Asteroid Collision Photographed for the First Time

By Charles Q. Choi
Published October 14, 2010| Space.com

NASA, ESA, and D. Jewitt (UCLA)

Close up of an X-shaped objected spotted by astronomers using the Hubble Space Telescope between January and May 2010. The images show the object P/2010 A2, an X-shaped objected created by two colliding asteroids. 

Astronomers now have the first confirmed snapshots of what appears to be the aftermath of an asteroid collision in space.

When scientists first discovered the object dubbed P/2010 A2 in the asteroid belt in January using the Rosetta spacecraft, the fact that it trailed a tail made them think it was a comet. A closer look, however, suggested it was something more peculiar -- images from the Hubble Space Telescope revealed it had a bizarre X-shape nucleus, for instance. [Photo of the odd X-shape in space.]

"When I saw the Hubble image I knew it was something special," said researcher Jessica Agarwal, a European Space Agency astronomer in the Netherlands.

Astronomers suspect a rock maybe 10-16 feet (3-5 meters) wide slammed into a larger asteroid at speeds of about 11,200 mph (18,000 kph) with a detonation as powerful as a small atomic bomb, said researcher David Jewitt, an astronomer at the University of California in Los Angeles and leader of the Hubble observations.

"We have directly observed a collision between asteroids for the first time, instead of having to infer that they happened from million-year-old remains," researcher Colin Snodgrass, a planetary scientist at the Max Planck Institute for Solar System Research in Katlenburg-Lindau, Germany, told SPACE.com.

The smaller asteroid was vaporized, stripping material from the larger one. Pressure from solar radiation then swept the debris behind the remnant asteroid, forming a comet-like tail.

Hubble images suggest the nucleus of the object is 390 feet (120 meters) wide, with its tail containing dust grains 1 to 2.5 millimeters large, enough material to make a ball 65 feet (20 meters) wide.

Mystery space 'X' unmasked

When it comes to why this object has such a weird X-shape, "think of throwing a brick into a swimming pool," Jewitt told SPACE.com.

"The splash pattern will not be a smooth curtain, but a series of jets, filaments and other structures that reflect the shape of the brick, angle of impact and so on," he explained. "For the case of A2, neither the projectile nor the target are likely to have been spherical, so the 'X' arms probably reflect shape irregularities in an off-center impact."

The two asteroids that created the object were probably familiar with collisions, since they were most likely born from impacts between larger asteroids tens of millions to hundreds of millions of years ago, the researchers said. 

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