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    This photo made available by NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington on Tuesday, Nov. 27, 2012 shows a 68-mile-diameter crater, large indentation at center, in the north polar region of Mercury which has been shown to harbor water ice, thanks to measurements by the Messenger spacecraft. Scientists made the announcement Thursday, Nov. 29, 2012. (AP Photo/NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington)

    NASA spacecraft maps planet Mercury

    The closest planet to the sun hasn't received as much scientific attention as some of its more flashy solar system neighbors, such as Mars, but NASA's Messenger spacecraft is helping to close the gap. The probe has been in orbit around Mercury since March 2011, and its team announced Feb. 28 that the spacecraft had finished mapping the planet's surface.