What is Vesta?
Vesta is the second-largest body in the asteroid belt, about 525 kilometres across. It is a layered world with a crust, mantle and iron core, and it is the source of the HED meteorites, including howardites.
Vesta was discovered in 1807 by the German astronomer Heinrich Olbers and named after the Roman goddess of hearth and home. It is the brightest asteroid as seen from Earth and can occasionally be glimpsed with the naked eye from a very dark site. With an average diameter of about 525 kilometres, it is the second most massive body in the asteroid belt after the dwarf planet Ceres.
What makes Vesta special is that it is a differentiated body. Early in its history it melted, and the heavy iron sank to form a core while lighter rock rose to form a mantle and a basaltic crust, just as happened on Earth. It is therefore often described as a surviving protoplanet, a planetary embryo that never grew into a full planet. Telescopes revealed that its surface spectrum, the pattern of light it reflects, matches the minerals in a family of meteorites: the eucrites, made of basalt; the diogenites, rich in the mineral orthopyroxene from deeper down; and the howardites, breccias that mix the two. Together these are called the HED meteorites.
NASA's Dawn spacecraft orbited Vesta from July 2011 to September 2012 and confirmed this link in detail. It mapped the giant Rheasilvia impact basin near the south pole, about 500 kilometres across, with a central peak around 20 kilometres high, among the tallest mountains in the Solar System. Rheasilvia and the older Veneneia basin beneath it are thought to have excavated huge amounts of crust, creating a family of small asteroids known as Vestoids, some of which feed fragments towards Earth.
Not every basaltic meteorite comes from Vesta; a few have unusual oxygen isotopes showing they come from other melted bodies. But the Vesta connection remains one of the clearest links between a meteorite type and a known asteroid.