The planet Mercury is the smallest of the inner planets, and the closest to the Sun. It was visited by the Mariner 10 spacecraft twice in the 1970s, and about 45% of the surface was mapped. On August 3rd, 2004, NASA launched a new mission to Mercury, with the Messenger probe. It is now in the last stages of multiple gravity-assist flybys of Earth, Venus and Mercury, en route to an insertion into orbit around Mercury in March of 2011. In just two flyby encounters, Messenger took some very detailled pictures of Mercury, and has already greatly increased our knowledge about Mercury's surface features.