Comparative imagery of nine asteroids. With a diameter of about 330 miles (530 kilometers), Vesta dwarfs all of these small bodies. Many scientists think it's a protoplanet left over from the solar system's first few million years. Image: NASA/JPL-Caltech/JAXA/ESA
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.
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]
"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," Russell told SPACE.com via email. "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."
"We have just started exploring Vesta’s secrets, and I’m sure other intriguing results will come along shortly," Marchi added.
The protoplanet Vesta
With a diameter of about 330 miles (530 kilometers), Vesta is roughly as wide as the U.S. state of Arizona. In the main asteroid belt, only the dwarf planet Ceres is bigger.
The $466 million Dawn spacecraft arrived at the huge asteroid in July 2011 to help unlock its many secrets. One of the probe's main missions, researchers said, is to determine if Vesta is indeed a long-surviving protoplanet — a body left over from the solar system's first few million years, many of which later coalesced to form rocky planets such as Earth and Mars.
Scientists got this idea mainly by examining fallen howardite-eucrite-diogenite (or HED) meteorites, which are thought to come from Vesta. The new Dawn results strongly support the protoplanet notion — by confirming that Vesta is indeed the HED meteorites' parent body, for starters.