Jupiter and Mars aren't the only recent impact victims in our solar system. In two talks today at the Division for Planetary Sciences in Pasadena, California, astronomers report that a small asteroid located in the inner asteroid belt between those two planets took a major hit early last year. Previously rendered only in artists' conceptions, the first asteroid collision known in modern times revealed itself in a tail of debris streaming from what astronomers at first assumed was a comet. But the roughly 120-meter-diameter object—given the comet designator P/2010 A2—showed no signs of emitting the gases that all comets emit when producing tails. Instead of a steady stream of dust, astronomers found boulders near the object with dust moving away from them. Backtracking, they calculated that a single impact by a smaller asteroid could have blasted it all off the asteroid in February or March 2009. No great loss, though; the tail debris adds up to the equivalent of only a 24-meter-diameter ball of rock.
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