By Ron Cowen
The fuzzy body with the long, bright tail spotted by astronomers in January was a dead ringer for a comet. But the object’s location put that notion on the rocks: the body lies in the innermost part of the asteroid belt between Mars and Jupiter, on an orbit that no comet could have.
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Instead, researchers have identified the body dubbed P/2010 A2 as a 120-meter-wide asteroid, the remnant of a slightly larger space rock that was recently hit by a much tinier denizen of the asteroid belt. The unseen collision vaporized the smaller body and stripped material from P/2010 A2, creating the debris initially mistaken for a comet’s tail.
Astronomers initially thought the suspected collision occurred just a few weeks before the asteroid was discovered. But a series of newly released images taken by the Hubble Space Telescope and the Rosetta spacecraft reveal that the dusty debris from the smashup is expanding sedately rather than flying off like shrapnel, indicating that the collision occurred about a year before P/2010 was discovered, two teams of astronomers report in the Oct. 14 Nature.