The giant asteroid Vesta resembles a planet more than it does other asteroids, according to Christopher Russell at the University of California, Los Angeles, and his colleagues. In six separate studies, the researchers report their analysis of data from NASA's Dawn spacecraft, which has been orbiting Vesta (pictured, relative to other asteroids) since July 2011.

Vesta was formed about 2 million years after the Solar System's first solid bodies and is the Solar System's second-largest asteroid. The authors report that Vesta is pockmarked with many impact craters, including two overlapping ones, several hundred kilometres wide, at the south pole. One of these polar impacts blasted off material that became more asteroids, known as Vestoids, and meteorites. Shocks from these two big impacts apparently created the troughs that ring Vesta's equator. The asteroid's large size — roughly 260 kilometres in radius — rapid growth and massive iron core may explain how Vesta survived all these collisions.

Credit: SCIENCE/AAAS

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