Vesta, minor-planet designation 4 Vesta, is one of the largest asteroids in the Solar System, with a mean diameter of 525 kilometres (326 mi). It was discovered by Heinrich Wilhelm Olbers on 29 March 1807, and is named after Vesta, the virgin goddess of home and hearth from Roman mythology.
Vesta is the second-most-massive asteroid after the dwarf planet Ceres, and comprises an estimated 9% of the mass of the asteroid belt. The less-massive Pallas is slightly larger, making Vesta third in volume. Vesta is the last remaining rocky protoplanet (with a differentiated interior) of the kind that formed the terrestrial planets. It lost some 1% of its mass less than a billion years ago in a collision that left an enormous crater occupying much of its southern hemisphere. Debris from this event has fallen to Earth as howardite–eucrite–diogenite (HED) meteorites, a rich source of information about the asteroid.
Vesta is the brightest asteroid visible from Earth. Its maximum distance from the Sun is slightly farther than the minimum distance of Ceres from the Sun, though its orbit lies entirely within the Cererian orbit. NASA's Dawn spacecraft entered orbit around Vesta on 16 July 2011 for a one-year exploration, and what is known about Vesta will be refined and extended as data from Dawn is analyzed and published. Dawn left Vestan orbit on 5 September 2012.