This picture of Vesta, the second-largest object in the asteroid belt, was taken on July 15th by Dawn, a robotic probe belonging to nasa, America's space agency, just after the craft had gone into orbit around the asteroid. Dawn will spend a year studying Vesta before firing up her high-tech ion engines and flying on to look at Ceres, the largest denizen of the belt.The asteroid belt is thought to be a mixture of three sorts of body. Some, such as Ceres and Vesta, are miniature planets whose gravity is strong enough to make them more or less spherical, and whose internal heat in the past has partially melted them and allowed geological processes such as the separation of an inner, metallic core from an outer, siliceous mantle to take place. Others are irregular fragments of such planetoids brought about by collisions.
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