At 531km in diameter, Vesta is the second most massive object in the asteroid belt. On Friday 15, NASA's Dawn spacecraft entered its orbit firing its ion thruster to reduce its speed. Then it captured this image.
This is the first time a man-made object has visited the main asteroid belt and entered orbit around one of the objects populating that area of the solar system. Vesta is a remnant protoplanet. After finishing its mission there, Dawn will fire its ion engine again to head to Ceres, the largest body in the belt. [NASA]