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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 20 Sep 2012 12:57:48 -0700 (PDT)
Message-ID: <201209201957.q8KJvmmx001636_at_zagami.jpl.nasa.gov>

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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Received on Thu 20 Sep 2012 03:57:48 PM PDT