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Forensic examination of asteroid crash scene
KEITH COOPER
ASTRONOMY NOW
Posted: October 05, 2009


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The four metre-wide asteroid that blew up in the sky above Sudan on 7 October 2008 was a tumbling, irregularly shaped piece of shrapnel from a larger body that had been bombarded with impacts billions of years ago before being destroyed.

Asteroid 2008TC3 burnt up over Sudan one year ago this week.

Asteroid 2008 TC3 is a unique case – it was spotted approaching Earth 21 hours before impact by the Catalina Sky Survey operating out of the Mount Lemmon Observatory in Arizona, and this was the first time an asteroid had ever been detected in space before colliding with Earth. Against all odds, Dr Peter Jenniskens of the SETI Institute and Mauwia Shaddad of the University of Khartoum led an expedition into the Nubian Desert to find fragments of the asteroid. In all, they found 280 pieces totalling 222 kilograms. After months of analysis, results being presented at the meeting of the Division of Planetary Sciences of the American Astronomical Society in Puerto Rico are beginning to tell us about the origin of this space rock.

Astronomer Peter Scheirich of the Ondrejov Observatory and Charles University in the Czech Republic has combined observations of the asteroid as it approached Earth to judge its shape and rotation based on how it was reflecting sunlight. Scheirich reports that 2008 TC3 was wildly tumbling, and irregularly shaped ‘like a loaf of walnut-raisin bread’.

“We have a gigantic jigsaw puzzle on our hands, from which we try to create a picture of the asteroid and its origins,” says Peter Jenniskens. “Now, Scheirich and his colleagues have provided us with a ‘composite sketch’ of the culprit, cleverly using eye-witness accounts of astronomers that saw the asteroid sneak up on us.”

Scientists have been kept busy analysing the chemical composition of the meteorite fragments spawned from the asteroid.

More intriguing is the asteroid’s composition. It’s tagged as a rare ureilite asteroid, but even among ureilites it is a little odd. Parts of the asteroid fragments show evidence of intense heating up to 1,300 degrees Celsius, before cooling at a rapid rate of tens of degrees per hour. The inference is that the asteroid was subject to some kind of sudden violence, and the rapid cooling turned olivine into a metallic iron. Looking deeper at the fragments via X-ray tomography, Jon Friedrich of Fordham University in New York and Mike Zolensky of NASA’s Johnson Space Center have found myriad tiny pores coated with olivine that are the outlines of coarse to fine grains that were welded together in the tremendous heat. Furthermore, the carbon present in the asteroid has been cooked to such a degree as to form graphite and even nanodiamonds. The growing picture is that 2008 TC3 was once part of a larger body that found itself peppered with impacts which eventually smashed the asteroid apart billion of years ago. Since then, 2008 TC3 had been floating through space on its wild tumble before its final demise in Earth’s atmosphere last year.

Despite all this, and in a boon to scientists who argue that the vital building blocks of life on Earth came from space, researchers at Stanford University have discovered that some organic molecules still survived in the fragments of 2008 TC3. Furthermore, Michael Callahan of NASA’s Goddard Space Flight Center even reports about the detection of amino acids in the fragments. Peter Jenniskens and Mauwia Shaddad now plan to return to the Nubian Desert to hunt for more fragments.

For an in-depth interview with Jenniskens, go to www.astronomynow.com/PeterJenniskensInterview.html
To see an animation of this tumbling rock, visit http://asima.seti.org/2008TC3/video/2008TC3-HD2.mov.
To see a speeded up view taken through a telescope, take a look at http://asima.seti.org/2008TC3/video/2008TC3-Clay.gif.

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