[meteorite-list] Dawn Spurs Rewrite of Vesta's Story

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?release=2013-321

It's Complicated: Dawn Spurs Rewrite of Vesta's Story
Jet Propulsion Laboratory
November 06, 2013

Just when scientists thought they had a tidy theory for how the giant 
asteroid Vesta formed, a new paper from NASA's Dawn mission suggests the 
history is more complicated. 

If Vesta's formation had followed the script for the formation of rocky 
planets like our own, heat from the interior would have created distinct, 
separated layers of rock (generally, a core, mantle and crust). In that 
story, the mineral olivine should concentrate in the mantle. 

However, as described in a paper in this week's issue of the journal Nature, 
that's not what Dawn's visible and infrared mapping spectrometer (VIR) 
instrument found. The observations of the huge craters in Vesta's southern 
hemisphere that exposed the lower crust and should have excavated the 
mantle did not find evidence of olivine there. Scientists instead found 
clear signatures of olivine in the surface material in the northern hemisphere. 

"The lack of pure olivine in the deeply excavated basins in Vesta's southern 
hemisphere and its unexpected discovery in the northern hemisphere indicate 
a more complex evolutionary history than inferred from models of Vesta 
before Dawn arrived," said Maria Cristina De Sanctis, Dawn co-investigator 
and VIR leader at the National Institute for Astrophysics in Rome, Italy. 

Perhaps Vesta only underwent partial melting, which would create pockets 
of olivine rather than a global layer. Perhaps the exposed mantle in Vesta's 
southern hemisphere was later covered by a layer of other material, which 
prevented Dawn from seeing the olivine below it. 

"These latest findings from Dawn stimulate us to test some different ideas 
about Vesta's origin," said Carol Raymond, Dawn's deputy principal investigator 
at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "They also show 
us what additional information we can learn by going into orbit around 
places like Vesta to complement the bits that come to us as meteorites 
or observations from long distances." 

Dawn is currently cruising toward its second destination, the dwarf planet 
Ceres, which is the biggest member of the main asteroid belt between Mars 
and Jupiter. It will arrive at Ceres in early 2015. 

The Dawn mission to Vesta and Ceres is managed by JPL for NASA's Science 
Mission Directorate, Washington, D.C. It is a project of the Discovery 
Program managed by NASA's Marshall Space Flight Center, Huntsville, Ala. 
UCLA is responsible for overall Dawn mission science. Orbital Sciences 
Corporation of Dulles, Va., designed and built the Dawn spacecraft. The 
visible and infrared mapping spectrometer was provided by the Italian 
Space Agency and is managed by Italy's National Institute for Astrophysics, 
Rome, in collaboration with Selex Galileo, where it was built.

Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook at jpl.nasa.gov 

2013-321