Pits in the Marcia crater on Vesta resemble features found on Mars, indicating the possible presence of water and other volatile substances on the asteroid.
NASA/JPL-Caltech/UCLA/MPS/DLR/IDA/JHUAPL
Vesta possesses features of both asteroids—of which it is one of the largest examples—and of planets. Recent observations by the Dawn mission have provided a detailed map of the asteroid's surface and a great deal of insight into its interior. This data shows Vesta to be part of the rubble of the early Solar System's history, with a structured interior similar to the terrestrial planets—Mercury, Venus, Earth, and Mars. Dawn recently departed Vesta orbit and is now headed to Ceres, the largest asteroid (and one of the five dwarf planets designated by the International Astronomical Union).
Even as Dawn is in transit, scientists are still going through data from its time at Vesta. A pair of studies published in Science reveals a new surprise: the possible presence of volatiles on the asteroid's surface. Additionally, Vesta's surface contains a much higher amount of hydrogen than expected. The asteroid's overall composition indicates that it may be the source of some meteorites found on Earth, and, like Earth, it received volatiles through a late bombardment.
Based on Dawn's observations, Vesta is chemically similar to the HED meteorites, and in fact is likely their source, as material could have been blasted free by collisions. ("HED" comes from three classes of meteorite structure: howardite, eucrite, and diogenite.) However, these meteorites are not high in volatiles, especially compared with the carbonaceous chondrite meteorites thought by many to be the origin of much of Earth's water.
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