Dawn at Vesta
Vesta is the second-most-massive asteroid after the dwarf planet Ceres,and comprises an estimated 9% of the mass of the asteroid belt. Vesta is thought to be a remnant protoplanet with a differentiated interior. It lost some 1% of its mass less than a billion years ago in a collision that left an enormous crater occupying much of its southern hemisphere. NASA's Dawn spacecraft has sent back the first images of the giant asteroid Vesta from its low-altitude mapping orbit. The images, obtained by the framing camera, show the stippled and lumpy surface in detail never seen before, piquing the curiosity of scientists who are studying Vesta for clues about the solar system's early history. The surface shows abundant small craters, and textures such as small grooves and lineaments that are reminiscent of the structures seen in low-resolution data from the higher-altitude orbits. Also, this fine scale highlights small outcrops of bright and dark material.
Vesta is the second-most-massive body in the asteroid belt, though only 28% as massive as Ceres. Vesta's shape is relatively close to a gravitationally relaxed oblate spheroid, but the large concavity and protrusion at the pole combined with a small mass precluded Vesta from automatically being considered a dwarf planet under International Astronomical Union rules. Vesta may be listed as a dwarf planet in the future,
A gallery of new Vesta images can be found online at: http://www.nasa.gov/mission_pages/dawn/multimedia/gallery-index.html.
The images were received on Earth on December 13. Dawn scientists plan to acquire data in the low-altitude mapping orbit for at least 10 weeks. The primary science objectives in this orbit are to learn about the elemental composition of Vesta's surface with the gamma ray and neutron detector and to probe the interior structure of the asteroid by measuring the gravity field.
For further information and photo: http://www.jpl.nasa.gov/news/news.cfm?release=2011-391&rn=news.xml&rst=3233#5