The asteroid Vesta is 530 km (329 mi) in diameter, and contains about 9% of the total mass of the asteroid belt. Nearly spherical in shape, some refer to it as a protoplanet rather than an asteroid. Like planets, Vesta differentiated during it’s formation: it has an iron core, a mantle and a crust.
DAWN will orbit Vesta for a year, studying it. It will then kick-off for an encounter with the dwarf planet Ceres, in July 2012