Asteroid Collision

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  blasted all the debris 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. Small, perhaps in the scheme of things but it was the first time such a thing was witnessed. We must watch the skies; oh yeah.

Call it the Super-Grand Canyon. Melas Chasma on Mars is 9 kilometers deep in some places, or nearly six times deeper than Earth's famous landmark on average. How the giant feature was formed, itself one small stretch of the 4000-kilometer-long Valles Marineris rift valley, remains a mystery. But one thing seems evident: water played a role in its history. In this view, one of several images of Melas Chasma released today, a computer has reconstructed 3D images taken with the European Mars Express orbiter's High-Resolution Stereo Camera. Part of the canyon wall collapsed in multiple landslides in the distant past, with debris fanning out into the valley below. Scientists analyzing the texture of the rocks deposited by the landslides say they were transported by liquid water, water ice, or mud. They also see evidence of sediments in the exposed sides of the canyon, and the lighter-colored rocks apparently are composed of sulfates, another strong sign of a wet martian past.