University of Calgary graduate student Ellen Milley poses with a fragment of a meteorite in a small pond. AP Photo/The Canadian Press, Geoff Howe
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On Nov. 27, planetary scientist Dr. Alan Hildebrand from the University of Calgary and graduate student Ellen Milley brought reporters to a site where they have found numerous meteorite fragments from the bolide that streaked across the sky in Western Canada on Nov. 20. The area where the meteroite fragments were found is called Buzzard Coulee, about 40 kilometers from the town of Lloydminster, on the Alberta-Saskatchewan border. There, around a frozen pond, numerous small rocks and pebbles could be seen that the scientists said were from the meteorite. No large chunks were spotted, however, reporters said.
Fragments of a meteorite were found in a small pond at Buzzard Coulee, Sask. on Friday. (Geoff Howe/CP)
The fireball that streaked across western Canadian skies was witnessed by thousands, and Hildebrand believes it was a 10-ton fragment from an asteroid. Videos from surveillance and police cameras showed the meteor exploding before it hit the ground. Reporters were told those observations, combined with the physical evidence, give scientists a treasure trove of data that could give them a better understanding of the solar system. The reports don’t offer any indications of the type of meteorite the fragments are, but from the images they appear to possibly be iron. We’ll add more images and information as they become available.
Fragments of the big meteorite that lit up the Canadian skies across the provinces of Alberta and Saskatchewan last week have been found, according to a report in CBC online. University of Calgary scientists said they located several meteorite fragments late Thursday afternoon, and they were planning to take reporters to the site Friday. Planetary scientist Dr. Alan Hildebrand and graduate student Ellen Milley believe thousands of meteorite bits from the 10-ton bolide are strewn over a 20-square-kilometre area. The video above of the fireball was taken by a video camera in a police car in Edmonton, Alberta. Continue reading “Fragments of Canadian Fireball Found”
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The search is on for fragments of a 10-ton rock that lit the sky over western Canada last Thursday evening. Scientists estimate that at the time it hit Earth’s atmosphere, the asteroid fragment weighed approximately 10 tons and was probably about the size of a desk. It exploded with the force of 300 tons of dynamite, and hundreds of fragments of the meteorite weighing more than 50 grams (1.76 ounces) are likely strewn over a wide area. The speed of entry was relatively slow, about 14 kilometers (8.7 miles) per second, well below the average 20 kilometers (12.4 miles) per second of most meteorites, said University of Calgary researcher Alan Hildebrand. Amateur astronomers, meteorite hunters and rock hounds have been combing the prairies in western Canada for a 10-ton meteorite that lit the sky and exploded with the force of 300 tons of dynamite, according to experts from the Canadian Space Agency.
The fireball first appeared approximately 80 kilometers above and just east of the border city of Lloydminster, Alberta/Saskatchewan, and traveled SSE towards the Battle River valley fragmenting spectacularly in a series of explosions. Researchers were able to estimate it’s size and energy from infrasound recordings, said Dr. Peter Brown, Canada Research Chair in Meteor Physics at the University of Western Ontario. Infrasound is very low frequency sound produced by explosions that can travel thousands of kilometers.
“At least half a dozen infrasound stations ranging from Greenland to Utah, including Canada’s Lac Du Bonnett, Manitoba and Elgin Field, Ontario stations, recorded energy from the fireball’s explosions. The indicated energy is approximately one third of a kiloton of TNT,” Brown said.
Dr. Brown also says that a fireball this size only occurs over Canada once every five years on average. About ten fireballs of this size occur somewhere over the Earth each year.
The fireball penetrated the atmosphere at a steep angle of approximately 60 degrees from the horizontal and lasted about five seconds from 17:26:40 to 17:26:45 MST with the largest explosion at 17:26:44. The fireball was recorded on all-sky and security cameras scattered across Saskatchewan and Alberta in addition to being witnessed by tens of thousands of people who saw it streak across the sky, and may be one of the best documented meteorite falls.
But the researchers are looking for any additional information they can find.
“We are now trying to get all the transient information about the fireball before it is lost. Many motels and gas stations only keep their security recordings for one week or less, so we urge everyone to check their systems to see if they recorded the fireball or the moving shadows that it cast,” Hildebrand said. “Three gas stations and motels in Lloydminster, Lashburn and Maidstone are known to have records, but dozens of other businesses in the area probably have the fireball or its shadows recorded.”
If fireball images are found, he suggests immediately saving a copy and contacting him. “With the security camera footage we can compute the fireball’s trajectory in the sky to calculate the prefall orbit. Meteorites have only ever been recovered from known orbits nine times previously and we want to make that ten. ”
Foton M3 after landing in Kazakhstan after the experiment. Samples, including Orkney sample, are screwed onto
[/caption]In an effort to understand how organic chemicals might survive after a period in the vacuum of space and then violent re-entry through the atmosphere, scientists have uncovered some interesting results. Last year, the ESA/Russian Foton-M3 mission was launched to test the effects of microgravity on various biological samples. However, a sample of Orkney rock had a harder journey than most. Attached to the outside of the craft, this sample underwent extreme heating during the descent toward the plains of Kazakhstan. Although most of the sample was vaporized, scientists have unveiled results that the sample still contains very obvious signs that it once harboured life. These exciting results set new limits on how organic chemicals may survive unaltered for long periods in space before plunging through a planetary atmosphere, plus it raises some interesting questions into how future searches for extraterrestrial life may be performed…
The principal mission objective for many planetary missions is the search for extraterrestrial life. Although many of our robotic explorers cannot detect life directly, they are able to carry out a host of mini lab experiments on samples taken from the planets surface. NASA’s Phoenix Mars Mission for example has been tirelessly slaving over its hot oven (a.k.a. the Thermal and Evolved-Gas Analyzer, or TEGA for short), dropping samples of Mars soil into its single-use kilns for the last few months. This effort is to vent any prebiotic chemicals into a gas form so instrumentation can then “sniff” the vapour. Should organic chemicals be found, there will be an improved chance that life may have evolved on the Red Planet’s surface.
But say if there is an easier (and cheaper) way to look for ET? Rather than sending hundreds of millions of dollars-worth of hardware to Mars to look for organic chemicals, why can’t we analyse all the rocky samples littered across the globe that originated from space? After all, we now know that some meteorites originate from Mars itself, surely we can perform a far more detailed analysis on these samples instead of depending on a robot millions of miles away?
The big stumbling block comes if we consider the extreme temperatures meteorites are put under during re-entry into the terrestrial atmosphere. Generally one would expect any evidence for past life (whether that be organic chemicals or fossilized remains) to be blow-torched out of existence by reentry temperatures up to 3,000°F (1,650°C). So, researchers from the University of Aberdeen, Scotland, decided to test a chunk of rock from a Scottish island by subjecting it to several days in space and then seeing if any evidence of life in the rock sample remained intact after the descent.
the Kazakhstan landing site of Foton-M3 in September 2007 (R. Demets/F. Brandstatter)
“The specially prepared piece of Orkney rock took part in the unmanned Foton M3 mission which aimed to examine the rock’s behaviour when it was exposed to the extreme temperatures involved in it’s re-entry through the Earth’s atmosphere,” Professor John Parnell, lead scientist in the study, said.
The reason why Orkney rock was used is because of the material’s robustness when exposed to extreme heat. After all, meteorites need to be made of tough stuff to make it to the ground. “Three quarters of the rock, which was about the size of a small pork pie, was burnt off in the experiment. However, the quarter which returned to Earth has shown us that if intelligent life were to have come into contact with the rock, it would have provided them with evidence that life exists on another planet.”
Now this is where the implications behind these results become abundantly clear. If this piece of rock was sent out into space, only for it to eventually encounter an alien world with intelligent life on its surface, it is conceivable that the rock would survive reentry, preserving the organic chemicals for further study by extraterrestrials. Of course, the reverse is true. If life existed (or exists) on Mars, perhaps we should take a closer look at those Martian meteorite samples…
In the case of the Orkney sample, it contains the remains of 400 million year-old algae, providing a rich chemical signature that Parnell and his team could detect. “We would be extremely excited if we found similar remains in a meteorite arriving from another world,” he added.
Although this experiment only scratches the surface of how organic chemicals may last, unaltered, in space (after all, should a meteoroid sample float in space for millions of years, could organic chemicals be altered by cosmic rays?), it does help us understand that for lower energy reentries, organic chemicals can indeed survive the burn…
Artist impression of the Asteroid Kleopatra. Credit: NASA
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Meteorites and asteroids from the inner solar system could be responsible for Earth’s store of precious metals such as platinum and iridium, brought to our nascent planet during the period of Late Heavy Bombardment, about 4,000 million years ago. Dr. Gerhard Schmidt from the University of Mainz, Germany, has calculated that about 160 metallic asteroids of about 20 kilometers in diameter would be sufficient to provide the concentrations of these metals, known as Highly Siderophile Elements (HSE), found in the Earth’s crust. “A key issue for understanding the origin of planets is the knowledge of the abundances of HSE in the crust and mantle of the Earth, Mars and the Moon. We have found remarkably uniform abundance distributions of HSE in our samples of the Earth’s upper crust. A comparison of these HSE values with meteorites strongly suggests that they have a cosmo-chemical source,” said Schmidt.
Schmidt and his colleagues have spent the last 12 years analyzing the concentrations of HSE at meteorite impact sites around the world, as well as in the samples from the Earth’s mantle and crust. In addition, he has compared the data from the Earth with data from impact breccias from the Moon brought by the Apollo missions and Martian meteorites, believed to be samples from the mantle and crust on Mars.
As the Earth formed, the heavy elements, including HSE that were present, sank to form the iron and nickel-rich metallic core. HSE were added again later by meteorite impacts, creating a veneer of material over the Earth’s surface after the core had formed, about 20-30 million years after the planet’s accretion. This could have been by the collision with a Mars-sized impactor that led to the formation of the Moon.
However, Schmidt believes that the meteorites responsible for the HSE elements on Earth are iron or stony-iron meteorites that match up with theoretical predications of asteroids formed in the Mercury-Venus region of our solar system.
Different classes of meteorites have characteristic elemental ratios of HSE that give indications where in the Solar System they formed. Chondrites are stony meteorites that represent the pristine material from the early Solar System, and iron or stony-iron meteorites, which are fragments of larger asteroids that had enough internal heat in the past to form a molten metal core. These most likely would have formed in the inner solar system.
The ratios of HSE found in Earth’s crust bear a much closer resemblance to iron or stony-iron meteorites, and Schmidt believes these meteorites came from the inner solar system.
There’s a problem, however. Of the 175 known impact craters on Earth, remains of the projectiles have been found for about 40, and none of these meteorites have been identified as being formed in the region between Mercury and Venus.
Intriguingly, some of the Martian meteorites found in Antarctica, which are probably represent samples of the Martian crust also have HSE values that resemble groups of iron meteorites and stony irons, suggesting that a similar process took place on Mars. Rock on Mars found by Opportunity rover, believed to be a meteorite. Credit: NASA/JPL
Also, the first meteorite found on Mars by the Opportunity Mars Exploration Rover in 2005 was an iron
meteorite.
Dr. Schmidt presented his findings at the European Planetary Science Congress in Muenster on Monday, 22nd September.
Team members gather to inspect and collect a meteorite being placed in a Teflon bag. Photo credit: M. Keiding, 2007
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Antarctica’s distinctive, unforgiving environment is truly unique. But add to that setting the otherworldly task of looking for meteorites — bits and pieces from the far reaches of our solar system that are strewn about Antarctica’s icy surface,– and Earth’s southern-most continent can provide a truly unparalleled scientific experience. “I had the privilege to explore a part of the world that few people get to,” said Dr. Lucy McFadden, a research professor in the astronomy department at the University of Maryland, College Park. She also is a scientist in the education and public outreach area for NASA’s Dawn mission that is traveling to study the asteroids Ceres and Vesta. McFadden had the opportunity to travel to Antarctica and spend over six weeks hunting for meteorites, specifically looking for meteorites from Ceres and Vesta. She shared her experiences recently in an online “webinar,” answering questions about her journey. “I love sharing my adventures,” she said. “My excitement about exploring the solar system was renewed because I had the opportunity to explore Earth as a planet.”
Although meteorites fall uniformly all over the Earth –estimates are between 30-80 tons a year, — most are in the form of dust. For the bigger rock-sized pieces, many fall in the ocean and those that fall on land can be buried by shifting terrain, broken down by chemical weathering, or are easily confused with Earth rocks. But Antarctica’s blue ice sheets are clear and barren, making it easy to spy a dark rock that’s likely a sample from space.
Aerial view of Antarctica. Photo credit: L. McFadden 2008
However, there’s another reason Antarctica is such a great place to look for meteorites. “There’s something special about Antarctica. Meteorites collect in certain areas there,” McFadden said. “The ice sheets are always moving, and the meteorites move with them. But the rocks get trapped by the barriers of the mountains, and that’s where the meteorites are found. Once you get a meteorite up against a barrier, the constant blowing of the polar winds ablates the ice, and rocks effectively come to the surface.” Over periods of tens or hundreds of thousands of years, very significant concentrations can build up in these areas.
Since 1976, the U.S. National Science Foundation has supported an annual search for meteorites during the Antarctic summer, through a program called ANSMET, the Antarctic Search for Meteorites. McFadden was part of an eight-member meteorite hunting team in November 2007 to January 2008.
McMurdo Station. Photo credit: L. McFadden, 2008
A C-17 cargo plane brought the team to Antarctica’s McMurdo Station. But one doesn’t just go out and start hunting for rocks without instructions on how to survive Antarctica’s harsh environment. The team underwent a week of training that included lessons on proper clothing. “I had to learn which coat to put on when, which hat and gloves to wear and be sure to have my boots on,” said McFadden. “It brought me back to kindergarten.” Also, learning snowmobile operation and repair is a must, as that would be their mode of transportation during their expeditions. “We were trained how to stay away from the crevasses in the ice and trained for rescue in case someone fell in,” she said.
A plane then brought the team, the snowmobiles, fuel and gear to their field site on the Miller Range to set up camp. They erected tents – their homes for six weeks, and had to chip ice to get water for drinking and cooking. Typical daytime temperature was about 20 degrees Fahrenheit (-6 C) when there wasn’t a storm. High winds at field camp. Photo credit: L. McFadden, 2007
At 70 degrees south latitude, the Antarctic summer sun never set. But the surroundings were desolate, to say the least. The region is mountainous, but constantly snow and ice covered. “I felt a sense of vulnerability of us humans,” McFadden said. “This is not a hospitable environment.” She also worried about the possibility of getting lost in the barren landscape with few landmarks. But with them was a seasoned, expert guide, John Schutt.
So what’s the trick of finding meteorites in Antarctica? “We practiced around the camp first, and walked up to all the rocks in the area,” said McFadden. “There are other rocks on the ground from rockslides from the mountains, so you have to learn what the local rocks look like.” Dr. Ralph Harvey, the head of the ANSMET program taught the team the art of meteorite hunting.
“When you find a field of rocks, you have to look closely and separate out the regular rocks from meteorites,” McFadden said. Most meteorites are black because they have a fusion crust: a thin glassy rind that forms on meteorites when they are coming through the atmosphere. The friction heats them up and the outside of the meteorite melts just a little.
“We looked at each rock,” said McFadden. “If we thought we found a meteorite, we waved our arms and everyone would come over and look. If we determined it was a meteorite, we would pick it up with tongs and put it in a Teflon bag and mark it. Then we planted a flag where we found a meteorite. It was very satisfying to look back where we’d been and see all the flags.”
Flags marking meteorite finds. credit: M. Keiding and ANSMET 2007-2008.
They followed a certain procedure to make notes on each meteorite, take pictures, note the position of each sample with a Global Positioning System monitor, and then wrap the meteorites in a certain way and put them in backpacks. “It was a big process to catalogue and account for all of them,” McFadden said.
At the end of the day they collected all the rocks from the backpacks and put them in bags in a specialized container to keep them cold. This would avoid contamination from any snow that might be attached to the rocks, until they are brought to Johnson Space Center where they are catalogued and then distributed to scientists around the world. A large meteorite found by the team. Photo credit: ANSMET 2007 Case Western Reserve University
Each of the meteorites tells a story about the processes of the early solar system. Scientists who study meteorites can find clues to the conditions as our solar system evolved, and find out more about the asteroids, moons and planets the meteorites originate from. Meteorites represent a “free” sample return mission for scientists.
The team didn’t do any scientific analysis out in the field, just collected the samples for transport to the laboratories in Houston. But that doesn’t mean they didn’t examine the rocks!
The team found lots of carbonaceous chondrites with very irregular and jagged shapes, some that may have come from the Moon, and others with a green mineral called olivine that may have come from Mars. One meteorite found made the team think of the famous ALH 84001 meteorite found in the Allan Hills region of Antarctica, that made headlines in 1996 when it was announced that the meteorite may contain evidence for traces of life from Mars. “We wondered if this one meteorite was related to ALH 84001,” said McFadden. But the team won’t know the answer until geochemical analyses are performed.
As for her search for samples from Ceres and Vesta, McFadden said, “I think we might have been successful in finding samples from Vesta, but I was really interested in looking for samples from Ceres. However, I wasn’t really sure what I was looking for. As far as we know we don’t have samples from Ceres.” Small meteorite. Photo credit: ANSMET 2007 Case Western Reserve University
How do scientists know a meteorite came from a specific asteroid? “The whole study of meteoritics addresses that through laboratory studies of many different attributes of rocks,” said McFadden. “We know we have rocks in our meteorite collection from Vesta because about one in every seven meteorites we find has characteristics, or spectral signature, that matches Vesta as viewed through a telescope. We look at Vesta and see a huge impact basin that the meteorites probably came from.”
But Ceres is a different matter. “We don’t know much about Ceres,” she said. “The spectral signature of Ceres doesn’t match anything we have in the meteorite collection. But maybe they’ll find one in the samples we brought back or eventually find one on a future expedition.”
Snowmobiles, the vehicle of choice for Antarctic meteorite hunting. Photo credit: L. McFadden, 2007
With stormy periods when they had to huddle in their tents, McFadden’s team had 22 full days of meteorite searching, and eight half days. They went out at 9:00 am, returning at 5:00 pm. “We had six guys and two women,” said McFadden. It’s different for each expedition. We didn’t know each other before hand, but we worked well together. We had this common experience and we had to look out for each other. But it was also very lonely; there wasn’t that much opportunity to interact. We were exhausted each night.”
They did have opportunities for recreation such as skiing, playing games or reading books. One particularly nice day they made a couch from snow and sat outside for awhile. Planes occasionally brought re-supply of food, letters, and other supplies. They were in Antarctica for Christmas, so they decorated and had a potluck supper. “The isolation and cold weather got to us after awhile, but we loved our time out there,” McFadden said. “We looked forward to going home, but we had a tremendous experience. We all appreciated the beauty of Antarctica.” Aerial view near McFadden's field camp in the Miller Range. Photo credit: M. Keiding, 2007
Their expedition found 710 meteorites, some as small as a little finger nail (about 1.0 x 0.5 x 0.5 cm) 3a), and others about 8 pounds and too big to hold in one hand (about 25 cm x 15 cm x 12).
“We had good hunting,” she said. “It wasn’t a record. Some days we wanted to keep going, but our guide had to keep us in check and keep us safe. In that climate you do have to stop and take care of yourself.”
Over the more than 25 years of these expeditions, over 26,000 meteorites have been found, expanding the volume of extraterrestrial materials that can be studied here on Earth to provide a context for our remote sensing explorations out in the solar system, such as the Dawn mission. “My experience searching for meteorites inspired me to continue trying to understand the meteorites themselves and pair that with my exploration with the Dawn spacecraft that is searching out in the solar system,” said McFadden.
And now another team of scientists is preparing to return to Antarctica in November this year to continue the hunt.
Dr. Lucy McFadden, Dawn Co-Investigator and Education and Public Outreach (E/PO) lead Photo credit: M. Keiding, 2007
McFadden responded to the question of why teams keep going back every year to look for meteorites. “There is the potential to find new types of meteorites. In 2006, they found a type of meteorite that had never been seen before. They believe it’s from another body in our solar system that was probably the size of the moon, but its isotopic signature is decidedly different from the moon or Mars. So we have indeed found evidence of planetesimals that are new to us that are out there in the asteroid belt. That’s very exciting and that keeps us going.”
Astronomers studying ways to deal with incoming near-Earth asteroids (NEA) that might be on a collision course with our planet want to know in detail what these space rocks are made of. The better they “know the enemy” the better they can come up with ways to destroy or change the course of NEAs. Since we’ve only studied a couple of asteroids up close with spacecraft, the best way to learn more about the composition of asteroids should be fairly easy: just look at meteorites that fall to Earth, which are small chunks of asteroids. But in doing so, researchers discovered quite a huge discrepancy. The vast majority of asteroids that whiz by Earth are of a type that matches only a tiny fraction of the meteorites that most frequently hit our planet. This difference has had astronomer scratching their heads. But a team of researchers has now found what it believes is the answer to the puzzle. The smaller rocks that most often fall to Earth, it seems, come straight in from the main asteroid belt out between Mars and Jupiter, rather than from the near-Earth asteroid population.
The researchers studied the spectral signatures of near-Earth asteroids and compared them with spectra obtained on Earth from the thousands of meteorites found on Earth. But the more they looked, the more they found that most NEAs — about two-thirds of them — match a specific type of meteorites called LL chondrites, which only represent about 8 percent of meteorites.
“Why do we see a difference between the objects hitting the ground and the big objects whizzing by?” asked Richard Binzel, a professor from MIT. “It’s been a headscratcher.” As the effect became gradually more and more noticeable as more asteroids were analyzed, “we finally had a big enough data set that the statistics demanded an answer. It could no longer be just a coincidence.”
Way out in the main belt, the population is much more varied, and approximates the mix of types that is found among meteorites. But why would the things that most frequently hit us match this distant population better than it matches the stuff that’s right in our neighborhood?
An obscure effect that was discovered long ago was recently recognized as a significant factor in moving asteroids around and putting them on a fast track towards the inner solar system, called the Yarkovsky effect.
This effect causes asteroids to change their orbits as a result of the way they absorb the sun’s heat on one side and radiate it back later as they rotate around, which alters the object’s path. This effect acts much more strongly on the smallest objects, and only weakly on the larger ones.
So, for smaller sized space rocks– the kinds of things that end up as typical meteorites — the Yarkovsky effect plays a major role, moving them with ease from throughout the asteroid belt on to paths that can head toward Earth. For larger asteroids a kilometer or so across, the kind that we worry about as potential threats to the Earth, the effect is so weak it can only move them small amounts.
The new study is also good news for protecting the planet. One of the biggest problems in figuring out how to deal with an approaching asteroid, if and when one is discovered on a potential collision course, is that they are so varied. The best way of dealing with one kind might not work on another.
But now that this analysis has shown that the majority of near-Earth asteroids are of this specific type — stony objects, rich in the mineral olivine and poor in iron — it’s possible to concentrate most planning on dealing with that kind of object, Binzel says. “Odds are, an object we might have to deal with would be like an LL chondrite, and thanks to our samples in the laboratory, we can measure its properties in detail,” he says. “It’s the first step toward ‘know thy enemy’.”
If you’ve ever held a real meteorite in your hand, you probably wanted to know, “Where has this rock been in space and where did it come from?” Until now, no one has been able to definitively establish where the majority of meteorites found on Earth came from because of the changes that occur in meteorites after they are ejected from the asteroids they were originally part of. The most common type of meteorite found on Earth, about 75% of those identified, are chondrites, stony bits of space rocks that didn’t undergo any melting while out in space. Two astronomers say have determined that most of these meteorites come from the asteroid belt between Mars and Jupiter. Using the GEMINI telescope, they found that asteroids in that region are similar to chondrites found on Earth.
This discovery is the first observational match between the most common meteorites and asteroids in the main belt. It also confirms the role of space weathering in altering asteroid surfaces.
To find the parent asteroid of a meteorite, the astronomers compared the spectra of a meteorite specimen to those of asteroids. This is a difficult task because meteorites and their parent asteroids underwent different processes after the meteorite was ejected. In particular, surfaces of asteroids are known to be altered by a process called “space weatheringâ€, which is probably caused by micrometeorite and solar wind action that changes the surface and spectra of asteroid surfaces.
Meteoroids are created, usually when there is a collision between asteroids. When an impact of a large asteroid occurs, the fragments broken off can follow the same orbit as the primary asteroid. These groups of fragments are called “asteroid families.†Until recently, most of the known asteroid families have been very old (they were formed 100 million to billions of years ago), and younger families are more difficult to detect because asteroid fragments are closer to each other.
Identifying the parent asteroid of a meteorite is a unique tool when studying the history of our solar system because one can infer both the time of geological events (from the meteorite that can be analyzed through dating techniques) and their location in the solar system (from the location of the parent asteroid).
Meteorites are also a major tool for knowing the history of the solar system because their composition is a record of past geologic processes that occurred while they were still incorporated in the parent asteroid.
Want to discover an impact crater, and even get it named after you? All you’ve got to do is spend a few (hundred) hours poring over images in Google Earth or Google Maps. That’s exactly what Geologist Arthur Hickman did, turning up a previously unknown impact crater when he was searching for iron ore in the mountains of West Australia.
While he was browsing through images on Google Earth, Hickman’s geology training helped him recognize the circular shape and raised rim of an impact crater. He sent a screenshot and coordinates to colleagues at Australian National University, and they confirmed that it’s a well-preserved meteor crater between 10,000 and 100,000 years old. And until now, totally unknown.
This isn’t the first time a crater has been discovered using Google Earth. One was found in the Saharan Desert two years ago. That crater is 31 km (19 miles) across – much bigger than Meteor Crater in Arizona.
The newly named “Hickman Crater” measures 270 metres (885 feet) across, and is about 35 km north of Newman, Australia. The region was mapped by the Geological Survey of Western Australia about 20 years ago, but the crater went unnoticed until now.
Since large meteorites hit the Earth every few thousand years, and when you consider that the landscape is millions of years old, there are many regions hiding meteorite impacts.
On September 15th of last year, a meteorite impacted the Earth near the town of Carancas in Peru. The story made worldwide headlines when hundreds of people who flocked to see the crater reported getting ill. As it turned out, there were no mysterious space illnesses plaguing the population; the super-hot meteorite likely vaporized arsenic-containing water that was near the surface of the impact site, and onlookers and investigators breathed in the noxious gas. The meteorite is again in the spotlight, though not for making people sick.
Researchers estimate from their analysis of the crater that the meteorite was of a rocky composition, and that it impacted the ground at a whopping 15,000 miles (24,150 kilometers) per hour. That is really fast for a stony meteorite! It is calculated to have been between .2 and 2 meters at the point of impact, and upwards of 3 meters when it entered the atmosphere.
“Normally with a small object like this, the atmosphere slows it down, and it becomes the equivalent of a bowling ball dropping into the ground. It would make a hole in the ground, like a pit, but not a crater. But this meteorite kept on going at a speed about 40 to 50 times faster than it should have been going.†said Peter Schultz, professor of geological sciences at Brown University, who presented the findings of his travels to the impact site at the 39th annual Lunar and Planetary Science Conference in Texas last week. Schultz collaborated on his research with a team of scientist from Brown University, Peru and Uruguay.
Stony meteorites – called chondrites – generally break up in the atmosphere and impact the ground at rather slow speeds. In fact, most of the objects that enter Earth’s atmosphere end up never hitting the ground because the gases are so thick that the heat caused by air compression vaporizes them.
Schultz and his team think the Carancas meteorite may have initially broken up and then reformed in such a way as to make it more aerodynamic, allowing it to bullet through the atmosphere instead of being braked by the friction with the gases in our atmosphere. As opposed to dissipating and burning up like other chondrites, the meteorite landed as one large chunk.
This contradicts the conventional theory that small, rocky asteroids either can’t impact at all, or create only small impact pits. If the new theory is correct, we may have to rethink the history and influence of meteorite impacts on the Earth, as well as consider what kind of damage they are capable of doing in the future.
