David Perlman writes in the SF Chronicle:

A puzzling object that seemed to be a comet flying inside the solar system’s asteroid belt is no comet at all, but the remains of a violent collision between two fossil rocks that populate the belt, astronomers say.

Captured in images by the Hubble Space Telescope, the crash of the asteroids provides scientists with their first opportunity to see clear evidence of the violent activity that has constantly churned the asteroid belt since its formation, probably when the planets themselves were forming about 4.5 billion years ago.

The object was first sighted in early January by astronomers at the Air Force LINEAR project telescope in New Mexico, who reported it as a comet that must have flown into the asteroid belt from the solar system’s outer…