[meteorite-list] NASA Dawn Spacecraft Sees Hydrated Minerals on Vesta

[Ron Baalke]

Sept. 20, 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: 12-334

NASA DAWN SPACECRAFT SEES HYDRATED MINERALS ON GIANT ASTEROID

WASHINGTON -- NASA's Dawn spacecraft has revealed the giant asteroid 
Vesta has its own version of ring around the collar. Two new papers, 
based on observations from the low-altitude mapping orbit of the Dawn 
mission, show volatile, or easily evaporated, materials have colored 
Vesta's surface in a broad swath around its equator. 

The volatiles were released from minerals likely containing water. 
Pothole-like features mark some of the asteroid's surface where the 
volatiles boiled off. Dawn did not find actual water ice at Vesta. 
However, it found evidence of hydrated minerals delivered by 
meteorites and dust in the giant asteroid's chemistry and geology. 
The findings appear Thursday in the journal Science. 

One paper, led by Thomas Prettyman, the lead scientist for Dawn's 
gamma ray and neutron detector (GRaND) at the Planetary Science 
Institute in Tucson, Ariz., describes how the instrument found 
signatures of hydrogen, likely in the form of hydroxyl or water bound 
to minerals in Vesta's surface. 

"The source of the hydrogen within Vesta's surface appears to be 
hydrated minerals delivered by carbon-rich space rocks that collided 
with Vesta at speeds slow enough to preserve their volatile content," 
said Prettyman. 

A complementary paper, led by Brett Denevi, a Dawn participating 
scientist at the Johns Hopkins University Applied Physics Laboratory 
in Laurel, Md., describes the presence of pitted terrain created by 
the release of the volatiles. 

Vesta is the second most massive member of our solar system's main 
asteroid belt. Dawn was orbiting at an average altitude of about 130 
miles (210 kilometers) above the surface when it obtained the data. 
Dawn left Vesta on Sept. 5 EDT (Sept. 4) and is on its way to a 
second target, the dwarf planet Ceres. 

Scientists thought it might be possible for water ice to survive near 
the surface around the giant asteroid's poles. Unlike Earth's moon, 
however, Vesta has no permanently shadowed polar regions where ice 
might survive. The strongest signature for hydrogen in the latest 
data came from regions near the equator, where water ice is not 
stable. 

In some cases, space rocks crashed into these deposits at high speed. 
The heat from the collisions converted the hydrogen bound to the 
minerals into water, which evaporated. Escaping water left holes as 
much as six-tenths of a mile (1 kilometer) wide and as deep as 700 
feet (200 meters). Seen in images from Dawn's framing camera, this 
pitted terrain is best preserved in sections of Marcia crater. 

"The pits look just like features seen on Mars, and while water was 
common on Mars, it was totally unexpected on Vesta in these high 
abundances," said Denevi. "These results provide evidence that not 
only were hydrated materials present, but they played an important 
role in shaping the asteroid's geology and the surface we see today." 

GRaND's data are the first direct measurements describing the 
elemental composition of Vesta's surface. Dawn's elemental 
investigation by the instrument determined the ratios of iron to 
oxygen and iron to silicon in the surface materials. The new findings 
solidly confirm the connection between Vesta and a class of 
meteorites found on Earth called the Howardite, Eucrite and Diogenite 
meteorites, which have the same ratios for these elements. In 
addition, more volatile-rich fragments of other objects have been 
identified in these meteorites, which supports the idea the 
volatile-rich material was deposited on Vesta. 

The Dawn mission is managed by NASA's Jet Propulsion Laboratory for 
the Science Mission Directorate in Washington. The spacecraft is as a 
project of the Discovery Program managed by NASA's Marshall Space 
Flight Center in Huntsville, Ala. The University of California, Los 
Angeles, is responsible for overall mission science. Orbital Sciences 
Corporation of Dulles, Va., designed and built the spacecraft. 

The framing cameras that saw the pitted terrain were developed and 
built under the leadership of the Max Planck Institute for Solar 
System Research, Katlenburg-Lindau, Germany, with contributions by 
the German Aerospace Center (DLR) Institute of Planetary Research, 
Berlin, and in coordination with the Institute of Computer and 
Communication Network Engineering, Braunschweig. The framing camera 
project is funded by NASA, the Max Planck Society and DLR. The gamma 
ray and neutron detector instrument was built by Los Alamos National 
Laboratory, N.M., and is operated by the Planetary Science Institute. 

To view new images and for more information about Dawn, visit: 

http://www.nasa.gov/dawn 
	
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