Published online by Cambridge University Press: 01 April 2022
The Dawn orbiter mission has revealed the mineralogical and chemical composition of Vesta’s surface materials and constraints on its interior structure. The surface is composed of breccias of basalt and ultramafic rocks, contaminated by exogenic carbonaceous chondrite. At the center of the asteroid is a metallic core about half the diameter of the body, and gravity data provide information on the thicknesses and densities of the mantle and crust. Huge, overlapping impact basins expose rocks of the lower crust and mantle. Howardite–eucrite–diogenite (HED) meteorites are samples of Vesta, mostly excavated by the giant impacts and delivered to Earth via an orbital resonance with Jupiter. Petrologic and geochemical studies of HEDs constrain interpretations of Dawn’s spectral and geochemical data, and offer otherwise unobtainable insights into the asteroid’s origin, bulk composition, global differentiation, impact history, and geochronology. Major unresolved questions include whether Vesta had an early magma ocean, as well as the source of “missing” olivine in mantle rocks, and a possible role for fluids. As the sole surviving rocky protoplanet, Vesta provides a unique perspective on the nebular raw materials that accreted to form the terrestrial planets.