A Murchison meteorite specimen at the National Museum of Natural History in Washington DC.
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Where does the methane on Mars come from? That has been one of the biggest unanswered questions in planetary science since the discovery of large plumes of methane gas in the Martian atmosphere. Scientists have been trying to figure out how the planet’s environment or geology can keep replenishing this short-lived gas, and of course, in the back of everyone’s mind is whether the methane has any connection to possible life on Mars.
A new potential explanation squelches both the life and environment prospect and offers a unique answer. A group of researchers found that meteorites, which continually bombard the surface of Mars, may contain enough carbon compounds to generate methane when they are exposed to strong UV sunlight.
“Whether or not Mars is able to sustain life is not yet known, but future studies should take into account the role of sunlight and debris from meteorites in shaping the planet’s atmosphere,” said Dr. Andrew McLeod, of the University of Edinburgh, co-author of a new study published in Nature this week.
The group of European researchers looked at the famous Murchison meteorite, a carbonaceous chondrite meteorites that fell in Australia more than 40 years ago. Carbonaceous chondrites are very common meteorites, so they likely will be falling on Mars. The team exposed particles of the Murchison meteorite to levels of ultraviolet radiation equivalent to sunlight on Mars.
When the meteorite pieces were exposed to ample amounts of UV light the meteor fragments rapidly released methane. After the UV exposure was reduced, the amount of methane produced would lessen, but if there were other activities, such as heating, shaking or lowering the pressure on the meteorite, the amount of methane released would rise again.
With Mars thin atmosphere, UV light easily gets to the surface of the planet. The thin atmosphere also allows more meteorites to hit Mars than on Earth (estimates range from just a few thousands of metric tons to as much as 60,000 metric tons.) The team said that temperature changes on Mars, especially during the summertime when it gets warm, could account for a boost of methane release from meteorites, and seasonal dust storms could shake or move the meteorites.
However, while only small amounts of methane are present in the Martian atmosphere, it seems to be coming from very specific, localized sources. Meteorites would likely be falling across the planet.
Top: Map of methane concentrations in Autumn (first martian year observed). Peak emissions fall over Tharsis (home to the Solar System's largest volcano, Olympus Mons), the Arabia Terrae plains and the Elysium region, also the site of volcanos. Bottom: True colour map of Mars. Credit: NASA/Università del Salento
Additionally, levels of methane vary in the seasons, and are highest in autumn in the northern hemisphere, with localized peaks of 70 parts per billion. There is a sharp decrease in winter, with only a faint band of methane appearing in the atmosphere between 40-50 degrees north.
Methane was first detected in the Martian atmosphere by ground based telescopes in 2003 and confirmed a year later by ESA’s Mars Express spacecraft. In 2009, observations using ground based telescopes showed the first evidence of a seasonal cycle.
Other research has said that the methane in the Martian atmosphere lasts less than a year, making it a flitting – and difficult – feature to study.
Another issue is that the estimates for the amount of meteorites hitting Mars’ surface would likely not bring enough carbon to explain the amount of methane seen in the atmosphere.
The researchers said, however, that their findings give valuable insights into the planet’s atmosphere and these findings would be helpful for future robotic missions to Mars so scientists could fine-tune their experiments, potentially making their trips more valuable.
Apollo 16 astronaut Charlie Duke collects lunar samples during EVA on April 23, 1972 (NASA)
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New investigations of lunar samples collected during the Apollo missions have revealed origins from beyond the Earth-Moon system, supporting a hypothesis of ancient cataclysmic bombardment for both worlds.
Samples of Apollo 16 breccia that contain chondritic material (JSC)
Using scanning electron microscopes, researchers at the Lunar-Planetary Institute and Johnson Space Center have re-examined breccia regolith samples returned from the Moon, chemically mapping the lunar rocks to discern more compositional detail than ever before.
What they discovered was that many of the rocks contain bits of material that is chondritic in origin — that is, it came from asteroids, and not from elsewhere on the Moon or Earth.
Chondrites are meteorites that originate from the oldest asteroids, formed during the development of the Solar System. They are composed of the initial material that made up the stellar disk, compressed into spherical chondrules. Chondrites are some of the rarest types of meteorites found on Earth today but it’s thought that at one time they rained down onto our planet… as well as our moon.
The Lunar Cataclysm Hypothesis suggests that there was a period of extremely active bombardment of the Moon’s surface by meteorite impacts around 3.9 billion years ago. Because very few large impact events — based on melt rock samples — seem to have taken place more than 3.85 billion years ago, scientists suspect such an event heated the Moon’s surface enough prior to that period to eradicate any older impact features — a literal resurfacing of the young Moon.
There’s also evidence that there was a common source for the impactors, based on composition of the chondrites. What event took place in the Solar System that sent so much material hurtling our way? Was there a massive collision between asteroids? Did a slew of comets come streaking into the inner solar system? Were we paid a brief, gravitationally-disruptive visit by some other rogue interstellar object? Whatever it was that occurred, it changed the face of our Moon forever.
Curiously enough, it was at just about that time that we find the first fossil evidence of life on Earth. If there’s indeed a correlation, then whatever happened to wipe out the Moon’s oldest craters may also have cleared the slate for life here — either by removing any initial biological development that may have occurred or by delivering organic materials necessary for life in large amounts… or perhaps a combination of both.
Timeline for the Lunar Cataclysm Hypothesis (LPI)
The new findings from the Apollo samples provide unambiguous evidence that a large-scale impact event was taking place during this period on the Moon — and most likely on Earth too. Since the Moon lacks atmospheric weathering or water erosion processes it serves as a sort of “time capsule”, recording the evidence of cosmic events that take place around the Earth-Moon neighborhood. While evidence for any such impacts would have long been erased from Earth’s surface, on the Moon it’s just a matter of locating it.
In fact, due to the difference in surface area, Earth may have received up to ten times more impacts than the Moon during such a cosmic cataclysm. With over 1,700 craters over 20 km identified on the Moon dating to a period around 3.9 billion years ago, Earth should have 17,000 craters over 20 km… with some ranging over 1,000 km! Of course, that’s if the craters could had survived 3.9 billion years of erosion and tectonic activity, which they didn’t. Still, it would have been a major event for our planet and anything that may have managed to start eking out an existence on it. We might never know if life had gained a foothold on Earth prior to such a cataclysmic bombardment, but thanks to the Moon (and the Apollo missions!) we do have some evidence of the events that took place.
Sample of lunar impact melt breccia, showing exterior and chondrule-filled interior. (Click for sample report.) Source: JSC
The LPI-JSC team’s paper was submitted to the journal Science and accepted for publication on May 2. See the abstract here, and read more on the Lunar Science Institute’s website here.
And if you want to browse through the Apollo lunar samples you can do so in depth on the JSC Lunar Sample Compendum site.
Meteorite expert and researcher Peter Jenniskens with a fragment of the bolide seen over California on April 22, 2012. Image via Franck Marchis' Cosmic Diary blog.
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Meteorite hunters have been successful in locating fragments from the huge meteor visible in the daytime skies over California last weekend. One of the successful hunters was Peter Jenniskens, an expert in meteors and meteorites, perhaps best known for retrieving the fragments of asteroid 2008 TC3 which fell in Sudan in 2008. Astronomer Franck Marchis wrote in his Cosmic Diary blog that Jenniskens realized the size of the California meteor was very similar to 2008 TC3, and so fragments should have reached the surface, just like they did in 2008.
Jenniskens went out searching and found a four-gram fragment of the meteor in a parking lot in Lotus, California.
Update: NASA and the SETI Institute are asking the public to submit any amateur photos or video footage of the meteor that illuminated the sky over the Sierra Nevada mountains and created sonic booms that were heard over a wide area at 7:51 a.m. PDT Sunday, April 22, 2012.
Marchis wrote that several scientists from the Bay Area met at NASA Ames Research Center on April 24 to discuss a strategy for a search campaign, examining a radar data map which showed that dozens of fragments from the 100g to 1 kg range may have reached the ground.
Jenniskens said the fragment he found was a Carbonaceous Chondrites from the CM group of meteorites, “a rare type of primitive meteorite rich in organic compounds,” he said.
“We are very interested in this rare find,” said Greg Schmidt, deputy director of the NASA Lunar Science Institute. “With the public’s help, this could lead to a better understanding of these fascinating objects.”
“Getting fresh fragments of meteoroids, called meteorites, is key for astronomers to understand the composition of those remnants of the formation of the solar system,” Marchis wrote. “Fresh fragments are unaltered by the Earth’s weather and erosion processes, so they are pristine samples which can be used to detect organic materials for instance.”
Photos and video footage would help the scientists to better analyze the trajectory of the meteor and learn about its orbit in space. This information will also help scientists to locate the places along the meteor path where fragments may have fallen to the ground.
People who have photos or video of the meteorite are asked to contact Jenniskens at [email protected].
Marchis noted that a storm is heading towards the region and rain could alter the remaining fragments. So if you live nearby, consider heading out to take a look. Here is the radar map:
Radar map by Marc Fries showing the possible location of fragments (green area) of the meteor between Auburn and Placerville.
Marchis also said that if anyone has access to security camera footage taken on April 22, 2012 in the area of the fireball sighting, it may be useful to check them to see if the fireball was visible. “Astronomers could use them to pin down the site of the fall, maximizing the hunt for fragments,” he said.
Location of daylight (8 AM) fireball over California on April 22, 2012. Credit: NASA's Meteor Watch
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A daytime fireball over the skies of central/northern California on Sunday morning, April 22, 2012 caused a loud explosion and the event was also detected on several seismographs stations in the area. According to Bill Cooke, head of NASA’s Meteoroid Environments Office, the source of the blast was a meteoroid about the size of a minivan, weighing in at around 70 metric tons (154,300 pounds) and at the time of disintegration released energy equivalent to a 5-kiloton explosion.
For comparison, conventional bombs yield energy from less than 1 ton to 44 tons, and the approximate energy released when the Chicxulub impact caused the mass extinction 65 million years ago was estimated to be equal to 96 million megatons of TNT.
“This was a BIG event,” said Elizabeth Silber of the Meteor Group at the Western University in Ontario, Canada.
“Most meteors you see in the night’s sky are the size of tiny stones or even grains of sand and their trail lasts all of a second or two,” said Don Yeomans of NASA’s Near-Earth Object Program Office at the Jet Propulsion Laboratory in Pasadena, Calif. “Fireballs you can see relatively easily in the daytime and are many times that size – anywhere from a baseball-sized object to something as big as a minivan.”
Silber estimates the location of its explosion in the upper atmosphere above California’s Central Valley. It is not known yet if any pieces of the space rock survived to land as meteorites, but the entire object was likely vaporized before hitting the ground. However, you can bet there are people out looking. (Silber said on the Meteorobs newsgroup that based on infrasonic data the approximate source coordinates are 37.6N, 120.5W).
Descriptions of the fireball range from a “silver flash” to like a “green glittering sparkler,” and one person said their sighting of the object was followed 4-5 minutes later by a loud sonic boom.
Unfortunately, since the huge fireball occurred during the day, all of NASA’s meteor-seeking cameras were turned off, so images of the event are sparse. You can see some at news station KTVN’s website.
This type of fireball is quite rare, and visual observations of them are even more rare. “An event of this size might happen about once a year,” said Yeomans. “But most of them occur over the ocean or an uninhabited area, so getting to see one is something special.”
That the fireball occurred during the Lyrid meteor shower is probably a coincidence, most experts are saying, as meteor shower meteors are generally small bits space dust that don’t produce large fireballs. However, another large fireball also occurred on April 20 in Brazil. See more information about that bolide here.
Example of a lunar flash, photographed in 1953. Credit: Leon Stuart/Columbia University Department of Astronomy
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For hundreds of years, people have seen tiny flashes of light on the surface of the Moon. Very brief, but bright enough to be seen from Earth, these odd flashes still hadn’t been adequately explained up until now. Also known as Transient Lunar Phenomena (TLPs), they’ve been observed on many occasions, but rarely photographed. On Earth, meteorites burning up in the atmosphere can produce similar flashes, but the Moon has no atmosphere for anything to burn up in, so what could be causing them? As it turns out, according to a new study, the answer is still meteorites, but for a slightly different reason.
The lights don’t result from burning up as on Earth, but rather are hot blobs of material produced by the impact itself. The impacts were calculated to be powerful enough to melt the meteorites, producing super hot liquid droplets, called melt droplets, that produced light as they formed and then began to cool afterwards. The meteorites themselves can be tiny, but still cause an impact that could be seen from Earth.
Sylvain Bouley, a planetary scientist at the Paris Observatory and co-author of the study, explains: “You have just a small piece of cometary material or asteroid, about 10 centimeters, that can do a very bright flash visible from the Earth.”
Fellow planetary scientist Carolyn Ernst of Johns Hopkins University’s Applied Physics Laboratory, adds: “Something is melting, and because it’s so hot, it radiates in the visible wavelength until it cools down.”
The study included observations from 1999 – 2007, for which the brightness of the flashes and sizes and speeds of the meteorites were calculated.
The impacts have also been replicated at the Meteoroid Environment Office at the Marshall Space Flight Center, where tiny aluminum spheres were shot into simulated lunar dirt. The results were similar, helping to confirm the other team’s findings.
Other previous possible explanations included reflections on the Moon by tumbling satellites or even volcanic activity. There may still be debate though, as an earlier report in 2007 had attributed the flashes to outgassing on the Moon’s surface.
The paper will be published in the March 2012 issue of Icarus.
A unique type of crystal appears to have its origins in meteorites, according to a new study. Quasicrystals are an unusual type of crystalline structure that were initially thought to have only occurred in artificial conditions in labs, and impossible in nature, until they were found by geologists in the Koryak mountains in Russia in 2009. Their origin was unknown, but now new evidence indicates that they most likely came from space in meteorites, dating back to the early stages of the formation of the solar system.
Regular crystals, such as diamonds, snowflakes and salt, are symmetrical, ordered and repeating geometrical arrangements of atoms that extend in all three spatial dimensions (at both microscopic and macroscopic scales); they are commonly found in different types of rock. Quasicrystals are different however, with variations from the standard structure and composition.
When the newly found quasicrystals were studied, they were found to be composed primarily of copper and aluminum, similar to carbonaceous meteorites. The clincher came when the isotope measurements (ratios of oxygen atoms) indicated an extraterrestrial origin.
From the paper:
“Our evidence indicates that quasicrystals can form naturally under astrophysical conditions and remain stable over cosmic timescales.”
“The rock sample was first identified for study as a result of a decade-long systematic search for a natural quasicrystal (4). Quasicrystals are solids whose atomic arrangement exhibits quasi-periodic rather than periodic translational order and rotational symmetries that are impossible for ordinary crystals (5) such as fivefold symmetry in two-dimensions and icosahedral symmetry in three-dimensions. Until recently, the only known examples were synthetic materials produced by melting precise ratios of selected elemental components and quenching under controlled conditions (6–8). The search consisted of applying a set of metrics for recognizing quasicrystals to a database of powder diffraction data (4) and examining minerals outside the database with elemental compositions related to those of known synthetic quasicrystals.”
“What is clear, however, is that this meteoritic fragment is not ordinary. Resolving the remarkable puzzles posed by this sample will not only further clarify the origin of the quasicrystal phase but also shed light on previously unobserved early solar system processes. Fitting all these clues together in a consistent theory of formation and evolution of the meteorite is the subject of an ongoing investigation.”
The report has been published in the January 2 issue of Proceedings of the National Academy of Science. The article (PDF) is here. More detailed information about quasicrystals is also available here and here.
The huge fireball event as seen from a remote camera in Orangeville, Ontario. Credit: University of Western Ontario
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In newly released footage from the University of Western Ontario, a bright, slow-moving fireball was captured in the skies near Toronto, Canada on December 12, 2011 by remote cameras watching for meteors. Although this meteor looks huge as it burns up in Earth’s atmosphere, astronomers estimate the rock to have been no bigger than a basketball. Footage reveals it entered the atmosphere at a shallow angle of 25 degrees, moving about 14 km per second. It first became visible over Lake Erie then moved toward the north-northeast.
See below for the video.
But in a meteorite-hunter alert, Peter Brown, the Director of Western’s Centre for Planetary & Space Exploration said that data garnered from the remote cameras suggest that surviving fragments of the rock are likely, with a mass that may total as much as a few kilograms, likely in the form of many fragments in one gram to hundreds of a gram size range.
“Finding a meteorite from a fireball captured by video is equivalent to a planetary sample return mission,” said Brown. “We know where the object comes from in our solar system and can study it in the lab. Only about a dozen previous meteorite falls have had their orbits measured by cameras so each new event adds significantly to our understanding of the small bodies in the solar system. In essence, each new recovered meteorite is adding to our understanding of the formation and evolution of our own solar system.”
Brown and his team are interested in hearing from anyone who may have witnessed or recorded this event, or who may have found fragments of the freshly fallen meteorite. See UWO’s website for contact information.
Another camera view of the meteor:
Western Meteor Group’s Southern Ontario Meteor Network sensor suite has seven all-sky video systems designed to automatically detect bright fireballs.
At 6:04 p.m. on December 12, six of the seven cameras of Western’s Southern Ontario Meteor Network recorded this meteor. In a press release, UWO said the fireball’s burned out at an altitude of 31 km just south of the town of Selwyn, Ontario. It is likely to have dropped small meteorites in a region to the east of Selwyn near the eastern end of Upper Stony Lake. See the map of the projected path below.
Although this bright fireball occurred near the peak of the annual Geminid meteor shower, the astronomers say it is unrelated to that shower.
Estimated flight path of the Dec. 12, 2011 meteor seen near Toronto, Canada. Credit University of Wester Ontario.
'Rainbow-Colored Palette' of Southern Hemisphere of Asteroid Vesta from NASA Dawn Orbiter. This mosaic using color data obtained by the framing camera aboard NASA's Dawn spacecraft shows Vesta's southern hemisphere in false color, centered on the Rheasilvia impact basin, about 290 miles (467 kilometers) in diameter with a central mound reaching about 14 miles (23 kilometers) high. The black hole in the middle is data that have been omitted due to the angle between the sun, Vesta and the spacecraft. The green areas suggest the presence of the iron-rich mineral pyroxene or large-sized particles. This mosaic was assembled using images obtained during Dawn's approach to Vesta, at a resolution of 480 meters per pixel. The German Aerospace Center and the Max Planck Institute for Solar System Research provided the Framing Camera instrument and funding as international partners on the mission team. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
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The giant Asteroid Vesta is among the most colorful bodies in our entire solar system and it appears to be much more like a terrestrial planet than a mere asteroid, say scientists deciphering stunning new images and measurements of Vesta received from NASA’s revolutionary Dawn spacecraft. The space probe only recently began circling about the huge asteroid in July after a four year interplanetary journey.
Vesta is a heavily battered and rugged world that’s littered with craters and mysterious grooves and troughs. It is the second most massive object in the Asteroid Belt and formed at nearly the same time as the Solar System some 4.5 Billion years ago.
“The framing cameras show Vesta is one of the most colorful objects in the solar system,” said mission scientist Vishnu Reddy of the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany. “Vesta is unlike any other asteroid we have visited so far.”
Scientists presented the new images and findings from Dawn at the American Geophysical Union meeting this week in San Francisco.
Comparative View of Terrains on Vesta - Oppia Crater
This image of Oppia Crater combines two separate views of the giant asteroid Vesta obtained by Dawn's framing camera. The far-left image uses near-infrared filters where red is used to represent 750 nanometers, green represents 920 nanometers and blue represents 980 nanometers. The image on the right is an image with colors assigned by scientists, representing different rock or mineral types on Vesta. The data reveal a world of many varied, well-separated layers and ingredients. The reddish color suggests a steep visible spectral slope, and areas of fresh landslides in the inner walls of the crater show deeper green colors. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
“Vesta is a transitional body between a small asteroid and a planet and is unique in many ways,” Reddy said. “We do not know why Vesta is so special.”
Although many asteroids look like potatoes, Reddy said Vesta reminds him more of an avocado.
Asteroid Vesta is revealed as a ‘rainbow-colored palette’ in a new image mosaic (above) showcasing this alien world of highly diverse rock and mineral types of many well-separated layers and ingredients.
Researchers assigned different colors as markers to represent different rock compositions in the stunning new mosaic of the asteroid’s southern hemisphere.
The green areas in the mosaic suggest the presence of the iron-rich mineral pyroxene or large-sized particles, according to Eleonora Ammannito, from the Visible and Infrared (VIR) spectrometer team of the Italian Space Agency. The ragged surface materials are a mixture of rapidly cooled surface rocks and a deeper layer that cooled more slowly.
What could the other colors represent?
“The surface is very much consistent with the variability in the HED (Howardite-Eucritic-Diogenite) meteorites,” Prof. Chris Russell, Dawn Principal Investigator (UCLA) told Universe Today in an exclusive interview.
“There is Diogenite in varying amounts.”
“The different colors represent in part different ratios of Diogenite to Eucritic material. Other color variation may be due to particle sizes and to aging,” Russell told me.
No evidence of volcanic materials has been detected so far, said David Williams, Dawn participating scientist of Arizona State University, Tucson. Fresh Impact Craters on Asteroid Vesta
The fresh impact craters in this view are located in the south polar region, which has been partly covered by landslides from the adjacent crater. This would suggest that a layer of loose material covers the Vesta surface. This image combines two separate views of the giant asteroid Vesta obtained by Dawn’s framing camera. The far-left image uses near-infrared filters where red is used to represent 750 nanometers, green represents 920 nanometers and blue represents 980 nanometers. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Before Dawn arrived, researchers expected to observe indications of volcanic activity. So, the lack of findings of volcanism is somewhat surprising. Williams said that past volcanic activity may be masked due to the extensive battering and resultant mixing of the surface regolith.
“More than 10,000 high resolution images of Vesta have been snapped to date by the framing cameras on Dawn,” Dr. Marc Rayman told Universe Today. Rayman is Dawn’s Chief Engineer from NASA’s Jet Propulsion Lab (JPL) in Pasadena, Calif.
Dawn will spend a year in orbit at Vesta and investigate the asteroid at different altitudes with three on-board science instruments from the US, Germany and Italy.
The probe will soon finish spiraling down to her lowest mapping orbit known as LAMO (Low Altitude Mapping Orbit), approximately 130 miles (210 kilometers) above Vesta’s surface.
“Dawn remains on course to begin its scientific observations in LAMO on December 12,” said Rayman.
The German Aerospace Center and the Max Planck Institute for Solar System Research provided the Framing Camera instrument and funding as international partners on the mission team. The Visible and Infrared Mapping camera was provided by the Italian Space Agency.
In July 2012, Rayman and the engineering team will fire up Dawn’s ion propulsion system, break orbit and head to Ceres, the largest asteroid and what a number of scientists consider to be a planet itself.
Ceres is believed to harbor thick caches of water ice and therefore could be a potential candidate for life.
Southern Hemisphere of Vesta -Rheasilvia and Older Basin
Colorized shaded-relief map showing location of 375-kilometer-wide Older impact basin that is overlapping with the more recent 500 km (300 mi) wide Rheasilvia impact structure at asteroid Vesta’s South Pole. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDAAsteroid Vesta from Dawn - Exquisite Clarity from a formerly Fuzzy Blob
NASA's Dawn spacecraft obtained this image of the giant asteroid Vesta with its framing camera on July 24, 2011. It was taken from a distance of about 3,200 miles (5,200 kilometers). Before Dawn, Vesta was just a fuzzy blob in the most powerful telescopes. Dawn entered orbit around Vesta on July 15, and will spend a year orbiting the body before firing up the ion propulsion system to break orbit and speed to Ceres, the largest Asteroid. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
Read continuing features about Dawn by Ken Kremer starting here:
Almahata Sitta 15. The black fragment of Almahata Sitta meteorite number 15 shows up black against the lighter coloured rocks of the Nubian desert in Northern Sudan. Image credit: Peter Jenniskens (SETI Institute/NASA Ames)
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It was an unprecedented event: On October 6, 2008, asteroid 2008 TC3 was spotted by the Catalina Sky Survey Telescope in Arizona. Plotting its trajectory, astronomers knew the 80-ton rock was heading for a collision course with Earth. Just 19 hours later, 2008 TC3 streaked over skies of northern Sudan and then exploded about 37 km above the Nubian Desert. This was the first time an asteroid was predicted – and predicted correctly — to impact Earth. Luckily, it wasn’t big enough to cause any problems, and its path brought it over a remote area. But this presented scientists with an exciting and unparalleled opportunity to possibly study fragments of an asteroid that had been spectrally classified before striking Earth.
Shortly afterwards, expeditions led by Dr. Peter Jenniskens, a meteor astronomer from SETI and NASA’s Ames Research Center, and Mauwia Shaddad, a physicist at the University of Khartoum, collected nearly 600 pieces of the asteroid strewn over 29 kilometers of desert. Altogether the meteorites weighed less than 10 kilograms – all that was left of the 80-ton asteroid.
But these fragments that fell to Earth are revealing secrets about the asteroid belt and the early days of the solar system, says Dr. Jon Friedrich from Fordham University, one of the many different researchers who have been studying pieces of the fragments, now called the “Almahata Sitta” meteorites.
“We can now say the asteroid belt has lots of different types of materials that give little snapshots of conditions within the early solar system,” Friedrich told Universe Today. “We’ve seen that these asteroids haven’t changed a whole lot since the Solar System formed, so it speaks to the diversity of the chemistry and the processes that were acting on these small bodies in the early Solar System.”
Scientists agree that understanding the composition of the asteroid belt is crucial to how we might deal with a larger asteroid that might be heading directly towards Earth.
Discovery images of asteroid 2008 TC3, as it was seen on October 6, 2008, by the Catalina Sky Survey at Mount Lemmon in Arizona (Richard Kowalski).
Although scientists have been able to study and catalog many thousands of meteorites and have also analyzed hundreds of asteroids in space, this is the first time a “fresh” chunk of an asteroid that has fallen to Earth as a meteorite — and been analyzed through spectroscopy while it was still in space — has been found so quickly after hitting Earth. These meteorites are the first to be unequivocally connected with its parent asteroid.
“It is amazing to be able to finally positively link an asteroid to a certain type of meteorite,” said Friedrich. “When we look at asteroids in space we are only looking at the outside, and the asteroid’s surface has changed from being in the environment of space. For the first time we can study the interior of an object we have seen the exterior of in space. That knowledge gives us a map as to how the exteriors of asteroids change. We can have a better understanding of the population of objects in space and their distribution in the solar system.”
About three-quarters of meteorites that are found on Earth are an “ordinary” kind of stony meteorites called chondrites. Analysis of the Almahata Sitta meteorites revealed a rare, carbon-rich type of meteorite called an ureilite. Ureilites are believed to come from a large organic–rich, primitive asteroid that had melted sometime in its past.
“These are a strange type of meteorite which are rather odd in the sense that it is an igneous rock, much like a volcanic rock here on Earth,” Friedrich said, “so this meteorite’s origin is from a magma, so they were surely melted at one point. That also means they are like rocks you might pick up on Earth, but they also contain what we might call relatively primitive materials also, like graphite, organic compounds and other things.”
And so ureilites, and in particular the Almahata Sitta meteorites, contain material from both primitive and evolved types of asteroids.
There are few ureilites in meteorite collections, which is another reason the Almahata Sitta meteorites are so interesting. They have an unusually fine-grained and porous texture, making the meteorites extremely fragile. The researchers think that is why Asteroid 2008 TC3 shattered high in Earth’s atmosphere.
Friedrich and a student at Fordham, Julianna Troiano, studied fragments of the meteorites using an inductively coupled plasma mass spectrometer, which specializes in looking at inorganic composition of rock.
“We found chemically that all the different pieces were indeed ureilites,” Friedrich said, “but one other interesting thing was that these don’t seem to have any evidence of terrestrial contamination at all, which is what you would expect from such a ‘fresh’ fall. Most ureilite meteorites have been found in Antarctica, and oftentimes, the Antarctic samples seem to have concentrations that are somewhat elevated in certain elements, such are rare Earth elements like lanthanum, cerium. But the Almahata Sitta meteorites don’t seem to have an obvious contamination signature.”
Various meteorites from 2008 TC3. Credit: P. Jenniskens, et. al. Click image for full description
This allows the researchers to better explore the solar system’s makeup.
While chondrites normally have not been modified due to melting or differentiation of the parent asteroid — and researchers suspect they are not necessarily representative of typical asteroid parent bodies — ureilites normally do show signs of the parent body being melted.
So what has happened to an asteroid that is has somehow been heated to the point of “melting?”
The latest research on the Almahata Sitta meteorites reveal that the parent asteroid was probably formed through collisions of three different types of asteroids. This would also explain why the meteorites contain both evolved and primitive asteroid materials.
Dr. Julie Gayon-Markt from the Observatoire de la Cote d’Azur in France also recently provided more insight on the family of asteroids from which 2008 TC3 originated.
“Because falls of meteorites of different types are rare, the question of the origin of an asteroid harbouring both primitive and evolved characteristics is a challenging and intriguing problem,” said Gayon-Markt, who presented her findings at the Europlanet Science Conference in October. “A workable explanation for how asteroid 2008TC3 could have formed involves low velocity collisions between these asteroid fragments of very different mineralogies.
Gayon-Markt and her team also looked at the dynamics and spectroscopy of asteroids in the main asteroid belt to shed light on the origin of the Almahata Sitta fragments. “We show that the Nysa-Polana asteroid family, located in the inner Main Belt is a very good candidate for the origin of 2008 TC3,” she said.
Primitive asteroids, which are relatively unchanged since the birth of the Solar System, contain high proportions of hydrated minerals and organic materials. However, many other asteroids have undergone heating at some point, probably through the decay of radioactive materials, and the molten magma has separated into an iron core surrounded by a rocky mantle.
Friedrich and Gayton-Markt are just two of the researchers who are studying the Almahatta Sitta meteorites to try and garner a better understanding of our solar system, as well as figuring out more about the asteroid that fell to Earth in 2008.
“The study of these meteorites has been interdisciplinary and collaborative, and our work is just a small piece of a greater puzzle,” Friedrich said.
Southern Hemisphere of Vesta; Rheasilvia and Older Basin. Colorized shaded-relief map showing identification of older 375-kilometer-wide impact basin beneath and overlapping with the more recent Rheasilvia impact structure at asteroid Vesta’s South Pole. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
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Scientists leading NASA’sDawn mission have discovered a 2nd giant impact basin at the south pole of the giant asteroid Vesta, which has been unveiled as a surprisingly “dichotomous” and alien world. Furthermore, the cosmic collisions that produced these two basins shuddered through the interior and created vast Vestan troughs, a Dawn scientist told Universe Today.
The newly discovered impact basin, nicknamed ‘Older Basin’, is actually significantly older in age compared to the initially discovered South Pole basin feature named ‘Rheasilvia’ – perhaps by more than a billion years. And that is just one of the many unexplained mysteries yet to be reconciled by the team as they begin to sift through the millions of bits of new data streaming back daily to Earth.
Scientists speculate that ‘Older Basin’ is on the order of 3.8 Billion years old, whereas ‘Rheasilvia’ might be as young as about 2.5 Billion years, but those are just tentative estimates at this time and subject to change. Measurements so far indicate Rheasilvia is composed of basaltic material.
Shaded-relief topographic map of Vesta southern hemisphere showing two large impact basins - Rheasilvia and Older Basin.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
“We found many surprising things at Vesta, which is quite unique and the results have exceeded our expectations”, said Dr. Carol Raymond, Dawn deputy principal investigator, of NASA’s Jet Propulsion Laboratory, Pasadena, Calif.
Researchers presented the latest findings from Dawn’s initial science mapping orbit at a news briefing at the annual meeting of the Geological Society of America in Minneapolis, Minn., on Oct. 13.
The team considers Vesta to be the smallest terrestrial planet.
Since achieving orbit in July, Dawn’s Framing Cameras (FC) have imaged most of Vesta at about 250 meter resolution and the Visible and Infrared mapping spectrometer(VIR) at about 700 meter resolution. The measurements were collected at the survey orbit altitude of 2700 km. Before Dawn, Vesta was just a fuzzy blob in humankind’s most powerful telescopes.
Vesta from Hubble (top) as a fuzzy blob and from Dawn in orbit (bottom) in crystal clear high resolution.
Credit: NASA/JPL-Caltech/ UCLA/MPS/DLR/IDA
“There is a global dichotomy on Vesta and a fundamental difference between the northern and southern hemispheres”, said Raymond. “The northern hemisphere is older and heavily cratered in contrast to the brighter southern hemisphere where the texture is more smooth and there are lots of sets of grooves. There is a massive mountain at the South Pole. One of the more surprising aspects is the set of deep equatorial troughs.”
“There is also a tremendous and surprising diversity of surface color and morphology. The south is consistent with basaltic lithology and the north with impacts. We are trying to make sense of the data and will integrate that with the high resolution observations we are now collecting.”
Indeed Vesta’s completely unique and striking dichotomy can be directly traced back to the basins which were formed by ancient cataclysmic impacts resulting in shockwaves that fundamentally altered the surface and caused the formation of the long troughs that ring Vesta at numerous latitudes.
“The troughs extend across 240 degrees of longitude,” said Debra Buczkowski, Dawn participating scientist, of the Applied Physics Laboratory at Johns Hopkins University, Laurel, Md. “Their formation can be tied back to the two basins at the South Pole.”
Asteroid Vesta and Equatorial Grooves
This full view of the giant asteroid Vesta was taken by NASA’s Dawn spacecraft, as part of a rotation characterization sequence on July 24, 2011, at a distance of 3,200 miles (5,200 kilometers). A rotation characterization sequence helps the scientists and engineers by giving an initial overview of the character of the surface as Vesta rotated underneath the spacecraft. This view of Vesta shows impact craters of various sizes and grooves parallel to the equator. The resolution of this image is about 500 meters per pixel. Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
In an exclusive follow up interview with Universe Today, Raymond said “We believe that the troughs formed as a direct result of the impacts,” said “The two sets of troughs are associated with the two large basins [Rheasilvia and Older Basin].”
“The key piece of evidence presented was that the set of troughs in the northern hemisphere, that look older (more degraded) are circumferential to the older impact basin,” Raymond told me.
“The equatorial set are circumferential to Rheasilvia. That Rheasilvia’s age appears in places to be much younger is at odds with the age of the equatorial troughs. An explanation for that could be resurfacing by younger mass wasting features (landslides, slumps). We will be working on clarifying all these relationships in the coming months with the higher resolution HAMO (High Altitude Mapping Orbit) data.”
Dawn has gradually spiraled down closer to Vesta using her exotic ion thrusters and began the HAMO mapping campaign on Sept. 29.
Surface features are dated by crater counting methodology.
“Preliminary crater counting age dates for the equatorial trough region yields a very old age (3.8 Billion years). So there is a discrepancy between the apparent younger age for the Rheasilvia basin and the old age for the troughs. These could be reconciled if Rheasilvia is also 3.8 Billion years old but the surface has been modified by slumping or other processes,” Raymond elaborated.
Time will tell as further data is analyzed.
Dawn launch on September 27, 2007 by a Delta II Heavy rocket from Cape Canaveral Air Force Station, Florida. Credit: Ken Kremer
“Vesta is full of surprises, no more so than at the South Pole,” said Paul Schenk at the GSA briefing. Schenk is a Dawn participating scientist of the Lunar and Planetary Institute, Houston, Texas.
The ‘Rheasilvia’ basin was initially discovered in images of Vesta taken a decade ago by the Hubble Space Telescope which revealed it as a gaping hole in the southern hemisphere. But it wasn’t until Dawn entered orbit on July 16, 2011 after a nearly four year interplanetary journey that Earthlings got their first close up look at the mysterious polar feature and can now scrutinize it in detail to elucidate its true nature.
“The South Pole [Rheasilvia] basin is a roughly circular, impact structure and a deep depression dominated by a large central mound,” said Schenk. “It shows sharp scarps, smooth areas, landslide deposits, debris flows. It’s about 475 km in diameter and one of the deepest (ca. 20 -25 km) impact craters in the solar system.”
The central peak is an enormous mountain, about 22 km high and 180 km across- one of the biggest in the solar system. “It’s comparable in some ways to Olympus Mons on Mars,” Schenk stated.
“We were quite surprised to see a second basin in the mapping data outside of Rheasilvia. This was unexpected. It’s called ‘Older Basin’ for now.”
‘Older Basin’ is about 375 km in diameter. They overlap at the place where Rheasilvia has a missing rim.
“These basins are interesting because we believe Vesta is the source of a large number of meteorites, the HED meteorites that have a spread of ages,” Schenk explained.
Images showing key components of Rheasilvia impact basin on Vesta in high resolution ,referred to Shaded-relief topographic map. Credit: NASA/JPL-Caltech/ UCLA/MPS/DLR/IDA
Multiple large impacts over time may explain the source of the HED (Howardite, Eucrite and Diogenite) meteorites.
“We did expect large impacts on Vesta, likely associated with the late heavy bombardment recognized in the lunar impact record,” Raymond told Universe Today. “The surprising element is that the two apparently largest impacts – keeping in mind that other larger impact basins may be lurking under the regolith – are overlapping.”
Dawn’s VIR spectrometer has detected pyroxene bands covering Vesta’s surface, which is indicative of typical basaltic material, said Federico Tosi, a VIR team member of the Italian Space Agency, Rome. “Vesta has diverse rock types on its surface.”
“VIR measured surface temperatures from 220K to 270 K at the 5 micron wavelength. The illuminated areas are warmer.”
So far there is no clear indication of olivine which would be a marker for seeing Vesta’s mantle, Tossi elaborated.
The VIR spectrometer combines images, spectral information and temperature that will allow researchers to evaluate the nature, composition and evolutionary forces that shaped Vesta’s surface.
The team is absolutely thrilled to see a complicated geologic record that’s been preserved for study with lots of apparent surface layering and surprisingly strong and complex structural features with a large range of color and brightness.
Stay tuned for a year of Vestan delights !
Asteroid Vesta from Dawn
South Pole Rheasilvia basin is at lower right. NASA's Dawn spacecraft obtained this image of the giant asteroid Vesta with its framing camera on July 24, 2011 from a distance of about 3,200 miles (5,200 kilometers). Dawn entered orbit around Vesta on July 16, and will spend a year orbiting the body.
Credit: NASA/JPL-Caltech/UCLA/MPS/DLR/IDA
