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Deep impact

·1 min

NASA’s Opportunity rover has delivered yet another surprise. This rock, named Marquette Island, is unlike any other the six-wheeled robot has found. Its coarse-grained composition shows it originated not on the planet’s surface but within its interior. Sometime in the past a massive object–probably a small asteroid–slammed through the Martian surface, ejecting rocks from inside the crust. After being flung high into the sky, the basketball-sized rock landed on Meridiani Planum, conveniently where Opportunity has been exploring for the past 6 years. “It is from deep in the crust and someplace far away on Mars,” says chief mission scientist Steve Squyres. “Though exactly how deep and how far we can’t yet estimate.” (Photo: NASA/JPL-Caltech/Cornell)