A NASA probe that has been visiting an asteroid since July has recorded images scientists say is proof the asteroid has a mineral make up more like that of Earth or Mars than a typical asteroid. Images from the Dawn space probe show differences in rock composition on the Vesta asteroid that are evidence of it's transition from asteroid to terrestrial-like planet.

"Vesta's iron core makes it special and more like terrestrial planets than a garden-variety asteroid," Carol Raymond, Dawn's deputy principal investigator at NASA's Jet Propulsion Laboratory, Pasadena, Calif said.

"The distinct compositional variation and layering that we see at Vesta appear to derive from internal melting of the body shortly after formation, which separated Vesta into crust, mantle and core."

Vesta appears in a rainbow-colored palette in the new images obtained by the Dawn spacecraft. The colors, assigned by scientists to show different rock or mineral types, reveal Vesta to be a world of many varied, well-separated layers and ingredients. Vesta is unique among asteroids visited by spacecraft to date in having such wide variation, supporting the notion that it is transitional between the terrestrial planets -- like Earth, Mercury, Mars and Venus -- and its asteroid siblings.

In images from Dawn's framing camera, the colors reveal differences in the rock composition associated with material ejected by impacts and geologic processes, such as slumping, that have altered the asteroid's surface. In other words, because of its iron-core, Vesta is more like a planet than an asteroid.

Dawn scientists presented the new images at the American Geophysical Union meeting in San Francisco on Monday, Dec. 5. Dawn launched in September 2007 and arrived at Vesta on July 15, 2011. Following a year at Vesta, the spacecraft will depart in July 2012 for the dwarf planet Ceres, where it will arrive in 2015.