As the space probe Dawn departs the giant asteroid Vesta, it took this image… (NASA/JPL-Caltech/UCLA/MPS/DLR/IDA )
After orbiting the giant asteroid Vesta for slightly more than 13 months, NASA's Dawn spacecraft left the space rock this week, headed for the dwarf planet Ceres. The craft is using a highly efficient ion thruster to spiral gently away from Vesta. In the system, electricity ionizes gaseous xenon and expels it to produce thrust. The engine is much less powerful than conventional rocket engines, but can operate for months at a time.
The craft is expected to reach Ceres in early 2015.
During its month at Vesta, Dawn discovered that the asteroid has completely melted in the past, forming a layered body with an iron core. The craft also found that Vesta had endured two massive collisions in its southern hemisphere over the last 2 million years. The dramatic troughs around Vesta are ripples from these collisions.
Dawn has revealed that Vesta "is a survivor from the earliest days of our solar system," said Christopher Russell of UCLA, Dawn's principal investigator. "We can now say with certainty that Vesta resembles a small planet more closely than an asteroid."
The Dawn mission is managed by JPL in La Canada-Flintridge. More information about the mission is available here.