NASA Dawn Mission Reveals Secrets of Large  Asteroid
NASA's Dawn spacecraft provides the first orbital analysis of the giant asteroid Vesta, yielding new insights into its creation with terrestrial planets and Earth's moon.
PASADENA,  Calif. - NASA's Dawn spacecraft has provided researchers with the first orbital analysis of the giant asteroid  Vesta, yielding new insights into its creation and kinship with terrestrial  planets and Earth's moon.Vesta  now has been revealed as a special fossil of the early solar system with a more  varied, diverse surface than originally thought. Scientists have confirmed a  variety of ways in which Vesta more closely resembles a small planet or Earth's  moon than another asteroid. Results appear in today's edition of the journal  Science."Dawn's  visit to Vesta has confirmed our broad theories of this giant asteroid's  history, while helping to fill in details it would have been impossible to know  from afar," said Carol Raymond, deputy principal investigator at NASA's  Jet Propulsion Laboratory in Pasadena, Calif. "Dawn's residence at Vesta  of nearly a year has made the asteroid's planet-like qualities obvious and  shown us our connection to that bright orb in our night sky."Scientists  now see Vesta as a layered, planetary building block with an iron core - the  only one known to survive the earliest days of the solar system. The asteroid's  geologic complexity can be attributed to a process that separated the asteroid  into a crust, mantle and iron core with a radius of approximately 68 miles (110  kilometers) about 4.56 billion years ago. The terrestrial planets and Earth's  moon formed in a similar way.Dawn  observed a pattern of minerals exposed by deep gashes created by space rock  impacts, which may support the idea the asteroid once had a subsurface magma  ocean. A magma ocean occurs when a body undergoes almost complete melting, leading  to layered building blocks that can form planets. Other bodies with magma  oceans ended up becoming parts of Earth and other planets.Data  also confirm a distinct group of meteorites found on Earth did, as theorized,  originate from Vesta. The signatures of pyroxene, an iron- and magnesium-rich  mineral, in those meteorites match those of rocks on Vesta's surface. These  objects account for about 6 percent of all meteorites seen falling on Earth.This  makes the asteroid one of the largest single sources for Earth's meteorites.  The finding also marks the first time a spacecraft has been able to visit the  source of samples after they were identified on Earth.Scientists  now know Vesta's topography is quite steep and varied. Some craters on Vesta  formed on very steep slopes and have nearly vertical sides, with landslides  occurring more frequently than expected.Another  unexpected finding was that the asteroid's central peak in the Rheasilvia basin  in the southern hemisphere is much higher and wider, relative to its crater  size, than the central peaks of craters on bodies like our moon. Vesta also bears  similarities to other low-gravity worlds like Saturn's small icy moons, and its  surface has light and dark markings that don't match the predictable patterns  on Earth's moon."We  know a lot about the moon and we're only coming up to speed now on Vesta,"  said Vishnu Reddy, a framing camera team member at the Max Planck Institute for  Solar System Research in Germany and the University of North Dakota in Grand  Forks. "Comparing the two gives us two storylines for how these fraternal  twins evolved in the early solar system."Dawn has  revealed details of ongoing collisions that battered Vesta throughout its  history. Dawn scientists now can date the two giant impacts that pounded Vesta's  southern hemisphere and created the basin Veneneia approximately 2 billion  years ago and the Rheasilvia basin about 1 billion years ago. Rheasilvia is the  largest impact basin on Vesta."The  large impact basins on the moon are all quite old," said David O'Brien, a  Dawn participating scientist from the Planetary Science Institute in Tucson,  Ariz. "The fact that the largest impact on Vesta is so young was  surprising."Launched in 2007, Dawn began exploring Vesta in mid-2011. The spacecraft will  depart Vesta on August 26 for its next study target, the dwarf planet Ceres, in  2015.Dawn's mission to Vesta and Ceres is  managed by JPL for NASA's Science Mission Directorate in Washington. Dawn is a  project of the directorate's Discovery Program managed by NASA's Marshall Space  Flight Center in Huntsville, Ala. UCLA is responsible for overall Dawn mission  science. Orbital Sciences Corp. in Dulles, Va., designed and built the  spacecraft. The German Aerospace Center, the Max Planck Institute for Solar  System Research, the Italian Space Agency and the Italian National  Astrophysical Institute are international partners on the mission team. The  California Institute of Technology in Pasadena manages JPL for NASA.For images  and videos related to the findings, visit:http://www.nasa.gov/mission_pages/dawn/news/dawn20120510.html.For more information about the Dawn mission, visit:http://www.nasa.gov/dawnandhttp://dawn.jpl.nasa.gov.