New observations from a NASA Dawn spacecraft show that the huge asteroid Vesta is a
battered protoplanet left over from the solar system’s early days, with a unique mix of characteristics unknown from any other space rock. Scientists had thought that Vesta, the second-largest body in the main asteroid belt between Mars and Jupiter, probably started down a planet-forming path shortly after the solar system’s birth. Many other Vesta-like objects were incorporated into rocky worlds such as Earth, but Vesta’s development along this path was halted. As said researchers Vesta’s stunted growth is chiefly a product of its location. The protoplanets that glommed together to form Mercury, Earth, Mars and Venus did so in the inner solar system, relatively far from the disruptive gravitational influence of a giant planet. The 330-mile-wide (530-kilometer) Vesta, on the other hand, grew up in the main asteroid belt between Mars and Jupiter. And the solar system’s largest planet made it tough for Vesta to hook up with others of its kind. As said David O’Brien, of the Planetary Science Institute in Tucson, Ariz., the velocities in the asteroid belt were really high, and the higher the velocity is, the harder it is for things to merge together under their own gravity. Those high velocities also set the stage for some incredibly violent collisions, which probably destroyed a fair number of Vesta-like bodies. Vesta itself was battered and bloodied by some huge impacts; one crater near its south pole is 314 miles (505 km) wide, and another underneath that one measures 250 miles (400 km) across. So while Vesta was doomed to a life of solitude, it has had the toughness and luck to stick around for the last 4.5 billion years.