NASA, ESA, and D. Jewitt (UCLA)

ScienceShot: An Asteroid Smashup

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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