Vesta

Image credit: NASA/JPL-Caltech/JAXA/ESA, source NASA/JPL

The asteroid Vesta is shown with size comparison to several other asteroids. This image of Vesta was taken by the Dawn spacecraft. When Dawn entered orbit around Vesta on July 15, 2011, it was the first probe to enter orbit around an object in the main asteroid belt between Mars and Jupiter.

This image of Vesta was taken as Dawn was leaving its orbit around the asteroid. Vesta is 330 miles (530 kilometers) in diameter and the second most massive object in the asteroid belt after Ceres. Ground- and space-based telescopes have obtained images of Vesta for about two centuries, but they have not been able to see much detail on its surface.

Minor planet (4) Vesta was first sighted through a telescope on March 29, 1807 by Heinrich Wilhelm Matthaus Olbers (1758-1840). Subsequent observations determined that the planetary body has an orbital period of 3.63 years, with a semi-major axis of around 2.36 AUs (slightly closer than Ceres's 2.77 AUs) and an eccentricity of 0.090 and an inclination of 7.14 degrees from the plane of the ecliptic. Its orbit places Vesta in the Main Asteriod Belt, but the object more closely resembles a small planet or Earth's Moon than another asteroid.

Image credit: Vesta site

"Unlike Ceres, which orbits just around or beyond the Solar System's ice line, Vesta's surface is not icy, like Ceres, Vesta appears to be an evolved body. In 1972, basaltic rocks (made of solidified lava) were detected on Vesta's surface, which indicated that the planetary body had melted early in its past. Vesta appears to have been large enough and hot enough to melt internally from decaying radioactive elements as well as impacts so that lighter elements floated upwards from denser material to form layers towards its surface. As a result, Vesta "differentiated" into a relatively dense metallic core (of approximately 136 miles or 220 kilometers across), lighter mantle, and crust, like the rocky inner planets, many large planetary satellite's like the Earth's Moon, and probably most, if not all, of the newly named "dwarf planets" like Ceres."solstation.com