Vesta and Ceres
This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Planetary Science. Please check back later for the full article.
Asteroids 1 Ceres and 4 Vesta are the two largest asteroids in the asteroid belt, with mean diameters of 946 km and 525 km, respectively. Ceres was reclassified as a dwarf planet by the IAU (International Astronomical Union) as a result of their new dwarf planet definition, which is a body that (a) orbits the sun, (b) has enough mass to assume a nearly round shape, (c) has not cleared the neighborhood around its orbit, and (d) is not a moon. Our understanding of these two bodies has been revolutionized in the last decade by the success of the Dawn mission that visited both bodies. Vesta is an example of a small body that has been heated substantially, and differentiated into a metallic core, silicate mantle, and basaltic crust. Ceres is a volatile-rich rocky body that did not experience significant heating and therefore has only partially differentiated. These two contrasting bodies have been instrumental in learning how inner solar system material formed and evolved.