to be due to the bombard- ment of the stellar surface by electron beams. Thus, young stars prolifically accelerate particles to relativistic energies. In rich young stellar clusters, X-rays are also produced by shocks in O-star winds, on both small (<102 R★) and large (parsec) scales. If the region has been producing rich clusters for a sufficiently long time, the resulting supernova remnants will dominate the X-ray properties. X-ray studies with the Chandra and XMM-Newton space observatories are propelling advances of our knowledge and understanding of high-energy processes during the earliest phases of stellar evolution. In the nearest young stars and clusters (d < 500 pc), they provide detailed information about magnetic reconnection processes. In the more distant and richer regions, the X-ray images are amazingly complex with diffuse plasma surrounding hundreds of stars exhibiting a wide range of absorptions. We concentrate here on results from three recent large surveys: the Chandra Orion Ultradeep Project (COUP), based on a nearly continuous 13-day observation of the Orion Nebula region in 2003; the XMM-Newton Extended Survey of Taurus (XEST) that maps ~5 deg2 of the Taurus Molecular Cloud (TMC); and an ongoing Chandra survey of high-mass star-formation regions across the galactic disk. Because the XEST study is discussed in specific detail in a closely related chapter (see chapter by Güdel et al.) together with optical and infrared surveys, we present only selected XEST results. This vol- 313 314 Protostars and Planets V ume has another closely related chapter: Bally et al. discuss X-ray emission from high-velocity protostellar Herbig-Haro outflows. The reader interested in earlier X-ray studies is referred to reviews by Feigelson and Montmerle (1999), Glassgold et al. (2000), Favata and Micela (2003), Paerels and Kahn (2003), and Güdel (2004). The COUP is particularly valuable in establishing a comprehensive observational basis for describing the physical characteristics of flaring phenomena and elucidating the mechanisms of X-ray production. The central portion of the COUP image, showing the PMS population around the bright Trapezium stars and the embedded OMC-1 populations, is shown in Plate 1 (Getman et al., 2005a). X-rays are detected from nearly all known optical members except for many of the bolometrically fainter M stars and brown dwarfs. Conversely, 1315 of 1616 COUP sources (81%) have clear cluster member counterparts and =75 (5%) are new obscured cloud members; most of the remaining X-ray sources are extragalactic background sources seen through the cloud (Getman et al., 2005b). X-ray emission and flaring is thus ubiquitous in PMS stars across the initial mass function (IMF). The X-ray luminosity function (XLF) is broad, spanning 28 < log L x[erg/ s] < 32 (0.5–8 keV), with a peak around log L x[erg/s] ~ 29 (Feigelson et al., 2005). For comparison, the contemporary Sun emits 26 < log L x[erg/s] < 27, with flares up to 1028 erg/ s, in the same spectral band. Results from the more distributed star formation clouds surveyed by XEST reveal a very similar X-ray population as in the rich cluster of the Orion Nebula, although confined to stars with masses mostly below 2 M (see chapter by Güdel et al.), although there is some evidence the XLF is not identical in all regions (section 4.1). There is no evidence for an X-ray-quiet, nonflaring PMS population. The empirical findings generate discussion on a variety of astrophysical implications, including the nature of magnetic fields in young stellar systems, the role of accretion in X-ray emission, the effects of X-ray irradiation of protoplanetary disks and molecular clouds, and the discovery of X-ray flows from HII regions. A number of important related issues are not discussed here, including discovery of heavily obscured X-ray populations, X-ray identification of older PMS stars, the X-ray emission of intermediate mass Herbig Ae/Be stars, the enigmatic X-ray spectra of some O stars, the generation of superbubbles by OB clusters and their multiple supernova remnants, and the large scale starburst conditions in the galactic center region and other galactic nuclei. 2. 2.1. FLARING IN PRE-MAIN-SEQUENCE STARS The Solar Model Many lines of evidence link the PMS X-ray properties to magnetic activity on the Sun and other late-type magnetically active stars such as dMe flare stars, spotted BY Dra variables, and tidally spun-up RS CVn post-main-sequence binaries. These systems have geometrically complex multipolar magnetic fields in arcades of loops rooted in the stellar photospheres and extending into the coronae. The field lines become twisted and tangled by gas convection and undergo explosive magnetic reconnection. The reconnection immediately accelerates a population of particles with energies tens of keV to several MeV; this is the “impulsive phase” manifested by gyrosynchrotron radio continuum emission, blue optical/UV continuum, and, in the Sun, high γ-ray and energetic particle fluences. These particles impact the stellar surface at the magnetic footprints, immediately heating gas that flows upward to fill coronal loops with X-ray emitting plasma. It is this “gradual phase” of the flare that is seen with X-ray telescopes. Schrijver and Zwaan (2000) and Priest and Forbes (2002) review the observations and physics of solar and stellar flares. Extensive multiwavelength properties of PMS stars indicate they are highly magnetically active stars (Feigelson and Montmerle, 1999). Hundreds of Orion stars, and many in other young stellar populations, have periodic photometric variations from rotationally modulated starspots covering 10–50% of the surface (Herbst et al., 2002). A few of these have been subject to detailed Doppler mapping showing spot structure. Radio gyrosynchrotron emission from flare electrons spiraling in magnetic loops has been detected in several dozen PMS stars (Güdel, 2002). A few nearby PMS stars have Zeeman measurements indicating that kiloGauss fields cover much of the surface (Johns-Krull et al., 2004). In the COUP and XEST studies, temperatures inferred from time-averaged spectra extends the Tcool–Thot and T–Lx trends found in the Sun and older stars to higher levels (Preibisch et al., 2005; Telleschi et al., in preparation). X-ray spectra also show plasma abundance anomalies that are virtually identical to those seen in older magnetically active stars (Scelsi et al., 2005; Maggio et al., in preparation). Taking advantage of the unprecedented length of the COUP observation, Flaccomio et al. (2005) find rotational modulation of X-ray emission in at least 10% of Orion PMS stars with previously determined rotation periods from optical monitoring. An example is shown in Fig. 1a. Amplitudes of variability range from 20% to 70% and X-ray periods generally agree with the optical periods. In a few cases, it is half the optical value, implying X-ray-emitting regions on opposite hemispheres. This result indicates that in at least some PMS stars, the X-rays are emitting from relatively long-lived structures lying low in the corona that are inhomogeneously distributed around the star. Similar X-ray rotational modulations are seen in the Sun and a few older stars. Wolk et al. (2005) examined the flaring behavior of a complete sample of solar analogs (0.9 < M/M < 1.2) in the Orion Nebula Cluster. The lightcurve in Fig. 1b shows one of the more spectacular flares in this subsample reaching log Lx(peak)[erg/s] = 32.2. Most flares show solar-type rapid rise and slower decay; the decay phase can last from <1 h to >3 d. The brightness and spectral variations during the decay phases of this and similarly powerful Orion flares have been analyzed by Favata et al. (2005a) using a loop Feigelson et al.: X-Ray Properties of Young Stars and Stellar Clusters 315 Fig. 1. Two of 1400+ X-ray lightcurves from the Chandra Orion Ultradeep Project. The abscissa is time spanning 13.2 d, and the ordinate gives X-ray count rate in the 0.5–8 keV band. (a) An Orion star showing typical PMS flaring behavior superposed on a rotational modulation of the “characteristic” emission. From Flaccomio et al. (2005). (b) COUP #1343 = JW 793, a poorly characterized PMS star in the Orion Nebula, showing a spectacular solar-type flare. From Wolk et al. (2005) and Favata et al. (2005a). model previously applied to “gradual” (i.e., powerful events spanning several hours) solar and stellar flares. The result for COUP #1343 and other morphologically simple cases is clear: The drop in X-ray emission and plasma temperature seen in PMS stellar flares is completely compatible with that of older stars. In some COUP flares, the decay shows evidence of continued or episodic reheating after the flare peak, a phenomenon also seen in solar flares and in older stars. The intensity of PMS flaring is remarkably high. In the solar analog sample, flares brighter than Lx(peak) ≥ 2 × 1030 erg/s occur roughly once a week (Wolk et al., 2005). The most powerful flares have peak luminosities up to several times 1032 erg/s (Favata et al., 2005a). The peak plasma temperature are typically T (peak) = 100 MK but sometimes appear much higher. The time-integrated energy emitted in the X-ray band during flares in solar-mass COUP stars is log Ex[erg] = 34–36. An even more remarkable flare with log Ex[erg] = 37 was seen by ROSAT from the nonaccreting Orion star Parenago 1724 in 1992 (Preibisch et al., 1995). These values are far above solar flaring levels: The COUP flares are 102× stronger and 102× more frequent than the most powerful flares seen in the contemporary Sun; the implied fluence of energetic particles may be 105× above solar levels (Feigelson et al., 2002). The Orion solar analogs emit a relatively constant “characteristic” X-ray level about three-fourths of the time (see Fig. 1). The X-ray spectrum of this characteristic state can be modeled as a two-temperature plasma with one component Tcool = 10 MK and the other component Thot = 30 MK. These temperatures are much higher than the quiescent solar corona. The concept of “microflaring” or “nanoflaring” for the Sun has been widely discussed (Parker, 1988) and has gained favor in studies of older magnetically active stars based on lightcurve and spectral analysis (Kashyap et al., 2002; Güdel et al., 2003, Arzner and Güdel, 2004). These latter studies of dMe flare stars indicate that a power-law distribution of flare energies, dN/dE ∝ E –α, is present with α = 2.0–2.7. The energetics is clearly dominated by smaller flares. The COUP lightcurves vary widely in appearance, but collectively can also be roughly simulated by a power law with α = 2.0–2.5 without a truly quiescent component (Flaccomio et al., 2005). Thus, when reference is made to the more easily studied superflares, one must always re- 316 Protostars and Planets V Fig. 2. X-ray flare from Class I protostar YLW 16A in the ρ Ophiuchi cloud, observed with Chandra. The flare has an unusual morphology and the spectrum shows very hot plasma temperatures with strong emission from the fluorescent 6.4 keV line of neutral iron attributable to reflection off the protoplanetary disk. From Imanishi et al. (2001). member that many more weaker flares are present and may have comparable or greater astrophysical effects. Not infrequently, secondary flares and reheating events are seen superposed on the decay phase of powerful flares (e.g., Gagné et al., 2004; Favata et al., 2005a). One puzzle with a solar model for PMS flares is that some show unusually slow rises. The nonaccreting star LkHα 312 exhibited a 2-h fast rise with peak temperature T = 88 MK, followed by a 6-h slower rise to log Lx(peak) [erg/s] = 32.0 (Grosso et al., 2004). The flare from the Class I protostar YLW 16A in the dense core of the ρ Ophiuchi cloud showed a remarkable morphology with two rise phases and similar temperature structure (Fig. 2) (Imanishi et al., 2001). Other flares seen with COUP show roughly symmetrical rise and fall morphologies, sometimes extending over 1–2 days (Wolk et al., 2005). It is possible that some of these variations are due to the stellar rotation where X-ray structures are emerging from eclipse, but they are currently poorly understood. By monitoring young stars with optical telescopes simultaneous with X-ray observations, the early impulsive phase of PMS flares can be revealed. This has been achieved with distributed groundbased telescopes and in space: The XMM-Newton satellite has an optical-band telescope coaligned with the X-ray telescope. During the impulsive phase, electron beams accelerated after the reconnection event bombard the stellar chromosphere, which produces a burst of short-wavelength optical and UV radiation. XMM-Newton observation of the Taurus PMS star GK Tau shows both uncorrelated modulations as well as a strong U-band burst preceding an X-ray flare in good analogy with solar events (Audard et al., in preparation) (Fig. 3a). Groundbased optical and Hα monitoring of the Orion Nebula during the COUP campaign revealed one case of an I-band spike simultaneous with a very short X-ray flare of intermediate brightness (Stassun et al., 2006) (Fig. 3b). 2.2. The Role of Accretion It was established in the 1980s and 1990s that elevated levels of X-ray emission in PMS stars appears in both “classical” T Tauri stars, with optical/infrared signatures of accretion from a protoplanetary disk, and “weak-lined” T Tauri stars, without these signatures. This basic result is confirmed but with some important refinements — and controversy — from recent studies. While the presence or absence of a K-band emitting inner disk does not appear to influence X-ray emission, the presence of accretion has a negative impact on X-ray production (Flaccomio et al., 2003; Stassun et al., 2004; Preibisch et al., 2005; Telleschi et al., in preparation). This is manifested as a statistical decrease in X-rays by a factor of Feigelson et al.: X-Ray Properties of Young Stars and Stellar Clusters 317 Fig. 3. Detection of the “white light” component during the impulsive phases of PMS X-ray flares. (a) Short-term behavior of the classical T Tau binary GK Tau in U-band light (upper curve) and X-rays (lower curve) from the XEST survey. The lightcurve covers approximately 9 h. From Audard et al. (in preparation). (b) Rapid X-ray flare (top panel) from COUP #816 = JW 522, an obscured PMS star in the Orion Nebula Cluster, apparently accompanied by impulsive I-band emission. This COUP X-ray lightcurve spans 13.2 d. From Stassun et al. (2006). 2–3 in accreting vs. nonaccreting PMS stars, even after dependencies on mass and age are taken into account. The effect does not appear to arise from absorption by accreting gas; e.g., the offset appears in the hard 2–8-keV band where absorption is negligible. The offset is relatively small compared to the 10 4 range in the PMS X-ray luminosity function, and flaring behavior is not affected in any obvious way. One possible explanation is that mass-loaded accreting field lines cannot emit X-rays (Preibisch et al., 2005). If a magnetic reconnection event liberates a certain amount of energy, this energy would heat the low-density plasma of nonaccretors to X-ray emitting temperatures, while the denser plasma in the mass-loaded magnetic field lines would be heated to much lower temperatures. The remaining field lines that are not linked to the disk would have low coronal densities and continue to produce solar-like flares. Note that the very young accreting star XZ Tau shows unusual temporal variations in X-ray absorption that can be attributed to eclipses by the accretion stream (Favata et al., 2003). The optical observations conducted simultaneously with the COUP X-ray observations give conclusive evidence that accretion does not produce or suppress flaring in the great majority of PMS stars (Stassun et al., 2006). Of the 278 Orion stars exhibiting variations in both optical and X-ray bands, not a single case is found where optical variations (attributable to either rotationally modulated starspots or to changes in accretion) have an evident effect on the X-ray flaring or characteristic emission. An example from the XEST survey is shown in Fig. 3a where the slow modulation seen in the first half is too rapid for effects due to rotation, but on the other hand shows no equivalent signatures in X-rays. The optical fluctuations are therefore unrelated to flare processes and, in this case, are likely due to variable accretion (Audard et al., in preparation). Similarly, a Taurus brown dwarf with no X-ray emission detected in XEST showed a slow rise by a factor of 6 over eight hours in the U-band flux (Grosso et al., 2006). Such behavior is uncommon for a flare, and because this brown dwarf is accreting, mass streams may again be responsible for producing the excess ultraviolet flux. The simplest interpretation of the absence of statistical links between accretion and X-ray luminosities and the absence of simultaneous optical/X-ray variability is that different magnetic field lines are involved with funneling gas 318 Protostars and Planets V Fig. 4. High-resolution transmission grating spectrum of the nearest classical T Tauri star, TW Hya. The spectrum is softer than other PMS stars, and the triplet line ratios imply either X-ray production in a high-density accretion shock or irradiation by ultraviolet radiation. From Kastner et al. (2002). from the disk and with reconnection events producing X-ray plasma. There is no evidence that the expected shock at the base of the accretion column produces the X-rays seen in COUP and XEST. There are some counterindications to these conclusions. A huge increase in X-ray emission was seen on long timescales from the star illuminating McNeil’s Nebula, which exhibited an optical/infrared outburst attributed to the onset of rapid accretion (Kastner et al., 2004). In contrast, however, X-rays are seen before, during, and after outburst of the EXor star V1118 Ori, with a lower temperature seen when accretion was strongest (Audard et al., 2005). These findings suggest that accretion, and perhaps the inner disk structure, might sometimes affect magnetic field configurations and flaring in complicated ways. The biggest challenge comes from TW Hya, the nearest and brightest accreting PMS star. It has an X-ray spectrum much softer than most COUP or other PMS sources (Fig. 4). Due to its proximity to the Sun, TW Hya is sufficiently bright in X-rays to be subject to detailed high-resolution spectroscopy using transmission gratings on the Chandra and XMM-Newton telescopes (Kastner et al., 2002; Stelzer and Schmitt, 2004; Ness and Schmitt, 2005). According to the magnetospheric accretion scenario, accreted material crashes onto the stellar surface with velocities of up to several hundred km/s, which should cause ~10 6 K shocks in which strong optical and UV excess emission and perhaps also soft X-ray emission is produced (Lamzin, 1999). Density-sensitive triplet line ratios of Ne IX and O VII are saturated, indicating either that the emitting plasma has densities log ne[cm–3] ~ 13, considerably higher than the log ne[cm–3] ~ 10 characteristic of low-level coronal emission although reminiscent of densities in flares. However, these densities were measured during an observation dominated by relative quiescence with no hot plasma present. Alternatively, the high triplet ratios might be induced by plasma subject to strong ultraviolet irradiation. A similar weak forbidden line in the O VII triplet is seen in the accreting PMS star BP Tau (Schmitt et al., 2005), and similar soft X-ray emission is seen from the Herbig Ae star HD 163296 (Swartz et al., 2005). If the plasma material in TW Hya is drawn from the disk rather than the stellar surface, one must explain the observed high Ne/Fe abundance ratio that is similar to that seen in flare plasmas. One possibility is that the abundance anomalies do not arise from the coronal first ionization potential effect, but rather from the depletion of refractory elements into disk solids (Brinkman et al., 2001; Drake et al., 2005). This model, however, must confront models of the infrared disk indicating that grains have sublimated in the disk around 4 AU, returning refractory elements back into the gas phase (Calvet et al., 2002). Finally, we note that current X-ray instrumentation used for PMS imaging studies is not very sensitive to the cooler plasma expected from accretion shocks, and that much of this emission may be attenuated by line-of-sight interstellar material. The possibility that some soft accretion X-ray emission is present in addition to the hard flare emission is difficult to firmly exclude. But there is little doubt that most of the X-rays seen with Chandra and XMM-Newton are generated by magnetic reconnection flaring rather than the accretion process. Feigelson et al.: X-Ray Properties of Young Stars and Stellar Clusters 2.3. The Role of Disks There are strong reasons from theoretical models to believe that PMS stars are magnetically coupled to their disks at the corotation radii typically 5–10 R★ from the stellar surface (e.g., Hartmann, 1998; Shu et al., 2000). This hypothesis unifies such diverse phenomena as the self-absorbed optical emission lines, the slow rotation of accreting PMS stars, and the magnetocentrifugal acceleration of HerbigHaro jets. However, there is little direct evidence for magnetic field lines connecting the star and the disk. Direct imaging of large-scale magnetic fields in PMS stars is only possible today using very long baseline interferometry at radio wavelengths where an angular resolution of 1 mas corresponds to 0.14 AU at the distance of the Taurus or Ophiuchus clouds. But only a few PMS stars are sufficiently bright in radio continuum for such study. One of the components of T Tau S has consistently shown evidence of magnetic field extensions to several stellar radii, perhaps connecting to the inner border of the accretion disk (Loinard et al., 2005). But X-ray flares can provide supporting evidence for star-disk magnetic coupling. An early report of star-disk fields arose from a sequence of three powerful flares with separations of ~20 h from the Class I protostar YLW 15 in the ρ Oph cloud (Tsuboi et al., 2000). Standard flare plasma models indicated loop lengths around 14 R , and periodicity might arise from incomplete rotational star-disk coupling (Montmerle et al., 2000). However, it is also possible that the YLA 15 flaring is not truly periodic; many cases of multiple flares without periodicities are seen in the COUP lightcurves. Analysis of the most luminous X-ray flares in the COUP study also indicates that huge magnetic structures can be present. Favata et al. (2005a) reports analysis of the flare decay phases in sources such as COUP #1343 (Fig. 1) using models that account for reheating processes, which otherwise can lead to overestimation of loop lengths. The combination of very high luminosities (log Lx(peak)[erg/s] = 31–32), peak temperatures in excess of 100 MK, and very slow decays appear to require loops much larger than the star, up to several 1012 cm or 5–20 R ★. Recall that these flares represent only the strongest ~1% of all flares observed by COUP; most flares from PMS stars are much weaker and likely arise from smaller loops. This is clearly shown in some stars by the rotational modulation of the nonflaring component in the COUP study (Flaccomio et al., 2005). Given the typical 2–10-d rotation periods of PMS stars, is seems very doubtful such long flaring loops would be stable if both footpoints were anchored to the photosphere. Even if MHD instabilities are not important, gas pressure and centrifugal forces from the embedded plasma may be sufficient to destroy such enormous coronal loops (Jardine and Unruh, 1999). Jardine et al. (2006) develop a model of magnetically confined multipolar coronae of PMS stars where accretion follows some field lines while others contain X-ray emitting plasma; the model also accounts for ob- 319 served statistical relations between X-ray properties and stellar mass. The magnetospheres of PMS stars are thus likely to be quite complex. Unlike the Sun where only a tiny fraction of the photosphere has active regions, intense multipolar fields cover much of the surface in extremely young stars. Continuous microflaring is likely responsible for the ubiquitous strong 10–30-MK plasma emission. Other field lines extend several stellar radii: Some are mass-loaded with gas accreting from the circumstellar disk, while others may undergo reconnection producing the most X-ray-luminous flares. 3. THE EVOLUTION OF MAGNETIC ACTIVITY The COUP observation provides the most sensitive, uniform, and complete study of X-ray properties for a PMS stellar population available to date. When combined with studies of older stellar clusters, such as the Pleiades and Hyades, and of volume-limited samples in the solar neighborhood, evolutionary trends in X-ray emission can be traced. Since chromospheric indicators of magnetic activity (such as Ca II line emission) are confused by accretion, and photospheric variations from rotationally modulated starspots are too faint to be generally measured in most older stars, X-ray emission is the only magnetic indicator that can be traced in stellar populations from 105 to 1010 yr. The result from the PMS to the giga-year-old disk population is shown in Fig. 5a (Preibisch and Feigelson, 2005). The two critical advantages here over other measures of magnetic activity evolution are the complete samples (and correct treatment of nondetections) and stratification by mass. The latter is important because the mass-dependence of X-ray luminosities (for unknown reasons) differs in PMS and main-sequence stars (Preibisch et al., 2005). If one approximates the decay of magnetic activity as a power law, then evolution in the 0.5 < M < 1.2 M mass range is approximately power-law with Lx ∝ τ –3/4 over the wide range of ages 5 < log τ [yr] < 9.5. Other X-ray studies of older disk stars suggest that the decay rate steepens: Lx ∝ τ –3/2 or τ –2 over 8 < log τ [yr] < 10 (Güdel et al., 1997; Feigelson et al., 2004). Note, however, that Pace and Pasquini (2004) find no decay in chromospheric activity in a sample of solar mass stars after 3 G.y. These results are similar to, but show more rapid decay than, the classical Skumanich (1972) τ –1/2 relation that had been measured for main-sequence stars only over the limited age range 7.5 < log τ [yr] < 9.5. The COUP sample also exhibits a mild decay in magnetic activity for ages 5 < log τ [yr] < 7 within the PMS phase, although the trend is dominated by star-to-star scatter (Preibisch and Feigelson, 2005). While these results would appear to confirm and elaborate the long-standing rotation-age-activity relationship of solar-type stars, the data paint a more complex picture. The Chandra Orion studies show that the rotation-activity relation is largely absent at 1 m.y. (Stassun et al., 2004; Preibisch et al., 2005). This finding suggests the somewhat 320 Protostars and Planets V Fig. 5. (a) Evolution of the median X-ray luminosities for stars in different mass ranges: 0.9–1.2 M (solid circles), 0.5–0.9 M (open squares), and 0.1–0.5 M (plusses). From Preibisch and Feigelson (2005). (b) The link between soft X-ray absorption and proplyd inclination is the first measurement of gas column densities in irradiated disks. From Kastner et al. (2005). surprising result that the activity-age decay is strong across the entire history of solar-type stars but is not entirely attributable to rotational deceleration. The PMS magnetic fields may either be generated by a solar-type dynamo that is completely saturated, or by a qualitatively different dynamo powered by turbulence distributed throughout the convective interior rather than by rotational shear at the tachocline. At the same time, the Orion studies show a small positive correlation between rotation period and X-ray activity, similar to that seen in the “supersaturated” regime of main-sequence stars. It is also possible that this effect is due to a sample bias against slowly rotating, X-ray-weak Orion stars (Stassun et al., 2004). The XEST findings in the Taurus PMS population give a different result, suggesting that an unsaturated solar-type dynamo may in fact be present in PMS stars when rotation periods are longer than a few days (Briggs et al., in preparation). It is possible that the somewhat more evolved Taurus sample, compared to the Orion Nebula Cluster stars, has produced sufficiently prominent radiative zones in some of these late-type PMS stars to put a solar-type dynamo into operation. The origins of magnetic fields in PMS stars are thus still not well established. It is possible that both tachoclinal and convective dynamos are involved, as discussed by Barnes (2003a,b). There is a hint of a transition between convective and rotational dynamos in the plot of Lx/Lbol against mass in Orion stars. The X-ray emissivity for many stars drops precipitously for masses above 2–3 M , which is also the boundary between lower-mass convective and highermass radiative interiors (Feigelson et al., 2003). Another possible influence is that accretion in younger PMS stars alters convection and thereby influences the magnetic field generation process (Siess et al., 1999; Stassun et al., 2004). The magnetic activity history for M stars with masses 0.1–0.4 M appears to be different than more massive PMS stars (Fig. 5a). Only a mild decrease in X-ray luminosity, and even a mild increase in Lx/Lbol, is seen over the 6 < log τ [yr] < 8 range, though the X-ray emission does decay over giga-year timescales. This result may be related to the wellestablished fact that the low-mass M stars have much longer rotational slow-down times than solar-type stars. But the difference in behavior compared to higher-mass stars could support the idea that the dynamos in PMS and dM stars both arise from a convective turbulent dynamo. These issues are further discussed in Mullan and MacDonald (2001), Feigelson et al. (2003), Barnes (2003a), and Preibisch et al. (2005). An unresolved debate has emerged concerning the onset of X-ray emission in PMS stars. There is no question that magnetic activity with violent flaring is common among Class I protostars with ages ~105 yr (Imanishi et al., 2001; Preibisch, 2004) (Fig. 2). The question is whether X-ray emission is present in Class 0 protostars with ages ~104 yr. There is one report of hard X-rays from two Class 0 protostars in the OMC 2/3 region (Tsuboi et al., 2001); however, other researchers classify the systems as Class I (Nielbock et al., 2003). An X-ray emitting protostar deeply embedded in the R Corona Australis cloud core has a similarly uncertain Class 0 or I status (Hamaguchi et al., 2005). In contrast, a considerable number of well-established Class 0 protostars appear in Chandra images and are not detected; Feigelson et al.: X-Ray Properties of Young Stars and Stellar Clusters e.g., in the NGC 1333 and Serpens embedded clusters (Getman et al., 2002; Preibisch, 2004). However, because Class 0 stars are typically surrounded by very dense gaseous envelopes, it is possible that the X-ray nondetections arise from absorption rather than an absence of emission. An interesting new case is an intermediate-mass Class 0 system in the IC 1396N region that exhibits extremely strong soft X-ray absorption (Getman et al., 2006b). 4. X-RAY STARS AND HOT GAS IN MASSIVE STAR-FORMING REGIONS Most stars are born in massive star-forming regions (MSFRs) where rich clusters containing thousands of stars are produced in molecular cloud cores. Yet, surprisingly little is known about the lower mass populations of these rich clusters. Beyond the Orion Molecular Clouds, nearinfrared surveys like 2MASS are dominated by foreground or background stars, and the initial mass functions are typically measured statistically rather than by identification of individual cluster members. X-ray surveys of MSFRs are important in this respect because they readily discriminate young stars from unrelated objects that often contaminate JHK images of such fields, especially for those young stars no longer surrounded by a dusty circumstellar disk. Furthermore, modern X-ray telescopes penetrate heavy obscuration (routinely AV ~ 10–100 mag, occasionally up to 1000 mag) with little source confusion or contamination from unrelated objects to reveal the young stellar populations in MSFRs. The O and Wolf-Rayet (WR) members of MSFRs have been catalogued, and the extent of their UV ionization is known through HII region studies. But often little is known about the fate of their powerful winds. The kinetic power of a massive O star’s winds injected into its stellar neighborhood over its lifetime is comparable to the input of its supernova explosion. Theorists calculate that wind-blown bubbles of coronal-temperature gas should be present, but no clear measurement of this diffuse plasma had been made in HII regions prior to Chandra. X-ray studies also detect the presence of earlier generations of OB stars through the shocks of their supernova remnants (SNRs). In very rich and long-lived star-forming cloud complexes, SNRs combine with massive stellar winds to form superbubbles and chimneys extending over hundreds of parsecs and often into the galactic halo. O stars are thus the principal drivers of the interstellar medium. The MSFR X-ray investigations discussed here represent only a fraction of this rapidly growing field. A dozen early observations of MSFRs by Chandra and XMM-Newton are summarized by Townsley et al. (2003). Since then, Chandra has performed observations of many other regions, typically revealing hundreds of low-mass PMS stars, known and new high-mass OB stars, and occasionally diffuse X-ray emission from stellar winds or SNRs. In addition to those discussed below, these include NGC 2024 in the Orion B mo- 321 lecular cloud (Skinner et al., 2003), NGC 6193 in Ara OB1 (Skinner et al., 2005), NGC 6334 (Ezoe et al., 2006), NGC 6530 ionizing Messier 8 (Damiani et al., 2004), the Arches and Quintuplet galactic center clusters (Law and YusefZadeh, 2004; Rockefeller et al., 2005), and Westerlund 1, which has an X-ray pulsar (Muno et al., 2006; Skinner et al., 2006). Chandra studies of NGC 6357, M 16, RCW 49, W 51A, W 3, and other regions are also underway. Both XMM-Newton and Chandra have examined rich clusters in the Carina Nebula (Evans et al., 2003, 2004; Albacete Colombo et al., 2003), NGC 6231 at the core of the Sco OB1 association, and portions of Cyg OB2. 4.1. Cepheus B, RCW 38, and Stellar Populations Each Chandra image of a MSFR shows hundreds, sometimes over a thousand, unresolved sources. For regions at distances around d = 1–3 kpc, only a small fraction (typically 3–10%) of these sources are background quasars or field galactic stars. The stellar contamination is low because PMS stars are typically 100-fold more X-ray luminous than 1–10-G.y.-old main-sequence stars (Fig. 5a). Since Chandra source positions are accurate to 0.2"–0.4", identifications have little ambiguity except for components of multiple systems. The XLF of a stellar population spans 4 orders of magnitude; 2 orders of magnitude of this range arises from a correlation with stellar mass and bolometric magnitude (Preibisch et al., 2005). This means that the X-ray flux limit of a MSFR observation roughly has a corresponding limit in K-band magnitude and mass. Day-long exposures of regions d = 2 kpc away are typically complete to log Lx[erg/ s] ~ 29.5, which gives nearly complete samples down to M = 1 M with little contamination. We outline two recent studies of this type. A 27-h Chandra exposure of the stellar cluster illuminating the HII region RCW 38 (d = 1.7 kpc) reveals 461 Xray sources, of which 360 are confirmed cluster members (Wolk et al., 2006). Half have near-infrared counterparts, of which 20% have K-band excesses associated with optically thick disks. The cluster is centrally concentrated with a half-width of 0.2 pc and a central density of 100 X-ray stars/ pc2. Obscuration of the cluster members, seen both in the soft X-ray absorption column and near-infrared photometry, is typically 10 < AV < 20 mag. The X-ray stars are mostly unstudied; particular noteworthy are 31 X-ray stars that may be new obscured OB stars. Assuming a standard IMF, the total cluster membership is estimated to exceed 2000 stars. About 15% of the X-ray sources are variable, and several show plasma temperatures exceeding 100 MK. A recent Chandra study was made of the Sharpless 155 HII region on the interface where stars from the Cep OB3b association (d = 725 pc) illuminates the Cepheus B molecular cloud core (Getman et al., 2006a). Earlier, a few ultracompact HII regions inside the cloud indicated an embedded cluster is present, but little was known about the embedded population. The 8-h exposure shows 431 X-ray sources, 322 Protostars and Planets V of which 89% are identified with K-band stars. Sixty-four highly absorbed X-ray stars inside the cloud provide the best census of the embedded cluster, while the 321 X-ray stars outside the cloud provide the best census of this portion of the Cep OB3b cluster. Surprisingly, the XLF of the unobscured sample has a different shape from that seen in the Orion Nebula Cluster, with an excess of stars around log Lx[erg/s] = 29.7 or M = 0.3 M . It is not clear whether this arises from a deviation in the IMF or some other cause, such as sequential star formation generating a noncoeval population. The diffuse X-rays in this region, which has only one known O star, are entirely attributable to the integrated contribution of fainter PMS stars. 4.2. M 17 and X-Ray Flows in HII Regions For OB stars excavating an HII region within their nascent molecular cloud, diffuse X-rays may be generated as fast winds shock the surrounding media (Weaver et al., 1977). Chandra has clearly discriminated this diffuse emission from the hundreds of X-ray-emitting young stars in M 17 and the Rosette Nebula (Townsley et al., 2003). Perhaps the clearest example of diffuse X-ray emission in MSFRs is the Chandra observation of M 17, a bright blownout blister HII region on the edge of a massive molecular cloud (d = 1.6 kpc). The expansion of the blister HII region is triggering star formation in its associated giant molecular cloud, which contains an ultracompact HII region, water masers, and the dense core M 17SW. M 17 has 100 stars earlier than B9 (for comparison, the Orion Nebula Cluster has 8), with 14 O stars. The Chandra image is shown in Plate 3, along with an earlier, wider-field image from the ROSAT satellite. Over 900 point sources in the ~172 × 172 field are found (Broos et al., in preparation). The diffuse emission of M 17 is spatially concentrated eastward of the stellar cluster and fills the region delineated by the photodissociation region and the molecular cloud. The X-ray spectrum can be modeled as a two-temperature plasma with T = 1.5 MK and 7 MK, and a total intrinsic Xray luminosity (corrected for absorption) of Lx,diffuse = 3 × 1033 erg/s (Townsley et al., 2003). The X-ray plasma has mass M ~ 0.1 M and density 0.1–0.3 cm–3 spread over several cubic parsecs. It represents only ~104 yr of recent O-wind production; past wind material has already flowed eastward into the galactic interstellar medium. The diffuse emission produced by the M 17 cluster, and similar but less dramatic emission by the Rosette Nebula cluster, gives new insight into HII region physics. The traditional HII region model developed decades ago by Strömgren and others omitted the role of OB winds, which were not discovered until the 1960s. The winds play a small role in the overall energetics of HII regions, but they dominate the momentum and dynamics of the nebula with 12 Mv2w ~ 1036–37 erg/s for a typical early-O star. If completely surrounded by a cold cloud medium, an O star should create a “wind-swept bubble” with concentric zones: a freely expanding wind, a wind termination shock followed by an X- ray emitting zone, the standard T = 104 K HII region, the ionization front, and the interface with the cold interstellar environment (Weaver et al., 1977; Capriotti and Kozminski, 2001). These early models predicted Lx ~ 1035 erg/s from a single embedded O star, 2 orders of magnitude brighter than the emission produced by M 17 (Dunne et al., 2003). Several explanations for this discrepancy can be envisioned: Perhaps the wind energy is dissipated in a turbulent mixing layer (Kahn and Breitschwerdt, 1990), or the wind terminal shock may be weakened by mass-loading of interstellar material (e.g., Pittard et al., 2001). Winds from several OB stars may collide and shock before they hit the ambient medium (Cantó et al., 2000). Finally, a simple explanation may be that most of the kinetic energy of the O star winds remains in a bulk kinetic flow into the galactic interstellar medium (Townsley et al., 2003). 4.3. Trumpler 14 in the Carina Nebula The Carina complex at d = 2.8 kpc is a remarkably rich star-forming region containing 8 open clusters with at least 64 O stars, several WR stars, and the luminous blue variable η Car. The presence of WR stars may indicate past supernovae, although no well-defined remnant has been identified. One of these clusters is Tr 14, an extremely rich, young (~1 m.y.), compact OB association with ~30 previously identified OB stars. Together with the nearby Trumpler 16 cluster, it has the highest concentration of O3 stars known in the galaxy. Over 20 years ago, an Einstein Observatory X-ray study of the Carina star-forming complex detected a few dozen high-mass stars and diffuse emission attributed to O-star winds (Seward and Chlebowski, 1982). Chandra studies show that thousands of the lower-mass stars in these young clusters were likely to be contributing to this diffuse flux; a major goal is to determine the relative contributions of stars, winds, and SNRs to the extended emission in the Carina Nebula. Plate 4a shows a 16-h Chandra exposure centered on HD 93129AB, the O2I/O3.5V binary at the center of Tr 14 (Townsley et al., in preparation). Over 1600 members of the Tr 14 and Tr 16 clusters can be identified from the Xray point sources and extensive diffuse emission is clearly present. The diffuse emission surrounding Tr 14 is quite soft with subsolar elemental abundances, similar to the M 17 OB-wind shocks. But the much brighter diffuse emission seen far from the massive stellar clusters is less absorbed and requires enhanced abundances of Ne and Fe. This supports models involving old “cavity” supernova remnants that exploded inside the Carina superbubble (e.g., Chu et al., 1993). Chandra resolves the two components of HD 93129AB separated by ~3": HD 93129B shows a typical O-star soft X-ray spectrum (T ~ 6 MK), while HD 93129A shows a similar soft component plus a T ~ 35 MK component that dominates the total X-ray luminosity. This hard spectrum and high X-ray luminosity are indicative of a colliding-wind Feigelson et al.: X-Ray Properties of Young Stars and Stellar Clusters binary (Pittard et al., 2001), in agreement with the recent finding that HD 93129A is itself a binary (Nelan et al., 2004). Other colliding wind binaries are similarly identified in the cluster. 4.4. The Starburst of 30 Doradus Plate 4b shows a 6-h Chandra exposure of 30 Dor in the Large Magellanic Cloud, the most luminous giant extragalactic HII region and “starburst cluster” in the Local Group. 30 Dor is the product of multiple epochs of star formation, which have produced multiple SNRs seen with ROSAT as elongated plasma-filled superbubbles on ~100-pc scales (Wang and Helfand, 1991). The new Chandra image shows a bright concentration of X-rays associated with the R136 star cluster, the bright SNR N157B to the southwest, a number of new widely distributed compact X-ray sources, and diffuse structures that fill the superbubbles produced by the collective effects of massive stellar winds and their past supernova events (Townsley et al., 2006a). Some of these are center-filled while others are edge-brightened, indicating a complicated mix of viewing angles and perhaps filling factors. Comparison of the morphologies of the diffuse X-ray emission with the photodissociation region revealed by Hα imaging and cool dust revealed by infrared imaging with the Spitzer Space Telescope shows a remarkable association: The hot plasma clearly fills the cavities outlined by ionized gas and warm dust. Spectral analysis of the superbubbles reveals a range of absorptions (AV = 1–3 mag), plasma temperatures (T = 3–9 MK), and abundances. About 100 X-ray sources are associated with the central massive cluster R136 (Townsley et al., 2006b). Some are bright, hard X-ray point sources in the field likely to be colliding-wind binaries, while others are probably from ordinary O and WR stellar winds. 5. 5.1. X-RAY EFFECTS ON STAR AND PLANET FORMATION X-Ray Ionization of Molecular Cloud Cores One of the mysteries of galactic astrophysics is why most interstellar molecular material is not engaged in star formation. Large volumes of most molecular clouds are inactive, and some clouds appear to be completely quiescent. A possible explanation is that star formation is suppressed by ionization: Stellar ultraviolet will ionize the outer edges of clouds, and galactic cosmic rays may penetrate into their cores (Stahler and Palla, 2005). Even very low levels of ionization will couple the mostly neutral gas to magnetic fields, inhibiting gravitational collapse until sufficient ambipolar diffusion occurs. The X-ray observations of star-forming regions demonstrate that a third source of ionization must be considered: X-rays from the winds and flares of deeply embedded Xray sources. The X-ray ionization zones, sometimes called X-ray dissociation regions (XDRs) or Röntgen spheres, do 323 not have sharp edges like ultraviolet Strömgren spheres, but rather extend to large distances with decreasing effect (Hollenbach and Tielens, 1997). The COUP observation provides a unique opportunity to calculate realistic XDRs in two molecular cloud cores: OMC-1 or the Becklin-Neugebauer region, and OMC-1 South. Several dozen embedded X-ray stars are seen in these clouds (Plate 1), and each can be characterized by X-ray luminosity, spectrum, and line-of-sight absorption (Grosso et al., 2005). Figure 6 illustrates the X-ray properties of deeply embedded objects. COUP #554 is a young star with a strong infrared-excess in the OMC-1 South core. The Chandra spectrum shows soft X-ray absorption of log NH[cm–2] = 22.7, equivalent to AV ~ 30 mag, and the light-curve exhibits many powerful flares at the top of the XLF with peak X-ray luminosities reaching ~1032 erg/s. COUP #632 has no optical or K-band counterpart and its X-ray spectrum shows the strongest absorption of all COUP sources: log NH[cm–2] = 23.9 or AV ~ 500 mag. Using the COUP source positions and absorptions, we can roughly place each star into a simplified geometrical model of the molecular cloud gas, and calculate the region around each where the X-ray ionization exceeds the expected uniform cosmic-ray ionization. Plate 2 shows the resulting XDRs in OMC-1 from the embedded BecklinNeugebauer cluster (Lorenzani et al., in preparation). Here a significant fraction of the volume is dominated by X-ray ionization. In general, the ionization of cloud cores =0.1 pc in size will be significantly altered if they contain clusters with more than ~50 members. 5.2. X-Ray Irradiation of Protoplanetary Disks The circumstellar disks around PMS stars where planetary systems form were generally considered to consist of cool, neutral molecular material in thermodynamic equilibrium with ~100–1000 K temperatures. But there is a growing understanding that they are not closed and isolated structures. A few years ago, discussion concentrated on ultraviolet radiation from O stars that can photoevaporate nearby disks (Hollenbach et al., 2000). More recently, considerable theoretical discussion has focused on X-ray irradiation from the host star (Fig. 7). This is a rapidly evolving field and only a fraction of the studies can be mentioned here. Readers are referred to reviews by Feigelson (2005) and Glassgold et al. (2005) for more detail. X-ray studies provide two lines of empirical evidence that the X-rays seen with our telescopes actually do efficiently irradiate protoplanetary disks. First, the 6.4-keV fluorescent line of neutral iron is seen in several embedded COUP stars with massive disks, as shown in Fig. 2 (Imanishi et al., 2001). This line is only produced when hard X-rays illuminate >1 g/cm2 of material; this is too great to be intervening material and must be reflection off of a flattened structure surrounding the X-ray source (Tsujimoto et al., 2005; Favata et al., 2005b). Second, X-ray spectra of PMS stars with inclined disks show more absorption than 324 Protostars and Planets V Fig. 6. X-ray properties of two stars deeply embedded in the OMC-1 South molecular cloud core from the Chandra Orion Ultradeep Project. (a) Lightcurve of COUP #554 over 13.2 d where the histogram shows the integrated brightness (lefthand vertical axis) and the dots show the energies of individual photons (righthand vertical axis). (b) Spectrum of COUP #632 showing very strong absorption at energies below 4 keV. From Grosso et al. (2005). Fig. 7. Cartoon illustrating sources of energetic irradiation (galactic cosmic rays, flare X-rays, flare particles) and their possible effects on protoplanetary disks (ionization of gas and induction of MHD turbulence, layered accretion structure, spallation of solids). From Feigelson (2005). Feigelson et al.: X-Ray Properties of Young Stars and Stellar Clusters spectra from stars with face-on disks. This is most clearly seen in the COUP survey, where column densities log NH[cm–2] ~ 23 are seen in edge-on proplyds imaged with the Hubble Space Telescope (Kastner et al., 2005). This demonstrates the deposition of ionizing radiation in the disk and gives a rare measurement of the gas (rather than dust) content of protoplanetary disks. Having established that X-ray emission, particularly Xray flaring, is ubiquitous in PMS stars, and that at least some disks are efficiently irradiated by these X-rays, one can now estimate the X-ray ionization rate throughout a disk. The result is that X-rays penetrate deeply toward the midplane in the jovian planet region, but leave a neutral “dead zone” in the terrestrial planet region (e.g., Igea and Glassgold, 1999; Fromang et al., 2002). The ionization effect of Xrays is many orders of magnitude more important than that of cosmic rays. However, differing treatments of metal ions and dust leads to considerable differences in the inferred steady-state ionization level of the disk (Ilgner and Nelson, 2006). The theory of the X-ray ionization rate thus appears satisfactory, but calculations of the X-ray ionization fraction depend on poorly established recombination rates. X-ray ionization effects become important contributors to the complex and nonlinear interplay between the thermodynamics, dynamics, gas-phase chemistry, and gas-grain interactions in protoplanetary disks. One important consequence may be the induction of the magnetorotational instability, which quickly develops into a full spectrum of MHD turbulence including both vertical and radial mixing. The radial viscosity associated with the active turbulent zone may cause the flow of material from the outer disk into the inner disk, and thereby into the bipolar outflows and onto the protostar. This may solve a long-standing problem in young stellar studies: A completely neutral disk should have negligible viscosity and thus cannot efficiently be an accretion disk. Ionization-induced turbulence should affect planet formation and early evolution in complex ways: suppressing gravitational instabilities, concentrating solids, producing density inhomogeneities that can inhibit Type I migration of protoplanets, diminishing disk gaps involved in Type II migration, and so forth. It is thus possible that X-ray emission plays an important role in regulating the structure and dynamics of planetary systems, and the wide range in X-ray luminosities may be relevant to the diversity of extrasolar planetary systems. PMS X-rays are also a major source of ionization at the base of outflows from protostellar disks that produce the emission line Herbig-Haro objects and molecular bipolar outflows (Shang et al., 2002). This is a profound result: If low-mass PMS stars were not magnetically active and profusely emitting penetrating photoionizing radiation, then the coupling between the Keplerian orbits in the disk and the magnetocentrifugal orbits spiralling outward perpendicular to the disks might be much less efficient than we see. X-ray ionization of a molecular environment will induce a complex series of molecular-ion and radical chemical reactions (e.g., Aikawa and Herbst, 1999; Semenov et al., 325 2004). CN, HCO+, and C2H abundances may be good tracers of photoionization effects, although it is often difficult to distinguish X-ray and ultraviolet irradiation from global disk observations. X-ray heating may also lead to ice evaporation and enhanced gaseous abundances of molecules such as methanol. X-ray absorption also contributes to the warming of outer molecular layers of the disk. In the outermost layer, the gas is heated to 5000 K, far above the equilibrium dust temperature (Glassgold et al., 2004). This may be responsible for the strong rovibrational CO and H2 infrared bands seen from several young disks. Finally, PMS flaring may address several long-standing characteristics of ancient meteorites that are difficult to explain within the context of a quiescent solar nebula in thermodynamic equilibrium: 1. Meteorites reveal an enormous quantity of flashmelted chondrules. While many explanations have been proposed, often with little empirical support, it is possible that they were melted by the >108 X-ray flares experienced by a protoplanetary disk during the era of chondrule melting. Melting might either be produced directly by the absorption of X-rays by dustballs (Shu et al., 2001) or by the passage of a shock along the outer disk (Nakamoto et al., 2005). 2. Certain meteoritic components, particularly the calcium-aluminum-rich inclusions (CAIs), exhibit high abundances of daughter nuclides of short-lived radioisotopic anomalies that must have been produced immediately before or during disk formation. Some of these may arise from the injection of recently synthesized radionuclides from supernovae, but other may be produced by spallation from MeV particles associated with the X-ray flares (Feigelson et al., 2002). Radio gyrosynchrotron studies already demonstrate that relativistic particles are frequently present in PMS systems. 3. Some meteoritic grains that were free-floating in the solar nebula show high abundances of spallogenic 21Ne excesses correlated with energetic particle track densities (Woolum and Hohenberg, 1993). The only reasonable explanation is irradiation by high fluences of MeV particles from early solar flares. We thus find that X-ray astronomical studies of PMS stars have a wide variety of potentially powerful effects on the physics, chemistry, and mineralogy of protoplanetary disks and the environment of planet formation. These investigations are still in early stages, and it is quite possible that some of these proposed effects may prove to be uninteresting while others prove to be important. 6. SUMMARY The fundamental result of X-ray studies of young stars and star-formation regions is that material with characteristic energies of keV (or even MeV) per particle is present in environments where the equilibrium energies of the bulk material are meV. Magnetic reconnection flares in lowermass PMS stars, and wind shocks on different scales in 326 Protostars and Planets V O stars, produce these hot gases. Although the X-ray luminosities are relatively small, the radiation effectively penetrates and ionizes otherwise neutral molecular gases and may even melt solids. X-rays from PMS stars may thus have profound effects on the astrophysics of star and planet formation. The recent investigations outlined here from the Chandra and XMM-Newton observatories paint a rich picture of Xray emission in young stars. Both the ensemble statistics and the characteristics of individual X-ray flares strongly resemble the flaring seen in the Sun and other magnetically active stars. Astrophysical models of flare cooling developed for solar flares fit many PMS flares well. PMS spectra show the same abundance anomalies seen in older stars. Rotationally modulated X-ray variability of the nonflaring characteristic emission show that the X-ray emitting structures lie close to the stellar surface and are inhomogeneously distributed in longitude. This is a solid indication that the X-ray emitting structures responsible for the observed modulation are in most cases multipolar magnetic fields, as on the Sun. At the same time, the analysis of the most powerful flares indicates that very long magnetic structures are likely present in some of the most active PMS stars, quite possibly connecting the star with its surrounding accretion disk. The evidence suggests that both coronal-type and star-disk magnetic field lines are present in PMS systems, in agreement with current theoretical models of magnetically funnelled accretion. There is a controversy over the X-ray spectra of a few of the brightest accreting PMS stars. TW Hya shows low plasma temperatures and emission lines, suggesting an origin in accretion shocks rather than coronal loops. However, it is a challenge to explain the elemental abundances and to exclude the role of ultraviolet irradiation. Simultaneous optical observations during the COUP X-ray observation clearly shows that the bulk of X-ray emission does not arise from accretion processes. Perhaps counterintuitively, various studies clearly show that accreting PMS stars are statistically weaker X-ray emitters than nonaccretors. A fraction of the magnetic field lines in accreting PMS stars are likely to be mass loaded and cannot reach X-ray temperatures. X-ray images of high-mass star-forming regions are incredibly rich and complex. Each image shows hundreds or thousands of magnetically active PMS stars with ages ranging from Class I (and controversially, Class 0) protostars to zero-age main-sequence stars. Hard X-rays are often emitted so that Chandra can penetrate up to AV = 500 mag into molecular cloud material. Chandra images of MSFRs also clearly reveal for the first time the fate of O-star winds: The interiors of some HII regions are suffused with a diffuse 10 MK plasma, restricting the 104 K gas to a thin shell. The concept of a Strömgren sphere must be revised in these cases. Only a small portion of the wind energy and mass appears in the diffuse X-ray plasma; most likely flows unimpeded into the galactic interstellar medium. The full population of stars down to ~1 M is readily seen in X-ray im- ages of MSFRs, with little contamination from extraneous populations. This may lead, for example, to X-ray-based discrimination of close OB binaries with colliding winds and identification of intermediate-mass PMS stars that are not accreting. In the most active and long-lived MSFRs, cavity SNRs and superbubbles coexist with, and may dominate, the stellar and wind X-ray components. X-ray studies thus chronicle the life cycle of massive stars from proto-O stars to colliding O winds, to supernova remnants and superbubbles. These star-forming regions represent the building blocks of galactic-scale star formation and starburst galaxies. Some of the issues discussed here are now well developed while others are still in early stages of investigation. It is unlikely that foreseeable studies will give qualitatively new information on the X-ray properties of low-mass PMS stars than obtained from the many studies emerging from the COUP and XEST projects. In-depth analysis of individual objects, especially high-resolution spectroscopic study, represents an important area ripe for follow-up exploration. The many X-ray studies of MSFRs now emerging should give large new samples of intermediate-mass stars, and new insights into the complex physics of OB stellar winds on both small and large scales. Although Chandra and XMMNewton have relatively small fields, a commitment to widefield mosaics of MSFR complexes like W3-W4-W5 and Carina could give unique views into the interactions of highmass stars and the galactic interstellar medium. Deep Xray exposures are needed to penetrate deeply to study the youngest embedded systems. Finally, the next generation of high-throughput X-ray telescopes should bring new capabilities to perform high-resolution spectroscopy of the Xray emitting plasmas. Today, theoretical work is urgently needed on a host of issues raised by the X-ray findings: magnetic dynamos in convective stars, accretion and reconnection in disk-star magnetic fields, flare physics at levels far above those seen in the Sun, and possible effects of X-ray ionization of protoplanetary disks. Acknowledgments. E.D.F. recognizes the excellent work by K. Getman and the other 36 scientists in the COUP collaboration. E.D.F. and L.K.T. benefit from discussions with their Penn State colleagues P. Broos, G. Garmire, K. Getman, M. Tsujimoto, and J. Wang. Penn State work is supported by the National Aeronautics and Space Administration (NASA) through contract NAS838252 and Chandra Awards G04-5006X, G05-6143X, and SV474018 issued by the Chandra X-ray Observatory Center, operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. M.G. warmly acknowledges the extensive work performed by XEST team members. The XEST team has been financially supported by the Space Science Institute (ISSI) in Bern, Switzerland. XMM-Newton is an ESA science mission with instruments and contributions directly funded by ESA Member States and the U.S. (NASA). K.G.S. is grateful for funding support from NSF CAREER grant AST-0349075. REFERENCES Aikawa Y. and Herbst E. (1999) Astron. Astrophys., 351, 233–246. Albacete Colombo J. F., Méndez M., and Morrell N. I. (2003) Mon. Not. R. 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After an extensive review process and passing a major development milestone, NASA is ready to proceed with final design and construction of its next Mars rover, currently targeted to launch in the summer of 2020 and arrive on the Red Planet in February 2021.
The Mars 2020 rover will investigate a region of Mars where the ancient environment may have been favorable for microbial life, probing the Martian rocks for evidence of past life. Throughout its investigation, it will collect samples of soil and rock and cache them on the surface for potential return to Earth by a future mission.
“The Mars 2020 rover is the first step in a potential multi-mission campaign to return carefully selected and sealed samples of Martian rocks and soil to Earth,” said Geoffrey Yoder, acting associate administrator of NASA’s Science Mission Directorate in Washington. “This mission marks a significant milestone in NASA’s Journey to Mars – to determine whether life has ever existed on Mars, and to advance our goal of sending humans to the Red Planet.”
To reduce risk and provide cost savings, the 2020 rover will look much like its six-wheeled, one-ton predecessor, Curiosity, but with an array of new science instruments and enhancements to explore Mars as never before. For example, the rover will conduct the first investigation into the usability and availability of Martian resources, including oxygen, in preparation for human missions.
Mars 2020 will carry an entirely new subsystem to collect and prepare Martian rocks and soil samples that includes a coring drill on its arm and a rack of sample tubes. About 30 of these sample tubes will be deposited at select locations for return on a potential future sample-retrieval mission. In laboratories on Earth, specimens from Mars could be analyzed for evidence of past life on Mars and possible health hazards for future human missions.
Two science instruments mounted on the rover’s robotic arm will be used to search for signs of past life and determine where to collect samples by analyzing the chemical, mineral, physical and organic characteristics of Martian rocks. On the rover’s mast, two science instruments will provide high-resolution imaging and three types of spectroscopy for characterizing rocks and soil from a distance, also helping to determine which rock targets to explore up close.
A suite of sensors on the mast and deck will monitor weather conditions and the dust environment, and a ground-penetrating radar will assess sub-surface geologic structure.
The Mars 2020 rover will use the same sky crane landing system as Curiosity, but will have the ability to land in more challenging terrain with two enhancements, making more rugged sites eligible as safe landing candidates.
“By adding what’s known as range trigger, we can specify where we want the parachute to open, not just at what velocity we want it to open,” said Allen Chen, Mars 2020 entry, descent and landing lead at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California. “That shrinks our landing area by nearly half.”
Terrain-relative navigation on the new rover will use onboard analysis of downward-looking images taken during descent, matching them to a map that indicates zones designated unsafe for landing.
“As it is descending, the spacecraft can tell whether it is headed for one of the unsafe zones and divert to safe ground nearby,” said Chen. “With this capability, we can now consider landing areas with unsafe zones that previously would have disqualified the whole area. Also, we can land closer to a specific science destination, for less driving after landing.”
There will be a suite of cameras and a microphone that will capture the never-before-seen or heard imagery and sounds of the entry, descent and landing sequence. Information from the descent cameras and microphone will provide valuable data to assist in planning future Mars landings, and make for thrilling video.
“Nobody has ever seen what a parachute looks like as it is opening in the Martian atmosphere,” said JPL’s David Gruel, assistant flight system manager for the Mars 2020 mission. “So this will provide valuable engineering information.”
Microphones have flown on previous missions to Mars, including NASA’s Phoenix Mars Lander in 2008, but never have actually been used on the surface of the Red Planet.
“This will be a great opportunity for the public to hear the sounds of Mars for the first time, and it could also provide useful engineering information,” said Mars 2020 Deputy Project Manager Matt Wallace of JPL.
Once a mission receives preliminary approval, it must go through four rigorous technical and programmatic reviews – known as Key Decision Points (KDP) — to proceed through the phases of development prior to launch. Phase A involves concept and requirements definition, Phase B is preliminary design and technology development, Phase C is final design and fabrication, and Phase D is system assembly, testing, and launch. Mars 2020 has just passed its KDP-C milestone.
“Since Mars 2020 is leveraging the design and some spare hardware from Curiosity, a significant amount of the mission’s heritage components have already been built during Phases A and B,” said George Tahu, Mars 2020 program executive at NASA Headquarters in Washington. “With the KDP to enter Phase C completed, the project is proceeding with final design and construction of the new systems, as well as the rest of the heritage elements for the mission.”
The Mars 2020 mission is part of NASA’s Mars Exploration Program. Driven by scientific discovery, the program currently includes two active rovers and three NASA spacecraft orbiting Mars. NASA also plans to launch a stationary Mars lander in 2018, InSight, to study the deep interior of Mars.
JPL manages the Mars 2020 project and the Mars Exploration Program for NASA’s Science Mission Directorate in Washington.
For more information about Mars 2020, visit: http://mars.nasa.gov/mars2020 | 0.80778 | 3.084196 |
High Resolution Stereo Camera (HRSC)
The HRSC is imaging the entire planet in full colour, 3D and with a resolution of about 10 metres. Selected areas will be imaged at 2-metre resolution. One of the camera's greatest strengths will be the unprecedented pointing accuracy achieved by combining images at the two different resolutions. Another will be the 3D imaging which will reveal the topography of Mars in full colour.
HRSC a multi-sensor pushbroom instrument comprising multiple charge coupled device (CCD) line sensors mounted in parallel for simultaneous high-resolution stereo, multicolour and multi-phase imaging of the martian surface. An additional Super Resolution Channel provides frame images embedded in the basic HRSC swath at five times greater resolution.
"The strength of HRSC is to perform high resolution digital terrain models of the martian surface in order to provide topographic context for the geoscientific evaluation of surface processes in space and time,” says Ralf Jaumann, HRSC Principal Investigator from the Institute of Planetary Research, DLR, Berlin, Germany.
Visible and Infrared Mineralogical Mapping Spectrometer (OMEGA)
OMEGA (Observatoire pour la Minéralogie, l'Eau, les Glaces et l'Activité) builds up maps of the surface mineral composition from the visible and infrared light reflected from the planet's surface in the wavelength range 0.5-5.2 microns. As the light reflected from the surface passes through the atmosphere before entering the instrument, OMEGA also measures the atmospheric composition.
"We want to know the iron content of the surface, the water content of the rocks and clay minerals and the abundance of non-silicate materials such as carbonates and nitrates. These measurements would allow us to reconstruct the history of the planet," says Jean-Pierre Bibring, OMEGA Principal Investigator from the Institut d’Astrophysique Spatiale, Orsay, France.
Ultraviolet and Infrared Atmospheric Spectrometer (SPICAM)
SPICAM (Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars) determines the composition of the martian atmosphere by measuring the light that passes though the atmosphere. The ultraviolet sensor measures ozone absorbing 0.25 micron light, while the infrared channel measures water vapour that absorbs at 1.38 micron. The instrument looks in nadir and also works in solar and stellar occultation geometry, enabling vertical profiling of the atmospheric constituents.
"Over the mission lifetime we build up comprehensive climatology of ozone and water vapour and monitor the dust cycle as well as perform key measurements of emissions in the upper atmosphere," says Franck Montmessin, SPICAM Principal Investigator from, LATMOS, Guyancourt, France.
Planetary Fourier Spectrometer (PFS)
The PFS determines the composition and structure of the martian atmosphere by measuring the sunlight absorbed by molecules and the infrared radiation they emit in the range 1.2–45 microns. In particular, PFS builds long-term, global scale maps of vertical temperature profiles in the atmosphere, as well as complete climate records of water vapour and carbon monoxide. The instrument is also continuously looking for minor constituents including methane, hydrogen peroxide and formaldehyde.
"We hope to get many, many measurements so that by taking the average of thousands we'll be able to see minor species," says Marco Giuranna, PFS Principal Investigator from Istituto Fisica Spazio Interplanetario, Rome, Italy.
Analyzer of Space Plasma and Energetic Atoms (ASPERA-3)
ASPERA-3 measures ions, electrons and energetic neutral atoms in the outer atmosphere to reveal the numbers of oxygen and hydrogen atoms (the constituents of water) interacting with the solar wind and the regions of such interaction. Constant bombardment by the stream of charged particles pouring out from the Sun is thought to be responsible for the losses from the martian atmosphere. The planet no longer has a global magnetic field to deflect the solar wind, which is consequently free to interact unhindered with atoms of atmospheric gas and sweep them out to space.
"We will be able to see this plasma escaping the planet and so estimate how much atmosphere has been lost over billions of years," says Mats Holmström, ASPERA Principal Investigator from the Swedish Institute of Space Physics in Kiruna, Sweden.
Mars Radio Science Experiment (MaRS)
MaRS uses the radio signals that convey data and instructions between the spacecraft and antenna on Earth to probe the planet's ionosphere, atmosphere, surface and even the interior. When the spacecraft disappears behind Mars or appears from behind the planet as seen from Earth (radio-occultation) the radio signal is modulated by the atmosphere. Resulting changes in frequency and power of the radio signal are used to derive the structure of the neutral atmosphere and ionosphere. Information on the interior is gleaned from the planet's gravity field, which is calculated from the changes in the velocity of the spacecraft relative to Earth. The surface roughness is deduced from the way in which the radio waves are reflected from the martian surface.
"Variations in the gravitational field of Mars will cause slight changes in the speed of the spacecraft relative to the ground station, which can be measured with an accuracy of less than one tenth the speed of a snail at full pace," says Martin Pätzold, MaRS Principal Investigator from Rheinishes Institut für Umweltforschung at Köln University, Germany.
Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS)
MARSIS is mapping the sub-surface structure to a depth of a few kilometres. The instrument's 40-metre long antenna sends low frequency radio waves towards the planet, which are reflected from any surface or subsurface boundary they encounter. For most, this will be the surface of Mars, but a significant fraction travels through the crust to be reflected at sub-surface interfaces between layers of different material, including ice, soil and rock.
"We can measure the thickness of the polar caps and estimate their composition. We are also probing volcanic and sedimentary rock layers outside of the polar regions," says Roberto Orosei, MARSIS Principal Investigator from Istituto di Astrofisica e Planetologia Spaziali, Bologna, Italy. “MARSIS is also studying the ionosphere, as this electrically charged region of the upper atmosphere reflects and modifies some radio waves.”
Visual Monitoring Camera (VMC)
VMC is the engineering camera installed on board the spacecraft to confirm separation of the Beagle-2 lander. Since 2007 VMC has been used for public outreach purposes and became known as “Mars webcam”.
“Since it was reactivated, this small camera has done a fantastic job in regular imaging of the planet, and through its outreach activities and social media channels is helping bring Mars closer to the public,” says Simon Wood, Mars Express spacecraft operations engineer at ESOC, Darmstadt.
In 2016 ESA began working on the conversion of the humble camera into a professional science instrument. “The VMC context images strongly complement HRSC and OMEGA observations by providing regular global monitoring of clouds, dust and atmospheric structures as well as characterization of transient surface features like frosts and polar caps,” says Agustín Sánchez-Lavega, the VMC team lead at the University of the Basque Country, Bilbao, Spain.
VMCs image processing is automated, meaning that the latest observations are processed and uploaded shortly after arriving on Earth. The VMC blog contains the archive of raw data files whilst processed images are uploaded to the cameras own flickr account. When new images are available VMC notifies the world via its Twitter account @esamarswebcam. | 0.898004 | 3.796277 |
Mapping stellar evolution, Eddington will determine the size and precise chemical composition of the stars, and will search for other Earth-sized worlds that harbour extraterrestrial life.
For more in-depth scientific and technical details of our Space Science Programme and missions, follow this link.
Eddington will be a space telescope designed to detect subtle changes in the light from stars. It will spot oscillations that show the star’s interior condition. It will also find planets half the size of Earth and upwards, within the star’s habitable zone, as they cross the face of the star.
Eddington is a precision photometer - a device that will measure small changes in the brightness of a celestial object. For example, if Eddington were to observe a swarm of 10 000 fireflies, it would notice if just one of them ‘turned off’.
All stars vary a little in brightness because they vibrate like ringing bells. The frequency of this oscillation is determined by factors such as the size, mass, composition, and age of the star. Eddington will study the brightness variations, allowing astronomers to relate them to the internal condition of the star. This technique is known as ‘asteroseismology’.
Eddington will also detect planets passing across the face of their parent star. When a planet crosses a star, it is called a transit and blocks out a tiny fraction of light. Eddington will detect the drop in light, revealing the existence of the planet.
Asteroseismology is the study of stellar oscillations in stars of all types (that is, the study of starquakes). Eddington will be the culmination of an international attempt to perform asteroseismology from space. Two small precursor space missions, MOST and Corot are planned to lead the way.
MOST is a Canadian mission using a 15-centimetre telescope due for launch in 2003. It will monitor a handful of the very brightest stars such as Procyon and Eta Boötes for about a month each.
Corot is a French mission, with some funding from ESA, that uses a 27-centimetre telescope. It will be launched in late 2005. Corot will make long-term observations of between 20-30 stars, leading to high-precision data. It will also attempt to discover transiting planets, larger than a few times the size of the Earth.
These smaller missions will pave the way for Eddington which will perform an extensive and far-reaching survey, beginning in 2008. From a better vantage point, further from the Earth, this mission will study the interior composition of about 50 000 stars. It will also survey about 500 000 stars, looking for planets down to the size of Mars (that is, about one third the size of the Earth).
The Eddington payload can be described as a wide-field, high-accuracy optical photometer, and it is characterised by its simplicity and robustness.
Thanks to its large field of view, Eddington will acquire data simultaneously on a very large number of targets: high-time-resolution asteroseismic data will be collected on about 50 000 stars, while planetary transits will be searched for on about 500 000 stars.
Its large collecting area will enable it to observe clusters and stars in crucial stages of stellar evolution which are not available among the bright stars in the sky. These facts will allow Eddington to achieve qualitatively different science goals than the small exploratory national projects which are currently under development.
After leaving Earth, Eddington will travel beyond the Moon to a special orbit called the second Lagrangian point (or L2 for short). Here it will begin its five-year mission.
Eddington builds on a solid heritage of smaller asteroseismology and transit-based planet-searching missions and of previous studies.
An asteroseismology mission was proposed to ESA in response to a Call for Proposals, under the name of STARS. STARS featured a 1-metre diameter telescope, and was selected for a study. Although in the final selection phase, the Planck mission (then COBRAS-SAMBA) was preferred to STARS, the mission and its scientific goals were rated very highly.
ESA recommended Planck, to first execute a smaller stellar seismology mission project in some Member States, before embarking on a full-scale STARS mission.
Eddington is a totally European mission. Spacecraft, telescope, launch, and spacecraft operations will all be provided by ESA. | 0.890835 | 3.917708 |
A new study suggests that the Earth's evolution from a hot, primordial mush into a rocky planet continuously resurfaced by plate tectonics may be triggered by extraterrestrial impacts. By examining the implications of these processes, the researchers believe that scientists can now start exploring how the modern habitable Earth came to be.
"We tend to think of the Earth as an isolated system, where only internal processes matter," said Craig O'Neill, director of Macquarie University's Planetary Research Center and one of the study authors.
"Increasingly, though, we're seeing the effect of solar system dynamics on how the Earth behaves," he added.
Modeling simulations and comparisons with lunar impact studies have shown that following Earth's accretion about 4.6 billion years ago, shattering impacts continued to mold the planet for hundreds of millions of years.
Although these happenings appear to have tapered off over time, spherule beds suggest that the Earth experienced a period of extreme bombardment roughly 3.2 billion years ago, around the same time the first signs of plate tectonics appear on rock record.
Spherule beds are distinctive layers of round particles condensed from rock vaporized during an extraterrestrial impact. These were found in South Africa and Australia.
Spherules in the Barberton greenstone belt in the Kaapvaal craton, South Africa. Image credit: Lowe et al., 2014
The coincidence led O'Neill and his co-authors Simone Marchi, William Bottke, and Roger Fu to find out if these events could be related.
"Modelling studies of the earliest Earth suggest that very large impacts-- more than 300 km (186 miles) in diameter -- could generate a significant thermal anomaly in the mantle," said O'Neill. This appeared to have changed the mantle's buoyancy enough to make upwellings that "could directly drive tectonics."
However, the limited evidence found to date from the Archaean-- about 4 to 2.5 billion years ago-- suggests that mostly smaller impacts less than 100 km (62 miles) in diameter happened during this interval.
The researchers used existing methods to expand the Middle Archaean impact record to identify whether these modest collisions were still large and often enough to trigger global tectonics.
They also developed numerical simulations to model the thermal effects of these impacts on the mantle.
The findings showed that during the Middle Archaean, 100 km (62 miles) wide impacts, which are about 30 km (19 miles) wider than the Chixclub crater, were able to weaken the planet's rigid, outermost layer. This could be the trigger for tectonic processes, particularly if Earth's exterior was already primed for subduction, explained O'Neill.
"If the lithosphere were the same thickness everywhere, such impacts would have little effect. But during the Middle Archean, he says, the planet had cooled enough for the mantle to thicken in some spots and thin in others."
The modeling also showed that if an impact were to occur in a place where these differences existed, it would create a point of fragility in a system that already had a large contrast in buoyancy, and eventually trigger modern tectonic processes.
"Our work shows there is a physical link between impact history and tectonic response at around the time when plate tectonics was suggested to have started," O'Neill stated.
"Processes that are fairly marginal today -- such as impacting, or, to a lesser extent, volcanism -- actively drove tectonic systems on the early Earth."
"The role of impacts on Archaean tectonics" - O'Neill, C. et al - Geology - https://doi.org/10.1130/G46533.1
Field evidence from the Pilbara craton (Australia) and Kaapvaal craton (South Africa) indicate that modern tectonic processes may have been operating at ca. 3.2 Ga, a time also associated with a high density of preserved Archaean impact indicators. Recent work has suggested a causative association between large impacts and tectonic processes for the Hadean. However, impact flux estimates and spherule bed characteristics suggest impactor diameters of <100 km at ca. 3.5 Ga, and it is unclear whether such impacts could perturb the global tectonic system. In this work, we develop numerical simulations of global tectonism with impacting effects, and simulate the evolution of these models throughout the Archaean for given impact fluxes. We demonstrate that moderate-size (~70 km diameter) impactors are capable of initiating short-lived subduction, and that the system response is sensitive to impactor size, proximity to other impacts, and also lithospheric thickness gradients. Large lithospheric thickness gradients may have first appeared at ca. 3.5–3.2 Ga as cratonic roots, and we postulate an association between Earth’s thermal maturation, cratonic root stability, and the onset of widespread sporadic tectonism driven by the impact flux at this time.
Featured image credit: Mark A. Garlick/YouTube | 0.840445 | 3.94964 |
Revealing the Complexity of Other Worlds
There are thousands of planets orbiting other stars—extrasolar planets, or “exoplanets,” yet in 1990, when Hubble was launched, the study of planets beyond our solar system was not even a field of research. Astronomers discovered the first so-called exoplanet in 1992. In 2008, a year before NASA's planet-hunting Kepler space telescope was launched to look for Earth-sized worlds around distant stars, Hubble took the first visible-light snapshot of a planet beyond the solar system.
These systems are very different than what astronomers had expected, and show us that star systems are quite unlike our solar system. Huge gas giant planets have been found extremely close to their stars, and many "super-Earths" two to 10 times the mass of our own planet have been discovered. Despite the unexpected discoveries, the question that drives us remains the same: Are there other planets out there that could, or do, support life?
In the last two decades, the Hubble Space Telescope has worked with other telescopes to open a window onto the mystery of planet formation. Hubble's ability to peer into nearby nebulae and to probe the regions around neighboring stars has shown us planetary systems under construction, the conditions planets form in, and numerous diverse exoplanets in unusual systems. Hubble's revelations have sometimes confirmed our ideas and sometimes showed us things we never imagined, all the while helping us better understand how planets form.
From debris disks to exoplanet diversity
Hubble early on unveiled debris disks, the scattering of small dust particles hypothesized to be produced by collisions between small planetary bodies such as asteroids in the regions around forming stars. The disks of material are produced from these grinding collisions. As disks form they flatten, become denser, and may produce planets. Hubble further unveiled planetary systems in formation through observation of stellar nurseries such as those found embedded in the Orion Nebula complex.
Exoplanet characteristics were uncovered in Hubble observations of transits and direct measurements of chemical compositions of planetary atmospheres. Numerous planets with clear skies were found, as well as others with hazy atmospheres, and several with cloudy atmospheres that could be obscuring water.
Through Hubble studies, researchers found that exoplanet characteristics vary widely, from the large “hot Jupiters”-- planets the size of Jupiter – and numerous other large gas planets, to those objects almost as small as the Earth.
Deeper understanding of parent stars
The parent stars in these systems are also diverse, from stars similar in mass to the Sun, to much smaller, active stars that may threaten the longevity of their planets. Hubble studies show that single, double and triple star systems can harbor planets.
STScI conducts a variety research programs and offers various tools for analyzing archive data on exoplanets from HST and other missions such as TESS, Kepler, and in the future, JWST. | 0.877333 | 4.033891 |
Would an exoplanet that has more ocean than Earth rotate at a different speed as a result of this? Would the amount of water impact the weight, gravitational pull, and/or tidal forces and cause a difference in the exoplanet's rotation period? (For simplicity's sake, say, if it was earth-like in every respect other than having more ocean than Earth does at about 70% of the surface area.)
Would an exoplanet that has more ocean than Earth rotate at a different speed as a result of this?
Basically no. Rotation speed, or angular velocity doesn't measurably change with your proposed example.
The basic formula is that Angular velocity (time for 1 full rotation) = Angular Momentum divided by Moment of Inertia. Formulas and explanations are in the link(s) above, and if I was to explain it, it would get wordy, but your question seemed to be more general, less about doing the mathematical calculations, so I'll skip the formulas.
In nutshell, talking about a planet, the state of matter doesn't affect the angular momentum. Angular momentum is conserved and that, divided by moment of inertia determines rotation speed. Now if you get something spinning fast enough the angular rotation can overwhelm the gravity and when this happens, the planet can begin to fly apart, which happens more easily with water than a rocky surface which has some cohesion, but ignoring crazy super fast rotations, a water world, a deep ocean world, a shallow ocean world and a rocky world all obey the the angular velocity law and composition doesn't matter. The angular momentum is conserved. The moment of inertia of a planet can change but for the most part, doesn't change much.
The Earth's moment of Inertia, for example, changes as glaciers grow or shrink, or when there's an earthquake. Even, every time we a tall building is built the Earth's moment of inertia increases a teeny tiny bit, similar to a skater extending their arms to slow down coming out of a spiral.
When there's an earthquake which, for the most part, settles the Earth, there's a small increases in the Earth's rotational speed. The total angular momentum and total mass remaining the same but shifting of material changes the moment of inertia. (Granted space dust and tidal effects change the Earth's moment of Inertia, but quite slowly).
Would the amount of water impact the weight, gravitational pull, and/or tidal forces and cause a difference in the exoplanet's rotation period?
This is harder question to answer precisely because adding water changes the mass of the planet and changing the mass changes the moment of inertia, but sticking to the principal of your question, there's no measurable effect.
Lets take a somewhat simpler example without changing the planet's mass. Ice ages. When the Earth is in an ice age there's less liquid oceans and more ice at the poles but the total mass is unchanged. More mass at the poles and less mass in the oceans decreases the Earth's moment of inertia because the bulk of the Earth's moment of inertia is around the equator, so, as a result, the Earth rotates slightly faster during an ice age and slightly slower after an ice age. Over time, the Earth's crust has a tendency adjust for this effect but that takes tens of thousands of years. Parts of the Earth's crust is still rebounding from the last ice age.
Gravitational pull isn't relevant. Neutron Stars with enormous gravitational pull can rotate very fast and the planet with the fastest rotation in our solar-system is Jupiter and the one with the slowest rotation is Mercury. Angular velocity has no direct correlation to mass or gravity though there is an indirect correlation. As a star, for example condenses it's rotation speeds up, because the angular momentum is conserved but as it settles the moment of inertia decreases. That's why young stars, White Dwarfs and Neutron stars can spin very fast.
Tidal forces can create drag on rotation but the effect is slow, taking millions or hundreds of millions of years. With enough time, tidal forces cause a planet or moon to stop rotating and become tidally locked but there's no short term affect. (I'll say a bit more on this later).
So, a planet with large oceans wouldn't rotate any slower than a planet with no oceans because liquid or solid can have equal angular velocity, but over time, tides will slow a planet with oceans more quickly than a planet without them.
Because the Earth has oceans, the Moon's gravitation on the Earth's tidal bulge does slow down the Earth's rotation, but this has been happening for 4 billion years and the Earth still rotates every 24 hours - one of the faster planets. If the Earth had more water the Moon's tidal tug would slow the earth down a bit faster, but it would still be very gradual.
Jupiter, which is basically a ball of gas, is the fastest rotating planet and Mercury, basically a rock, the slowest, so those are 2 examples of composition not being a factor, though Mercury's slow rotation is in large part due to the strong tidal forces it receives from the Sun.
Now, I Understand the logical approach to your question, as there's something apparent about water resisting rotation - touched on in this question, but the fact that water doesn't spin with a glass when you spin a glass is an example of conservation of angular momentum, not an argument against it. On a planet, the oceans are rotating with the planet and the angular momentum is already there.
Hope that wasn't too long, but that's the gist of it. I can try to clean up or clarify if needed.
If the mass, radius and total angular momentum of the planet is the same as Earth, then I can put forward an answer. (Of course if the angular momentum is allowed to be different you could have any rotation rate...)
First, surface gravity is unchanged since this only depends on the mass and radius of a planet.
Second, if the mass is constant then the average density must be the same as Earth. But water is less dense than the average density of the Earth, so the interior of the planet would need to be denser than that of the Earth in order for the average to be similar.
If the density is higher than Earth on the inside, but lower on the outside, then the moment of inertia, which depends on how far mass is from the axis of rotation squared, will be lower. Then, because angular momentum (assumed constant) is the product of moment of inertia and rotation rate, we deduce that the rotation rate would need to be faster.
NB: Simply covering a larger area with Earthlike ocean would make hardly any difference whatsoever. You need a lot of surface water to make a difference.
I would assume so seeing as how it would change the density
If it is exactly like earth but has a crap ton more of an ocean- it is perceivable that it's (average) density would be lower, Also, minutely, it would compress this water more and heat it and make something of an atmosphere given that it doesn't escape. Trapping more and more energetic particles into a thick foggy atmosphere can change the rotation so slightly it will probably never be noticed.....
Also, if it has a moon, tides/ waves due to gravity can also minutely push the planet in a different state of rotation. Very slightly
I read it wrong, but I'm keeping that in case it helps.
It really depends on how much more water there is. If it was 100% coverage, it would be more "tidy" and the ocean would certainly be more compact (same mass as earth, but add A HUGE amount of water to that to get from 70% to 100% coverage of the area)-- tides may not be as wild. I suppose it would effect the rotation period, but not much.
Note, it might be easier to post this on physics stack exchange, you get better answers, much sooner. This seems like a good question to get up votes off of... | 0.818112 | 3.714138 |
He saw sunspots, demonstrating that the sun itself was not the perfect orb demanded by the Greek cosmology that had been adopted by the church.
But he also saw something else, a thing that is often now forgotten. He saw that the Milky Way, that cloudy streak across the sky, is made of stars. That observation was the first hint that, not only is the Earth not the centre of things, but those things are vastly, almost incomprehensibly, bigger than people up until that date had dreamed. And they have been getting bigger, and also older, ever since. Astronomers' latest estimates put the age of the universe at about That is three times as long as the Earth has existed and about , times the lifespan of modern humanity as a species.
The true size of the universe is still unknown.
Its age, and the finite speed of light, means no astronomer can look beyond a distance of But it is probably bigger than that. Nor does reality necessarily end with this universe. Physics, astronomy's dutiful daughter, suggests that the object that people call the universe, vast though it is, may be just one of an indefinite number of similar structures, governed by slightly different rules from each other, that inhabit what is referred to, for want of a better term, as the multiverse.https://ziedeburrebond.gq
The 10 Greatest Scientists of All Time
The shattering of the crystal spheres which Galileo's contemporaries thought held the planets and the stars, with the sphere containing the stars representing the edge of the universe, is along with Darwin's discovery of evolution by natural selection the biggest revolution in self-knowledge that mankind has undergone. The world that Galileo was born into was of comprehensible compass. The Greeks had a fair idea of the size of the Earth and the distance to the moon, and so did the medievals who read their work.
- Fast forwarding Higher Education Institutions for Global Challenges: Perspectives and Approaches.
- Fermented Milks (Society of Dairy Technology)!
- A John Dewey source page.
- Book Revolution In Science: How Galileo And Darwin Changed Our World.
- Mohameds Journey;
But these were distances that the imagination might, at a stretch, embrace. Kuhn dated the genesis of his book to , when he was a graduate student at Harvard University and had been asked to teach a science class for humanities undergraduates with a focus on historical case studies. Kuhn later commented that until then, "I'd never read an old document in science. Kuhn wrote " About motion, in particular, his writings seemed to me full of egregious errors, both of logic and of observation.
While perusing Aristotle's Physics , Kuhn formed the view that in order to properly appreciate Aristotle's reasoning, one must be aware of the scientific conventions of the time.
ISBN 13: 9780230202689
Kuhn concluded that Aristotle's concepts were not "bad Newton," just different. Prior to the publication of Kuhn's book, a number of ideas regarding the process of scientific investigation and discovery had already been proposed. Ludwik Fleck developed the first system of the sociology of scientific knowledge in his book The Genesis and Development of a Scientific Fact He claimed that the exchange of ideas led to the establishment of a thought collective, which, when developed sufficiently, served to separate the field into esoteric professional and exoteric laymen circles.
Kuhn was not confident about how his book would be received. Harvard University had denied his tenure, a few years before. However, by the mids, his book had achieved blockbuster status. Kuhn also addresses verificationism , a philosophical movement that emerged in the s among logical positivists. The verifiability principle claims that meaningful statements must be supported by empirical evidence or logical requirements. Kuhn's approach to the history and philosophy of science focuses on conceptual issues like the practice of normal science , influence of historical events, emergence of scientific discoveries, nature of scientific revolutions and progress through scientific revolutions.
A selection of "Central Spiritual Insights" gleaned from Christian sources
What types of lexicons and terminology were known and employed during certain epochs? Stressing the importance of not attributing traditional thought to earlier investigators, Kuhn's book argues that the evolution of scientific theory does not emerge from the straightforward accumulation of facts, but rather from a set of changing intellectual circumstances and possibilities. Kuhn did not see scientific theory as proceeding linearly from an objective, unbiased accumulation of all available data, but rather as paradigm-driven.
Rather, they are concrete indices to the content of more elementary perceptions, and as such they are selected for the close scrutiny of normal research only because they promise opportunity for the fruitful elaboration of an accepted paradigm. Far more clearly than the immediate experience from which they in part derive, operations and measurements are paradigm-determined.
Science does not deal in all possible laboratory manipulations. Instead, it selects those relevant to the juxtaposition of a paradigm with the immediate experience that that paradigm has partially determined. As a result, scientists with different paradigms engage in different concrete laboratory manipulations. Kuhn explains his ideas using examples taken from the history of science. For instance, eighteenth-century scientists believed that homogenous solutions were chemical compounds.
Therefore, a combination of water and alcohol was generally classified as a compound. Nowadays it is considered to be a solution , but there was no reason then to suspect that it was not a compound. Water and alcohol would not separate spontaneously, nor will they separate completely upon distillation they form an azeotrope. Water and alcohol can be combined in any proportion. Under this paradigm, scientists believed that chemical reactions such as the combination of water and alcohol did not necessarily occur in fixed proportion.
This belief was ultimately overturned by Dalton's atomic theory , which asserted that atoms can only combine in simple, whole-number ratios. Under this new paradigm, any reaction which did not occur in fixed proportion could not be a chemical process. This type world-view transition among the scientific community exemplifies Kuhn's paradigm shift. A famous example of a revolution in scientific thought is the Copernican Revolution. In Ptolemy 's school of thought, cycles and epicycles with some additional concepts were used for modeling the movements of the planets in a cosmos that had a stationary Earth at its center.
As accuracy of celestial observations increased, complexity of the Ptolemaic cyclical and epicyclical mechanisms had to increase to maintain the calculated planetary positions close to the observed positions. Copernicus proposed a cosmology in which the Sun was at the center and the Earth was one of the planets revolving around it. For modeling the planetary motions, Copernicus used the tools he was familiar with, namely the cycles and epicycles of the Ptolemaic toolbox.
Yet Copernicus' model needed more cycles and epicycles than existed in the then-current Ptolemaic model, and due to a lack of accuracy in calculations, his model did not appear to provide more accurate predictions than the Ptolemy model. Copernicus' contemporaries rejected his cosmology , and Kuhn asserts that they were quite right to do so: Copernicus' cosmology lacked credibility.
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- Revolution in Science: How Galileo and Darwin Changed Our World (Macmillan Science);
- Book Revolution In Science: How Galileo And Darwin Changed Our World.
- "Central Spiritual Insights" drawn from "non-Christian" Inter-Faith sources?
Kuhn illustrates how a paradigm shift later became possible when Galileo Galilei introduced his new ideas concerning motion. Intuitively, when an object is set in motion, it soon comes to a halt. A well-made cart may travel a long distance before it stops, but unless something keeps pushing it, it will eventually stop moving.
Revolution in Science - How Galileo and Darwin Changed Our World | M. Brake | Palgrave Macmillan
Aristotle had argued that this was presumably a fundamental property of nature : for the motion of an object to be sustained, it must continue to be pushed. Given the knowledge available at the time, this represented sensible, reasonable thinking. Galileo put forward a bold alternative conjecture: suppose, he said, that we always observe objects coming to a halt simply because some friction is always occurring.
Galileo had no equipment with which to objectively confirm his conjecture, but he suggested that without any friction to slow down an object in motion, its inherent tendency is to maintain its speed without the application of any additional force. The Ptolemaic approach of using cycles and epicycles was becoming strained: there seemed to be no end to the mushrooming growth in complexity required to account for the observable phenomena.
Johannes Kepler was the first person to abandon the tools of the Ptolemaic paradigm. He started to explore the possibility that the planet Mars might have an elliptical orbit rather than a circular one. Clearly, the angular velocity could not be constant, but it proved very difficult to find the formula describing the rate of change of the planet's angular velocity. After many years of calculations, Kepler arrived at what we now know as the law of equal areas. Galileo's conjecture was merely that — a conjecture. So was Kepler's cosmology. But each conjecture increased the credibility of the other, and together, they changed the prevailing perceptions of the scientific community.
Later, Newton showed that Kepler's three laws could all be derived from a single theory of motion and planetary motion. Newton solidified and unified the paradigm shift that Galileo and Kepler had initiated. One of the aims of science is to find models that will account for as many observations as possible within a coherent framework.
Once a paradigm shift has taken place, the textbooks are rewritten.
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- Timothy Goodman.
Often the history of science too is rewritten, being presented as an inevitable process leading up to the current, established framework of thought. There is a prevalent belief that all hitherto-unexplained phenomena will in due course be accounted for in terms of this established framework. Kuhn states that scientists spend most if not all of their careers in a process of puzzle-solving. Their puzzle-solving is pursued with great tenacity, because the previous successes of the established paradigm tend to generate great confidence that the approach being taken guarantees that a solution to the puzzle exists, even though it may be very hard to find.
Kuhn calls this process normal science. As a paradigm is stretched to its limits, anomalies — failures of the current paradigm to take into account observed phenomena — accumulate. Their significance is judged by the practitioners of the discipline. Some anomalies may be dismissed as errors in observation, others as merely requiring small adjustments to the current paradigm that will be clarified in due course. | 0.845471 | 3.02619 |
Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.
2020 May 12
Explanation: Where are all of these meteors coming from? In terms of direction on the sky, the pointed answer is the constellation of Small Harp (Lyra). That is why the famous meteor shower that peaks every April is known as the Lyrids -- the meteors all appear to came from a radiant toward Lyra. In terms of parent body, though, the sand-sized debris that makes up the Lyrid meteors come from Comet Thatcher. The comet follows a well-defined orbit around our Sun, and the part of the orbit that approaches Earth is superposed in front of Lyra. Therefore, when Earth crosses this orbit, the radiant point of falling debris appears in Lyra. Featured here, a composite image containing over 33 meteors (can you find them all?) from last month's Lyrid meteor shower shows several bright meteors that streaked over a shore of Seč Lake in the Czech Republic. Also visible are the bright stars Vega and Altair, the planet Jupiter, and the central band of our Milky Way Galaxy.
Authors & editors:
Jerry Bonnell (UMCP)
NASA Official: Phillip Newman Specific rights apply.
A service of: ASD at NASA / GSFC
& Michigan Tech. U. | 0.897795 | 3.001131 |
The famous supergiant on Orion’s shoulder has rapidly dimmed, stoking excitement that a supernova may be in the offing.
Do you hear that ticking? Doesn’t it sound like a stellar timer is counting down to the inevitable demise of a massive star? While the excitement may be the amplified construct of social media predictions of the death of Betelgeuse, our stellar neighbor really is close to going supernova.
“Close”, however, is relative. It could be as “human close” as blowing up any minute now… to “galactic close” as blowing up in a hundred thousand years, maybe more.
So, what’s all the fuss about? In a nutshell, the brightest star in the famous constellation of Orion is bright no more. In the past few weeks, Betelgeuse has dimmed noticeably, stoking predictions that it could be about to spectacularly erupt at any time, becoming as bright as a full Moon and casting its own shadows at night.
While this may sound ominous, a Betelgeuse supernova poses no threat to life on Earth. It’s located a safe 600 light-years away, so if it did explode, we’d be treated to a historic cosmic firework display and not doomsday. Any energetic particles spewing from the explosion may reach the solar system in 100,000 years, but would have a minimal impact; the heliosphere (our Sun’s extended magnetic “bubble” that encompasses all the planets) would be more than powerful enough to deflect the tenuous gases.
There has always been excitement over Betelgeuse and its explosive potential. It’s a massive star, with a mass 12-times that of our Sun, which has reached the end of its life. But with a lifespan of only eight million years or so, it may sound odd that it’s dying of old age. As a comparison, our Sun—an “average” yellow dwarf star—sounds geriatric in comparison; it’s approximately five billion years old. But the strange physics of stellar evolution dictates that the more massive the star, the shorter its lifespan. Betelgeuse is on borrowed time, whereas our Sun is only middle-aged. In other words, Betelgeuse has lived fast and it will die young.
As a star that’s about to die, Betelgeuse is experiencing the final throes of violent processes that signify the conclusion of stellar evolution—a phase that sees a massive star puff up into a red supergiant. In the case of Betelgeuse, while it is 12-times more massive than our Sun, it has expanded into a grotesque, bubbling mess of superheated plasma, puffed up to nearly 1,000-times wider than our Sun. If Betelgeuse were transplanted into the middle of our solar system, it would swallow all the planets out to Saturn. Yes, even Jupiter would be ingested.
After guzzling all of its hydrogen fuel long ago, it’s now fusing heavier elements inside its tortured interior to the point where iron is being created. For any massive star, the fusion of iron is the death knell; energy is being absorbed, and soon, its immense gravity will cause the whole mess to collapse, generating an almighty shockwave that will, ultimately, rip Betelgeuse apart as a supernova.
As reported by astronomers before Christmas, the observed dimming could be interpreted as a precursor to the anticipated supernova, and for good reason. But Betelgeuse is known to regularly vary in brightness, so astronomers suspect that, while this is an unprecedented dimming event, the famous star will soon return to its “regular” brightness once more, reclaiming its rank as ninth brightest star in the sky.
In short, don’t place any serious money on Betelgeuse exploding soon. While there is a tiny chance that it might have already exploded, the light from the supernova currently galloping across the 600 light-year interstellar divide between us and Betelgeuse, it’s way more likely that it’s just Betelgeuse being Betelgeuse and keeping variable star astronomers on their toes.
That’s not to say the dimming event isn’t exciting, on the contrary. Seeing a prominent star in the night sky fade with your own eyes is something to behold, so when you get clear skies, look for Orion and ponder The Hunter’s missing shoulder. | 0.834622 | 3.861809 |
At present, the big bang cosmology cannot explain galaxy formation and can not make its statements consistent, it is really in a disastrous state, the property of pseudo science is getting more and more apparent,and more and more scholars are abandoning the doctrine. The real universe is changing gradually and continuously, no matter what galaxies or objects keep in continuous change, however big bang cosmology belongs to the catastrophic theory which can not describe and reflect these actual process of change, the big bang theory dooms lumpish and useless, will certainly be replaced by the gradualistic cosmology. However, do not go to find the problem from general relativity itself, instead from another fresh road trying to start the establishment of alternative models of the big bang theory is superficial, at all can't be replaced and at best coexist. Chinese scholar by modifying the Einstein gravitational field equation complete the replacement to the big bang theory, clearly established the gradualistic cosmology, has improved and extended the the theory and application of general relativity. Many industry insiders believe that if general relativity continues to stop or grow complacent it will probably be overthrown or replaced. The new modified field equations continues to have the simplicity and elegancy of the original equation, unlike other modifications that only in order to cater to the cosmological application, free added items to field equation so that cannot go back to Newton's law of gravitation in spherically symmetric gravitational field in the distance, so such modified field equations can no longer continue to be called gravitational field equation because it didn’t have contact with gravity again. Jian liang yang’s pioneer paper “Modification of Field Equation and Return of Continuous Creation----- Galaxies Form from Gradual Growth Instead of Gather of Existent Matter”was published in international journal. The new alternative model of the big bang theory abandons the moment creation and accepts the concept of negative pressure which makes naturally the mass of celestial bodies increase and new matter generate constantly in celestial bodies, and today is the key to understand the past and the future, on logic more reasonable, can more rationally explain the observed facts. The new theory shows that not only the space between galaxies is expanding but also galaxies themselve and the average density of the universe remains unchanged, and also can explain accurately in the solar system the observed gravitational anomalies, such as the other backward movement of unknown cause of the moon after considering the tide effect, and the observed change of length of day is inconsistent with the tidal theory, and the radius of the earth is detected to increase 0.2-1 mm by the monitoring satellites each year, and the increase of distance between the sun and the earth. Obviously the continuous expansion of universe is the need of material’s generation, and vividly interprets that the space-time and matter are an indivisible unity. Besides the above distinguishing features the new gradualistic theory of universe has the following characteristics:
1. the modified field equation requires the pressure is negative, some people may feel uncomfortable, however this is actually a kind of secular bias. In fact both classical mechanics and relativity don’t really reject negative pressure, only appears in the equation of motion the pressure’s derivative in classical mechanics and the size of the pressure can be any value, do not rule out the negative. In relativity not only the size of the pressure but also pressure’s derivative appears in the equation of motion, which requires pressure value can not be arbitrary, but isn’t ruled out the negative pressure yet. It is the emergence of negative pressure that leads to the continuous generation of material, as the field equation is applied to an celestial object dm + P dv = 0, the increase of mass of celestial bodies comes from the work done by the negative pressure, new matter arises doesn’t mean the infringement to the law of energy conservation. Further calculation dm=3Hmdt.
2. Although galaxies or celestial objects increase with universal expansion, the angular velocity of their rotation or revolution keeps constant, i.e. periodic invariant, like using a magnifying glass to watch the circular motion, not only the radius of the orbit but also the speed is amplified and the period constant, all energy come still from the work done by the negative pressure. Orbital expansion can completely be derived from geodesic equations rather than additional assumptions. The new theory has important guiding significance in solar physics, space physics, geophysical and seismic genesis and so on
3. Similar to the big bang, the new theory still explain the microwave background radiation for comprehensive reflection of light after red shift emitted from far bodies whose distances can not be distinguished in our instrument, but do not think from so-called final scattering surface. Compared with vast space galaxies amount to molecules, these molecules form extremely thin and deep gas, in other words our universe is equivalent to a cavity, so the light from far has black-body spectrum. But the big bang can not rationally explain the black-body spectrum, in the big bang frame universal temperature is decreased, the so-called thermal equilibrium didn’t exist at all.
4. The rapid generation of matter (such as the big bang) is contrary to common sense, but slow generation is not contrary to common sense, should be allowed, and any absolutization to physical laws is never a scientific attitude.
6. Space-time is infinite, no longer rely on the so-called critical density, the universe's expansion and contraction cycle, alternately, the scale factor meets the sine function R(t)=Csinat, excluding the irrational expansion: big bang --- decelerating ---- inflation --- decelerating ---accelerating .......
The new relation between distance and redshift derived from the modified field equations is highly consistent with observations, and universal expansion is still decelerated and the shoddy conclusion that expansion of universe is accelerating no longer exists. In the new theory sometime in the past the scale factor R (t) =0, at which mass of any body was zero, the absolute temperature of universe was also zero, with mass to increase temperature gradually rose to meet mass-luminosity ratio. That is to say, universal temperature is higher and higher but not lower and lower, and the big bang fireball didn’t exist at all.
7. The new theory has unified the dark matter and dark energy, the modified gravitational field equation is including all effects of dark matter and dark energy and is a complete field equations. Due to negative pressure has the multiple properties of pressure, dark matter and dark energy, dark matter and dark energy arise no longer, all effects of dark matter and dark energy are fully absorbed in the negative pressure. The more important thing is that the negative pressure can be solved through the gravitational field equation, so reduce three cosmological parameters.
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How do you go about hunting for life on another planet elsewhere in our galaxy? A useful starting point is to imagine looking from afar for signs of life on Earth. In a telescope like those we have on Earth, those aliens would likely just see the Earth and sun merged together into a single pale yellow dot.
If they were able to separate the Earth from the sun, they'd still only see a pale blue dot. There would be no way for them to image our planet's surface and see life roving upon it.
However, those aliens could use spectroscopy, taking Earth's light and breaking it into its component colours, to figure out what gases make up our atmosphere. Among these gases, they might hope to find a "biomarker", something unusual and unexpected that could only be explained by the presence of life.
On Earth, the most obvious clue to the presence of life is the abundance of free oxygen in our atmosphere. Why oxygen? Because it is highly reactive and readily combines with other molecules on Earth's surface and in our oceans. Without the constant resupply coming from life, the free oxygen in the atmosphere would largely disappear.
But the story isn't quite that simple. Life has existed on Earth for at least 3.5 billion years. For much of that time, however, oxygen levels were far lower than those seen today.
And oxygen alone is not enough to indicate life; there are many abiological processes that can contribute oxygen to a planet's atmosphere.
The concentration of oxygen in the Earth's atmosphere over the last billion years. As a reference, the dashed red line shows the present concentration of 21%. [Wikimedia]
For example, ultraviolet light could produce abundant oxygen in the atmosphere of a world covered with water, even if it was devoid of life.
The upshot of this is that a single gas does not a biomarker make. Instead, we must instead look for evidence of a chemical imbalance in a planet's atmosphere, something that can not be explained by anything other than the presence of life.
Here on Earth, we have one: our atmosphere is not just rich in oxygen, but also contains significant traces of methane. While abundant oxygen or methane could easily be explained on a planet without life, we also know that methane and oxygen react with each other strongly and rapidly.
When you put them together, that reaction will cleanse the atmosphere of whichever is least common. So to maintain the amount of methane in our oxygen-rich atmosphere, you need a huge source of methane, replenishing it against oxygen's depleting influence. The most likely explanation is life.
Observing exoplanetary atmospheres
If we find an exoplanet sufficiently similar to our own, there are several ways in which we could study its atmosphere to search for biomarkers.
When a planet passes directly between us and its host star, a small fraction of the star's light will pass through the planet's atmosphere on its way to Earth. If we could zoom in far enough, we would actually see the planet's atmosphere as a translucent ring surrounding the dark spot that marks the body of the planet.
How much starlight passes through that ring gives us an indication of the atmosphere's density and composition. What we get is a "transmission spectrum", which is an absorption spectrum of the planetary atmosphere, illuminated by the background light of the star.
Our technology has only now become capable of collecting and analysing these spectra for the first time. As a result, our interpretation remains strongly limited by our telescopic capabilities and our burgeoning understanding of planetary atmospheres.
Despite the current challenges, the technique continues to develop with great success. In the past few years, astronomers have discovered a wide variety of different chemical species in the atmospheres of some of the biggest and baddest of the known transiting exoplanets.
Many exoplanets may have no atmosphere at all. [NASA/JPL-Caltech]
Another approach involves observing a transiting planet and its star as they orbit one another. The goal here is to collect some observations when the planet is visible (but not in transit), and others when it is eclipsed by its star.
With some effort, astronomers can subtract one observation from the other, effectively cancelling the hugely dominant contribution of light from the star. Once that light is removed, what we have left is the day-side spectrum of the planet.
[Star + Planet] — [Star] = [Planet] [NASA/JPL-Caltech/R. Hurt (SSC/Caltech)]
Astronomers are constantly developing new techniques to glean information about exoplanetary atmospheres. One that shows particular potential, especially for the search for planets like our own, is the use of polarised light.
Most of the light we receive from planets is reflected, originating with the host star. The process of reflection brings with it a subtle benefit — the reflected light gains a degree of polarisation. Different surfaces yield different levels of polarisation, and that polarisation might just hold the key to finding the first oceans beyond the solar system.
By rotating a polarising filter, we can block light of certain polarisation. This is how polarised sunglasses cut the glare from puddles and the ocean on a sunny day.[Wikimedia]
These methods are still severely constrained by two factors: the relative faintness of the exoplanets, and their proximity to their host star. The ongoing story of exoplanetary science is therefore heavily focused on overcoming these observational challenges.
Further down the line, advances in technology and the next generation of telescopes may allow the light from an Earth-like planet to be seen directly. At that point, the task becomes (slightly) easier, in part because the planet can be observed for far longer, rather than just relying on eclipse/transit observations.
But even then, spectroscopy will be the way to go; the planets will still be just pale blue dots.
What we have seen so far
The exoplanets we have discovered to date are highly inhospitable to life as we know it. None of the planets studied so far would even be habitable to the most extreme of extremophiles.
The planets whose atmospheres we have studied are primarily "hot Jupiters", giant planets orbiting perilously close to their host stars. As they skim their host's surface, they whizz around with periods of just a few days, yielding transits and eclipses with every orbit.
Because of the vast amounts of energy they receive from their hosts, many of these "hot Jupiters" are enormous, inflated far beyond the scale of our solar system's largest planet. That size, that heat and their speed, make them the easiest targets for our observations.
But as our technology has improved, it has also become possible to observe, through painstaking effort, some smaller planets, known as "super-Earths".
Atmospheres of distant planets…
The hot Jupiter HD189733 has one of the best understood planetary atmospheres beyond the solar system.
Artists impression of the broiling blue marble, HD 189733 b. [NASA, ESA, M. Kornmesser]
Observations by the Hubble Space Telescope, in 2013, suggest a deep-blue world, with a thick atmosphere of silicate vapour. Other studies have shown its atmosphere to contain significant amounts of water vapour, and carbon dioxide.
Overall, however, it appears to be a hydrogen-rich gas giant like Jupiter, albeit super-heated, with cloud tops exceeding 1,000 degrees. Beneath the cloud turps lies a widespread dust layer, featuring silicate and metallic salt compounds.
The young giant planets in the HR8799 system appear to have hydrogen-rich but complex atmospheres, with compounds such as methane, carbon monoxide and water. They are likely larger, younger, and hotter versions of our own giant planets — with their own unique subtleties.
For the super-Earth GJ1214b the lesson is to be careful about making conclusions. Early suggestions that this might be a "water world" or have a cloudless hydrogen atmosphere have since been superseded by models featuring a haze of hydrocarbon compounds (like on Titan), or grains of potassium salt or zinc sulphide.
While the search for Earth-like planets continues using ground- and space-based telescopes, exoplanetary scientists are eagerly awaiting the launch of the James Webb Space Telescope JWST.
That immense telescope, scheduled for launch in around October 2018, could mark the true beginning of the exciting search for distant atmospheric biomarkers and exoplanetary life.
Brad Carter, Professor (Physics), University of Southern Queensland; Amanda Bauer, PhD; Astronomer and Outreach Officer, Australian Astronomical Observatory, and Jonti Horner, Vice Chancellor's Senior Research Fellow, University of Southern Queensland
This article was originally published on The Conversation. | 0.913672 | 3.787464 |
The Hunt for Life Beyond Earth, by Michael D. Lemonick, photographs by Mark Thiessen
The Hunt for Life Beyond Earth is pretty much just like it says: it’s about scientists’ attempts to find life on other planets. Needless to say, Mars is one of the planets they are considering as home for this extraterrestrial life, but Mars is too close. Rocks travel back and forth between Earth and Mars periodically. As a result, the discovery of life on Mars would not prove that said life developed there. It could be terrestrial life that made the trip between the two planets.
Based on the premise that life should be develop in places with liquid water, we are also looking at two of Jupiter’s moon Europa and Saturn’s moon Enceladus, as possible sites of life. Saturn’s moon Titan also has liquid, but that liquid is methane and not water. As a result, scientists who are looking for life haven’t ruled Titan out, but they are uncertain what kind of life would develop in liquid methane.
Then there is the possibility of life beyond our solar system. In 1961, an astronomer named Frank Drake created what is now known as the Drake Equation, which is an equation to calculate how many extrasolar civilizations we should be able to contact. The equation included the number of sunlike stars in our galaxy, the number of those stars that had planetary systems, the number of planetary systems that have planets capable of sustaining life, the number of planets that actually do develop life, the number of those whose residents develop intelligence, and the number of those who develop radio signals that we could detect. We are just now starting to be able to apply numbers to these variables.
As someone who has read and watched entirely too much science fiction for her own good, I think that the Drake Equation may understate the number of planets that we might be able to communicate with. What if a society jumped right to television? Or used some other form of radiation that we cannot yet detect to communicate? Or evolved while orbiting a sun completely different from ours? The Drake Equation might be a good estimate, but there are no guarantees that it is the only way for life to develop. It’s just the way that our life developed.
The Next Breadbasket, by Joel K. Bourne, Jr., photographs by Robin Hammond
The Next Breadbasket is another installment in the Future of Food series. For this installment, we travel to Africa to watch the various ways that the fertile land, and those who work it, are being both used and exploited by agribusiness. In too many African countries, the government allows the agribusiness entities to run people, some of whom have been farming this land for generations, off of their land. Bourne names names, both of the companies that have treated the indigenous people well and those who have treated the people poorly.
So far, two of the ones that Bourne seems to support are a company called African Century Agriculture which uses an “outgrower” model, in which African Century provides soybeans, weeding, and training in conservation agriculture to small farmers. The farmers then sell the soybeans that they grow back to African Century, which deducts the costs of their services from the payment. This way, the small farmers get to keep their land and also get education in the latest agricultural techniques.
Another company that Bourne seems to me to think well of is Bananalandia, the largest banana farm in Mozambique. The owner of Bananalandia, Dries Gouws, pays his workers at least 110% of the Mozambican minimum wage and he also has done things to improve the lives of the people in the surrounding villages, including paving roads, providing electricity, building a school, and making improvements to the sewage system. I know well that 110% of minimum wage is in no way going to raise these people out of poverty, but I feel that the other improvements in the quality of life that Gouws has made are not insignificant either.
The Wells of Memory, by Paul Salopek, photographs by John Stanmeyer
In The Wells of Memory, the second installment of Salopek’s Out of Eden Walk series, Salopek is walking up the western coast of Saudi Arabia, through an area known as the Hejaz. The Hejaz was added to what is now Saudi Arabia in 1925. Both Mecca and Medina are in the Hejaz, so until the era of airplane flight, most of the pilgrims coming from around the world had to pass through the Hejaz. Jeddah, also in the Hejaz is the burial place of Eve, according to legends.
Salopek focuses in part on the wells that are spread, a day’s walk apart, through the Hejaz. The wells date back to the Caliphate of Caliph Umar in 638. There were also guesthouses, forts, and hospitals along the route, courtesy fo the Caliph. Today, in addition to the ancient wells, there are asbila, outdoor electric water coolers along the route these days.
Salopek is one of the first, if not the first, Westerner to travel this route in close to a century, but this is the route taken by other Westerners in the past, including Lawrence of Arabia.
As with nearly all National Geographic stories, The Wells of Memory is punctuated by photographs. However, some of the photographs in this story were taken with a smartphone and then edited to look like vintage, sepia-toned photographs with an app called Hipstamatic. Stanmeyer chose this approach to reflect his feeling that he “had one foot in the present, and the other had stepped back a hundred years.”
Big Fish, by Jennifer S. Holland, photographs by David Doubilet and Jennifer Hayes
For the past 25 years, the Altantic goliath grouper has been a protected species. Once sport fishermen would catch them by the dozen, but goliath groupers are long-lived and reproduce slowly. This meant that the fish were not able to replace their numbers as quickly as they were being harvested. This resulted in the species being granted legal protection as an endangered species.
Now, some fishermen believe that their numbers have rebounded enough that it should be safe to start catching them again. In part they want the trophies, but these fishermen also believe that the goliath grouper is eating fish that the fishermen should legally be able to catch, thus reducing the numbers of legal fish even farther.
Holland seems unswayed by these fisherman’s arguments. She has spoken with scientists who are studying goliath grouper and who believe that the population is still too low. Goliath groupers tend to stick to one area, and until they start to overpopulate that area, they will not spread elsewhere in their range. Additionally, according to Holland, there are a number of studies (she doesn’t tell us which ones) that show that there is not much overlap between the targets of the fishermen and those of the goliath grouper. If the fishermen are finding it difficult to find fish to catch, it is not the fault of the goliath grouper.
Additionally, just because their numbers are rebounding now does not mean that this will continue indefinitely. Goliath grouper juveniles live in mangrove swamps, and the mangroves in their home range are being decimated. To make matters worse, due to mercury levels, goliath grouper are coming down with lesions in their livers. This may also have an impact on their population numbers in the long term. It also makes goliath grouper unsafe to eat, so fishermen who catch them would need to throw them back, or use them only for trophy purposes, which would be wasteful.
Empire of Rock, by McKenzie Funk, photographs by Carsten Peter
Alas, Empire of Rock has nothing to do with popular music. It is, in fact, about the karst caves underneath Guizhou, China. This part of China was once covered by a sea. Over the centuries, the mollusks left their shells behind, which compressed into a limestone formation known as karst. Karst is limestone which is punctured by holes. Water seeps down into the holes, which wears the holes away until they join together and eventually form caves. This area is relatively unique in that this process has taken place over so many centuries that there are entire mountains of karst on the surface. Have you ever seen photographs or Chinese paintings of large, steep stone mountains, usually surrounded by mist? Those are karst mountains.
Funk accompanied a group of scientists and cavers who were attempting to measure the volume of one of the largest cave chambers in the world, the Hong Meigui chamber. Though Funk’s eyes we watch them descend into the chamber and see their laser scanners, which Funk tells us is about the same size as a human head, measure the volume of the cave. Funk and her hosts also visit other caves and karst formations in the area.
“Hong Meigui,” by the way, is the word that inspired me make my last post, on my experiences with foreign language. “Hong Meigui,” depending on the tones, can mean “red rose.” And I suspect that may be the meaning here, since there is a caving organization called the Hong Meigui Cave Exploration Society and the characters for the name of that group are the “hong,” “mei,” and “gui” of “red rose.” Another chamber mentioned is the Miao Room, and my first instinct was that the “miao” in question is “temple,” but, when looking at a list of other “miao”s, it could also be the “miao” that means “infinity,” or any of a number of other Mandarin words that can be transliterated as “miao.” I just don’t know. To make things more frustrating, Funk does imply one translation when he tells us that the Yanzi cave is named for the swallows that live in the walls.
Two months after the cover date on this magazine, in September 2014, the title of the largest cave in the world was granted to the Miao Room.
(originally posted June and July 2015)
2/3/2019 On or around November 28, 2018, I realized that I need to start monetizing this blog. To that end, I’m starting to put what I call Gratuitous Amazon Links into my posts. As of January 12, 2019, I’m going back to add GALs to my older posts. If I can’t find anything exactly on-topic to the post, I’m choosing from among the highest-rated items on the same topic as the post. For example, for a post on a park, I’ll search Amazon for books on parks and choose one of the ones with the highest reader ratings. Here is the GAL for this post:
National Geographic Animal Encyclopedia: 2,500 Animals with Photos, Maps, and More! by Lucy Spelman (Author) | 0.87891 | 3.344669 |
As reported earlier this week, the Cassini spacecraft is now preparing to make a series of very close passes by the edges of Saturn’s rings, known as Ring-Grazing Orbits. A couple days ago, Cassini conducted a close flyby of Saturn’s largest moon Titan; this is the second-to-last ever flyby of Titan before Cassini enters the Grand Finale phase of its mission, culminating in a deliberate plunge into Saturn’s atmosphere on Sept. 15, 2017. During this flyby, Cassini focused on mapping the surface and surface temperatures and used Titan’s gravity to help place the spacecraft into the Ring-Grazing Orbits.
The Cassini spacecraft has been orbiting Saturn for many years now, studying the massive planet and its moons in unprecedented detail. Now, Cassini might be able to help shed light on another Solar System mystery: the possible existence of a ninth planet in the outer Solar System far past Pluto, or “Planet Nine” as it has been dubbed. There is also a new report, based on old data, that the Huygens lander observed methane ground fog as it descended to the surface of Saturn’s moon Titan in 2005.
Saturn’s largest moon, Titan, has seas and lakes of liquid methane and ethane dotting its surface, but one question scientists have been trying to figure out is how the hollows in the ground, which hold the lakes, form to begin with. Now, a new study offers a solution: The depressions in the surface are formed in a process similar to sinkholes on Earth.
The exploration of the outer Solar System has revealed a plethora of amazing worlds, the likes of which were little known or even unheard of just a decade ago. Among the most remarkable and tantalizing discoveries are the “ocean moons” such as Europa and Enceladus, which have oceans or seas of liquid water beneath their icy surfaces. Other moons like Titan, Ganymede, and Callisto may also have them, and even some asteroids. Titan also has seas and lakes of liquid methane/ethane on its surface. With all that water, these small worlds have become a primary focus in the search for possible life elsewhere in the Solar System. Now, a new NASA budget proposal wants to take that a step further and fund new missions to these watery moons.
The search for life elsewhere has long focused on what we are most familiar with on Earth – in other words, “life as we know it,” or organisms which are carbon-based and require water to survive. However, a growing number of scientists are now thinking that alternative forms of life are possible, ones which have never been seen on Earth, but could flourish in other types of alien environments. A new study from Cornell University addresses this very question, demonstrating a form of microscopic life which would be possible on Saturn’s largest moon Titan. | 0.81014 | 3.835889 |
There’s a new contender for the “most exotic exoplanet” title.
The crown may have rested for a while now on the head of HD 189733 b, a cobalt-blue alien world where molten-glass rain whips sideways through the air at up to 5,400 mph (8,790 km/h). But a new study reports that iron rain likely falls through the thick, turbulent air of WASP-76 b, a bizarre “ultrahot Jupiter” that lies about 640 light-years from the sun, in the constellation Pisces.
WASP-76 b zips around its host star once every 1.8 Earth days, an orbit so tight that the gaseous planet is “tidally locked,” always showing the star the same face. Temperatures on this dayside climb above 4,350 degrees Fahrenheit (2,400 degrees Celsius) — hot enough to vaporize metals — whereas the nightside is a much cooler (but still ridiculous) 2,730 F (1,500 C), researchers said.
“These are likely the most extreme climates we could ever find on a planet,” said study lead author David Ehrenreich, an associate professor of astronomy at the University of Geneva in Switzerland.
“We have to stretch our understanding of what is a climate, what is a planetary atmosphere, to understand this object,” Ehrenreich told Space.com.
WASP-76 b was discovered in 2013. The alien planet is about as massive as Jupiter but nearly twice as wide, likely because the massive radiation loads the exoplanet receives from its host star puff up its atmosphere considerably. (And one quick note about the object’s distance: Some sources say that WASP-76 b is about 390 light-years away, but that number is inaccurate, Ehrenreich said. He and his colleagues calculated WASP-76 b’s distance using data from Europe’s ultraprecise star-mapping spacecraft Gaia.)
For the new study, the researchers studied WASP-76 b using the Echelle Spectrograph for Rocky Exoplanets and Stable Spectroscopic Observations (ESPRESSO), an instrument installed on the European Southern Observatory’s Very Large Telescope in Chile.
ESPRESSO detected a strong signature of iron vapor at the “evening” border that separates WASP-76 b’s dayside from its nightside. But no such signature was spotted at the “morning” border on the other side of the planet, where the nightside melds into day.
“Something must be happening on the nightside that makes iron disappear,” Ehrenreich said.
The best explanation, he added, is that winds and WASP-76 b’s rotation carry vaporized iron from the dayside to the nightside. The nightside is cool enough for the iron vapor to condense into clouds, which then dump rain into the air over there. That rain could consist of compounds such as iron sulfide or iron hydride.
But, “given the conditions, the most likely [scenario] is that iron condenses into liquid droplets of pure iron,” Ehrenreich said. (This iron rain probably eventually makes its way back to the dayside again via atmospheric circulation, perpetuating the cycle, he added.)
And that rain probably isn’t sprinkling down in a gentle mist, because the big temperature disparity between WASP-76 b’s two halves generates winds of startling ferocity. The iron in the planet’s dayside air, for example, is hurtling toward the nightside at about 11,000 mph (18,000 km/h), Ehrenreich said.
WASP-76 b’s exoticism doesn’t end there. The dayside atmosphere may be much more puffed up than that of the nightside because of the higher heat loads, the researchers said. So the “evening” and “morning” borders between the two hemispheres might be marked by towering clouds that fall from the light toward darkness.
“And the drizzle of this fall would not be water droplets but iron droplets,” Ehrenreich said.
The craziness of WASP-76 b has more than just gee-whiz appeal. The new information about this odd exoplanet should help scientists refine and test climate and global circulation models, leading to a better understanding of exoplanetary atmospheres in general, Ehrenreich said. And WASP-76 b also serves as a compelling reminder for researchers to keep an open mind, because nature churns out a dizzying diversity of worlds.
“Exoplanets are a real treasure trove full of surprises,” Ehrenreich said. “The more you look, the more you find.”
He and his colleagues aim to dig up more such surprises. The new results, which were published online today (March 11) in the journal Nature, come from the very first science observations ever made with ESPRESSO, back in September 2018. The researchers are now conducting a broad survey of exoplanet atmospheres using ESPRESSO, which could reveal if WASP-76 b is an outlier or a member of a very weird class of worlds.
“What we have now is a whole new way to trace the climate of the most extreme exoplanets,” Ehrenreich said in a statement. | 0.891125 | 3.846222 |
A comet is a small, icy, asteroid-like body, typically tens of kilometers across, that releases streams of dust and gas from its surface when its orbit takes it close enough to the Sun. This dust and gas, produced when the comet’s surface is heated by the Sun, forms an non-gravitationally-bound ‘atmosphere’ around the comet, called a ‘coma’. The gas and dust can also be blown away from the comet’s surface by the solar wind to produce spectacular luminous ‘tails’, which can reach millions of kilometers in length.
The word comet derives from Greek word for hair, since they resembled stars with hair or long beards, due to their comae and tails, which can stretch for great distances across the night sky.
Short- and Long-Period Comets
Most comets have highly-elliptical orbits and are divided into two distinct categories: short-period comets and long-period comets. Short-period comets generally have orbital periods of less than 200 years, and are thought to mainly originate from the Kuiper Belt, the Scattered Disc and the Centaurs. Long-period comets, however, are believed to originate mainly from the Oort Cloud.
Comets often develop two distinct tails as they approach the Sun, one produced from gas and another from dust particles. A comet’s dust tail can develop a curved shape as the dust is left behind as the comet orbits the Sun; however, a comet’s gas, or ion tail, composed of charged, ionized gas molecules, will always point directly away from the Sun, as it more strongly influenced by the Solar Wind.
A comet can sometimes appear from Earth to have what is known an ‘antitail’, pointing in the opposite direction to the comet’s dust tail. However, antitails are also composed of dust particles ejected from the comet, which can form a disc-like shape around the comet’s nucleus. The disc usually extends much further from the comet in one direction, to form the comet’s main dust tail, but viewed side-on from Earth, this disc can appear to form a short antitail on the opposite side of the comet.
Comet Halley is perhaps the most famous of all comets, named after Edmond Halley, who first realised, in 1705, that the bright comets witnessed in 1531, 1607 and 1682, were in fact the same object, returning from the outer reaches of our solar system every 75 to 76 years.
Halley’s comet, officially designated 1P/Halley, has been observed and recorded by astronomers since at least 240 BC, and also appears in the Bayeux Tapestry, the embroidered record of the Norman conquest of England, in 1066 AD.
Comet Halley’s latest appearance was in 1986, and it is due to return again in 2061.
Particles shed from Halley’s tail during previous visits are responsible for the Eta Aquariids and the Orionids meteor showers.
Comet Shoemaker-Levy 9 was discovered in 1993 by amateur astronomers Carolyn and Eugene Shoemaker and David Levy. The comet had previously been captured by the gravitational field of Jupiter and had broken up into a string of fragments, which were on a collision course with the planet.
In 1994, astronomers were able to watch as the fragments struck the upper atmosphere of Jupiter, leaving several large, brown, ‘bruise-like’ impact marks across the planet. The cometary fragments actually impacted Jupiter on the side facing away from the Earth, although close enough to the planet’s limb for fireballs to be seen above the edge of Jupiter’s disc. Luckily, NASA’s Galileo spacecraft, sent to study Jupiter’s moons, had an excellent direct view of the impacts, shortly before Jupiter’s rotation brought the impact sites into view for Earth-bound telescopes.
Comet Hale Bopp
Comet Hale Bopp was a spectacular comet, visible to the naked eye for a record 18 months (569 days) from May 1996 to December 1997, shining brighter than magnitude 0 for a record eight weeks. Hale Bopp was discovered by Alan Hale and Thomas Bopp, as it approached the Sun in 1995. Hale Bopp is a long-period comet, due to return for its next perihelion in approximately the year 4385. (See main picture of Hale Bopp, above.)
Missions to Comets:
The International Cometary Explorer (ICE) was the first ever spacecraft to be sent on a rendezvous mission with a comet. ICE was launched in 1978, as a joint project between NASA and the European Space Agency (ESA), and was originally designated the International Sun-Earth Explorer-3 (ISEE-3) satellite, but was re-tasked and sent to target Comet Giacobini-Zinner in 1985.
The Halley Armada
Also in 1985, the approach of Comet Halley, inspired the launch of the Japanese Institute of Space and Astronautical Science (ISAS) Sakigake and Suisei probes, as well as the ESA’s Giotto mission – all three of which were sent to rendezvous with the comet. The ICE spacecraft was also deployed to pass through Comet Halley’s tail, and the joint-Soviet-and-French Vega 1 and Vega 2 probes, following their successful missions to Venus, added to what became unofficially known as the Halley ‘armada’, while the Pioneer 7 and Pioneer Venus Orbiter probes also watched Comet Halley from afar.
Giotto also targeted Comet Grigg-Skjellerup after its rendezvous with Halley.
The Stardust Mission
In 1999, NASA’s Stardust mission returned a sample from the coma of Comet 81P / Wild 2, for analysis on Earth. The sample, captured in a sponge-like aerogel, was returned to Earth in 2006, and was found to contain glycine, an amino acid that is one of the fundamental building blocks of life.
In July 2005, NASA’s Deep Impact probe conducted a flyby of comet Tempel 1, releasing an impactor probe designed to collide with the comet. The impactor returned images up to 3 seconds before the collision and send debris into space for analysis by the spacecraft. Observations showed that the comet was about 75 per cent empty space, and the outer layers of the comet were said to have a similar makeup to a ‘snow bank’.
The Deep Impact spacecraft went on to conduct a further flyby of Comet Hartley 2, as well as observing two more comets, Comet Garradd (C/2009 P1) and Comet ISON (C/2012), from longer range.
Rosetta and Philae
The ESA’s Rosetta mission was the first mission to successfully land a probe on the surface of a Comet. Rosetta’s Philae lander touched down on Comet Churyumov-Gerasimenko, also known as Comet 67P, on 12 November 2014; however, harpoons designed to anchor Philae to the comet’s surface failed to fire, resulting in the lander bouncing twice before coming to rest in the shadow of a nearby cliff or crater wall. This meant that Philae’s solar panels could not produce enough power to keep its batteries charged, and contact with the lander was soon lost. Philae sporadically re-initiated contact with the Rosetta spacecraft several months later between June and July 2015, as the comet neared the Sun, although most of the scientific objectives of the lander mission were not successfully completed. The Rosetta orbiter, however, discovered that the ratio of deuterium to hydrogen in the water from the comet is three times that found in water here on Earth, making it unlikely that Earth’s water originated from a bombardment of comets similar to 67P. | 0.806961 | 4.112466 |
Leonid Meteor Shower Visible From UK This Weekend
It feels like we've been spoilt for choice with celestial goings-on lately and this weekend we're set for another meteor shower that can potentially be seen from the UK.
After the yearly return of the Orionids, which are visible every October or November, this weekend it's the turn of the Leonids. They're known for being bright and colourful, and some of the moving rocks fly through space at about 44 miles per second.
Putting a spanner in the works though, natural light pollution will mean that fewer shooting stars maybe visible, thanks to the almost full moon.
There should still be about 14 or 15 an hour though - of course, how many you see is dependent on the weather and cloud cover.
It's also best to look out for it after midnight, with NASA advising any photographers out there to use a wide-angle lens, meaning you will see as much of the sky as possible.
It's also best to avoid light pollution from street lights and if possible, lie flat with your feet towards the east.
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Only time will tell, but on the off-chance that it's not cloudy during the peak of the Leonids on Saturday night, the best places in the UK to see the meteor shower are the Shetland Islands and the South East.
Shooting stars are pieces of space debris that often leave visible trains behind them - they can stay around for a few seconds, giving them their name.
The Leonid shower happens because small rocks break off from the Comet Tempel-Tuttle and fall toward the earth. These rocks, or meteoroids, burn up and vaporise before they hit the Earth's surface - causing a streak of hot air as it hits the atmosphere.
It's even better when the comet is closer to the Earth. As it takes 22 of our years to orbit the sun, the next time it will be closest is in about 15 years' time.
The term Leonid comes from the point where they look like the meteors appear, which in this case is from the constellation Leo.
It's predicted by researchers that in 2034, we'll have a chance to see about 2,000 meteors per hour in what they call a 'meteor storm'.
If that seems like a bit long to wait for your next hit of star-geeking, the next major shower will be in the middle of December, when the Geminids will be visible.
Featured Image Credit: PA | 0.839897 | 3.267583 |
In a astronomical effort that horrified the enviornment, scientists final 365 days unveiled thefirst bid checklist of a shadowy gap, allowing folks to leer what exists on the cusp of the monster’s maw. Now, astronomers be pleased aged a decided technique spicy x-ray “echoes” toleer even closerat one amongst these gravitational behemoths.
The shadowy gap coming into focal level is parked within the center of a galaxy known asIRAS 13224-3809, which sits a few billion light-years away. The supermassive object is surrounded by a swirling disk of million-stage topic and is sheathed by an x-ray corona with a temperature exceeding a billion levels. By charting how these x-rays behave, scientists created an especially detailed design of the blueprint around the shadowy gap’s event horizon, the zone beyond which now not even light can rating away.
“Black holes don’t give off any light themselves, so the single manner we are in a position to peep right here’s by watching what topic does because it falls onto it,” says the University of Cambridge’sWilliam Alston, whose crewstories the observationsthis day within the journalNature Astronomy.
It’s a mighty more genuine size than even the Event Horizon Telescope, which produced final 365 days’s shadowy gap checklist, would possibly maybe maybe construct for an object to this level away. The new measurements of IRAS 13224-3809’s shadowy gap helped scientists pin down its mass and disappear, properties that would possibly maybe maybe level to a will have to be pleased clues in regards to the shadowy gap’s evolution. If same measurements will likely be made for a greater inhabitants of nearby supermassive shadowy holes, they also can support scientists learn more about how galaxies grow.
“Realizing the disappear distribution of shadowy holes in many galaxies tells us about how we inch from the early universe to the inhabitants we gaze this day,” Alston says.
No topic the innocuous name, IRAS 13224-3809 is one amongstprimarily the most stress-free galaxies within the x-ray sky: It isan packed with life galaxy, which procedure that its innermost blueprint shines more brightly than will likely be defined by stars by myself, and its x-ray brightness fluctuates by a factor of 50, infrequently over correct a few hours. Alston and his colleagues chose to peep this mutter galaxy because they wanted a dynamic, fluctuating source that would possibly maybe maybe aid them nail down particular properties of the central supermassive shadowy gap.
To enact that, Alston and his colleagues studied IRAS 13224-3809 the use of the European Region Agency’sXMM-Newton spacecraft. An Earth-orbiting telescope that stories the cosmos in x-rays, XMM-Newton stared on the some distance away galaxy over the course of 16 orbits—totaling more than 550 hours—between 2011 and 2016.
From these many hours’ payment of recordsdata, Alston and his colleagues assembled a design of the supermassive shadowy gap’s x-ray corona and its accretion disk, a ring of swirling topic that’s correct commence air the event horizon. One of the emitted x-rays head without delay into the cosmos, however others slam into the accretion disk and recall a runt little bit of longer to exit the bruiser’s on the spot atmosphere.
“This extra direction dimension causes a time delay between the x-rays that had been produced before all the pieces within the corona,” Alston explains. “We are in a position to measure the echo—this time delay—which we call a reverberation.”
This technique, known as reverberation mapping, helped the scientists probe the gassy arena topic around the shadowy gap. Alston compares the technique to echolocation, wherein animals equivalent to bats soar grasp forth objects to support them navigate in flight. And, unlike the technique aged by the Event Horizon Telescope to assemble an checklist of a shut-by shadowy gap, reverberation mapping will likely be aged to peep objects which will doubtless be some distance, some distance-off and probe areas even closer to the event horizon.
“Reverberation mapping doesn’t rely on spatial resolution the least bit,” says Georgia Suppose University’sMisty Bentz, who uses the identical technique to peep some distance away shadowy holes. “In its place, it uses light echoes at some stage within the object to teach us about structures, even very runt and primarily some distance-off ones.”
The sunshine echoes captured from IRAS 13224-3809 allowed Alston and his crew to search out out the genuine geometry of the arena cloth surrounding the shadowy gap, at the side of the dimensions of its dynamic x-ray corona, which powers these echoes. The crew would possibly maybe maybe then use that knowledge to calculate the shadowy gap’s mass and disappear, two properties that enact now not fluctuate on human timescales.
“To measure the mass and disappear of the shadowy gap, we be pleased to know exactly where this gas is sooner than it falls into the shadowy gap,” Alston says. Scientists be pleased aged this technique to peep supermassive shadowy holes sooner than, however these observations had been neither as lengthy, nor the source as variable, as they are for IRAS 13224-3809.
In response to the brand new mapping, the crew concluded that this supermassive shadowy gap contains as mighty mass as two million suns, and that it’s miles spinning nearly about as hasty because it presumably can with out breaking the regulations of physics. Bentz, who became now not bearing in ideas the work, says the authors’ wide observations construct the consequences extraordinarily convincing.
“The authors implemented the identical experiment 16 times, which is a great deal more than any previous stories,” Bentz says. “That primarily helped them to pin down the pieces that had been now not changing.”
Alston and his crew also assembled a dynamic checklist of how the x-ray corona swaddling the shadowy gap adjustments over time, with its dimension varying considerably dramatically over a day.
Every mighty galaxy within the universe is probably going anchored to a central supermassive shadowy gap. Decoding the methods wherein these anchors pirouette would possibly maybe maybe provide clues to how they, and their host galaxies, fashioned and evolved over the age of the universe.
“One of many things we don’t know is how supermassive shadowy holes construct,” Alston says. “What are the seeds of these within the early universe? Most of our fashions on the second predict seeds which will doubtless be too runt, and they’ll’t primarily grow hasty sufficient.”
One manner wherein galaxies would possibly maybe maybe construct entails numerous runt galaxies colliding and merging. As these galaxies merge, so enact their central shadowy holes. If these collisions are chaotic, they also can now not only make a contribution to the following greater shadowy gap’s mass, however also to the style it spins, Alston says.
Every other manner wherein shadowy holes would possibly maybe maybe bulk up is by a right stream of inflowing gas. If this is the case, the following disappear is probably going to be speedier, as IRAS 13224-3809’s disappear looks to be, though Alston says it’s too rapidly to enact that this mutter galaxy accreted mass by this mechanism.
In the end, he and his colleagues would admire to make use of reverberation mapping to pin down the spins—and thus the formation histories—of a entire bunch of nearby supermassive shadowy holes, in raise out taking a census of these objects. Then, per how some distance-off these shadowy holes are, scientists can see at how galaxies grew right by the age of the universe. | 0.844758 | 3.858471 |
It's such a tiny thing, the molecule, yet one found 25,000 light-years away could help solve one of the biggest mysteries about how life forms in the universe.
The molecule, propylene oxide, demonstrates a property called chirality. This is also called "handedness" as, like your hands, chiral molecules exist in forms that mirror each other. Here on Earth, living things use molecules that only have one "side". The sugars in DNA, for instance, are exclusively right-handed, which gives DNA its spiral double helix shape. This is called homochirality.
The discovery of this propylene oxide marks the first time a chiral molecule has been found outside the solar system. Scientists don't yet understand how life came to rely on homochirality, but this discovery could help.
One hypothesis has to do with the way chiral molecules form in space before being incorporated into asteroids that fall onto planets. Meteorites in the solar system have been found to contain chiral molecules that predate Earth.
"By discovering a chiral molecule in space, we finally have a way to study where and how these molecules form before they find their way into meteorites and comets, and to understand the role they play in the origins of homochirality and life," explained co-author Brett McGuire of the National Radio Astronomy Observatory in Virginia.
The molecule was found in a cloud of star-forming gas called Sagittarius B2, located 390 light-years from the centre of the Milky Way galaxy.
Of the 180 interstellar molecules discovered so far, the chiral propylene oxide molecule is the first that offers clues to the mystery of homochirality.
"Detecting this molecule opens the door for further experiments determining how and where molecular handedness emerges and why one form may be slightly more abundant than the other," said co-author Brandon Carroll of the California Institute of Technology. | 0.887574 | 3.536382 |
The Hubble Diagram Redshifts. Perfection and Man ironsharpeningiron.com.
site:example.com find submissions Redshift/Blueshift vs. Constant Speed of Light (self.AskPhysics) how can stars red-shift/blue-shift?. Since we know the universe is expanding because of red shifts in galaxies being observed how could we have the andromeda galaxy have a blue shift? example they.
Introduction of doppler effect Light waves from a moving source experience the Doppler effect to result in either a red shift or blue shift for example, you I have a problem in understanding about blue shift and red shift in I know about blue shift and red shift but why Some demonstrative examples are
8/06/2017В В· Red Shift. Discussion in ' and a huge reasons the pvp leaderboard are red and grinding is blue. How DARE you talk to daffy duck that!!! Red shift and blue shift refer to the change in the frequency of light when an object shifts away (red) from and towards (blue) the center of potential energy.
2/03/2004В В· red shift is basiaclly where a distant object crying to the forums cause NO 1 GIVES A FLYING DUCK swan anohter colour. No Blue swans, no red. Eg Distant galaxies show red shift Eg can measure rate by comparing red shift of when it is turning away from us c.f. blue shift of eg a duck can be.
“The Red Shift Song YouTube”.
Redshift is a 'shift' of light waves traveling away from red, orange, yellow, green, blue and purple Redshift Definition: Lesson for Kids Related Study Materials..
Explanation of Doppler Effect Equations for Light by Ron Kurtus Example. If the astronomer (blue-shift) or away (red-shift).. noun. a shift in the spectral lines of a stellar spectrum towards the blue end of the visible region relative to the wavelengths of these lines in the terrestrial. site:example.com find submissions Redshift/Blueshift vs. Constant Speed of Light (self.AskPhysics) how can stars red-shift/blue-shift?. | 0.811962 | 3.038136 |
How Are Matter, Space, and Time Unified?
Physicists have long believed that a fundamental, encompassing theory of matter, space, and time must be attainable. The remarkable progress described in Chapter 2 suggests that the opportunity to achieve that unification may be at hand. Realizing that opportunity will involve obtaining information both from high-energy physics laboratory and accelerator experiments and from observations in astronomy and cosmology. This chapter explores the open questions and opportunities for progress in the coming years in exploring the implications of physics beyond the Standard Model for the early universe. Further, it addresses opportunities to use particles from sources outside Earth to reveal physics beyond the Standard Model.
The earliest history of the universe is dominated by physics of the highest energies, so that gaining an understanding of it depends on progress in understanding microscopic physics in these extreme domains. Conversely, the universe, unlike accelerators where experiments are limited by available beam lines and interaction regions, is an ever-open laboratory, one that produces a great range of phenomena that span an incredible energy range and that can be used to probe and extend ideas on microphysics. Some important relics that could have been produced only at these early times may remain today. Astronomical and astrophysical studies add immeasurably and often uniquely to important aspects of particle physics beyond the Standard Model, addressing questions such as these: Do protons decay? Do neutrinos have mass? Is nature supersymmetric? What constitutes the dark energy? Are there additional dimensions of space beyond the familiar three?
The triumph of the Standard Model is based largely on data from particle accelerators of ever-increasing energies, constructed over the past 50 years. Without the Standard Model, it would have been impossible to make with any confidence the very large extrapolations in energy that have yielded insights into the conditions of the early universe.
What can be expected from accelerator-based facilities, the center of the traditional high-energy physics effort? The search for the Higgs boson and for supersymmetric partners of the known particles is a primary focus of the programs at the highest-energy accelerators, such as at the Tevatron at Fermilab and the Large Hadron Collider (LHC) at CERN and even at the next large accelerator to be built after the LHC, which will be designed to perform incisive studies of these particles’ properties.
Accelerator experiments permit irreplaceable measurements for exploring the Standard Model and beyond, including studies of neutrino masses and the violation charge-parity (CP) symmetry (see Chapter 5, section “Dark Energy”), as well as the creation of an exotic form of matter known as the quark-gluon plasma to mimic an important phase in the early universe. Accelerators are also capable of seeing manifestations of extra dimensions that are macroscopic. This possibility, a recent speculation from string theory, has profound implications for understanding the physics of the very early universe. Experimental signatures include the apparent loss of energy in particle interactions, which, in fact, has gone off into the additional dimensions. Experiments at the Tevatron and the LHC should have significant sensitivity to this exciting possibility.
Rather than address ongoing and proposed accelerator programs that are reviewed elsewhere by other responsible scientific groups (laboratory program committees, the NRC, and the DOE/NSF High Energy Physics Advisory Panel and the Nuclear Science Advisory Committee), this committee focuses on identifying additional and complementary opportunities for the use of new techniques and technologies to probe the most fundamental questions at the interface between particle physics and astronomy and astrophysics. This chapter discusses, in turn, experiments seeking signatures of unification, identifying the dark matter, and probing the very foundations of our science.
LOOKING FOR SIGNATURES OF UNIFICATION
The hypothesis that a single unified theory can account for the three separate forces of the Standard Model is attractive in many ways. Such a theory would organize the quarks and leptons into a simple, beautiful structure and would explain the patterns of charges, which otherwise seem quite arbitrary. And most impressively, by including low-energy supersymmetry, it would account quantitatively for the relative values of the different observed coupling strengths.
Unified theories predict additional effects that go beyond the Standard Model. In the following subsections the most promising of these new phenomena are discussed.
A great cosmological question is how the current preponderance of matter over antimatter in the universe came about. Presumably the abundances of both were equal immediately after the big bang, just as the numbers of negative and positive charges were equal. The subsequent interactions that established the matter-antimatter imbalance at very high energies must also allow proton decay, although at a very low rate given the low energy (mass) of the proton.
Unified theories predict that protons are unstable. Early estimates based on the simplest unified theories suggested lifetimes on the order of 1030 years. But those predictions were discounted with the first round of experiments. Today, the predicted lifetime of protons is on the order of 1035 years or less in the most viable models. Experiments currently set lower limits (depending on the mode of decay) of roughly 1032 to 1033 years.
Because it would imply the instability of all nuclear matter, the discovery of proton decay would be a historic event that provides a unique window onto some of the most fundamental questions in physics and cosmology. Different unified models make different predictions for the most likely modes of proton decay. Models with supersymmetry, for example, favor decays that include K mesons and neutrinos.
Much effort has already been devoted to the search for proton decay, the principal original goal of the Kamiokande and Super-Kamiokande detectors in Japan, the Frejus experiment in Europe, and the Irvine-Michigan-Brookhaven (IMB) and Soudan detectors in the United States. Although no protons were observed to decay in these experiments, the scientists working there made impressive discoveries in neutrino physics. Furthermore, these experiments allowed limits to be defined on proton decay that already rule out the simplest grand unified theories.
Clearly, achieving substantial improvements in experimental sensitivity to proton decay will be important to improving our understanding of the early universe. As a bonus, such experiments could also accommodate an extensive neutrino physics program including the study of neutrino properties by detecting neutrino beams from distant accelerators and supernovae in our galaxy and nearby galaxies.
Neutrino Masses and Neutrino Oscillations
As far as physicists know, neutrinos interact only by the weak force, passing through Earth, for example, with ease. Until recently, it was widely believed that neutrinos were also massless, like photons. Despite having properties that render them very elusive, neutrinos can be and have been studied extensively in particle accelerators and nuclear reactors, and they can have major consequences in the cosmos.
For example, even though they interact extraordinarily weakly, there was a time in the early universe when even neutrinos were in thermal equilibrium with the high-density, seething plasma of particles and force carriers. At about 1 second after the big bang, the universe became too diffuse to maintain that equilibrium, and neutrinos were free to expand and cool just as the photons of the microwave background did 400,000 years later. Created in numbers comparable to the number of photons (and a billionfold more abundant than protons), neutrinos with a small but nonzero mass of only a few eV/c2 (electron-volts divided by the speed of light squared; in this unit, the electron mass is 511,000) would contribute a significant fraction of the dark matter (though still not enough to allow them to be the seeds of galactic and large-scale structure formation). Neutrinos from weak processes that power the Sun and neutrinos generated in the atmosphere from the decay of secondary particles produced by cosmic rays are providing key information about these elusive particles and their role in the cosmos. A burst of neutrinos was detected on Earth from the explosion of supernova SN1987A, broadly confirming the predictions of supernova models and opening up an astronomical window for the study of a variety of effects beyond the Standard Model. No experiment has directly detected the cosmic neutrino background, but it is likely that the effects of even a 1 eV/ c2 neutrino on structure formation could be seen indirectly by its imprint on the large-scale distribution of matter in the universe. The Sloan Digital Sky Survey, a map of the universe being made from the positions of 1 million galaxies, will soon enable detecting the effect of neutrinos on large-scale structure.
In the early universe, neutrinos played a critical role in the formation of elements beyond hydrogen through their ability to transform protons into neutrons and vice versa. The particular pattern of abundances of hydrogen, helium, and lithium nuclei produced depends critically on the rates of neutron production, capture, and decay, which in turn depend on the nature and properties of neutrinos. The predicted abundances have been confirmed spectacularly in studies of the abundances of these elements today.
We know that there are only three light neutrino types (also called “flavors”)—the electron neutrino, the muon neutrino, and the tau neutrino— named for the particles into which they are transmuted by emission or absorption of a W boson (recall Figure 2.1). The concordance between the predicted and observed cosmic abundances of the light elements would not be nearly as good were there more than these three flavors of neutrinos, and this result from cosmology gave an important early constraint on the number of neutrinos. Subsequently, the number of neutrino flavors was very accurately measured by experiments at the Stanford Linear Accelerator Center’s Linear Collider and CERN’s Large Electron-Positron Collider (LEP).
Within the Standard Model, the total number of electron neutrinos and electrons minus the total number of electron antineutrinos and positrons in the universe never changes. Similar lepton-family-number conservation laws apply to the mu and tau families as well. However, physicists have long been alert to the possibility that the lepton-number conservation laws may be only approximate. Indeed, this may be suggested by the fact that similar laws for the conservation of different quark types are known to be only approximate. In a unified theory, it would be natural for quarks and leptons to appear on an equal footing, compelling researchers to think that the conservation of lepton-number really will be violated.
A subtle phenomenon that can cause lepton-family-number violation is neutrino oscillation: One flavor of neutrino produced initially may be detected later as another flavor, with a probability that changes as the neutrino moves through space or passes through matter (see diagram in Figure 3.1a and 3.1b). The changes are oscillatory in the sense that the probability of a change in flavor occurring reaches a maximum at a certain distance, diminishes to zero at twice that distance, and so on. The effect can occur only if different neutrinos have different masses. The rate of oscillation depends on the energy of the neutrino, on the mass differences between the various neutrinos, and on the value of a “mixing factor” that controls the process of conversion from one to the other. If the mass differences are tiny, then sensitivity to neutrino oscillations can be achieved only by looking at neutrinos that have traveled a very long distance, since the oscillations are then very gradual, although the oscillation rate can be enhanced for electron-type neutrinos traveling through dense matter, for example in the Sun.
The first real hints that neutrinos oscillate came from studies of solar neutrinos. The nuclear reactions that power the Sun produce electron neutrinos. Because they interact so weakly, these neutrinos from the Sun can be detected only in experiments on a heroic scale. For many years the only suitable detector was a gigantic vat of cleaning fluid, mounted and
instrumented by Ray Davis in the Homestake Mine in South Dakota. Davis succeeded in observing electron neutrinos, but at roughly one-third the expected rate. Several later experiments have confirmed this deficit by looking at lower-energy neutrinos, whose rate prediction is less sensitive to details of the model of the Sun. The leading interpretation of these observations is that electron neutrinos emitted from the Sun have partially oscillated into muon or tau neutrinos that cannot be detected using the experiments designed by Davis and his successors.
Recent dramatic experimental developments in neutrino oscillations have emerged from the study of neutrinos originating in the atmosphere as by-products of cosmic ray interactions. Since cosmic rays have been carefully studied for many decades, it is possible to predict with considerable confidence the expected relative abundance of the different types of neutrinos so produced. The experiments designed to search for proton decay, the Irvine-Michigan-Brookhaven (IMB) and Kamiokande experiments, observed that the ratio of the number of muon neutrinos to electron neutrinos fell below theoretical expectations. The ratio, naively expected to be 2 (twice as many muon neutrinos as electron neutrinos come from pion decay) is calculable to an accuracy of about 5 percent. It was found to be low by about 40 percent.
A recent development, from the Super-Kamiokande detector in Japan (see Figure 3.2), is the observation that the ratio of muon to electron neutrinos depends on the distance that these neutrinos have traveled since their creation. Researchers at Super-Kamiokande see this effect as a modulation of the flux of muon neutrinos as a function of the angle in the sky at which they originate. Muon neutrinos created in Earth’s atmosphere and arriving at the Super-Kamiokande detector having traveled through the Earth’s mass are detected at about one half the rate of those created in the atmosphere directly above the detector. Observation of this dependence on distance from point of creation strongly suggests that the muon neutrinos have oscillated, and, since there is no corresponding angular dependence in the flux of electron neutrinos, the oscillation most likely involves another neutrino, such as the tau neutrino. Even more recently, the Sudbury Neutrino Observatory in Canada (see Figure 3.3) has confirmed that electron-type neutrinos are less than half of the total number of solar neutrinos reaching Earth.
Solar neutrino experiments have recently given added evidence for electron neutrino oscillation. The early results giving less-than-expected electron-neutrino flux from the Sun have been confirmed. The Sudbury Neutrino Observatory detector has given an accurate measurement of the electron neutrino flux. The Super-Kamiokande detector in Japan observes a
larger total flux, but this detector is sensitive at different levels to all types of neutrinos. The comparison of the two results thus gives a clear indication that neutrinos produced in the Sun as electron-type arrive at Earth as a mixture containing other types, showing that neutrinos have mass and that neutrino oscillation occurs. The combination of the solar and atmospheric results indicates that the mixing angles that characterize the defined-mass neutrinos in terms of the defined-flavor species have a pattern quite different from the equivalent matrix for quarks.
Since the initial experiment of Clyde Cowan and Frederick Reines that discovered the neutrino in 1957, reactors and accelerators have been a mainstay of research into neutrino properties. An accelerator-based neutrino oscillation experiment at Los Alamos National Laboratory, Liquid Scintillator Neutrino Detector (LSND), has also found evidence for oscillation between the electron neutrino and the muon neutrino. This experiment found a difference in mass between 0.15 eV/c2 and 1.5 eV/c2, a much larger value than was obtained in other experiments. If there are only three neu-
trino types, this result and the evidence from atmospheric and solar neutrinos cannot be accommodated simultaneously. Either some additional sterile neutrino is playing a role, or one or more of the results have been misinterpreted. Only additional precise experimental tests can tell.
There is now strong evidence that neutrinos have mass. It is important to pursue these studies further. Large neutrino detectors located deep underground can study oscillations from laboratory-produced neutrino beams, as well as look for angular dependence in neutrinos from the atmosphere. These solar and atmospheric neutrino results describe neutrino disappearance effects, i.e., they detect a shortage of the neutrino type produced. More convincing would be an experiment in which an appearance effect is observed, i.e., detection of a type of neutrino not produced at the source.
Neutrino oscillation experiments measure only differences between the masses of neutrinos (more precisely, the difference between the squares of their masses), not the actual value of either mass. To determine the mass itself requires a different approach. Direct measurements are limited in precision both by technical capabilities and by the amount of the energy released in the relevant decays producing neutrinos. (The determination of their mass requires the use of low-energy neutrinos: the lower the energy, the better.) Careful studies of the end-point behavior of the spectrum of electrons from tritium beta decay could in principle yield indications of neutrino mass, but the smaller the mass, the more difficult this approach becomes.
One means of illuminating some aspects of the neutrino mass scale might be the study of a rare process in which a nucleus decays weakly with the emission of an electron and a positron but with no neutrinos. The predicted rate for this double-beta decay depends on the neutrino mass and also on the relationship of the neutrino to its antiparticle. Among the mysteries remaining to be resolved for the neutrinos, one is whether each neutrino is identical to its own antiparticle (in which case it is called a Majorana particle) or whether, like other massive fermions, such as the electron, it has a distinct antiparticle partner (a Dirac particle). Owing to the weak interaction’s enforcement of opposite handedness for neutrinos and antineutrinos, most direct experimental tests of this question are impossibly difficult. But observation of neutrinoless double-beta decay would demonstrate the Majorana character of neutrinos. No signal has been seen to date for this type of decay, setting a neutrino mass limit of a few tenths of an eV, provided neutrinos are Majorana particles. New double-beta decay experiments using radioactive sources on the scale of tons will be needed to achieve a neutrino mass sensitivity in the range of 0.01 eV/c2. This is the interesting range suggested by the neutrino-oscillation evidence described above.
Single- and double-beta decay experiments directly probe the mass of the electron neutrino. But the small mass differences that are representative of oscillations forge links among various masses. When these mass differences are known, to measure any one neutrino mass is to measure them all.
The probable values of the neutrino masses indicated by the oscillation experiments are very small, far smaller than the analogues for any other leptons or quarks. The occurrence of neutrino oscillations is the only known phenomenon in particle physics that is not accounted for by the Standard Model in its minimal form. What might this mean?
In grand unified theories, the Standard Model describes only the most accessible part of a larger theory, so it is not complete. The extra particles in a complete theory might be very heavy, so that their effects, on neutrino masses in particular, will be small. Remarkably, by analyzing these extensions of the Standard Model, theorists predicted neutrino masses of roughly the right magnitude before they were observed. Thus the recent experimental discoveries about neutrinos suggest that these bold ideas may be on the right track, and further experimental tests might help refine or refute them.
Very-High-Energy Cosmic Rays
Several serious ideas related to unification and unknown forces, including cosmic strings and dark-matter decays and annihilation (discussed below), would result in signatures in the high-energy cosmic rays detected at Earth. Gamma-ray bursts and ultrahigh-energy cosmic rays have been observed, but their origins are not well understood (see Chapter 7, sections “Understanding the Destiny of the Universe” and “Exploring the Unification of the Forces from Underground”). Further, cosmic rays provide the highest-energy particle beams observable on Earth and hence can be used to probe physics inaccessible at accelerator laboratories. Modern cosmic ray detectors, using sensitive phototubes deployed on a large scale, measure the huge, energetic showers created by very-high-energy primary particles either at Earth’s surface or in the atmosphere. The same technologies can be applied on a much larger scale. Space-based versions of such detectors have been proposed.
UNIFICATION AND THE IDENTITY OF DARK MATTER
The amount of matter in the universe is an essential cosmological parameter. Evidence has accumulated for the existence of a large amount of exotic “dark matter”—almost 10 times the amount of ordinary matter (see
Chapter 5). According to the current paradigm for structure formation in the universe, ordinary matter falls into clumps of dark matter. The dark matter has been detected through its gravitational effect on the motion of stars and, more recently, through its gravitational lensing of light from more distant galaxies. This matter, whatever it is, interacts very weakly with photons.
A major puzzle is what dark matter is made of. Neutrinos are the only candidate of all the known particles. But they cannot constitute all of the dark matter; with their small masses and velocities near the speed of light, they would not have been gravitationally trapped in density fluctuations in the early universe. Alternative candidates are needed to account for the “cold” (i.e., massive, slowly moving) dark matter that seems to govern structure formation. Remarkably, some compelling ideas in particle physics both predict the existence of particles that could make up this dark matter and suggest ways of detecting them.
The simplest implementations of supersymmetry suggest a new, electrically neutral, stable particle type that interacts very weakly—the neutralino. It is thought to have a mass in the range of 100 GeV/c2. Despite varying estimates of the neutralino’s abundance from production in the early stages of the big bang, the amount required for dark matter is easily accommodated. Several promising ways to look for neutralinos are discussed in Chapter 5.
Another hypothetical particle that could be a significant component of dark matter is the axion, which was introduced into particle physics to solve a deficiency in the Standard Model. Although the Standard Model is generally a reliable guide to the interactions that can occur in nature, it fails to explain why the strong force does not violate matter-antimatter symmetry, technically known as charge-parity (CP) symmetry. One suggestion introduces an additional, but slightly broken symmetry, into the theory; a general consequence of adding such a symmetry is the prediction of an additional low-mass and very weakly interacting particle, the axion.
Fortunately, the idea of an axion is testable. If axions exist, they would have been produced abundantly during the big bang and could quite naturally provide the required dark matter. It is possible to carry out an experiment sensitive to the cosmic axion background using large electromagnetic cavities embedded in strong magnetic fields (see Chapter 5).
Many additional dark matter candidates are suggested by other theories (some more speculative than others), but the neutralino and the axion stand out because they are motivated by important concepts in particle physics, and their properties are well characterized and predictable.
EXAMINING THE FOUNDATIONS OF UNIFICATION
Searching for Violation of Basic Symmetries
The universe around us is made of matter, not antimatter. To explain the observed difference in the amounts of antimatter and matter seen today requires, in addition to the baryon-number changing processes discussed above in this chapter, violation of CP symmetry.
There are well-established laboratory manifestations of CP violation, seen in the decays of the neutral K meson, or kaon. But very little is known about the fundamental nature of this important phenomenon. Is the pattern of CP violation consistent with that of the Standard Model of particle physics? The search for new sources of CP violation is important. It appears that there must be at least one new source since the magnitude of the CP violation allowed by the Standard Model appears to be far smaller than that needed in the very early universe to account for the dominance of matter over antimatter. Evidence of CP violation in the neutrino sector could lead to a quite different model for the development of the matter-antimatter asymmetry of the present universe. There is much still to be learned in this area.
Important new studies of CP nonconservation in B decays have recently yielded first results, showing a definite CP-violating effect in one channel, consistent with that predicted by the Standard Model. An ongoing program studying the many additional modes is needed, as are additional experiments sensitive to other B decays or to very rare kaon decays.
Some of the hypothesized sources of CP violation beyond the Standard Model predict electric dipole moments of elementary particles such as the neutron and the electron, which could one day be detectable in ambitious experiments. (A symmetry principle called time-reversal invariance, or T symmetry, holds that the laws of physics should be the same when time is run backwards. An electric dipole moment would be a violation of T symmetry.) Many unification models, especially those incorporating low-energy supersymmetry, predict an additional and quite different sort of T violation that could be visible through its very tiny effects on ordinary matter. In response to an applied electric field, the macroscopic material would generate, by T violation, a small magnetic field (or, conversely, an applied magnetic field could generate a small electric field). Modern precision spectroscopic techniques provide sensitive tools with which to look for such effects.
In all field theories, T violation and CP violation are intimately connected, since such theories incorporate an overall prediction of a combined CPT symmetry that must be exact. However, the higher the energy, the less string theory looks like a field theory. Thus, the search for violations of CPT symmetry is a potential test for the validity of string theory.
Probing Unification with Gravitation Experiments
After more than 300 years, Newton’s law of gravitation remains experimentally valid in and around Earth (at least up to the tiny corrections resulting from general relativity). It states that the net force between two uncharged objects is proportional to mass and independent of internal composition (the equivalence principle) and decreases as the inverse square of the separation. Strangely, high-precision tests of Newton’s basic law on laboratory scales may provide important probes of unification.
The axion is but one of several hypothetical very light, very weakly coupled particles suggested to resolve issues in particle physics. Others are familons, dilatons, and moduli fields. (A proper explanation of these possibilities would take this discussion far afield.) One way to be sensitive to light particles such as the axion is to detect the forces they generate. Since an inverse relationship exists between the mass of a particle and the range of the associated force, such light particles could generate new forces on macroscopic scales of microns and larger. These forces would appear as deviations from Newton’s inverse-square law of gravity. Also, since these putative particles could interact differently with different kinds of material, they could result in testable violations of the principle of equivalence. The violation of the equivalence principle is a generic prediction of string theory, although the level of the violation is not currently predictable.
To address the speculation that nature contains extra spatial dimensions, possibly some of macroscopic size, it is necessary to explain why we experience only three spatial dimensions. According to one explanation, the ordinary particles we are made of are confined to three-dimensional structures (“branes”) that exist within the larger space, while the graviton is not so confined. This arrangement would also modify the behavior of the gravitational force at distances comparable to the size of the extra dimension.
Discovery of deviations from Newton’s gravity at any distance scale would revolutionize knowledge of the physical world. Tests of the principle of equivalence in the laboratory and using the Moon have reached the level of parts in 1013 and could be improved by another order of magnitude,
while a space experiment could yield improvement by a factor of 105. At scales of 1 mm or less, sensitive laboratory inverse-square law experiments that are clever variations on the original one by Henry Cavendish are under way, with the goal of probing the force between bodies in the submillimeter range (while excluding the dominating effects of electromagnetic forces). See Figure 3.4 for an experimental design.
Are the “Constants” Constant?
Modern theories of particle physics suggest that some or all of the quantities regarded as constants of nature are in reality associated with dynamical fields that change. The axion field is an excellent example; familons, dilatons, and moduli fields are other examples. In string theory, as
currently understood, it appears that all “constants” are in principle dynamical. Modern precision spectroscopic techniques can be used to search for the evolution of the electromagnetic coupling with great sensitivity, by looking at the spectra of distant, and hence ancient, stars.
The mass of the photon is strictly zero in the Standard Model. It is severely constrained by astronomical observations of electromagnetic fields at distances of 1020 meters from their source, providing an impressive limit of about 10−33 of the electron mass. Speculative ideas about the quantum structure of space allow the speed of light to vary with photon energy. This concept is testable by monitoring the arrival times of gamma rays of different energies in gamma-ray bursts from distant sources, probing a fundamental property of light in a new regime.
Monitoring the arrival times of neutrinos from astrophysical sources such as supernovae also provides a means of directly probing neutrino masses (especially those of muon and tau neutrinos, which are much less accessible in the laboratory). Unfortunately, supernovae are rare events, one per 30 years or so within our galaxy, so such measurements cannot be scheduled; rather, experiments must be prepared to catch a supernova whenever it happens.
All of the research fields discussed above span, in one way or another, the boundary between particle physics and the physics of the universe. In recent years it has been the physics at this boundary that presents and probes ideas at the limits of the knowledge of matter and of space-time. It will take the concerted efforts of astrophysicists and particle physicists to mine this rich area for all that can be learned from it. The discussion in this chapter can be summarized by posing four of the crosscutting fundamental science questions for the new century outlined in this report.
Are Protons Unstable?
The discovery of proton decay and improved understanding of CP violation would provide evidence for unification and help to answer the question of why matter in the universe dominates antimatter. Large-volume detectors with greater sensitivity could dramatically improve limits on the proton lifetime, and further laboratory and accelerator tests of CP violation could distinguish among competing models of unification.
What Are the Masses of the Neutrinos?
There is strong evidence that neutrinos have a mass and that oscillations occur among the various neutrino flavors. Several opportunities are ripe for experimental progress. The needed measurements or observations include confirming various effects of neutrino oscillations and identifying the neutrino species involved in each, measuring the values of the mixing parameters responsible for the observed solar neutrino abundances, and measuring the values of the neutrino masses themselves. Answers to these problems are within reach. Much more difficult and subtle issues remain, such as the particle-antiparticle properties of neutrinos and possible CP-symmetry violations in their transitions. New global-scale investigations in the planning stages should culminate in precise results describing these elusive fundamental particles.
What Is Dark Matter?
Well-founded ideas from unification and particle physics suggest interesting candidates for dark matter, such as neutralinos and axions, with calculable properties. Do these particles exist? Are any of them the actual dark matter observed astronomically? Initial experiments to detect these particles have been mounted, but more sensitivite searches will be needed to detect or rule out these candidates.
Are There Extra Dimensions?
Attempts to unify space, time, and matter beyond the Standard Model and general relativity introduce additional interactions and extra space-time dimensions. Tests of the strength of gravity at short range, experiments at particle accelerators, and tests of the principle of equivalence can probe for such signatures of unification. | 0.837046 | 4.095531 |
Exchange of impact-generated dust between the Galilean moons
1University of Oulu, Faculty of Science, Astronomy
|Online Access:||PDF Full Text (PDF, 7 MB)|
|Persistent link:|| http://urn.fi/URN:NBN:fi:oulu-202004251556
Oulu : K. Matilainen,
|Publish Date:|| 2020-04-27
|Thesis type:||Master's thesis
The dust environment of Jupiter consists of various dynamically different parts: tenuous dust rings around the planet, dust streams emanating from the volcanic plumes of Io, impact-generated dust clouds around the Galilean moons, and dilute populations of dust in the outer parts of the Jupiter system. The main source of dust material in the jovian system is impact ejection from the surface of (especially the smaller) moons, caused by high-velocity micrometeoroid impacts. The dust particles are relatively short-lived, and their orbital evolution is influenced by various different forces, including gravitational forces, solar radiation forces, electromagnetic forces and drag due to plasma in the system.
In the vicinity of the Galilean moons there exists a faint ring, consisting of dust material ejected from the surface of Galilean moons by micrometeoroid impacts. In contrast to the dust detached from the small moons in the inner Jupiter system, most of the material ejected from the Galilean moons moves on ballistic trajectories and re-impacts the surface of the moons. From the dust material ejected from the surface of the Galilean moons, only a small fraction manages to escape into circumjovian orbits. These escaped grains form a broad, but extremely faint ring, concentrated between the orbits of Io and Europa.
Historically, a good majority of research in the Jovian dust environment has focused on the dynamics of the ring system, whereas dust in the vicinity of the Galilean satellites has attracted less attention. However, the measurements in this region by the Galileo dust instrument and the detection of impact-generated clouds have stipulated new interest, especially in view of the forthcoming missions to the Jupiter system, like the Jupiter Icy Moons Explorer by the European Space Administration, and the Europa Clipper -mission by the National Aeronautics and Space Administration, both planned for launch in the 2020s.
The goal of the thesis was to derive the fluxes of dust on the surfaces of each of the Galilean moons, using the results on the dust environment of the moons from the Jovian Meteoroid Environment Model (JMEM). To this end, a program using the software Interactive Data Language was created, that directly employs functions from JMEM and then constructs the fluxes on a given surface element of a moon. To visualize the final results, contour plots of the flux distributions on the surface of the four moons were produced, explaining the effect of different parameters for the dust configuration.
To support the interpretation of the final dustmap results in terms of orbital motion and evolution of dust, a simple analytical model using a fixed semimajor axis and a model distribution of eccentricities for the simulated orbits of dust, was used to produce a theoretical distribution of impact angles of dust on the surface of the Galilean moons. Through the created contour plots, leading-trailing asymmetries for the flux of dust impacting on the surface of the moons were identified and interpreted in light of this analytical model.
© Katja Matilainen, 2020. This publication is copyrighted. You may download, display and print it for your own personal use. Commercial use is prohibited. | 0.838765 | 3.88036 |
Evidence for GeV Cosmic Rays from White Dwarfs in the Local Cosmic Ray Spectra and in the Gamma-ray Emissivity of the Inner Galaxy
2017 December 12
Recent hard X-ray observations found that electrons are accelerated in magnetic white dwarfs (WDs). Detection of GeV gamma rays from novae by Fermi-LAT infers that protons are accelerated to hundreds of GeV there. These facts motivated us to search for the cosmic rays (CRs) from historic outbursts of WDs accumulated in the local bubble around us. We propose CR model spectra at the heliopause including the local CRs from historic WD outbursts. The total CR spectra are assumed to consist of these and the Galactic components deduced from Fermi-LAT -ray observations. The two components are fitted to reproduce the Voyager-1 spectra and the high-energy CR data on/near Earth when summed, species by species. We find that a common local spectral shape and simple power-law Galactic spectral reproduce all nuclear CR spectra at the heliopause. The hardening of the nuclear CRs is found to be caused by the roll-down of the soft local WD CRs at around ~300 GeV. The WD CRs induce a hump in -ray emissivity in the GeV range. Such a hump is found in the inner Galaxy indicating that the fluxes of CRs from WD outbursts CRs ~2.5 times higher there than inside the local bubble. | 0.861567 | 3.861486 |
It may have looked like a futuristic scene from Star Wars, but ESA’s latest technique for aiding space exploration might shed some “green light” on greenhouse gases. A recent experiment involving the Spanish Canary Islands was conducted by shooting laser beams from a peak on La Palma to Tenerife. The two-week endeavor not only increased the viability of using laser pulses to track satellites, but increased our understanding of Earth’s atmosphere.
Known as infrared differential absorption spectroscopy, the laser method is an accurate avenue to measure trace gases such as carbon dioxide and methane. It is accomplished by linking two Earth-orbiting satellites – one a transmitter and the other a receiver – and examining the atmosphere as the beam passes between the two. As satellites orbit, they both rise and set behind Earth and radio occultation occurs. It’s a time-honored way of employing microwave signals to measure Earth’s atmosphere, but new wave thinking employs shortwave infrared laser pulses. When the correct wavelength is achieved, the atmospheric molecules impact the beam and the resultant data can then be used to establish amounts of trace gases and possibly wind. By different angular repetitions, a vertical picture can be painted which stretches between the lower stratosphere to the upper troposphere.
While it all sounded good on paper – the proof of a working model is when it is tested. Enter ESA’s optical ground station on Tenerife – a facility built on a peak 2390 meters above sea level and part of a larger astronomical installation called the Observatorio del Teide run by the Instituto de Astrofisica de Canarias (IAC).With equipment placed on two islands, the Tenerife location offered the perfect setting to install receiver hardware grafted to the main telescope. The transmitter was then assigned to a nearly identical peak on La Palma. With nothing but 144 kilometers of ocean between them, the scenario was ideal for experimentation.
Over the course of fourteen days, the team of researchers from the Wegener Center of the University of Graz in Austria and the Universities of York and Manchester in the UK were poised to collect this unique data.
While the infrared beam wasn’t visible to the unaided eye, the green guidance laser lit up the night during its runs to record atmospheric turbulence. Gottfried Kirchengast from the Wegener Center said, “The campaign has been a crucial next step towards realising infrared-laser occultation observations from space. We are excited that this pioneering inter-island demonstration for measuring carbon dioxide and methane was successful.”
Armin Loscher from ESA’s Future Mission Division added, “It was a challenging experiment to coordinate, but a real pleasure to work with the motivated teams of renowned scientists and young academics.” The experiment was completed within ESA’s Earth Observation Support to Science Element.
Original Story Source: ESA News Release. | 0.834835 | 3.727174 |
The universe is highly magnetic, with everything from stars to planets to galaxies producing their own magnetic fields. Astrophysicists have long puzzled over these surprisingly strong and long-lived fields, with theories and simulations seeking a mechanism that explains their generation.
Using one of the world’s most powerful laser facilities, a team led by University of Chicago scientists experimentally confirmed one of the most popular theories for cosmic magnetic field generation: the turbulent dynamo. By creating a hot turbulent plasma the size of a penny, which lasts a few billionths of a second, the researchers recorded how the turbulent motions can amplify a weak magnetic field to the strengths of those observed in our sun, distant stars and galaxies.
The paper, published this week in Nature Communications, is the first laboratory demonstration of a theory explaining the magnetic field of numerous cosmic bodies, which has been debated by physicists for nearly a century. Using the FLASH physics simulation code, developed by the Flash Center for Computational Science at UChicago, the researchers designed an experiment conducted at the OMEGA Laser Facility in Rochester, N.Y. to recreate turbulent dynamo conditions.
Confirming decades of numerical simulations, the experiment revealed that turbulent plasma could dramatically boost a weak magnetic field up to the magnitude observed by astronomers in stars and galaxies.
“We now know for sure that turbulent dynamo exists, and that it's one of the mechanisms that can actually explain magnetization of the universe,” said Petros Tzeferacos, research assistant professor of astronomy and astrophysics at the University of Chicago and associate director of the Flash Center. “This is something that we hoped we knew, but now we do.” | 0.805727 | 3.721842 |
Stargazers of all ages will be able to take a few short steps outside this week to enjoy the final supermoon of the year -- no telescope required. The only thing needed is cloud-free conditions from Mother Nature.
The full moon will rise on Wednesday evening shortly before sunset and glow all night long. It will officially become full at 6:45 a.m. EDT Thursday.
This will be the final in a series of four supermoons that began in early February, with one rising every month since then.
The term supermoon has become popularized in recent years to describe a full moon that falls near perigee, the point in its orbit when it is closest to the Earth. As a result, the moon appears slightly bigger and brighter than normal, although the difference may be tough to notice. While it may be a small difference, it can impact life on Earth.
"The supermoon plays a role in the tides and has a stronger influence than other full moons," AccuWeather Senior Meteorologist David Samuhel said.
After this week, people around the globe will have to wait until April 27, 2021, for the next chance to spot a supermoon in the night sky.
In addition to being a supermoon, this week's full moon has also earned the nickname Flower Moon, as it occurs during May, a month when flowers are blooming in abundance. This has led some to call this the ‘Super Flower Moon.'
The moon could even briefly take on the color of some blossoming flowers shortly after rising or moments before setting. When it appears just above horizon, the Earth's atmosphere can make the moon appear yellow, pink or even red for a brief period of time.
"There's one notable way in which the Moon's appearance is actually different when it's low in the sky," NASA explained. "This happens because the Moon's light travels a longer distance through the atmosphere. As it travels a longer path, more of the shorter, bluer wavelengths of light are scattered away, leaving more of the longer, redder wavelengths."
Other nicknames for May's full moon include the Mother's Moon, the Milk Moon and the Corn Planting Moon, according to the Old Farmer's Almanac.
In addition to seeing the moon, stargazers may be able to spot a few meteors from the recent Eta Aquarids.
The meteor shower peaked earlier this week, but it could still bring a few shooting stars per hour, especially for those stargazers outside during the second half of the night.
People that are trying to look for meteors should try to focus on darker areas of the sky away from the bright moon, as the moonlight will make it harder to see many of the dimmer meteors. | 0.886721 | 3.310647 |
When Distant Voyagers Calls Home
For the last 50 years, large radio antennas located just outside Australia’s Capital city, Canberra - have been keeping in touch with both humans and spacecraft as humanity takes its first giant leaps into the solar system and the cosmos. As the boundaries of human exploration stretched - it was Canberra who heard it first.
Not many people can make the claim that they were there, in the very control room, as signals came in from the robot explorers sent forth to visit the other worlds in our Solar System.
Blasted out into the darkness of space in search of the answers that have driven our curiosity for tens of thousands of years – these faint signals, some of which are many times weaker than your home Wi-Fi, have been beaming in Earth’s direction from across the lifeless, cold gulf of interplanetary space where the quietness stretches for billions of kilometres.
Some of us were not even born, as a few of our robotic explorers - tasked with their enormous missions of in-situ observation and documentation of the planets in the Solar System - were sailing past the Gas and Ice Giants of the outer solar system.
But Gordon Clee can make this claim.
Gordon has been at the controls of the NASA's Canberra Deep Space Communication Complex (CDSCC) for over 34 years and was there as the first signals observed by humanity, came in from Jupiter, Saturn, Uranus, Neptune, Pluto and even Arrokoth.
Even now, as several of these spacecraft race away from the planetary bodies of the Solar System and start to enter interstellar space, Gordon sits steady at the helm as a DSN Link Controller, sending and receiving the feeble signal keeping humanity connected with distant explorers, from a time gone past. In more technical terms, Gordon’s role involves configuring, operating, controlling and monitoring the antennas of the CDSCC to point and communicate with spacecraft across the solar system and beyond.
“Being here for 34 years, the first planetary body encounter is always special. But I think my favourite would have to be the Curiosity mission - when it landed on Mars, as far as cool moments are concerned,”
“I was operating one of our 34-metre dishes, and I was tracking Mars Odyssey and it wasn't until we were halfway through the support that I realised that the images that I could see were being relayed from the surface of Mars, via the Odyssey orbiter to my station.”
Then there’s Barbara Peters, who has also contributed to the success of every NASA and other agencies deep space missions - from multiple lunar and Mars missions, planetary probes to Jupiter and Saturn and of course the Grand Tour by the twin Voyager spacecraft.
“I’ve been asked many times, what special moments I can recall or if I have a favourite mission,”
“They are all special to me. These missions mean so much to the scientists and engineers who designed, built and fly them. It’s just an honour to play my small part in their success.”
Her role started as a DSN Link Controller almost 25 years ago at the CDSCC and since then, Barbara has been talking with our robotic travellers.
“My first two applications were not successful, but I was convinced that this was the job for me and so I applied a third time and got it.”
Barbara has now been a Link Operator at the Canberra Deep Space Communication Complex for the past 25 years.
Coming from a background in Communications and Electronics, Barbara worked as an oil rig communications officer before moving to the Australian National University as an electronics technician.
Barbara never shied away from the challenge of working in what was, at the time, thought of as traditionally male-dominated fields.
“I found that after I had my children, I wanted to seek a role that would balance with my lifestyle and expertise and the position came up at the space tracking station.”
Since the launch of Pioneer 10 in 1972, our understanding of the solar system beyond Earth - including the thousands of images that have opened our eyes in wonder - have come through these channels, with people like Gordon and Barbara monitoring the health and telemetry of the in-situ observatories in the outer reaches of our system.
Only a handful of locations around the world are equipped to communicate with our explorers today, as they continually sail onwards beyond their destinations – having served their mission objectives and still, reporting in on every new frontier they cross.
This network of communication stations is known as the Deep Space Network (DSN), with three primary locations set across Earth, separated by 120-degrees, providing the ability to continually provide coverage across the entire sky over a 24-hour period.
In early December, I spent a day with Glen Nagle, Outreach and Administration lead at the southern hemisphere DSN facility, located just outside Canberra, in the Tidbinbilla Valley. The facility has over the last ten years been directly managed by Australia's science agency, CSIRO.
Cocooned by the natural surrounding mountain ranges that provide radio interference protection, the location is surrounded by small rural hills, where fields of pale yellow tall grass grow at the base of gentle green hills and the road vanishes at a distant point ahead.
Glen’s been at the Canberra DSN for nearly 18 years, but as we walked around the grounds of the facility – it felt as if he had only started yesterday – emanating with excitement and nostalgic knowledge. For him, it was sharing the pride his passion had given him, to be amongst some of history’s greatest moments as humanity reached for the stars.
For me, it was like I was transported back to those exact moments when humanity came together, united through triumph or potential tragedy, that gave me goosebumps for my entire visit that day - even if I had not yet been born during some of these significant events.
The Establishment of the Deep Space Network
Originally, three portable tracking stations were designed to track the first satellite launched by the United States (Explorer-1), situated in Nigeria, Singapore, and California. At the time, it was run by the Jet Propulsion Laboratory (JPL) - which fell under the command of the US army.
It was during this period that the US Government recognised the value in establishing a central civilian-based agency for all space exploration programs, generated from its military branches: the Air Force, Navy and Army - and thus, NASA was established in October of 1958. By December of the same year, JPL would be transferred over to NASA - tasked with the design and implementation of lunar and planetary exploration using robots.
The concept of a deep space network (for communication) was developed as a means to be more efficient (costs, processes, learnings) for future objectives - the alternate approach was each mission would be required to establish its own costly communication network. Foreseeing this value, NASA established the global DSN, announcing formally it would lead in deep-space missions in December of 1963.
The purpose of the DSN is to send commands and receive data, as well as track and monitor the health and safety of distant spacecraft as they travel along their journeys through and beyond the Solar System. However, the three global facilities also enable and participate in important advancements of scientific research - for example, measuring radio signals between the spacecraft and Earth can better improve the understanding of distant locations in the Solar System, what lies in between the planets and moons or test our understanding of gravity.
Radio and radar instrumentation development and testing is another area of science and engineering that the DSN facilities have continually added value to since the early 1960s, becoming world-leaders in the advancement of low-noise amplifiers; tracking, telemetry and command systems; large parabolic dish antennas; digital signal processing and deep space navigation.
To date, the DSN still makes the longest-distance calls in human history, utilising the world’s best and most sensitive scientific telecommunications systems to speak with the two Voyager spacecraft - now said to be beyond the Sun’s solar wind reach and entering interstellar space.
The DSN is able to do this by ensuring continual, round-the-clock coverage across the sky using three tracking stations:
- Goldstone Complex - located in California
- Canberra Complex - located just outside Australia’s capital city
- Robledo de Chavela - located outside Madrid, in Spain
Tracking Station: Tidbinbilla
Each of the DSN facilities is equipped to look after all missions during their allocated time slots - that is to take control of all global DSN antennas and manage through the one complex before handing over to the next.
As Glen described this, confusion set in - prior assumption and understanding had dictated that each facility would look after their own telescopes with rotating local teams to ensure continual coverage.
The genius of this idea was made evident when Glen and I walked into the control room of the Canberra DSN facility. It had everything you would expect for a typical control centre - hanging large TV-screen with tables and graphs; workstations with five-six monitors resembling scenes from the Matrix films and clocks with different global time zones ticking over.
But amongst all the technicality, flashes of humanities and a co-working team were present - in the centre of a room, standing high above a table a small, 1m Christmas tree wrapped in tinsel stood tall. At a few work stations, staff had personal belongings like photos of family members or personalised cups peppered across the clean, tidy desks. Along the floor, circumnavigating the outside of the workstations - rows of LED Christmas lights flashed on and off in a spectrum of colour.
Here is where I caught up with Gordon who described how he originally started working at the CSIRO Parkes radio telescope, roughly 340 km north-west of the Canberra DSN, working in the visitor centre.
It was when Voyager was about to cross paths with Uranus in 1986, that Gordon was approached to work down at the Canberra facility, handling tapes as a first look into operations. After reaching out that he’d like to work in the city, a new position was created revolving around documentation at the Canberra DSN, before being offered a role in comms work.
One day his supervisor approached Gordon and asked if he’d like to run the antennas at the deep-space mission facility - and he hasn’t looked back since.
“I remember seeing the shots of the big cliffs on Miranda [one of Uranus’s Moon] and just being blown away by it - I thought to myself, wow - this was received on Earth 14 minutes ago, and now we’ve got that picture,”
Gordon would proudly experience a career full of these special moments as the data streamed in, and changed our understanding of the Solar System. I couldn’t help but think of how exciting it must have felt, being present for so many groundbreaking moments in science history, some of which (in particular the visit to the Ice Giants) have not been experienced by anyone since.
In fact, a sense of pride in achievement radiated across the whole facility. Located just outside the control room, a number of memorable plaques tell the story that commemorates the human exploration of space over the last 60 or so years.
Missions to the inner and outer planets, missions with humans that succeeded and others that failed. It was all there, mirrored in plaques like a precious time capsule of accomplishments.
Among the Giants
Canberra DSN is a big site - and as we drove between the historic telescopes and buildings, the quirky names of the roads amplified the context of the setting. Names like Discovery Drive, Comet Place, and The Milky Way are juxtapositioned against the wide-open flats that turn into distant hills, surrounding the complex.
The Coolamon Ridge, Urambi Hills, and Bullen Range all help shield the facility from Canberra city’s radio frequency interference (RFI) - generated only 20km away. Whilst some of the biggest dishes in the world reside here at Canberra DSN, the signals they are collecting are extremely weak, only one-tenth of a billion-trillionth of a watt due to the vast distances they must travel. So the naturally surrounding semi-mountainous, bowl-shaped terrains that protect the antennas from RFI is welcome, and a feature of all three DSN global facilities.
The first thing that draws people’s attention upon arrival at Canberra DSN, are the large antennas - their size and shape transporting visitors to memories from science-fiction movie scenes. The large white dishes standing tall and bright against the background - often slowly slewing to a new target or tracking the incoming signal of a spacecraft message.
In fact, all three global DSN facilities feature a number of three antenna designs - distinguished by their size and purpose.
The largest of these at the Canberra facility is designated Deep Space Station (DSS) 43 - a 70-meter diameter antenna that stands at a height of 73 meters. The antenna’s dish is so big, you could fit an Olympic pool within it and still have 10 meters to spare on either end. Weighing in at approximately 3,000 tonnes - the reflective paraboloid covers a surface area of 3.85 square kilometers, maintained to a precision of 1cm - ensuring absolute minimal interference with the operations the antenna performs.
Its sheer size has earned this impressive structure the largest steerable parabolic radio telescope in the Southern Hemisphere, only just surpassing the Parkes Radio Telescope (64m diameter).
However, unlike the Parkes Dish, DSS 43 can both receive signals from deep space and transmit signals back out, giving it an advantage for missions requiring commands to be sent to robotic explorers - especially those with southern declinations.
There are three active 34-meter dishes at the Canberra DSN facility - which come in the beam waveguide design - where the transmission and reception equipment are located underground, and radio signals are guided down by reflecting mirrors, much like a giant periscope.
Glen talks me through the advantages of housing instrumentation underground, highlighting how the weight on the antenna is reduced - which minimises strain, wear and tear. He also indicates how it helps make maintenance much easier and safer to access, with technicians no longer required to climb high into the structures.
Some added benefits are that the sensitive instruments are not exposed to the harsh variations of the Australian climate as well as further isolating the electronics from unwanted radio noise.
The last antenna on-site happens to also be Glen’s favourite - the now decommissioned DSS 46 which features a smaller 26-meter dish on top of a unique X-Y axis mount - two interlocking horseshoe rings that allow the telescope to both point at very low elevations and track objects across the sky quickly.
Glen explains how this historical antenna has played a very important role in previous missions as we walk to its four base legs, cemented into the ground in large concrete blocks.
Towering 35-meters above me, this famous dish was once known as the Honeysuckle Creek Antenna, and today forms part of a legacy of the human space story.
A big part of human history
Most Australian’s would be unaware that within 3 hours drive of Sydney, residing on Canberra’s doorstep is one of the most historically important space communication facilities in the world.
Since the early 60s, the Canberra DSN has received signals from humanities endeavours to explore the cosmos, including:
- The Apollo program, inclusive of the Apollo 11 moon landing
- Missions to the outer Solar System such as Voyager, Pioneer and New Horizons
- Cassini’s epic mission to Saturn
Today, over 30 missions continue to stream data through the antennas in Tidbinbilla, including Martian orbiters, Jupiter’s Juno, several solar observatories and exoplanet-hunting spacecraft. All three global DSN stations are always in operation and online visitors can see which spacecraft each antenna is talking to through a publicly available website.
The first eight minutes of vision of the Apollo 11 moon landing - including Neil Armstrong’s immortalised words and first step, came in through the Honeysuckle creek antenna before they were broadcast out to the world (the Parkes Dish picked it up after this). Though it wasn’t just the all-important television images that were being received - telemetry data from both the Eagle and the Columbia crafts in lunar space, and the health of the three astronauts was received by this antenna.
It didn’t stop there for the 26-meter antenna located just outside Canberra. In April 1970, when the Apollo 13 spacecraft coasted towards the moon, an accident occured on the capsule. From 330,000km away from the Earth’s surface, the famous sentence “Ok Houston, we’ve had a problem” came streaming through the antenna before being relayed to NASA. It was in those vital moments, between an embattled craft heading towards the Moon with three astronauts aboard and everyone on Earth - that the Honeysuckle Creek antenna played one of its most important communications roles.
After the Apollo program, the Honeysuckle antenna continued to participate in gathering data for the experiments that astronauts left on the moon and then the Skylab program.
As of February in 2016, the original grounds that the Honeysuckle Antenna use to reside on (Honeysuckle Creek tracking station) have been listed as a heritage item under the Australian Capital Territory’s (ACT) register, by the ACT Heritage Council. However, the important antenna - which currently resides at the DSN, is yet to be listed anywhere.
Another important and ongoing mission that the Canberra DSN manages is one of humanity’s most iconic - our further object that currently sails away from the Sun and leads our first steps into interstellar space. The Voyager 2 mission.
Voyager 2 left Earth in 1977 to travel to the outer planets of our Solar System. First, it visited the Gas Giants Jupiter and Saturn, which were also visited by Voyager 1 and the Pioneer spacecraft. However, the perfect planetary alignment also provided an opportunity for Voyager 2 to visit the Ice Giants, Uranus, and Neptune - still the only human-made object to do so to this day.
After completing its planetary missions, Voyager has continued onwards with recent reports that it has now officially left the outskirts of the Solar System and entered into deep, interstellar space. It’s currently over 18 billion kilometers from Earth and moving at a velocity of approximately 55,000 km/h.
Remarkably, of its 10 original instruments, five continue to operate - even after 42 years of travelling through space - beaming in what the craft is observing as it crosses these new, uncharted frontiers in the direction of the southern constellation, Pavo.
Due to its very south location in the sky, the only DSN tracking station that can currently communicate with Voyager is the Canberra facility. Whilst other antennas at Canberra DSN can receive Voyager’s extremely faint signal, only the 70m DSS 43 is capable of transmitting signal commands to the spacecraft, which moves away from the Earth by over 1.3 million kilometers per day.
Earlier this year, Voyager 2 gave NASA scientists and DSN operators a scare, when it tried to execute a regular command - rolling 360-degrees to re-calibrate its magnetometer - a maneuver it has completed many times before.
Through smart programming built into the spacecraft’s brain, the computer shut itself down to allow it to preserve energy during the maneuver - which caused a scare to the entire space science community. Was this it? Was this the end of one of humanities furthest probe and a chance to learn about the beyond?
Thankfully, scientists and engineers worked through painfully long wait periods (the light travel time is about 17 hours each way, so sending commands takes 17 hours to get there and then the response takes 17 hours to get back), and eventually brought it back into nominal operating levels. The entire ordeal has been streaming back and forth through DSS 43 at the Canberra DSN.
Looking Out, Into the Horizon
DSS 43 has just been powered down for a period of 10-months as instrumentation and equipment are upgraded to prepare the antenna for its important role it will play in NASA’s new frontier - the Artemis program - which will see the first woman walk and next man return to the Moon by the mid-2020s.
The global space community is anxious about losing our only umbilical cord of communication with Voyager 2 - but the upgrades are a necessity to keep the telescope in optimal condition to continue with operations.
Australia’s unique position - and the excellent infrastructure managed by the CSIRO at the Canberra DSN will once again play a pivotal role in humanity's next steps into the cosmos. Already operating across 30 missions, the station will be pivotal to future exploration robots, sent back into the darkness of space.
It’s hoped that we’ll one day also send our next generation of robots to the Ice Giants of the outer solar system, which will change our perspective of our place in the Universe once more.
As I drove away from the facility, some lasting words from Gordon stayed with me that day. He said “I like the fact that what we are doing here today, go into the textbooks of science next year” and it made me think about how much our knowledge of the Solar System has changed even during my own 30-odd years of understanding the space program.
My visit to the Canberra DSN centre was over - and I smiled ear to ear, feeling so much more enriched that I was able to hear about the lives of the people involved, and the wonderful infrastructure that has played such an important role in our shared space history.
It also filled me with a sense of pride to know that Australia has contributed to this momentous record and our country’s vital role in the triumph, tragedy, discovery, and knowledge of humanity’s space programs will continue.
All of this, from our own backyard. | 0.903132 | 3.479101 |
NASA's Phoenix Mars Lander, led by The University of Arizona, has detected snow falling from Martian clouds. Spacecraft soil experiments also have provided evidence of past interaction between minerals and liquid water, processes that occur on Earth.
A laser instrument designed to gather knowledge of how the atmosphere and surface interact on Mars has detected snow from clouds about 4 kilometers (2.5 miles) above the spacecraft's landing site. Data show the snow vaporizing before reaching the ground.
"Nothing like this view has ever been seen on Mars," said Jim Whiteway, of York University, Toronto, lead scientist for the Canadian-supplied Meteorological Station on Phoenix. "We'll be looking for signs that the snow may even reach the ground."
Phoenix experiments also yielded clues pointing to calcium carbonate, the main composition of chalk, and particles that could be clay. Most carbonates and clays on Earth form only in the presence of liquid water.
"We are still collecting data and have lots of analysis ahead, but we are making good progress on the big questions we set out for ourselves," said Phoenix Principal Investigator Peter Smith of the UA's Lunar and Planetary Laboratory.
Since landing on May 25, Phoenix already has confirmed that a hard subsurface layer at its far-northern site contains water-ice. Determining whether that ice ever thaws would help answer whether the environment there has been favorable for life, a key aim of the mission.
The evidence for calcium carbonate in soil samples from trenches dug by the Phoenix robotic arm comes from two laboratory instruments called the Thermal and Evolved Gas Analyzer, or TEGA, and the wet chemistry laboratory of the Microscopy, Electrochemistry and Conductivity Analyzer, or MECA.
"We have found carbonate," said William Boynton of the UA, lead scientist for the TEGA. "This points toward episodes of interaction with water in the past."
The TEGA evidence for calcium carbonate came from a high-temperature release of carbon dioxide from soil samples. The temperature of the release matches a temperature known to decompose calcium carbonate and release carbon dioxide gas, which was identified by the instrument's mass spectrometer.
The MECA evidence came from a buffering effect characteristic of calcium carbonate assessed in wet chemistry analysis of the soil. The measured concentration of calcium was exactly what would be expected for a solution buffered by calcium carbonate.
Both TEGA, and the microscopy part of MECA, have turned up hints of a clay-like substance. "We are seeing smooth-surfaced, platy particles with the atomic-force microscope, not inconsistent with the appearance of clay particles," said Michael Hecht, MECA lead scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
The Phoenix mission, originally planned for three months on Mars, now is in its fifth month. However, it faces a decline in solar energy that is expected to curtail and then end the lander's activities before the end of the year. Before power ceases, the Phoenix team will attempt to activate a microphone on the lander to possibly capture sounds on Mars.
"For nearly three months after landing, the sun never went below the horizon at our landing site," said Barry Goldstein, JPL Phoenix project manager. "Now it is gone for more than four hours each night, and the output from our solar panels is dropping each week. Before the end of October, there won't be enough energy to keep using the robotic arm."
The Phoenix mission is led by Smith at the UA. Project management is the responsibility of JPL with development partnership by Lockheed Martin in Denver. International contributions come from the Canadian Space Agency; the University of Neuchatel, Switzerland; the universities of Copenhagen and Aarhus, Denmark; Max Planck Institute, Germany; and the Finnish Meteorological Institute. | 0.860129 | 3.789252 |
CHIPSat (CHIPS Satellite)
CHIPSat (Cosmic Hot Interstellar Plasma Spectrometer Satellite) is a technology demonstration mission of UCB (University of California at Berkeley, PI: M. Hurwitz), supported by NASA's UNEX (University-class Explorer) program, with the objective to obtain spectral sky maps of the scientifically critical EUV (Extreme Ultraviolet) band between 90-260 Å. CHIPSat is in fact NASA's first UNEX mission. The CHIPS full-sky survey helps to determine the electron temperature, ionization conditions, and cooling mechanisms of the so-called “local interstellar bubble,” a cloud of hot gas surrounding our solar system that extends about 300 light-years from the sun. 1) 2) 3) 4) 5)
Background: The CHIPS (Cosmic Hot Interstellar Plasma Spectrometer) project was selected by UNEX in 1998. The CHIPS mission (i.e. the instrument) was initially proposed as a secondary payload aboard a FAISat communications S/C. This approach was dropped in favor of a small spacecraft with a single instrument payload. Thus the CHIPS project mutated to CHIPSat.
Figure 1: Artist's view of CHIPSat (image credit: NASA)
CHIPSat is a dedicated microsatellite built by SpaceDev, Inc. of Poway, CA for UCB/SSL (Space Sciences Laboratory). CHIPSat is a three-axis stabilized S/C using 4 momentum wheels (Dynacon MicroWheel 200), three torque coils, two sun sensors, magnetometer, a moon sensor, and rate sensors to provide an attitude pointing accuracy within ±2º. The magnetorquers are being used to balance residual spacecraft dipole and dump built-up momentum from the wheels. The S/C is nominally sun-pointing with complete freedom to yaw about the solar array normal vector allowing the CHIPS instrument to obtain a full-sky survey within six months, while avoiding pointing the instrument FOV at the sun, Earth, moon and in the orbital RAM direction. The design permits access to all points on the celestial sphere within the one year mission lifetime. 6) 7) 8)
The S/C structure employs the BD-II spacecraft bus of SpaceDev, using a milled aluminum transition adapter and aluminum honeycomb panels with facesheets for structural integrity. Power (106 W EOL) is provided by body-mounted solar arrays using dual-junction GaAs/InP/Ge solar cells; NiCd batteries are used during solar eclipses. In addition, small keep-alive arrays are positioned on the other five sides of the S/C providing enough power to run critical subsystems regardless of the S/C attitude. A passive thermal subsystem is used for CHIPSat. The C&DH (Communications and Data Handling) subsystem employs a single-board computer (Motorola Power PC 750 CPU, memory, and I/O for distributed processors). The S/C mass is 64 kg, power = 42 W, its size is about 1 m x 1 m x 0.5 m, the design life is 18 months (one year mission).
The CHIPSat system provides a design that utilizes COTS (Commercial-off-the-Shelf) philosophy. The avionics electronic components are primarily commercial grade with industrial temperature range. For internal communications within the bus, standard COTS interface protocols are used, most notably RS-422 and RS-485. Because TCP/IP is used for end-to-end communications, almost all hardware in the ground segment is COTS; in addition, almost all communications-related software is built into the COTS operating systems used for both the ground and space segments. The interface between the spacecraft and the ground segment consists of an HDLC point-to-point link layer. Layered within the HDLC frames is a standard TCP/UDP/IP protocol stack that, when combined with VPN (Virtual Private Network) and firewall-protected use of the commercial Internet, allows end-to-end data flow between mission control centers, science operations centers, and the spacecraft. The use of COTS Internet tools opened up a wide range of easily implemented operational capability including distributed and easily portable integration and test and mission operations.
Figure 2: Illustration of the CHIPSat spacecraft (image credit: SpaceDev Inc.)
Figure 3: View of CHIPSat -Z direction (auxiliary solar arrays), image credit: SpaceDev Inc.
Figure 4: CHIPSat undergoes final preparation at VAFB before launch (image credit: Boeing Company)
Launch: CHIPSat was launched as a secondary payload, along with ICESat as primary payload, on January 13, 2003 (UTC) on a Delta-2 7320-10 rocket from VAFB, CA. 9)
Orbit: circular orbit, altitude of 190 km x 1200 km (initial) and 590 km (final), inclination = 94º, orbital period of 96.23 minutes. - Note: The 190 km x 1200 km orbit was the initial orbit in which the Delta-2 2nd stage, with CHIPSat still attached, was left when the 3rd stage separated. Then, the 2nd stage was fired twice again, first to lower the apogee, then after 45 minutes, to raise the perigee. Only then did CHIPSat separate from the 2nd stage. The CHIPSat spacecraft doesn't provide any onboard propulsion.
CHIPSat is the first NASA mission to use end-to-end satellite operations with TCP/IP and FTP (File Transfer Protocol). This concept has been analyzed and demonstrated by the NASA OMNI team via UoSAT-12. However, CHIPSat is the first spacecraft to implement the TCP/IP concept as the only means of satellite communications.
The RF communications are in S-band. The transceiver is composed of a transmitter and separate receiver which are combined via a highly selective diplexer and split into two (RHCP & LHCP) antennas to provide near 4π coverage. The system utilizes FSK modulation for both uplink and downlink, and utilizes rates of 4-9.6 kbit/s and 38.4 - 115.2 kbit/s respectively.
The TCP/IP and UDP/IP (User Datagram Protocol/Internet Protocol) protocol suite is used to communicate all data between the S/C and the ground user directly. Data is received, archived, and monitored at MCC (Mission Control Center) at SpaceDev, and then sent to SOC (Science Operation Center) at UCB/SSL via Internet.
The UDP/IP (User Datagram Protocol) protocol is selected for real-time monitoring and real-time commanding (it de-couples both directions) and presents much less overhead. The setup permits the reception of engineering and status packets (telemetry) in case the uplink isn't working. Conversely, the setup permits also to command “into the blind” by uplinking UDP packets in case the telemetry isn't working.
Note: The UDP service of the TCP/IP protocol permits to send discrete packets of information called “datagrams” that aren't guaranteed to get there and may arrive out of order depending upon their routing through the IP system. A two-way communication isn't needed in this setup because the data are broadcast. So, if a guarantee is needed that at least some packets get through, even if one direction of the communication link fails, then UDP may be used. - TCP deals with making sure that all the packets arrive and are in the correct order. TCP implies a two-way connection and a higher level of communications overhead to assure that all the packets arrive and are in the correct order.
The spacecraft takes advantage of the innate capabilities and common tools of the Internet to manage time synchronization between the ground and the spacecraft. These include NTP (Network Time Protocol) on the SpaceDev TCP/IP data routers located at the ground stations and SNTP (Simple Network Time Protocol) running on the spacecraft operating system. The software running on the spacecraft periodically requests a time update from the ground station, and after a successful SNTP echo, the spacecraft clock is aligned to UTC (estimated at better than 100 milliseconds).
Status of mission:
• The CHIPSat mission was retired on April 11, 2008 — after 5 years of successful operations. The reason for its retirement was simply that NASA didn't provide a budget to continue the low-cost operations of the mission. 10) 11) 12)
• In mid-January 2005, CHIPSat was operating for two years in orbit. 13)
• During the first six months of the mission, the CHIPSat spacecraft has been able to perform per its design requirements. However, several anomalies (both expected and unexpected) have occurred. Since the start of science data collection, the net duty cycle for the acquisition of science data is ~ 95%. - Due to the use of non-radiation-hardened commercial electronics, a number of SEE (Single-Event Effect) events were expected.
• Throughout the early period, mission operations were conducted from the mission operations center at SpaceDev Inc., with only instrument commands originated at Berkeley. Operation of the satellite from the SpaceDev facility was crucial, as it enabled the most experienced and knowledgeable spacecraft engineers to participate in the day-today (sometimes moment-to-moment) decision making. As operations as a whole became routine, however, it became advantageous to rely on the mission operations personnel and infrastructure developed primarily for the HESSI and FAST missions already in place at Berkeley. Operations were transitioned to Berkeley in late May 2003, with SpaceDev continuing to participate in periodic meetings and as required to resolve anomalies (Ref. 14).
• Three anomalies have occurred to date relating to the onboard reaction wheels. CHIPSat is the second mission with four microwheels (the first mission is FedSat); like the flight computer, the wheel design primarily employs commercial parts. One wheel incurred a communication failure; as a result, the spare wheel is being used for active ACS control.
• The spacecraft was detumbled on January 20, 2003. Checkout and commissioning of the attitude control system and spectrograph occurred over the following weeks. The detector door was opened on January 26. By February 2, all six of the entrance slit covers had been opened to their 1mm or "wide" positions (the first detente following the closed positions employed during launch). Astrophysical observations ramped up in early February as commissioning activities wound down. 14)
Sensor complement: (CHIPS)
CHIPS (Cosmic Hot Interstellar Plasma Spectrometer):
CHIPS is a low-cost instrument with high sensitivity and spectral resolution in the spectral band near 170 Å, designed and built at UCB/SSL. The science objectives are to carry out EUV spectroscopy to determine how the million degree gas-cloud surrounding our solar system, cools. - The CHIPS instrument uses an array of grazing-incidence optics to achieve a peak resolving power of f/150 for diffuse emission in a field of view (FOV) of 5º × 26.7º (the gratings are aligned in one dimension on the sky).
Light enters the spectrograph through the array of six entrance slits (channels). The entrance apertures are narrow slits, each covered by a rotating mechanism with closed, narrow, and wide settings to protect the interior from contamination during launch. The gratings disperse and focus the diffuse extreme ultraviolet radiation onto a single detector through a filter assembly. The detector is a planar, photon-counting MCP (Micro Channel Plate) with a crossed delay line anode. In-band photon locations are determined from the anode, which converts the light into analog electronic pulses. 15) 16) 17)
Figure 5: Light path of the six channels of the CHIPS spectrograph (image credit: UCB/SSL, Ref. 14)
Note: The use of variable line-spaced gratings in instruments is of EUVE and ORFEUS (Orbiting Retrievable Far and Extreme Ultraviolet Spectrograph) instrument heritage. The ORFEUS payload flew twice with the ASTRO-SPAS missions on STS-51 (Sept. 12-22, 1993)) and on STS-80 (Nov. 19 - Dec. 7, 1996). The NASA satellite EUVE (Extreme Ultraviolet Explorer) was launched June 7, 1992.
Table 1: CHIPS instrument performance parameters
Figure 6: Schematic concept of CHIPS (image credit: UCB/SSL)
Figure 7 provides a block diagram of the CHIPS electrical system and principal interfaces. The photon-counting system converts light focused on the spectrometer's photosensitive front surface into a stream of digitized photon coordinates. In-band photon locations are determined using a XDL anode, converting the light into analog electrical pulses. RF amps amplify the anode signal and the pulses are converted into digitized coordinates by a TDC (Time Digital Converter) in the instrument EBOX (Electronics Box). The digitized events are transmitted to a DPU/HK (Data Processing and Housekeeping Unit) for processing. The DPU/HK board packages and formats all instrument data for transmission to the CHIPSat SBC (Single Board Computer) via redundant asynchronous RS-422 links. Science and instrument HK data is then stored within the spacecraft memory and combined with orientation data prior to downlink.
Low-current power to the instrument LVPS (Low Voltage Power Supply) and high-current power to the instrument door and cover actuators is supplied directly from the spacecraft 14 V batteries. The LVPS incorporates its own power converters to generate the required secondary voltages. The spacecraft provides switched heaters to keep the instrument within its survival temperature range.
Figure 7: Block diagram of the CHIPS electrical system (image credit: UCB/SSL)
The TDC (Time to Digital Converter) is responsible for processing valid photon events [converting analog pulses from the RF amps to digital detector (x, y) coordinates and charge amplitudes] and rejecting subthreshold or incomplete events.
Figure 8: Photo of the CHIPS spectrometer (image credit: UCB/SSL)
Figure 9: Cutaway view of the spectrometer configuration (image credit: UCB/SSL)
Among the challenges on CHIPS were initial coalignment of the spectrometer channels, and maintenance of coalignment in the presence of thermal gradients and launch dynamics. Each spectrometer channel is a relatively slow (f/14) optical system, and therefore optical misalignments on the order of the slit width are tolerable with small degradation in spectral resolution. Because the spectrograph combines slit images from six separate channels, slit images must be coaligned, and coalignment maintained, within a small fraction of their size on the focal plane (~250 µm).
Initial alignment was achieved using 5mm visible ruling patches on the ends of the gratings. A HeNe laser was split into four beamlets by 25%, 33% and 50% reflection beamsplitters. Beamwalk mirrors were used to direct pairs of beamlets through the entrance slit, off the visible patches, to the focal plane at the cross-dispersion extremes of the detector. During visible light alignment, the detector was replaced with a ground glass surrogate detector, and a pair of CMOS cameras used to image the ground glass screen near the extremes of the spectral feature. A wire fiducial mounted on the ground glass served as a coalignment target. The alignment technique is beyond the scope of this paper, but based on recognizing optical distortion and misalignment by the differences in the “speed” of motion of the near and far visible patch spots, on the focal plane, for a given grating angular motion. Initial alignment was achieved when all four spots were positioned on the wire. Fine alignment was performed with removable 80 thread per inch micrometers, based on measurements made at EUV wavelengths in the vacuum calibration facility.
1) E. Taylor, M. Hurwitz, W. Marchant, M. Sholl, S. Dawson, J. Janicik, J. Wolff, “CHIPS: A NASA University Explorer Astronomy Mission,” Proceedings of AIAA/USU Conference on Small Satellites, Logan, UT, USA, Aug. 11-14, 2003, SSC03-V-3
2) W. Marchant, E. Riddle Taylor, “Status of CHIPS: A NASA University Explorer Astronomy Mission,” Proceedings of the 14th AIAA/USU Conference on Small Satellites, Logan, UT, Aug. 21-24, 2000, SSC00-V-6
3) M. Hurwitz, W. Marchant, M. Sholl, E. Riddle Taylor, “Status of CHIPS: A NASA University Explorer Astronomy Mission,” AIAA/USU Conference on Small Satellites, Aug. 13-16, 2001, Logan, UT, SSC-091-V-7
4) Courtesy of Will Marchant of UCB/SSL
5) Jeffrey Janicik, Jonathan Wolff, “The CHIPSat Spacecraft Design - Significant Science on a Low Budget,” Proceedings of SPIE,'UV/EUV and Visible Space Instrumentation for Astronomy II,' Vol. 5164, Aug. 2003, San Diego, CA, USA, URL: http://chips.ssl.berkeley.edu/JanicikSPIE.pdf
7) “Cosmic Hot Interstellar Plasma Spectrometer (CHIPS): Studying the Interstellar Medium,” NASA/GSFC, FS-2002-11-048-GSFC, URL: http://www.nasa.gov/centers/goddard/pdf/110914main_FS-2002-11-048-GSFC-CHIPS.pdf
9) “Delta / ICESat/CHIPSat Mission from VAFB Pad SLC-2,” URL: http://science.ksc.nasa.gov/payload/missions/icesat/
10) “CHIPSat Quietly Shut Down,” June 4, 2008, URL: http://www.redorbit.com/news/space/1417075/chipsat_quietly_shut_down/
11) Information provided by Mark Hurwitz of SSL at UCB (University of California, Berkeley)
12) M. J. Sholl, Geoff Gaines, Martin Sirk, Ellen Taylor, Mark Hurwitz, “CHIPS Microsatellite Optical System: Lessons Learned,” Proceedings of SPIE, Vol. 7071, 707104-1, 2008, doi: 10.1117/12.799573, URL: http://220.127.116.11/ft/CONF/16419962/16419964.pdf
13) “SpaceDev's CHIPSat Celebrates Second Anniversary in Space,” SpaceRef, Jan. 20, 2005, URL: http://www.spaceref.com/news/viewpr.html?pid=15956
14) Mark Hurwitz, the CHIPS Instrument Team, and CHIPSat Spacecraft Team, “Current status of the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) University-class Explorer Mission ,” Proceedings of SPIE, 'UV/EUV and Visible Space Instrumentation for Astronomy II,' Ed. Oswald H. W. Siegmund, Vol. 5164, 24, San Diego, CA, August 2003, URL: http://chips.ssl.berkeley.edu/Hurwitz_CHIPS_SPIE_San_Diego_II.pdf
16) M. Sholl, B. Donakowski, G. Gaines, M. Lampton, M. Hurwitz, M. M. Sirk, E. Taylor, “Optics design and performance for the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS),” URL: http://chips.ssl.berkeley.edu/SPIE-5164-09_V0.pdf
17) M. Sholl, W. Donakowski, M. M. Sirk, T. Clauss, M. Lampton, J. Edelstein, M. Hurwitz, “Opto-mechanical Design of the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS),” URL: http://www.astro.caltech.edu/~srk/MiniSat/InterestingProjects/OptMechDesign.pdf
The information compiled and edited in this article was provided by Herbert J. Kramer from his documentation of: ”Observation of the Earth and Its Environment: Survey of Missions and Sensors” (Springer Verlag) as well as many other sources after the publication of the 4th edition in 2002. - Comments and corrections to this article are always welcome for further updates. | 0.895228 | 3.638968 |
PIC: A color view from NASA's Juno spacecraft made from some of the first images taken by JunoCam after the spacecraft entered orbit around Jupiter on July 5. (AFP/NASA)
NASA has published the first-ever images of Jupiter's north pole and its southern aurora, taken during the Juno spacecraft's first orbital flyby of the gaseous giant.
Juno came within 2,500 miles (4,200 kilometers) of Jupiter on August 27 during a six-hour transit from the north pole to the south.
"It looks like nothing we have seen or imagined before," said Scott Bolton, principal investigator of Juno from the Southwest Research Institute in San Antonio.
"The largest planet in our solar system is truly unique. We have 36 more flybys to study just how unique it really is."
A camera dubbed the "JunoCam" took the high-definition images. It is one of the nine instruments onboard the spacecraft.
Juno notably sent the first infrared close-ups of the planet's north and south poles.
"These first infrared views of Jupiter's north and south poles are revealing warm and hot spots that have never been seen before," said Alberto Adriani, of the Istituto di Astrofisica e Planetologia Spaziali in Rome.
Adriani is one of the researchers who developed the Jovian Infrared Auroral Mapper (JIRAM) that allowed scientists to acquire the images.
"While we knew that the first-ever infrared views of Jupiter's south pole could reveal the planet's southern aurora, we were amazed to see it for the first time," he said.
Auroras are streamers of light in the sky caused by energy from the sun and electrically charged particles trapped in the magnetic field.
Another Juno instrument recorded sounds from Jupiter -- "ghostly-sounding transmissions emanating from the planet," said NASA.
Scientists have known about Jupiter's radio emissions since the 1950s, but had never analyzed them from such a close distance.
"Jupiter is talking to us in a way only gas-giant worlds can," said Bill Kurth, co-investigator from the University of Iowa.
Juno's main mission began in July and is scheduled to end in February 2018, when the probe will self-destruct by diving into the planet's atmosphere.
The $1.1 billion project aims to peer beneath the clouds around Jupiter for the first time to learn more about the planet's atmosphere.
Scientists want to know how much water the planet contains, because it can tell them a lot about when and how the planet formed.
Juno will also probe how the planet's intense magnetic field is generated, and study the formation of auroras. | 0.803652 | 3.491961 |
Candidate exoplanets as seen by TESS in a southern sky mosaic from 13 observing sectors. (NASA/MIT/TESS)
NASA’s Transiting Exoplanet Survey Satellite (TESS) has finished its one year full-sky observation of Southern sky and has found hundreds of candidate exoplanets and 29 confirmed planets. It is now maneuvering its array of wide-field telescopes and cameras to focus on the northern sky to do the same kind of exploration.
At this turning point, NASA and the Massachusetts Institute of Technology — which played a major role in designing and now operating the mission — have put together mosaic images from the first year’s observations, and they are quite something.
Constructed from 208 TESS images taken during the mission’s first year of science operations, these images are a unique space-based look at the entire Southern sky — including the Milky Way seen edgewise, the Large and Small Magellenic galaxies, and other large stars already known to have exoplanet.
“Analysis of TESS data focuses on individual stars and planets one at a time, but I wanted to step back and highlight everything at once, really emphasizing the spectacular view TESS gives us of the entire sky,” said Ethan Kruse, a NASA Postdoctoral Program Fellow who assembled the mosaic at NASA’s Goddard Space Flight Center.
The mission is designed to vastly increase the number of known exoplanets, which are now theorized to orbit all — or most — stars in the sky.
TESS searches for the nearest and brightest main sequence stars hosting transiting exoplanets, which are the most favorable targets for detailed investigations.
While previous sky surveys with ground-based telescopes have mainly detected giant exoplanets, TESS will find many small planets around the nearest stars in the sky. The mission will also provide prime targets for further characterization by the James Webb Space Telescope, as well as other large ground-based and space-based telescopes of the future.
The TESS observatory uses an array of wide-field cameras to perform a survey of 85% of the sky.… Read more | 0.817657 | 3.480852 |
Hungry galaxies grow fat on flesh of their neighbours
Galaxies grow large by eating their smaller neighbours, finds an international research team, including York University.
Exactly how massive galaxies attain their size is poorly understood, not least because they swell over billions of years. But now through a combination of observation and modelling, researchers, including the Faculty of Science’s Leo Alcorn, a York Science Fellow, have found a clue.
The research team, led by Post-Doctoral Researcher Anshu Gupta from Australia’s ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), included scientists from Australian, the United States, Canada, Mexico, Belgium and the Netherlands. They ran their modelling on a specially designed set of simulations known as IllustrisTNG.
In the paper, MOSEL Survey: Tracking the Growth of Massive Galaxies at 2 < z < 4 Using Kinematics and the IllustrisTNG Simulation, published in The Astrophysical Journal, the scientists combine data from an Australian project called the Multi-Object Spectroscopic Emission Line (MOSEL) survey with a cosmological modelling program running on some of the world’s largest supercomputers to glimpse the forces that create these ancient galactic monsters.
By analysing how gases within galaxies move it is possible to discover the proportion of stars made internally – and the proportion effectively cannibalised from elsewhere.
“We found that distant, massive galaxies, about 10 billion light years away from us, have more chaotic or random internal motions,” says Alcorn. “This is likely because these galaxies have merged with smaller galaxies, producing gravitational disruptions to the orbits of stars and gas. This matter is incorporated into the massive galaxies, growing the galaxy in mass and size”
Because light takes time to travel through the universe, galaxies further away from the Milky Way are seen at an earlier point in their existence. The team found that observation and modelling of these very distant galaxies revealed much less variation in their internal movements.
“As these huge galaxies gain more stars, they are able to gravitationally attract and merge with more surrounding small galaxies. Over billions of years, these old, massive galaxies grow increasingly chaotic, disordered, and large, constantly feeding on nearby neighbours,” says Alcorn.
This is a multi-year, international project that aims to build a series of large cosmological models of how galaxies form. The program is so big that it has to run simultaneously on several of the world’s most powerful supercomputers.
Back to Research News | 0.83689 | 3.907356 |
|Pronunciation||/[invalid input: 'ɨ'] /, genitive /[invalid input: 'ɨ'] [invalid input: 'ɨ'][invalid input: 'ɨ']/|
|Symbolism||the lesser Dog|
|Area||183 sq. deg. (71st)|
|Stars with planets||1|
|Stars brighter than 3.00m||2|
|Stars within 10.00 pc (32.62 ly)||4|
|Brightest star||Procyon (α CMi) (0.34m)|
|Visible at latitudes between +90° and −75°.|
Best visible at 21:00 (9 p.m.) during the month of March.
Canis Minor is a constellation in the northern sky. It is Latin for "smaller dog" or "the lesser dog". The astronomer Ptolemy listed it when he made a list of 48 constellations in the 2nd century. Both Canis Minor and Canis Major (which means "larger dog" in Latin) represent dogs that follow the hunter named Orion in Greek Mythology.
The main shape of Canis Minor is made by two stars, which are named Procyon (Alpha Canis Minoris) and Gomeisa (Beta Canis Minoris). These stars are the only stars in Canis Minor that have a magnitude that is brigher than 4. Procyon has a magnitude of 0.39, which means that it is the seventh brightest star in the night sky.[a] It is also very close to Earth, since it is only 11.4 light years away. Procyon is a binary star, which means that it actually has two stars that orbit each other. It has a white dwarf star and a white type F5 main-sequence star. Gomeisa has a magnitude of 2.9. Its temperature is 11,500°K, which means that it is very hot. It is a blue type B8 main-sequence star. It is 3 times the mass of the sun and 250 times more luminous than the sun.
Notes[change | change source]
- If the magnitudes of binary stars are combined, then Procyon is the eighth brightest star in the night sky.
References[change | change source]
- Ridpath, Ian. "Canis Minor: The Lesser Dog". Star Tales. Retrieved 27 Jan 2013.
- Kaler, Jim. "Canis Minor". Stars. Retrieved 28 Jan 2013.
- "Procyon (HIP 37279)". Ashland Astronomy Studio. Retrieved 28 Jan 2013.
- Kaler, Jim. "Pyrocyon". Stars. Retrieved 28 Jan 2013.
- Kaler, Jim. "Gomeisa". Stars. Retrieved 28 Jan 2013. | 0.867314 | 3.445902 |
The Fermi paradox (or Fermi’s paradox) is the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilization and humanity’s lack of contact with, or evidence for, such civilizations. The basic points of the argument, made by physicists Enrico Fermi and Michael H. Hart, are:
The Sun is a young star. There are billions of stars in the galaxy that are billions of years older;
Some of these stars likely have Earth-like planets which, if the Earth is typical, may develop intelligent life;
Presumably some of these civilizations will develop interstellar travel, as Earth seems likely to do;
At any practical pace of interstellar travel, the galaxy can be completely colonized in just a few tens of millions of years.
According to this line of thinking, the Earth should have already been colonized, or at least visited. But no convincing evidence of this exists. Furthermore, no confirmed signs of intelligence elsewhere have been spotted, either in our galaxy or the more than 80 billion other galaxies of the observable universe. Hence Fermi’s question “Where is everybody?”.
Stand by for an animated exploration of the famous Fermi Paradox. Given the vast number of planets in the universe, many much older than Earth, why haven’t we yet seen obvious signs of alien life? The potential answers to this question are numerous and intriguing, alarming and hopeful.
Stand by for an animated exploration of the famous Fermi Paradox. Given the vast number of planets in the universe, many much older than Earth, why haven't we yet seen obvious signs of alien life? The potential answers to this question are numerous and intriguing, alarming and hopeful.
Probes, colonies, and other artifacts
As noted, given the size and age of the universe, and the relative rapidity at which dispersion of intelligent life can in principle occur, evidence of alien colonization attempts might plausibly be discovered. Evidence of exploration not containing extraterrestrial life, such as probes and information gathering devices, may also await discovery.
Some theoretical exploration techniques such as the Von Neumann probe (a self-replicating device) could exhaustively explore a galaxy the size of the Milky Way in as little as half a million years, with comparatively little investment in materials and energy relative to the results. If even a single civilization in the Milky Way attempted this, such probes could spread throughout the entire galaxy. Evidence of such probes might be found in the Solar System—perhaps in the asteroid belt where raw materials would be plentiful and easily accessed.
Another possibility for contact with an alien probe—one that would be trying to find human beings—is an alien Bracewell probe. Such a device would be an autonomous space probe whose purpose is to seek out and communicate with alien civilizations (as opposed to Von Neumann probes, which are usually described as purely exploratory). These were proposed as an alternative to carrying a slow speed-of-light dialogue between vastly distant neighbours. Rather than contending with the long delays a radio dialogue would suffer, a probe housing an artificial intelligence would seek out an alien civilization to carry on a close range communication with the discovered civilization. The findings of such a probe would still have to be transmitted to the home civilization at light speed, but an information-gathering dialogue could be conducted in real time.
Since the 1950s, direct exploration has been carried out on a small fraction of the Solar System and no evidence that it has ever been visited by alien colonists, or probes, has been uncovered. Detailed exploration of areas of the Solar System where resources would be plentiful—such as the asteroids, the Kuiper belt, the Oort cloud and the planetary ring systems—may yet produce evidence of alien exploration, though these regions are vast and difficult to investigate.
There have been preliminary efforts in this direction in the form of the SETA and SETV projects to search for extraterrestrial artifacts or other evidence of extraterrestrial visitation within the Solar System. There have also been attempts to signal, attract, or activate Bracewell probes in Earth’s local vicinity, including by scientists Robert Freitas and Francisco Valdes. Many of the projects that fall under this umbrella are considered “fringe” science by astronomers and none of the projects has located any artifacts.
Should alien artifacts be discovered, even here on Earth, they may not be recognizable as such. The products of an alien mind and an advanced alien technology might not be perceptible or recognizable as artificial constructs. Exploratory devices in the form of bio-engineered life forms created through synthetic biology would presumably disintegrate after a point, leaving no evidence; an alien information gathering system based on molecular nanotechnology could be all around us at this very moment, completely undetected. The same might be true of civilizations that actively hide their investigations from us, for possible reasons described further in this article. Also, Clarke’s third law suggests that an alien civilization well in advance of humanity’s might have means of investigation that are not yet conceivable to human beings.
Advanced stellar-scale artifacts
Further information: Dyson sphere, Kardashev scale, Alderson disk, Matrioshka brain, Stellar engine
A variant of the speculative Dyson sphere. Such large scale artifacts would drastically alter the spectrum of a star.
In 1959, Freeman Dyson observed that every developing human civilization constantly increases its energy consumption, and theoretically, a civilization of sufficient age would require all the energy produced by its star. The Dyson Sphere was the thought experiment that he derived as a solution: a shell or cloud of objects enclosing a star to harness as much radiant energy as possible. Such a feat of astroengineering would drastically alter the observed spectrum of the star involved, changing it at least partly from the normal emission lines of a natural stellar atmosphere, to that of a black body radiation, probably with a peak in the infrared. Dyson himself speculated that advanced alien civilizations might be detected by examining the spectra of stars, searching for such an altered spectrum.
Since then, several other theoretical stellar-scale megastructures have been proposed, but the central idea remains that a highly advanced civilization—Type II or greater on the Kardashev scale—could alter its environment enough as to be detectable from interstellar distances.
However, such constructs may be more difficult to detect than originally thought. Dyson spheres might have different emission spectra depending on the desired internal environment; life based on high-temperature reactions may require a high temperature environment, with resulting “waste radiation” in the visible spectrum, not the infrared. Additionally, a variant of the Dyson sphere has been proposed which would be difficult to observe from any great distance; a Matrioshka brain is a series of concentric spheres, each radiating less energy per area than its inner neighbour. The outermost sphere of such a structure could be close to the temperature of the interstellar background radiation, and thus be all but invisible.
There have been some preliminary attempts to find evidence of the existence of Dyson spheres or other large Type-II or Type-III Kardashev scale artifacts that would alter the spectra of their core stars. These surveys have not located anything yet, though they are still incomplete. Similarly, direct observation of thousands of galaxies has shown no explicit evidence of artificial construction or modifications.
Explaining the paradox theoretically
Certain theoreticians accept that the apparent absence of evidence implies the absence of extraterrestrials and attempt to explain why. Others offer possible frameworks in which the silence may be explained without ruling out the possibility of such life, including assumptions about extraterrestrial behaviour and technology. Each of these hypothesized explanations is essentially an argument for decreasing the value of one or more of the terms in the Drake equation. The arguments are not, in general, mutually exclusive. For example, it could be both that life is rare, and technical civilizations are short lived, or many other combinations of the explanations below.
Few, if any, other civilizations currently exist
One explanation is that the human civilization is alone (or very nearly so) in the galaxy. Several theories along these lines have been proposed, explaining why intelligent life might be either very rare, or very short lived. Implications of these hypotheses are examined as the Great Filter.
Chris Anderson, Educator
Andrew Park, Animator | 0.876417 | 3.653247 |
In practice, however, Saturn's orbit is very close to circular; its distance from the Sun only varies by about 11.5% between perihelion and aphelion. This means that the difference in the amount of heat and light it receives from the Sun between aphelion and perihelion is extremely small.
Saturn's distance from the Sun doesn't affect its appearance. From Cambridge, at the moment of aphelion it will be visible in the dawn sky, rising at 01:06 (EDT) and reaching an altitude of 25° above the southern horizon before fading from view as dawn breaks around 05:28.
The position of Saturn at the moment it passes aphelion will be:
|Object||Right Ascension||Declination||Constellation||Magnitude||Angular Size|
The coordinates above are given in J2000.0.
|The sky on 17 April 2018|
1 day old
All times shown in EDT.
The circumstances of this event were computed using the DE405 planetary ephemeris published by the Jet Propulsion Laboratory (JPL).
This event was automatically generated by searching the ephemeris for planetary alignments which are of interest to amateur astronomers, and the text above was generated based on an estimate of your location.
|17 Apr 2018||– Saturn at aphelion|
|27 Jun 2018||– Saturn at opposition|
|02 Jan 2019||– Saturn at solar conjunction|
|09 Jul 2019||– Saturn at opposition| | 0.899488 | 3.395186 |
The open star cluster NGC 6633 (mag 4.6) in Ophiuchus will be well placed, high in the sky. It will reach its highest point in the sky at around midnight local time.
At a declination of +06°30', it is visible across much of the world; it can be seen at latitudes between 76°N and 63°S.
From Fairfield, it will be visible all night. It will become visible around 21:55 (EDT) as the dusk sky fades, 37° above your south-eastern horizon. It will then reach its highest point in the sky at 00:53, 55° above your southern horizon. It will be lost to dawn twilight around 04:00, 35° above your south-western horizon.
At magnitude 4.6, NGC6633 is too faint to be seen with the naked eye from any but the very darkest sites, but is visible through a pair of binoculars or small telescope.
The position of NGC6633 is as follows:
|Object||Right Ascension||Declination||Constellation||Magnitude||Angular Size|
The coordinates above are given in J2000.0.
|The sky on 29 June 2019|
26 days old
All times shown in EDT.
The circumstances of this event were computed using the DE405 planetary ephemeris published by the Jet Propulsion Laboratory (JPL).
This event was automatically generated by searching the ephemeris for planetary alignments which are of interest to amateur astronomers, and the text above was generated based on an estimate of your location. | 0.901567 | 3.166673 |
A new NASA portrait of Jupiter reveals its disappearing Great Red Spot in unprecedented color
- NASA has released a new image of Jupiter that shows the bands of the planet's atmosphere in unprecedented color.
- The photo also highlights the planet's Great Red Spot, a centuries-old storm that's shrinking.
- The Great Red Spot could disappear in the next 20 years, but scientists don't know why.
- Visit Business Insider's homepage for more stories.
A new NASA portrait immortalizes the dying storm on Jupiter's surface.The Hubble Space Telescope captures annual snapshots of our solar system's gas giant planets, and NASA just published the latest set. The image of Jupiter stands out, however, since it shows the Great Red Spot and the clouds in Jupiter's turbulent atmosphere in unprecedented color.Advertisement
The Great Red Spot is an ancient storm that's now about the size of Earth. But when scientists first spotted it in the 1800s, it was four times bigger.
The reasons the iconic tempest is shrinking are still mysterious, however.
Jupiter's annual portrait is more colorful than everHubble's images help scientists keep track of storms, winds, and clouds on Jupiter, Saturn, Uranus, and Neptune.
The cloud bands flow in opposite directions across the planet, and are kept in place by jet streams and 400 mile-per-hour winds, which prevent them from moving north and south. The bands sometimes change color though, and scientists can track those changes to find out what's going on in the Jupiter's atmosphere.
The white dots in the planet's southern hemisphere are anticyclones.NASA projected Hubble's flat image of Jupiter onto a sphere to create an animation (below) of Jupiter's rotation. The planet spins quickly, completing a rotation every 9.8 hours.Advertisement
(The animation excludes the planet's polar regions, since Hubble's flat image did not capture those.)
The Great Red Spot could disappear in the next two decades
Jupiter's Great Red Spot is an anticyclone that swirls around a center of high atmospheric pressure. It rotates counterclockwise, the opposite direction of hurricanes on Earth.Advertisement
When astronomers first spotted the spot in the late 1800s, it was about 35,000 miles wide. When the nuclear-powered spacecraft Voyager 2 flew by the planet in 1979, the storm had shrunk to just over twice the width of our own planet.Today, it is only 1.3 times the size of Earth.Advertisement
Scientists aren't sure why or how the Great Red Spot is shrinking. To make matters more mysterious, it's also getting taller at the same time.a 2018 study, a team of NASA scientists analyzed observations of the anticyclone from the last 140 years. They found that as the storm shrinks, the force of its contraction is pushing it upward, like clay on a potter's wheel.Advertisement
They also found that the spot recently started drifting west faster than ever before, and that its orange color has been getting deeper since 2014. That could be because the chemicals that color it are exposed to more UV radiation as the storm is pushed higher up.
"If the trends we see in the Great Red Spot continue, the next five to 10 years could be very interesting from a dynamical point of view," Rick Cosentino, the co-author of that study, said in a press release. "We could see rapid changes in the storm's physical appearance and behavior, and maybe the red spot will end up being not so great after all." | 0.847063 | 3.296188 |
The moon came into existence after several planet-size space bodies smashed into the nascent Earth one after the other, with the final one actually forming our satellite, while several impacts repeatedly blew off our planet’s atmosphere, according to a new study.
Until now, scientists thought it was unlikely that the early Earth could lose its atmosphere because of a giant moon-forming impact. But the new research, based on recent studies showing that at its infancy our planet had magma oceans and was spinning so rapidly that a day was only two or three hours long, argues that this may have been possible.
"Part of the Earth remembers its infancy, and it's giving us clues to the stages of growth of the Earth," said planetary scientist Sarah Stewart, a professor at Harvard University. [The Moon: 10 Surprising Lunar Facts]
Stewart presented her idea, developed along with Harvard colleagues Sujoy Mukhopadhyay, Simon Lock and Jonathan Tucker, at a Royal Society conference in London on the origin of the moon. The study will be published in the journal Philosophical Transactions of the Royal Society.
The teambased the research on two recent studies, one of which Stewart conducted with Matija Cuk of the SETI (Search for Extraterrestrial Intelligence) Institute in Mountain View, Calif., in 2012.
That research argued that the moon is actually a giant merger of bits and pieces of our own planet, partially destroyed by a catastrophic collision with a space body 4.5 billion years ago.
Back then, the Earth had a two- or three-hour day, she said, and the impact made it throw off enough material to coalesce into what became our satellite, making it the Earth’s geochemical twin. [How the Moon Evolved: A Video Tour]
This ultra-rapid spin is one of the important conditions necessary to make the atmospheric loss theory work, Stewart said.
The other criterion is the presence of terrestrial magma oceans — and this hypothesis has now got support thanks to new data obtained from volcanoes.
Tucker and Mukhopadhyay, who presented their work at the 44th Lunar and Planetary Science Conference in March, sampled elements from volcanoes in Iceland, which have rocks that are among the oldest on Earth and thus retain the geochemical signatures of the Earth's so-called lower-most mantle, closestto the planet’s core.
They also looked at elements found in volcanoes that sample the upper mantle, such as mid-ocean ridge basalts at the bottom of the Atlantic.
They found that elements in the deep mantle that retain a very ancient chemistry, from the times of the Earth's formation, are very different from those in the upper mantle we see today.
In particular, the presence of two noble gases, helium and neon, is very different today from what it used to be, Stewart said. Both these gases are very rare on today's Earth, but they are found in the solar system in abundance.
And as "documented" by the deep Earth, when our planet was just forming it contained much more helium and neon as well.
"The implication is that [the lower-most mantle] hasn’t been completely overprinted by subsequent evolution, and it’s helping us pinpoint events that had to happen to lead to the planet we see today," Stewart said.
So how and why did these gases disappear?
While helium is not gravitationally bound to the Earth, neon is, and it needs a powerful "kick" to escape.
"For such a dramatic change to happen, you can’t do that with just open loss off the top — instead, you need to eject the whole atmosphere in a catastrophic type of event, a giant impact," Stewart said.
Besides atmospheric loss caused by impacts that melt all rock to create magma oceans, to get to the present-day neon-to-helium ratio Earth would have to suffer multiple impacts. In other words, the Earth probably lost its primordial atmosphere multiple times, and the magma oceans were melting more than once.
The final impact, Stewart says, led to the creation of the moon, and resulted in the ratio of the gases we have today. "One single impact is not sufficient, there had to be at least two, probably more, to make that work," Stewart said.
The idea that stages of Earth's growth are recorded in chemistry is relatively new.
Previously, researchers argued that during our planet’s formation (known as accretion) with a moon-forming impact, the proto-Earth was melted and mixed to the point that it "forgot" its growth — all the data was erased.
"But now what we've learned is that data wasn’t erased, and it's exciting because now we have clues to the stages of growth," Stewart said.
She added that the next step would be to calculate exactly under what impact conditions the early atmosphere actually might have been blown off.
But if the early atmosphere disappeared due to an impact, how did the Earth get its atmosphere back and how did it finally evolve into the one we have today?
Stewart says that after the last giant smashup that finally formed the moon, the Earth continued to form, accreting planetesimals — mountain-size space rocks that stuck to it, making it bigger.
"Theseplanetesimals delivered some of Earth’s volatiles," she says, eventually bringing the atmosphere to the state it is in today. Volatiles are elements able to escape very easily.
Ian Crawford of Birkberk College, University of London, who was not involved in the study, said that the theory sounded plausible "because multiple impacts are expected to happen in the context we think the solar system was put together."
"It's true that each time you have a giant impact you expect a magma ocean to form. And the early planets are expected to have a transient atmosphere, so it is possible that the atmosphere would be released if the magma ocean solidified."
Another researcher who did not take part in the research, Robin Canup of the Southwest Research Institute in Boulder, Colo., said Stewart's theory sounded "very interesting."
But, she said, "The issue is whether we require a specific sequence of multiple impacts to form the moon. Once you do that, [you assume] that each of them probably have a somewhat small probability. When you multiply these probabilities together, you end up with a very small probability.
"Then you have to ask, is this really the right solution?" | 0.846572 | 3.821896 |
eso1632 — Science Release
ALMA Uncovers Secrets of Giant Space Blob
21 September 2016
An international team using ALMA, along with ESO’s Very Large Telescope and other telescopes, has discovered the true nature of a rare object in the distant Universe called a Lyman-alpha Blob. Up to now astronomers did not understand what made these huge clouds of gas shine so brightly, but ALMA has now seen two galaxies at the heart of one of these objects and they are undergoing a frenzy of star formation that is lighting up their surroundings. These large galaxies are in turn at the centre of a swarm of smaller ones in what appears to be an early phase in the formation of a massive cluster of galaxies. The two ALMA sources are expected to evolve into a single giant elliptical galaxy.
Lyman-alpha Blobs (LABs) are gigantic clouds of hydrogen gas that can span hundreds of thousands of light-years and are found at very large cosmic distances. The name reflects the characteristic wavelength of ultraviolet light that they emit, known as Lyman-alpha radiation . Since their discovery, the processes that give rise to LABs have been an astronomical puzzle. But new observations with ALMA may now have now cleared up the mystery.
One of the largest Lyman-alpha Blobs known, and the most thoroughly studied, is SSA22-Lyman-alpha blob 1, or LAB-1. Embedded in the core of a huge cluster of galaxies in the early stages of formation, it was the very first such object to be discovered — in 2000 — and is located so far away that its light has taken about 11.5 billion years to reach us.
A team of astronomers, led by Jim Geach, from the Centre for Astrophysics Research of the University of Hertfordshire, UK, has now used the Atacama Large Millimeter/Submillimeter Array’s (ALMA) unparallelled ability to observe light from cool dust clouds in distant galaxies to peer deeply into LAB-1. This allowed them to pinpoint and resolve several sources of submillimetre emission .
They then combined the ALMA images with observations from the Multi Unit Spectroscopic Explorer (MUSE) instrument mounted on ESO’s Very Large Telescope (VLT), which map the Lyman-alpha light. This showed that the ALMA sources are located in the very heart of the Lyman-alpha Blob, where they are forming stars at a rate over 100 times that of the Milky Way.
Deep imaging with the NASA/ESA Hubble Space Telescope and spectroscopy at the W. M. Keck Observatory showed in addition that the ALMA sources are surrounded by numerous faint companion galaxies that could be bombarding the central ALMA sources with material, helping to drive their high star formation rates.
The team then turned to a sophisticated simulation of galaxy formation to demonstrate that the giant glowing cloud of Lyman-alpha emission can be explained if ultraviolet light produced by star formation in the ALMA sources scatters off the surrounding hydrogen gas. This would give rise to the Lyman-alpha Blob we see.
Jim Geach, lead author of the new study, explains: “Think of a streetlight on a foggy night — you see the diffuse glow because light is scattering off the tiny water droplets. A similar thing is happening here, except the streetlight is an intensely star-forming galaxy and the fog is a huge cloud of intergalactic gas. The galaxies are illuminating their surroundings.”
Understanding how galaxies form and evolve is a massive challenge. Astronomers think Lyman-alpha Blobs are important because they seem to be the places where the most massive galaxies in the Universe form. In particular, the extended Lyman-alpha glow provides information on what is happening in the primordial gas clouds surrounding young galaxies, a region that is very difficult to study, but critical to understand.
Jim Geach concludes, “What’s exciting about these blobs is that we are getting a rare glimpse of what’s happening around these young, growing galaxies. For a long time the origin of the extended Lyman-alpha light has been controversial. But with the combination of new observations and cutting-edge simulations, we think we have solved a 15-year-old mystery: Lyman-alpha Blob-1 is the site of formation of a massive elliptical galaxy that will one day be the heart of a giant cluster. We are seeing a snapshot of the assembly of that galaxy 11.5 billion years ago.”
The negatively charged electrons that orbit the positively charged nucleus in an atom have quantised energy levels. That is, they can only exist in specific energy states, and they can only transition between them by gaining or losing precise amounts of energy. Lyman-alpha radiation is produced when electrons in hydrogen atoms drop from the second-lowest to the lowest energy level. The precise amount of energy lost is released as light with a particular wavelength, in the ultraviolet part of the spectrum, which astronomers can detect with space telescopes or on Earth in the case of redshifted objects. For LAB-1, at redshift of z~3, the Lyman-alpha light is seen as visible light.
Resolution is the ability to see that objects are separated. At low resolution, several bright sources at a distance would seem like a single glowing spot, and only at closer quarters would each source be distinguishable. ALMA’s high resolution has resolved what previously appeared to be a single blob into two separate sources.
The instruments used were the Space Telescope Imaging Spectograph (STIS) on the NASA/ESA Hubble Space Telescope and the Multi-Object Spectrometer For Infra-Red Exploration (MOSFIRE) mounted on the Keck 1 telescope on Hawaii.
This research was presented in a paper entitled “ALMA observations of Lyman-α Blob 1: Halo sub-structure illuminated from within” by J. Geach et al., to appear in the Astrophysical Journal.
The team is composed of J. E. Geach (Centre for Astrophysics Research, University of Hertfordshire, Hatfield, UK), D. Narayanan (Department of Physics and Astronomy, Haverford College, Haverford PA, USA; Department of Astronomy, University of Florida, Gainesville FL, USA), Y. Matsuda (National Astronomical Observatory of Japan, Mitaka, Tokyo, Japan; The Graduate University for Advanced Studies, Mitaka, Tokyo, Japan), M. Hayes (Stockholm University, Department of Astronomy and Oskar Klein Centre for Cosmoparticle Physics, Stockholm, Sweden), Ll. Mas-Ribas (Institute of Theoretical Astrophysics, University of Oslo, Oslo, Norway), M. Dijkstra (Institute of Theoretical Astrophysics, University of Oslo, Oslo, Norway), C. C. Steidel (California Institute of Technology, Pasadena CA, USA ), S. C. Chapman (Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Canada ), R. Feldmann (Department of Astronomy, University of California, Berkeley CA, USA ), A. Avison (UK ALMA Regional Centre Node; Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester, Manchester, UK), O. Agertz (Department of Physics, University of Surrey, Guildford, UK), Y. Ao (National Astronomical Observatory of Japan, Mitaka, Tokyo, Japan), M. Birkinshaw (H.H. Wills Physics Laboratory, University of Bristol, Bristol, UK), M. N. Bremer (H.H. Wills Physics Laboratory, University of Bristol, Bristol, UK), D. L. Clements (Astrophysics Group, Imperial College London, Blackett Laboratory, London, UK), H. Dannerbauer (Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain; Universidad de La Laguna, Astrofísica, La Laguna, Tenerife, Spain), D. Farrah (Department of Physics, Virginia Tech, Blacksburg VA, USA), C. M. Harrison (Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham, UK), M. Kubo (National Astronomical Observatory of Japan, Mitaka, Tokyo, Japan), M. J. Michałowski (Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, UK), D. Scott (Department of Physics & Astronomy, University of British Columbia, Vancouver, Canada), M. Spaans (Kapteyn Astronomical Institute, University of Groningen, Groningen, Netherlands) , J. Simpson (Institute for Astronomy, University of Edinburgh, Royal Observatory, Edinburgh, UK), A. M. Swinbank (Centre for Extragalactic Astronomy, Department of Physics, Durham University, Durham, UK ), Y. Taniguchi (The Open University of Japan, Chiba, Japan), E. van Kampen (ESO, Garching, Germany), P. Van Der Werf (Leiden Observatory, Leiden University, Leiden, The Netherlands), A. Verma (Oxford Astrophysics, Department of Physics, University of Oxford, Oxford, UK) and T. Yamada (Astronomical Institute, Tohoku University, Miyagi, Japan).
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the US National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science Council of Taiwan (NSC) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).
ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
ESO is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive ground-based astronomical observatory by far. It is supported by 16 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and two survey telescopes. VISTA works in the infrared and is the world’s largest survey telescope and the VLT Survey Telescope is the largest telescope designed to exclusively survey the skies in visible light. ESO is a major partner in ALMA, the largest astronomical project in existence. And on Cerro Armazones, close to Paranal, ESO is building the 39-metre European Extremely Large Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.
Centre for Astrophysics Research, University of Hertfordshire
Tel: +46 (0)8 5537 8521
ESO Public Information Officer
Garching bei München, Germany
Tel: +49 89 3200 6655
Cell: +49 151 1537 3591 | 0.823821 | 3.898924 |
Despite recent cuts to its manned space program, NASA continues to research ways that astronauts might live safely in space during prolonged missions. The agency recently completed tests of a prototype astronaut habitation unit in the rugged, barren, almost-Martian landscape of the Arizona desert. The habitat could be tested in space within a decade, and might one day serve as a home away from home for astronauts on the moon or Mars.
The tests, completed last month, included sending in crews for overnight stays, and running simulations of work that would be done in a single day.
The current prototype housing unit has a hard cylindrical shell, contains four rooms, two outside additions for dust mitigation and hygiene, and an inflatable component that adds a second level for sleeping and relaxing.
The inflatable loft design was part of a university competition called XHab. The researchers explain that a final design could be fully inflated, or could have a small hard shell inside an inflated exterior. Hard shells, while heavier to transport, are better at blocking dangerous radiation from space.
A Deep-Space Home for Astronauts
Inflatable space habitats have been a popular idea since the 1970s, but the new project is the most advanced to date. Inflatable units are a typical option because they offer a lot of volume for the weight of materials, so the cost of getting the housing to space is lower.
The team also tested a prototype robot that could explore the surface of Mars and be controlled by an astronaut from inside the habitation.
“It changes things if you’re running that robot in close proximity, versus trying to operate it from Earth with a 50-second time delay,” says Kriss Kennedy, project manager of the Habitat Demonstration Unit project. The results were presented this week at the American Institute for Aeronautics and Astronautics (AIAA) Space 2011 conference in Long Beach, California.
The habitation system uses embedded sensors to reduce the need for checkups by crew and ground control. “We are infusing more technologies so that crew wouldn’t have to repair the unit if there were a problem. Inside the unit, the electronics can be controlled by iPads and iPhones, allowing the crew to adjust the lights and temperature.
Deep space missions are inherently risky. Radiation from galactic cosmic rays, which can cause cancer, and from solar flares, which can cause quick death, is a serious issue for long-term space habitation. Cargo bags, used to carry loads up to space, could used to change urine into water via a purification technique called forward osmosis and then help pad the walls with water to protect the crew inside.
The unit could be adapted for missions to the moon, Mars, an asteroid, or simply as a free-flying habitat in space. “Different missions require different sizes of habitation,” says Tracy Gill, who works within the Space Station Utilization Division at NASA’s Kennedy Space Center, because of the different items needed onboard. Within 10 years, the team plans to have a demonstration unit either flying in space or attached to the International Space Station.
Flying habitats need to be easy to repair, says Jeffrey Hoffman, a former astronaut and professor of aeronautics and astronautics at MIT. “Unlike the International Space Station, it won’t be possible to send up replacement parts, so local materials will be key,” he says.
Daniel Lester, an astronomer at the University of Texas at Austin, says a habitation like the one NASA is testing could be a useful place to house a crew servicing space telescopes, or assembling spacecraft to travel to farther-off places like Mars. | 0.834063 | 3.079544 |
You can help NASA’s upcoming lunar mission.
NASA’s Lunar Atmosphere and Dust Environment Explorer (LADEE) is slated to lift off from Wallops Island this September 5th in a spectacular night launch. LADEE will be the first mission departing Wallops to venture beyond low Earth orbit. A joint collaboration between NASA’s Goddard Spaceflight Center & the AMES Research Center, LADEE will study the lunar environment from orbit, including its tenuous exosphere.
Scientists hope to answer some long standing questions about the lunar environment with data provided by LADEE. How substantial is the wispy lunar atmosphere? How common are micro-meteoroid impacts? What was the source of the sky glow recorded by the Surveyor spacecraft and observed by Apollo astronauts before lunar sunrise and after lunar sunset while in orbit?
The micro-meteoroid issue is of crucial concern for any future long duration human habitation on the Moon. The Apollo missions were only days in length. No one has ever witnessed a lunar sunrise or sunset from the surface of the Moon, as all six landings occurred on the nearside of the Moon in daylight. (Sunrise to sunset on the Moon takes about two Earth weeks!)
And that’s where amateur astronomers come in. LADEE is teaming up with the Association of Lunar & Planetary Observers (ALPO) and their Lunar Meteoritic Impact Search Program in a call to watch for impacts on the Moon. These are recorded as brief flashes on the nighttime side of the Moon, which presents a favorable illumination after last quarter or leading up into first quarter phase.
We wrote recently about a +4th magnitude flash detected of the Moon on March 17th of this year. That explosion was thought to have been caused by a 35 centimetre impactor which may have been associated with the Eta Virginid meteor shower. The impact released an explosive equivalent of five tons of TNT and has set a possible new challenge for Moon Zoo volunteers to search for the resulting 6 metre crater.
We’ve also written about amateur efforts to document transient lunar phenomena and studies attempting to pinpoint a possible source of these spurious glows and flashes on the Moon observed over the years.
NASA’s Meteoroid Environment Office is looking for dedicated amateurs to take part in their Lunar Impact Monitoring campaign. Ideally, such an observing station should utilize a telescope with a minimum aperture of 8 inches (20cm) and be able to continuously monitor and track the Moon while it’s above the local horizon. Most micro-meteoroid flashes are too fast and faint to be seen with the naked eye, and thus video recording will be necessary. A typical video configuration for the project is described here. Note the high frame rate and the ability to embed a precise time stamp is required. I’ve actually run WWV radio signals using an AM short wave radio transmitting in the background to accomplish this during occultations.
Finally, you’ll need a program called LunarScan to analyze those videos for evidence of high speed flashes. LunarScan is pretty intuitive. We used the program to analyze video shot during the 2010 Total Lunar Eclipse for any surreptitious Geminid or Ursid meteors.
Brian Cudnik, coordinator of the Lunar Meteoritic Impact Search section of the ALPO, noted in a recent forum post that we’re approaching another optimal window to accomplish these sorts of observations this weekend, with the Moon headed towards last quarter on June 30th.
Interestingly, the June Boötids are currently active as well, with historical sporadic rates of anywhere from 10-100 per hour. In 1975, seismometers left by Apollo astronauts detected series of impacts on June 24th thought to have been caused by one of two Taurid meteor swarms the Earth passes through in late June, another reason to be vigilant this time of year.
Don’t have access to a large telescope or sophisticated video gear? You can still participate and make useful observations.
LADEE is also teaming up with JPL and the Lewis Center for Educational Research to allow students track the spacecraft en route to the Moon. Student groups will be able to remotely access the 34-metre radio telescopes based at Goldstone, California that form part of NASA’s Deep Space Communications Network. Students will be able to perform Doppler measurements during key mission milestones to monitor the position and status of the spacecraft during thruster firings.
And backyard observers can participate in another fashion, using nothing more than their eyes and patience. Meteor streams that are impacting the Moon affect the Earth as well. The International Meteor Organization is always looking for information from dedicated observers in the form of meteor counts. The Perseids, an “Old Faithful” of meteor showers, occurs this year around August 12th under optimal conditions, with the Moon only five days past New. This is also three weeks prior to the launch of LADEE.
Whichever way you choose to participate, be sure to follow the progress of LADEE and our next mission to study Earth’s Moon!
-Listen to Universe Today’s Nancy Atkinson and her interview with Brian Day of the NASA Lunar Science Institute.
-Also listen to the 365 Days of Astronomy interview with Brian Day and Andy Shaner from the Lunar Planetary institute on the upcoming LADEE mission. | 0.837814 | 3.649311 |
Some of you might remember that, back in 2013, a meteor exploded in an air burst over Chelyabinsk Oblast in Russia, generating a bright flash and a hot cloud of dust and gas that penetrated up to 16.3 miles (26km) and produced a large shock wave.
The Chelyabink meteor went largely undetected as its radiant (the celestial point of view in the sky that a terrestrial observer can see) was very close to the Sun.
The meteor had an initial mass of around 12,000 – 13,000 tonnes and measured around 66ft (20m) in diameter. It’s known as the largest known natural object that has entered Earth’s atmosphere since the Tunguska incident back in 1980.
Now a new asteroid, known as 2006 QV89, is double the width of the Chelyabink object and will be making a close encounter with Earth on the morning of September 9th.
Since the news broke out, a number of tabloids have sensationalized it and were just shy of announcing imminent destruction at the hands of this space rock overlord but, according to the European Space Agency, there’s a one in 7,000 chance we’ll even get hit.
The models made of the asteroid’s orbit show that the closest it could possibly get to Earth would be at 4.2 million miles (6.8 million km) and that there is only one hundreth of 1% of a chance that the model is wrong and that the object will hit Earth instead.
To make sure, the European Space Agency has been measuring and re-measuring images of the asteroid from over a decade ago but none of the calculations have changed much in the meantime.
Our galactic friend will pass by Earth at a distance of over 6.8 million kilometers. For scale, the Moon stands somewhere at around 380,000 km from Earth and another asteroid, measuring 30m wide (98ft) passed by us in April at a distance of ‘only’ 1.8 million and we were none the wiser.
As it is, 2006 QV89 is actually fourth on the list of objects that might end up hitting us, according to this list, released by the European Space Agency. The first one on the list has a diameter of just 9 meters while the actual beast rests on the second place: an object called 1979XB, with a diameter of 900 meters that’s expected to say hello to us sometime around 2113.
The real problems don’t come with the asteroids we know of but the ones we cannot see coming, as was the case with in the Chelyabink incident – the astronomers only managed to see it when it was already colliding with the Earth’s atmosphere. | 0.838436 | 3.186469 |
9 relations: Andromeda (constellation), Apparent magnitude, Centre de données astronomiques de Strasbourg, Durchmusterung, Henry Draper Catalogue, Mira variable, SIMBAD, Variable star, Variable star designation.
Andromeda is one of the 48 constellations listed by the 2nd-century Greco-Roman astronomer Ptolemy and remains one of the 88 modern constellations.
The apparent magnitude of a celestial object is a number that is a measure of its brightness as seen by an observer on Earth.
The Centre de Données astronomiques de Strasbourg (CDS; English translation: Strasbourg Astronomical Data Center) is a data hub which collects and distributes astronomical information.
In astronomy, Durchmusterung or Bonner Durchmusterung (BD), is the comprehensive astrometric star catalogue of the whole sky, compiled by the Bonn Observatory (Germany) from 1859 to 1903.
The Henry Draper Catalogue (HD) is an astronomical star catalogue published between 1918 and 1924, giving spectroscopic classifications for 225,300 stars; it was later expanded by the Henry Draper Extension (HDE), published between 1925 and 1936, which gave classifications for 46,850 more stars, and by the Henry Draper Extension Charts (HDEC), published from 1937 to 1949 in the form of charts, which gave classifications for 86,933 more stars.
Mira variables ("Mira", Latin, adj. - feminine form of adjective "wonderful"), named for the prototype star Mira, are a class of pulsating variable stars characterized by very red colours, pulsation periods longer than 100 days, and amplitudes greater than one magnitude in infrared and 2.5 magnitude at visual wavelengths.
SIMBAD (the Set of Identifications, Measurements, and Bibliography for Astronomical Data) is an astronomical database of objects beyond the Solar System.
A variable star is a star whose brightness as seen from Earth (its apparent magnitude) fluctuates.
Variable stars are designated using a variation on the Bayer designation format of an identifying label (as described below) combined with the Latin genitive of the name of the constellation in which the star lies. | 0.865307 | 3.663969 |
(BEING CONTINUED FROM 15/05/16)
The Standard Model predicts that there are Four fundamental forces of Nature. Each of the forces is moderated by a Boson.
Gravity is by far the weakest of the forces, but because the 2 nuclear forces have such a short range and the Universe is generally electricly neutral, Gravity in fact rules the Universe.
The Uncertainty Principle
There are two Basic laws of Quantum Mechanics. One is the Exclusion Principle which states that no two particles can occupy the exact same quantum state (An idea we will return to later).
The other is the Uncertainty Priciple. Which says that the more we know about where a particle is located the less we know about its momentum. The more we know about its momentum, the less we know about its location.
How would we measure the location of an electron? Bounce light off it. But electrons are small and if you hit them with a with a photon of visible light which has a wavelength of 500 nm, you cannot pinpoint the location to within 500 nm (5,000 times the size of an atom). In order to pinoint the location to higher precision you need to use shorter wavelength photons. Like X-rays. But there is a problem. If you hit it with an X-ray you will give the electron a huge energy kick (X-rays have tons more energy than visible photons). That changes its momentum. So you gained info about the electrons location at the expense of its momentum.
Likewise to measure the momentum you would need to hit the electron with a low energy photon (say a microwave). But the wavelengths of a microwave are big (a few cm). You’ll have no idea where the electron is to within a few cm.
This is not a technical issue. Again this is the way of nature.
Mathematically we can write the uncertainty principle as such:
Where h is Planck’s constant. Alternatively, we may write it in terms of time and Energy:
The electron behaves as both a wave and a particle. If we measure the location to greater and greater precision it is more like a particle. If we measure the momentum to greater and greater precision it is more like a wave, all smeared out with no certain location.
The Uncertainty principle leads to the idea that an electron can only be described by a probability that it will be in a certain location with a certain momentum (or have a certain energy within a certain time). In an atom we know the momentum/energy of the electron fairly well so the location is smeared out into a wave.
The interpretation of the electron as a wave within an atom helps us understand why it can only take on certain energy states. Think of the electron as a standing wave (a wave anchored on both ends which does not appear to travel along the distance but just vibrate in place). The electric force serves as the anchors for the electron to the nucleus. In a standing wave only certain wavelengths are allowed. So in the atom only certain wavelengths/energies are allowed for the electron to occupy.
The Sun: The Nearest Star
Photosphere: The Sun’s visible “surface”. It’s the lowest level of the Sun’s atmosphere. Its diameter is about 1.4 x 106 km (0.5° in the sky). In the core the temperature is about Tcore = 1.5 x 107 K. From there the temperature steadily decreases out to the photosphere where the temperature is about T = 5,800 K.
By monitoring long lived sunspots one can see that the Sun spins on its axis about once per month. (It’s not equal, the higher latitudes move slower than equatorial ones: differential rotation)
Chromosphere: Thin layer (104 km). T 104 K (hotter than the photosphere). It’s red due to the emission of photons from the electronic transition in Hydrogen from level 3 to level 2 (H- = 6563 Å)
Corona: Large, low-density envelope (T 2 x 106 K — lots of X-rays). Structure due to magnetic field.
Solar Wind: electrons and positive ions streaming from the Sun (v 500 km/s). Interacts with the planets’ magnetic fields and with comets.
Solar Flare: Violent release of energy from the Sun. (T 5 x 106 !). The matter from these can sometimes collide with Earth causing radio communication disruptions and fantastic auroras.
Prominence: more gentle eruption on Sun’s surface. Loops of gas following magnetic fields lines above the Chromosphere, glowing red (T 104 K).
Sunspots: dark blotches on the photosphere. Appear black or dark grey because they are around 2000 K cooler than their surroundings.
The Sun’s surface (photosphere) is hot and opaque. That means that it acts as a thermal emitter. For thermal radiation there is a relationship between the amount of energy emitted per unit area per unit time, , and the Temperature, T. It’s called the Stefan-Boltzmann Law:
Where is the Stefan-Boltzmann constant ( = 5.67 x 10-8 W m-2 K-4). So, we can see that for a thermal emitter a hot object emits much more energy than cold objects per unit area. This is why the temperature difference between the Sunspots and the surrounding Photosphere makes such a difference in brightness.
Sunspots are regions of strong magnetic fields that inhibit the rise of hot gas from below the photosphere.
Solar Activity Cycle: Sunspots, prominences, and flares are numerous during peaks of an 11 year cycle. Previous maxima were in 1990, and 2001.
The cycle is thought to be related to how the Sun rotates differentially and winds up and twists its magnetic field. The field becomes most twisted in 11 years and then breaks and reforms. The Solar cycle is thought to be related to climate changes on Earth.
What Makes the Sun Go?
We observe that the Sun is very massive, hot, and gives off an enormous luminosity. What holds the Sun up under its own weight? What is the energy source providing the luminosity?
Gas exerts a pressure outward, which resists the force of gravity. Pressure is a force per unit area. You may recall from chemistry that it is proportional to density and Temperature
(the perfect gas law: P = nkT, n is the number density of particles, k is another constant)
Toward the center of the Sun temperature and density increases and so then does the outward pressure. The Sun is at a point where the internal pressure outward exactly balances the force of gravity inward. This point of mechanical balance is called Hydrostatic equilibrium.
So pressure holds the Sun up. But what gives the particles their kinetic energy (Temperature) which allows such high pressures?
Could it be simple gravitational contraction, turning gravitational potential energy into kinetic energy? No? This could only provide the Sun with the needed energy for about 25 Million years. We know that the Solar System is more like 4.6 Billion years old. The early Protosun used gravitational contraction, but the Sun could not still be using it as a primary energy source.
What if the Sun were undergoing Chemical Burning? Is it “on fire”? No, that cannot be it either. Detailed calculations show that Chemical burning could provide the needed energy for only a few thousand years. Clearly not enough.
In the center of the Sun the conditions are so hot (T = 1.5 x 107 K) and dense that atoms have all of their electrons stripped away from them, they are completely ionized. Thus we have atomic nuclei (mostly hydrogen, single protons) all zipping to and fro in the core. Conditions are ripe for nuclear reactions which can produce a long-term energy source for the Sun.
In chemical reactions the electrons of atoms and molecules interact and reconfigure themselves into different energy states. When they configure themselves into states that have lower energy than the initial states energy is released: exothermic reactions.
For atomic nuclei the principle is the same; they interact with other atomic nuclei to make new configurations that have less energy than initially (more tightly bound) thus releasing energy in the reaction. (this reaction involves the strong nuclear force which is the strongest of the 4 fundamental forces of nature)
2He4 is more tightly bound than 41H1, so energy is emitted. It turns out that the Helium nucleus has less mass than the sum of 4 individual protons. In the reaction 0.7% of the mass of 41H1 is converted to energy:
E = mc2
(In the Sun, 600 million tons of H -> He every second!!)
The reason we need hot temperatures and high densities for nuclear reactions to occur is that the strong nuclear force is a very short range force.
The electric force makes protons repel one another.
The nuclei (protons) have to be moving very fast and have enough near collisions with each other so that they can get close enough for the strong nuclear force to take effect.
Once it does it is far, far stronger than the electrical repulsion that the protons feel.
Iron (Fe) – 26 protons – has the most tightly bound nucleus, so fusion of nuclei up to Fe will release energy.
Fission of heavier nuclei into lighter one also releases energy, for example 92U238, but these nuclei are very rare and don’t contribute any energy to the star.
Nuclear power plants and the orginal atomic bombs use fission reactions. The so-called H-bomb is actually a fission bomb which implodes to cause a fusion reaction that subsequently explodes.
Fusion on Earth for power has yet to be successfully achieved. Reactions still require more energy to get them going that we get back from them. When we eventually work out the kinks Fusion energy will solve the World’s energy problem. It produces tons of energy and the bi-products are not radioactive.
By mass, Sun is 70% H, 28% He, and 2% heavier elements: Lot’s of raw material to fuse ! The Sun can fuse hydrogen into helium for about 10 Billion years before running out of fuel. So the Sun is a middle-aged star, 5 Billion down, another 5 billion to go.
NOTE: The photons produced in the core take millions of years to leak out from the core out to the photosphere where they then stream away freely into cold, dark space.
Several reactions can occur depending on the temperature of the core. Net Effect: conversion of 4 protons to a Helium nucleus (2 protons + 2 neutrons) plus energy.
The reaction that converts 4 protons to a He nucleus involves the conversion of protons into neutrons.
neutrinos () have very little (if any) mass, and travel near the speed of light. They hardly react with anything. They can escape directly from the core, unlike photons. Hence we can observe them to probe directly the conditions in the core of the Sun.
To do this we build giant tanks filled with a liquid compound akin to cleaning solution and put them far underground. Since neutrinos hardly react to anything we expect to detect only 1 neutrino per day interacting with the liquid in the tank! We actually detect about a third fewer!
Most probable solution is that neutrinos have some (non-zero) mass which allows them to mutate from one kind of neutrino to another. We can only currently detect electron neutrinos, which are those produced in the center of the Sun.
(TO BE CONTINUED)
SOURCE http://cse.ssl.berkeley.edu LEC12 | 0.819233 | 3.753615 |
Five astronomers have won three Carnegie Science Venture Grants in the past year. Carnegie Science Venture Grants bring together researchers from different backgrounds to tackle new questions that cross traditional disciplinary boundaries. Andrew McWilliam and Johanna Teske are collaborating on a novel approach detect exoplanet atmospheric gases, including molecules important for life. Nick Konidaris is collaborating with colleagues from Carnegie’s Department of Global Ecology to develop instrumentation that will measure photosynthesis at planetary scales. Juna Kollmeier and Guillermo Blanc are collaborating on new ways to extract new information from the large and complex data sets that have become standard in modern astrophysics.
Each grant provides $100,000 for these interdisciplinary projects that are likely to grow in unexpected ways. They are generously supported, in part, by trustee Michael Wilson and his wife, Jane, and by the Monell Foundation.
“I am excited that Carnegie offers these kinds of opportunities for creative approaches to questions that span our scientific disciplines,” said Observatories Director, John Mulchaey.
Detecting Exoplanet Atmospheres
Astronomer Andrew McWilliam of the Observatories has teamed up with postdoctoral fellow Johanna Teske of Observatories and the Department of Terrestrial Magnetism to develop a novel technique for detecting the atmospheres of Earth-sized exoplanets, including looking for the molecules that are important to the emergence of life.
A priority target for detecting molecules essential to life is the TRAPPIST-1 system (artist’s concept, courtesy NASA/JPL-Caltech). It has seven Earth-sized planets and three of them are in the habitable zone, not too far from the host star, nor too close, so that temperatures allow liquid surface water.
A priority target is the TRAPPIST-1 system, with seven Earth-sized planets roughly 40 light-years away, making it a “nearby neighbor’’ to the Sun. They will analyze the light transmitted through the exoplanetary atmospheres as the planets move in front of their host stars, searching for the faint molecular fingerprints of water, carbon dioxide, oxygen and methane buried in the bright light of the host star. The TRAPPIST-1 system is particularly interesting because three of the planets are just the right temperature to have liquid water on their surfaces. However, it’s also particularly challenging because the star is so cool that it also has water in its atmosphere. This is where the Venture Grant will help—higher-resolution observations will tease apart the difference light from stars and from planets.
The researchers will work with the Observatories’ world-class instrumentation team to adapt a new, high-resolution near-infrared spectrograph from the University of Tokyo to be deployed on the Magellan-Clay telescope, and to develop custom reduction and analysis tools for exo-atmospheric detection.
Measuring Photosynthesis at Large Scales
A cross-disciplinary collaboration between an astronomer and several global ecologists will apply new developments in astronomical instrumentation to large-scale questions in ecology. Instrument designer Nick Konidaris of the Observatories and global ecologists Greg Asner, Joe Berry and Ari Kornfeld will be developing a high-precision instrument that will allow measurements of photosynthesis to be coupled with structural characteristics of plants to expand the existing leaf-level understanding of plant processes to the canopy and regional scale.
Carnegie Airporne Observatory LIDAR height map of a single hetacre of amazon rainforest, courtesy CAO.
Measuring photosynthesis has applications from precision farming, to forestry, to understanding and predicting global climate change. But while leaf-level photosynthesis is fairly well understood, extending that knowledge to larger scales has been impeded by the complexity of canopies, as they are composed of millions of leaves on thousands of trees each responding independently to environmental variables such as light, temperature, humidity, and water availability. Without good measurements, scaling our leaf-level understanding to canopy- and regional- processes remains a fundamental challenge in ecological science.
Recent advances in optical remote sensing have opened a new possibility of measuring photosynthesis across all scales. Illuminated plants fluoresce light in proportion to the rate of photosynthesis. In the past few years, a method first developed by astronomers has been used to disentangle a faint fluorescence signal from the bright solar background. Konidaris will be working with the global ecologists to develop an instrument that applies these advances in astronomy to a device that will be integrated into the Carnegie Airborne Observatory (CAO). In complement with the sophisticated package of sensors currently on the CAO, these new tools will provide an unprecedented view of the canopy chemistry, structure, and function, while providing the foundation for a new understanding of photosynthesis at the landscape scale
Astrophysical Data Extraction
The Venture Grant awarded to Juna Kollmeier and Guillermo Blanc of the Observatories will allow them to collaborate with others to apply a new astronomical data-extraction technique to optical astronomy data sets that are currently inaccessible. The new techniques will allow superior visualization and analysis of distant astronomical objects.
Astronomers Juna Kollmeier and Guillermo Blanc
For decades, astronomers have taken two-dimensional images through filters to try to understand what's going on inside galaxies, such as the ages of stars and whether they host black holes. But the image information is limited. To elucidate more-detailed information about galaxies, such as their motions, finer frequency information is needed.
The researchers will use new mathematical techniques to interrogate data from Integral Field Unit Spectrometers (IFU). These instruments take spectra at multiple locations within a target such as a distant galaxy. The "data cubes" from these instruments are extraordinarily rich and complex and the team will be applying algorithms developed in mathematics and computer science to extract features and remove noise from these astrophysical data.
The researchers learned of the method during a visit to the Scientific Computing and Imaging Institute (SCI) at the University of Utah, where Bei Wang Phillips and collaborator Paul Rosen have been working to analyze similar data cubes taken at radio frequencies with the ALMA telescope in Chile. They hope this is the beginning of an exciting joint venture with SCI on theoretical and observational data analysis. | 0.865556 | 3.444882 |
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Previous attempts to assign ordinary chondrites (OC) to meteoroid streams have been unsuccessful because the orbits of the proposed members had different radiants and, in some cases, the meteorites had significantly different cosmic-ray exposure (CRE) ages. Using more conservative criteria, we have identified four pairs of equilibrated OC (L6 Nejo, Salem; L6 Perpeti, Vouillé; L6 Drake Creek, Forsyth; H5 Okabe, Kerilis) wherein each member of the pair could conceivably have been derived from the same immediate precursor body (IPB). The members of each pair are of the same chondrite group and petrologic type; they have similar CRE ages and fell within 1 calendar day of each other (in different years). Because there is a moderate range in oxidation state (represented by mean olivine Fa) among equilibrated OC in each group, similarities in this intrinsic geochemical property between the members of two of the proposed pairs offer some support for the hypothesis that these rocks were derived from the same IPB. If the pairs are genuine, their precursor bodies were probably meter-size near-Earth asteroids (NEAs) with aphelia within or beyond the Main Asteroid Belt. Fragmentation of such NEAs is most likely to have occurred near aphelia; in principle, the ejecta could have spread somewhat along the NEAs' orbits and collided with Earth on approximately the same calendar date but in different years. However, literature data show that, although ∼670 meteorites with masses ≥10 kg reach the Earth's surface each year, only five or six falls (typically in this mass range) are observed and recovered. This suggests that the chances of recovering more than one meteorite from a disrupted meter-size body in Earth-crossing orbit are small. It thus seems likely that the similar properties of the proposed OC pairs are due to coincidence. | 0.874702 | 3.674822 |
Figure 7.27. Disk-integrated irradiance spectra of the giant planets recorded by both ISO/SWS and ISO/LWS, plotted together on a log-scale. Jupiter: solid line; Saturn: dotted line; Uranus: dashed line; Neptune: dot-dashed line. The SWS Uranus spectrum has been divided by 105 in order to distinguish it from the SWS Neptune spectrum. The spectra can be seen to be in good agreement with the synthetic spectra shown previously in Figure 7.8.
cryogenically cooled telescope that forms the final element in NASA's Great Observatory Program. The four major scientific objectives of Spitzer are: (1) to study the early universe; (2) to search for and study brown dwarfs and superplanets; (3) to study ultraluminous galaxies and active galactic nuclei; and (4) to discover and study protoplanetary and planetary debris disks.
The telescope incorporates a 0.85 m primary mirror cooled to 5.5 K by liquid helium and at launch weighed 950 kg (Figure 7.28). The telescope was placed in an Earth-trailing, heliocentric orbit, where the background radiation levels are low and where it may observe chosen targets for long integration times, uninterrupted by orbital considerations, as was the case for the Infrared Space Observatory (ISO) (Section 7.7.2). The low thermal radiation environment means that Spitzer's optics naturally cool to low temperatures without the need for a very large supply of cryogen, and the cryogens that are carried are only used to cool the mirror and detectors to their final operating temperatures. Hence, the lifetime of Spitzer will be much longer than it was for ISO, and Spitzer is expected to remain operational until April 2009.
Spitzer has three instruments and performs imaging, photometry, and spectrometry from 3 ^m to 180 ^m, as will now be described.
Was this article helpful? | 0.874376 | 3.652656 |
A pair of astronomers from the US and Italy have discovered a stream of stars moving through the sky at 230 km/second (500,000 mph). The stream has been found to extend 30,000 light years across the sky, but it could extend even further. The discoverers believe the stream is all the remains of a gigantic star cluster that was torn apart by the Milky Way’s gravity. If correct, there could be hundreds more of these streams circling our galaxy.
A long, slender stream of ancient stars has been discovered racing across the northern sky. The stream is about 30,000 light-years distant from Earth and is flowing high over the Milky Way Galaxy at some 230 kilometers per second, or more than half a million miles per hour.
The discovery was made by Dr. Carl Grillmair, of the Spitzer Science Center in Pasadena, Calif. and his colleague Odysseas Dionatos from the Astronomical Observatory of Rome. Grillmair presented his findings at the American Astronomical Society meeting in his hometown of Calgary, Canada.
“What we can see of the stream is over 30,000 light years long, although it may actually be much longer than that since we are currently limited by the extent of the survey data. I would actually be somewhat surprised if the stream doesn’t extend completely around the Galaxy,” says Grillmair.
The astronomers believe the stars on this cosmic “highway” date back nearly to the beginning of the Universe and are the fossil remains of a star cluster that, in its prime, contained between 10,000 and 100,000 stars. The ancient cluster was torn apart over billions of years by the tidal forces of our Milky Way Galaxy.
“The discovery gives new weight to a theory that, while the Milky Way now contains only about 150 such giant star clusters, it may once have been swarming with thousands of them. If this idea is correct, there may be hundreds or even thousands of such stellar streams ringing our Galaxy,” says Grillmair.
On the sky, the stream is narrower than the pinky finger held at arm’s length. Although it spans more than 130 times the diameter of the full moon, or roughly one-third of the northern sky, the individual stars in the stream are too faint to be seen with the unaided eye. The narrowness of the stream indicates that the original cluster was not torn apart violently, but rather that the stars were pulled out gently, perhaps a thousand or so each time the cluster passed near the center of our Galaxy. The orphaned stars continue to follow one another along their original orbit, long after their parent cluster has dissolved completely away.
The stream was discovered using a public database known as the Sloan Digital Sky Survey, through a technique called matched filtering. Using the colors and brightness of stars like DNA markers, the scientists assigned to each star a probability that it could have a particular age and distance. By examining how these probabilities are distributed across the sky, Grillmair and Dionatos were able to push through the vast sea of foreground stars in the Milky Way and see the stream floating out among the dark and lonely reaches of the galactic halo.
“The stream’s path on the sky is very smooth. The lack of any substantial wobbling tells us that, at least within a distance of 30,000 light years, there are no large concentrations of invisible dark matter. The stream is a remarkable find and provides a new avenue of research into the makeup of our galaxy and how gravity behaves on large scales,” says Grillmair.
Six such streams have been found in recent years, three of them by Grillmair and his team, and all but one of them in the Sloan Digital Sky Survey. Studies of the streams discovered so far point to a massive halo of invisible dark matter surrounding our galaxy that is very close to spherical in shape. How far this halo extends, how it was formed, how lumpy it is, and what the dark matter is made of are among the big questions that astronomers are currently trying to answer.
Funding for the Sloan Digital Sky Survey has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the U.S. Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England.
Grillmair is the lead author of a paper on the stream’s discovery which was published in the May issue of Astrophysical Journal.
Original Source: Spitzer News Release | 0.80112 | 3.920349 |
Astronomers at the University of Florida and the University of Texas at San Antonio, have observed the magnetic field of a black hole within the Milky Way from multiple wavelengths.
The object of their study is the black hole called V404 Cygni (a binary microquasar system), located in the constellation of Cygnus, the swan at the distance of approximately 7,800 light-years. V404 Cygni contains about 10 times the mass of our own sun.
Still, its magnetic field is much weaker than it was previously thought.
A black hole is a place in space where gravity pulls so strongly that even light cannot escape its grasp. Black holes usually form when a massive star explodes and the remnant core collapses under the force of intense gravity.
“The Earth, like many planets and stars, has a magnetic field that sprouts out of the North Pole, circles the planet and goes back into the South Pole. It exists because the Earth has a hot, liquid iron rich core,” said Chris Packham, associate professor of physics and astronomy at The University of Texas at San Antonio (UTSA).
“That flow creates electric currents that create a magnetic field. A black hole has a magnetic field as it was created from the remnant of a star after the explosion.”
Flaring Black Hole Accretion Disk in the Binary System V404 CygniThere is also an earlier (2015) research on V404 Cygni from the University of Florida that revealed a much weaker magnetic field than predicted by currently used models — link below.
Magnetism Of Supermassive Black Holes Much Weaker Than Previously Thought, New Study Shows
“We need to understand black holes in general,” Packham said.
“If we go back to the very earliest point in our universe, just after the big bang, there seems to have always been a strong correlation between black holes and galaxies.
“It seems that the birth and evolution of black holes and galaxies, our cosmic island, are intimately linked. Our results are surprising and one that we’re still trying to puzzle out.”
Original story – here. | 0.86636 | 3.844332 |
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