Dawn Sees Hydrated Minerals on Giant Asteroid

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 PHONE 818-354-5011
http://www.jpl.nasa.gov

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

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

News release: 2012-297 Sept. 20, 2012

Dawn Sees Hydrated Minerals on Giant Asteroid

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.php?release=2012-297&cid=release_2012-297

PASADENA, Calif. – NASA's Dawn spacecraft has revealed that 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 that volatile, or easily evaporated materials, have colored
Vesta's surface in a broad swath around its equator.

Pothole-like features mark some of the asteroid's surface where the volatiles, likely water, released
from hydrated minerals boiled off. While Dawn did not find actual water ice at Vesta, there are signs
of hydrated minerals delivered by meteorites and dust evident in the giant asteroid's chemistry and
geology. The findings appear today 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 based 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 the main asteroid belt. The orbit at which these data
were obtained averaged about 130 miles (210 kilometers) above the surface. Dawn left Vesta earlier
this month, on Sept. 4 PDT (Sept. 5 EDT), and is now on its way to its 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, other space rocks crashed into these deposits later at high speed. The heat from the
collisions converted the hydrogen bound to the minerals into water, which evaporated. The holes that
were left as the water escaped stretch as much as 0.6 miles (1 kilometer) across and go down 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, but 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 that the volatile-rich
material was deposited on Vesta.

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

The framing cameras 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 the Max Planck Society, DLR and NASA. The gamma ray and neutron detector instrument
was built by Los Alamos National Laboratory, N.M., and is operated by the Planetary Science
Institute, Tucson, Ariz.

JPL is a division of the California Institute of Technology, Pasadena.

To view new images and for more information about Dawn, visit: http://www.nasa.gov/dawn and
http://dawn.jpl.nasa.gov .

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