Vesta as seen by the Dawn spacecraft from a distance of about 5,200 km. Left: original image. Right: in contrast and brightness stretched image. Image Credit: NASA/JPL-Caltech/UCLA/MPS/ DLR/IDA
Vesta is the third largest, and second-most massive asteroid in the main belt, having a mean diameter of about 525 km. Vesta orbits the Sun at a distance of 350 million kilometers and rotates once around its axis in 5 hours and 20 minutes. As Vesta is relatively close to the Sun, liquids and ices that were once exposed on the surface evaporated, sublimated, and escaped into space. Thus, Vesta is currently “dry”.
Vesta has the shape of a flattened ellipsoid. Its south pole is characterized by the presence of a huge crater with a diameter of about 500 km. This crater is named Rheasilvia, and it is the largest impact crater in relation to parent body size discovered to date in the solar system. The Rheasilvia impact generated numerous smaller asteroids that now orbit the Sun: the Vestoid family. Parts of the excavated material even reached Earth as meteorites. Because of their spectral properties (the way how an object reflects different wavelengths of light), we know that these meteorites, known as "HED meteorites", were once part of Vesta. The abbreviation HED stands for the rock types of howardite, eucrite and diogenite. These different rocks originate from different depths inside Vesta.
A geologic flight over Vesta, simulated by the DLR department for planetary geodesy