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Asteroid Vesta: Is it really an asteroid?

The humongous asteroid Vesta is actually a protoplanet left over from the early days of our solar system, new observations from a NASA space probe suggest. 

By Mike WallMike Wall / May 10, 2012

Global, colorized and hill-shaded digital terrain model of the ancient protoplanet Vesta, based on data gathered by NASA's Dawn spacecraft.

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New observations from a NASA spacecraft show that the huge asteroid Vesta is a battered protoplanet left over from the solar system's early days, with a unique mix of characteristics unknown from any other space rock.

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Scientists had thought that Vesta, the second-largest body in the main asteroid belt between Mars and Jupiter, probably started down a planet-forming path shortly after the solar system's birth. Data gathered by NASA's Dawn probe have now confirmed that suspicion, researchers announced in a raft of studies that came out today (May 10) in the journal Science.

"We now know that Vesta is the only intact, layered planetary building block surviving from the very earliest days of the solar system," Dawn deputy principal investigator Carol Raymond, of NASA's Jet Propulsion Laboratory in Pasadena, Calif., told reporters today. 

The other objects like Vesta, researchers added, were probably incorporated into full-fledged planets or destroyed by collisions long ago.  [Photos: Asteroid Vesta by Dawn Probe]

Some surprises

"Those studying meteorites that have fallen to Earth, many from Vesta, had produced a theory on the evolution of the solar system and what Vesta should be made of," said Dawn principal investigator Chris Russell of UCLA, lead author of one of the six new Science papers.

"They were very, very right," Mr. Russell told SPACE.com via e-mail. "This is good, because we can now use that model to understand more about the solar system."

But Dawn has also delivered some surprising new results. The gigantic Rheasilvia basin at Vesta's south pole, for example, apparently was created by a massive impact just 1 billion years ago or so — long after the solar system's collision-filled "shooting gallery" stage is thought to have ended.

"An age of about 1 billion years for Rheasilvia is unexpectedly young," Simone Marchi of the Southwest Research Institute in Boulder, Colo., lead author of another of the new papers, said in a statement. "This result has important implications for our understanding of the evolution of Vesta, its asteroid family and the inner main asteroid belt in general."

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