[meteorite-list] NASA's Dawn Sees New Surface Features on Giant Asteroid Vesta

[Ron Baalke]

March 21, 2012

Dwayne Brown 
Headquarters, Washington 
202-358-1726 
dwayne.c.brown at nasa.gov 

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

RELEASE: 12-091

NASA'S DAWN SEES NEW SURFACE FEATURES ON GIANT ASTEROID VESTA

WASHINGTON -- NASA's Dawn spacecraft has revealed unexpected details 
on the surface of the giant asteroid Vesta. New images and data 
highlight the diversity of Vesta's surface and reveal unusual 
geologic features, some of which were never previously seen on 
asteroids. 

Vesta is one of the brightest objects in the solar system and the only 
asteroid in the so-called main belt between Mars and Jupiter visible 
to the naked eye from Earth. Dawn found that some areas on Vesta can 
be nearly twice as bright as others, revealing clues about the 
asteroid's history. 

"Our analysis finds this bright material originates from Vesta and has 
undergone little change since the formation of Vesta over 4 billion 
years ago," said Jian-Yang Li, a Dawn participating scientist at the 
University of Maryland, College Park. "We're eager to learn more 
about what minerals make up this material and how the present Vesta 
surface came to be." 

Bright areas appear everywhere on Vesta but are most predominant in 
and around craters. The areas vary from several hundred feet to 
around 10 miles across. Rocks crashing into the surface of Vesta seem 
to have exposed and spread this bright material. This impact process 
may have mixed the bright material with darker surface material. 

While scientists had seen some brightness variations in previous 
images of Vesta from NASA's Hubble Space Telescope, Dawn scientists 
also did not expect such a wide variety of distinct dark deposits 
across its surface. The dark materials on Vesta can appear dark gray, 
brown and red. They sometimes appear as small, well-defined deposits 
around impact craters. They also can appear as larger regional 
deposits, like those surrounding the impact craters scientists have 
nicknamed the "snowman." 

"One of the surprises was the dark material is not randomly 
distributed," said David Williams, a Dawn participating scientist at 
Arizona State University, Tempe. "This suggests underlying geology 
determines where it occurs." 

The dark materials seem to be related to impacts and their aftermath. 
Scientists theorize carbon-rich asteroids could have hit Vesta at 
speeds low enough to produce some of the smaller deposits without 
blasting away the surface. 

Higher-speed asteroids also could have hit the asteroid's surface and 
melted the volcanic basaltic crust, darkening existing surface 
material. That melted conglomeration appears in the walls and floors 
of impact craters, on hills and ridges, and underneath brighter, more 
recent material called ejecta, which is material thrown out from a 
space rock impact. 

Vesta's dark materials suggest the giant asteroid may preserve ancient 
materials from the asteroid belt and beyond, possibly from the birth 
of the solar system. 

"Some of these past collisions were so intense they melted the 
surface," said Brett Denevi, a Dawn participating scientist at the 
Johns Hopkins University Applied Physics Laboratory in Laurel, Md. 
"Dawn's ability to image the melt marks a unique find. Melting events 
like these were suspected, but never before seen on an asteroid." 

Dawn launched in September 2007. It will reach its second destination, 
Ceres, in February 2015. 

"Dawn's ambitious exploration of Vesta has been going beautifully," 
said Marc Rayman, Dawn chief engineer at NASA's Jet Propulsion 
Laboratory (JPL) in Pasadena, Calif. "As we continue to gather a 
bounty of data, it is thrilling to reveal fascinating alien 
landscapes." 

Dawn's mission 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. 

To view the new images, visit: 

http://www.nasa.gov/dawn 
	
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