4 Vesta

Vesta is the third-largest known asteroid, 525 kilometers in diameter, discovered in 1807. Among the large asteroids, only Vesta has a surface of basaltic rock from ancient lava flows that may overlay an olivine mantle. This indicates that in the distant past Vesta likely differentiated into layers and underwent many of the same geological processes that the early Earth and Mars underwent. Dozens of Vesta-like asteroids are presumed to have existed at one time, but since then have been broken apart into families of smaller asteroids; nickel-iron asteroids are thought to come from the cores of such bodies, with stony ones coming from their crusts and mantles.

In 1996 the Hubble Space Telescope detected a huge crater on Vesta, 430 kilometers across and perhaps a billion years old. It is thought that this crater may be the source of the small V-type asteroids observed today.