NASA's Dawn spacecraft has documented strange "pitted terrain" on the asteroid, which seems to be the result of water that has "degassed into space."
Right now, in the asteroid belt which lies between Mars and Jupiter, some 2.246 astronomical units from Earth (some 209 million miles) is NASA's spacecraft Dawn, which recently left its orbit around the giant asteroid Vesta. While it was there, it collected the most detailed observations of Vesta so far, observations which have now brought scientists to a conclusion they did not expect: a volatile material, likely water, appears to have evaporated from Vesta's surface, leaving behind a pockmarked texture and excess hydrogen.
Two papers published in the latest issue of Science both support this new conclusion. The researchers believe that water-laden meteorites once brought water to the asteroid, impacting at speeds low enough that the water was preserved. Later collisions heated the rock, causing the water to evaporate and creating hundreds of pits in the terrain, some as deep as 200 meters. There are no signs that there continues to be any water present.
All of these clues will be instrumental in helping scientists gain a better understanding of how what happened in the solar system's early days that led to the evolution of different planets such as Mars, Mercury, and our own.