A week after NASA/JPL's Dawn Space Probe moved into orbit around the asteroid Vesta images of the hole of the surface have been released. Vesta is the second largest object in the Asteroid Belt and has a surface area of 883 000 km², twice that of California or 42 times that of Wales. It shows considerable variation over its surface.
Animation of the Surface of Vesta.
There is a higher resolution version on the Dawn website here.
Much of the south of the asteroid is smooth, while northern part of Vesta is heavily pitted, the result of many small impacts. This implies the northern surface is older than the southern; the most likely scenario is that both hemispheres were pitted heavily by impacts early in the solar system's history (though still over a very long period of time), and that the southern hemisphere was then resurfaced by a single large impact.
Overlapping craters nicknamed 'The Snowman'
in the Northern Hemisphere of Vesta.
The equatorial region of Vesta show heavy grooving, which is unexpected. Similar grooves are also seen on the Martian moon, Phobos, where they are attributed to repeated impacts by debris in the same orbit as the moon, repeatedly striking from the same direction. The Russian Phobos-Grunt mission is due to visit the moon and collect samples in 2013, which should vastly improve our understanding of Phobos' history.
Grooves on the surface of Phobos.
This is surprising on Vesta as it occupies a more sparse area of space; our current understanding implies the Asteroid Belt to be made up of scattered, remote objects. The grooving implies that early in the Solar System's history the Asteroid Belt may have been more densely packed.
The Dawn Probe should remain in orbit about Vesta for a year, during which time it should gather considerable information about the asteroid's structure and mineralogy. After this it will move on to Ceres, the largest object in the Asteroid Belt.
See also Visiting Vesta, 2010 TK₇, Earth's Trojan Asteroid and Asteroid 2011MD.