The camera system on board the NASA spacecraft Dawn took these two images of the asteroid Vesta on 1 June 2011. The asteroid rotates left to right as shown by the dark spot on the equator (left image was taken first, the right image second). A loop of twenty images can be seen at NASA’s web site. The loop shows about 30 degrees of rotation.
The images were processed by researchers at the Max Planck Institute for Solar System Research (MPS) in Germany and show the equatorial dark spot and a huge crater in the southern hemisphere just on the edge of image. It will be another two weeks before the spacecraft is close enough to Vesta to begin to reveal the nature of the dark spot. Both the southern crater and the dark spot are known from Hubble images.
The space probe is expected to go into orbit around Vesta on July 16th and then accompany the asteroid for about a year. Vesta circles the Sun between the orbits of Mars and Jupiter within the so-called asteroid belt.