[meteorite-list] Dawn: Vesta Got Special Delivery of Hydrated Minerals

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 26 Sep 2012 11:32:56 -0700 (PDT)
Message-ID: <201209261832.q8QIWuRA028511_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2012-301

Dawn: Vesta Got Special Delivery of Hydrated Minerals
Jet Propulsion Laboratory
September 26, 2012

The mechanism that incorporates water into the terrestrial planets is a
matter of extensive debate for planetary scientists. Now, observations
of the giant asteroid Vesta by NASA's Dawn mission suggest that hydrated
materials were delivered to it mainly through a buildup of small
particles during an epoch when the solar system was rich in dust. This
is a radically different process from the way hydrated materials have
been deposited on the moon and may have implications for the formation
of terrestrial planets, including the delivery of the water that formed
Earth's ocean. Maria Cristina De Sanctis and the Dawn team present the
scenarios today at the European Planetary Science Congress in Madrid,
Spain.

"Vesta's surface shows distinct areas enriched with hydrated materials,"
said De Sanctis, of the Italian National Institute for Astrophysics in
Rome. "These regions are not dependent on solar illumination or
temperature, as we find in the case of the moon. The uneven distribution
is unexpected and indicates ancient processes that differ from those
believed to be responsible for delivering water to other airless bodies,
like the moon."

A team led by De Sanctis studied data from Dawn's visible and infrared
mapping spectrometer, which complement recently reported data on
hydrogen distribution from Dawn's gamma ray and neutron detector. Their
analysis showed large regional concentrations of hydroxyl - a hydrogen
and an oxygen atom bound together - clearly associated with geological
features, including ancient, highly-cratered terrains and a crater named
Oppia.

Hydroxyl on the surface of the moon is thought to be created
continuously by the interaction of protons from the solar wind with the
top 10 feet (few meters) of the lunar surface, or regolith. Highest
concentrations are found in areas near the lunar poles and in
permanently shadowed craters where it is very cold. By contrast, the
distribution of hydroxyl on Vesta is not dependent on significant
shadowing or unusual cold temperatures. It is also stable over time, so
its origin does not appear to be due to short-term processes.

The hydroxyl-rich regions on Vesta broadly correspond to its oldest
surfaces. Around relatively large and young impact craters, hydroxyl
detections are weak or absent, suggesting that the delivery of the
substance is not an ongoing process.

The evidence from Dawn's visible and infrared mapping spectrometer
suggests that much of Vesta's hydroxyl was delivered by small particles
of primitive material, less than a few centimeters in diameter, over a
time-limited period. This period may have occurred during the primordial
solar system, around the time water is believed to have accumulated on
Earth, or during the Late Heavy Bombardment, when collisions with space
rocks would have produced a significant amount of dust.

However, this is not the whole story of hydrated materials on Vesta. The
Oppia Crater is hydroxyl-rich, but not covered with the primitive dark
material. This suggests there is more than one mechanism at work for
depositing hydroxyl on Vesta's surface.

"The origin of Vesta's hydroxyl is certainly complex and possibly not
unique: there could be various sources, like formation of hydroxyl
actually on Vesta, in addition to the primordial impactors," said De
Sanctis. "Vesta is providing new insights into the delivery of hydrous
materials in the main asteroid belt, and may offer new scenarios on the
delivery of hydrous minerals in the inner solar system, suggesting
processes that may have played a role in the formation of terrestrial
planets."

Following more than a year at Vesta, Dawn departed in September 2012 for
the dwarf planet Ceres, where it will arrive in 2015. Dawn's mission to
Vesta and Ceres is managed by NASA's Jet Propulsion Laboratory,
Pasadena, Calif., for NASA's Science Mission Directorate in Washington.
JPL is a division of the California Institute of Technology in Pasadena.
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 Dawn visible and
infrared (VIR) mapping spectrometer was built by Selex Galileo and the
Italian National Institute for Astrophysics.

For more information about Dawn, visit http://www.nasa.gov/dawn and
http://dawn.jpl.nasa.gov/ .

Jia-Rui C. Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jia-rui.c.cook at jpl.nasa.gov

Anita Heward 011-44-7756-034243
European Planetary Science Congress, Madrid, Spain
anita.heward at europlanet-eu.org

2012-301
Received on Wed 26 Sep 2012 02:32:56 PM PDT