Researchers are baffled by a space rock trailed by six comet-like tails that has been spotted in the asteroid belt between Mars and Jupiter. Comets are essentially "dirty snowballs" that form tails of dust and gas when they orbit close enough to the sun to melt the ice in their cores, while asteroids are just rocks, which don't have any ice to melt. "This thing should just be a rock. Imagine if you went in your backyard and a rock suddenly started spouting this stuff off," said David Jewitt of the University of California, Los Angeles, lead author of a paper on the discovery published in Astrophysical Journal Letters. Jewitt speculates that the asteroid's spin rate has increased, causing it to fall apart and creating trails of dust.