March 25, 2009

Scientists Match Asteroid To Space Rocks Found On Earth

For the first time in history, scientists have matched a meteorite on Earth with a specific asteroid, providing insight into how the planets were formed and how to best avoid a potential asteroid catastrophe sometime in the future.

Last October, astronomers began tracking a small asteroid heading toward Earth before it became a "shooting star."  The asteroid appeared to mostly blow up in the sky 23 miles above the ground, leading scientists to believe there would not be any space rocks left to study.

However, a meticulous search by several students through the remote Sudanese desert uncovered 8.7 pounds of black jagged rocks, the remains from the 2008 TC3 asteroid. The rocks turned out to be full of surprises and tiny diamonds, according to scientists.

"This was a meteorite that was not in our collection, a completely new material," said Peter Jenniskens of NASA's Ames Research Center in California, the lead author of a report about the study.

Astronomers have long sought to send a robot probe to an asteroid, retrieve a sample and return it to Earth for scientists to analyze the material.  Instead, a chunk of this particular asteroid fell right into their laps.

Scientists believe the asteroid is the likely remains from 4.5 billion years ago, when chunks of rock tried and failed to become a planet.

"This is a look back in time and it came to us," University of Maryland astronomer Lucy McFadden, who was not involved in the study, told AFP.

She and four other independent experts commended the findings as important to the current understanding of our solar system.

"It's a beautiful example of looking at an earlier stage of planet development that was arrested, halted," NASA cosmic mineralogist Michael Zolensky, one of the study's co-authors, told AFP.

The findings also provide a lesson for the future should a similar but larger asteroid begin hurtling toward Earth.

Simply blowing it up as in the Bruce Willis movie "Armageddon" would likely not work because this type of asteroid behaves like a "traveling sandpile," Zolensky said.

"If you blow it up, all the pieces are heading toward Earth."

Rather, a spacecraft-aided prod would be more effective, said NASA Ames Research Center director Simon "Pete" Worden, also a co-author of the study.

Worden is a longtime supporter of a global initiative to prepare for the threat of asteroids and comets impacting the Earth.

"The real important issue is to understand the physics of these objects," Worden told AFP.

Asteroids come in many different types, which scientists classify  based on color and light wavelengths.   The type of asteroid in the current study is known as class F, and is primarily porous and fragile.

McFadden said a class F asteroid, even a larger one, would not likely become a danger to our planet because its porous consistency would cause it to break up prior to impact.

This asteroid was full of metals like nickel and iron, and organic graphites, Zolensky said.   Remarkably, it contained "nanodiamonds" all over the rocks, formed by space collisions and high pressure, which made them glitter like geodes, he said. 

But the diamonds were extremely small.

"If bacteria had engagement rings, these would be the right size for them," Zolensky added.

The study will be published Thursday in the journal Nature.


Image Caption: Small asteroid 2008 TC3 fell to Earth at dawn on October 7, 2008, tracking through the skies over the Nubian Desert in northern Sudan. That event was remarkable because it was the first time an asteroid was detected in space before crashing into planet Earth's atmosphere. It was generally assumed the asteroid itself had completely disintegrated to dust. But, based on satellite and ground observations of the atmospheric impact event, Dr. Mauwia Shaddad of the University of Khartoum, aided by Dr. Peter Jenniskens of the SETI Institute and NASA Ames Research Center, led an expedition of students and staff to the area, combing the desert for surviving fragments. On December 6, 2008, two hours after their search began, the first meteorite was found. The team ultimately collected some 280 small meteorites, now called Almahata Sitta, with a total mass of about 5 kilograms -- the first material recovered from a known asteroid. In stark contrast to the lighter-colored stones, the black fragment in the picture is Almahata Sitta meteorite number 15. About 4 centimeters in diameter, it is seen as it came to rest on the desert floor. Courtesy Peter Jenniskens (SETI Institute/NASA Ames)


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