Impacts on giant asteroid left evidence

NASA says a study of images from its Dawn mission has identified remarkable, dark-as-coal material spread across the surface of the giant asteroid Vesta. Images taken by the Dawn spacecraft's framing camera are helping astronomers understand the impact environment early in Vesta's evolution, the space agency reported Thursday. The dark material, thought to be rich in carbon, tends to appear around the edges of two giant impact basins in Vesta's southern hemisphere, astronomers said. Analysis of the Dawn images suggests the dark material was most likely delivered by an object that crashed in Vesta 2 billion-3 billion years ago, creating the older of the two basins known as Veneneia, they said. Some of those materials were apparently covered up by a later impact that formed the younger basin, Rheasilvia, the said, leaving speckles of the dark material on the rims of smaller craters and their immediate surroundings. The Dawn spacecraft spent more than a year orbiting Vesta before departing in September 2012 for a journey to the dwarf planet Ceres, expected to arrive there in early 2015.