[meteorite-list] Dawn Sees 'Young' Surface on Vesta

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 31 Oct 2012 12:17:18 -0700 (PDT)
Message-ID: <201210311917.q9VJHIw4003086_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2012-342

Dawn Sees 'Young' Surface on Giant Asteroid
Jet Propulsion Laboratory
October 31, 2012

Like a Hollywood starlet constantly retouching her makeup, the giant
asteroid Vesta is constantly stirring its outermost layer to present a
young face. Data from NASA's Dawn mission show that a form of weathering
that occurs on the moon and other airless bodies we've visited in the
inner solar system does not alter Vesta's outermost layer in the same
way. Carbon-rich asteroids have also been splattering dark material on
Vesta's surface over a long span of the body's history. The results are
described in two papers released today in the journal Nature.

"Dawn's data allow us to decipher how Vesta records fundamental
processes that have also affected Earth and other solar system bodies,"
said Carol Raymond, Dawn deputy principal investigator at NASA's Jet
Propulsion Laboratory, Pasadena, Calif. "No object in our solar system
is an island. Throughout solar system history, materials have exchanged
and interacted."

Over time, soils on Earth's moon and asteroids such as Itokawa have
undergone extensive weathering in the space environment. Scientists see
this in the accumulation of tiny metallic particles containing iron,
which dulls the fluffy outer layer. Dawn's visible and infrared mapping
spectrometer (VIR) and framing camera detected no accumulation of such
tiny particles on Vesta, and this particular protoplanet, or
almost-planet, remains bright and pristine.

Nevertheless, the bright rays of the youngest features on Vesta are seen
to degrade rapidly and disappear into background soil. Scientists know
frequent, small impacts continually mix the fluffy outer layer of broken
debris. Vesta also has unusually steep topography relative to other
large bodies in the inner solar system, which leads to landslides that
further mix surface material.

"Getting up close and familiar with Vesta has reset our thinking about
the character of the uppermost soils of airless bodies," said Carle
Pieters, one of the lead authors and a Dawn team member based at Brown
University, Providence, R.I. "Vesta 'dirt' is very clean, well mixed and
highly mobile."

Early pictures of Vesta showed a variety of dramatic light and dark
splotches on Vesta's surface. These light and dark materials were
unexpected and now show the brightness range of Vesta is among the
largest observed on rocky bodies in our solar system.

Dawn scientists suspected early on that bright material is native to
Vesta. One of their first hypotheses for the dark material suggested it
might come from the shock of high-speed impacts melting and darkening
the underlying rocks or from recent volcanic activity. An analysis of
data from VIR and the framing camera has revealed, however, that the
distribution of dark material is widespread and occurs both in small
spots and in diffuse deposits, without correlation to any particular
underlying geology. The likely source of the dark material is now shown
to be the carbon-rich material in meteoroids, which are also believed to
have deposited hydrated minerals from other asteroids on Vesta.

To get the amount of darkening we now see on Vesta, scientists on the
Dawn team estimate about 300 dark asteroids with diameters between 0.6
to 6 miles (1 and 10 kilometers) likely hit Vesta during the last 3.5
billion years. This would have been enough to wrap Vesta in a blanket of
mixed material about 3 to 7 feet (1 to 2 meters) thick.

"This perpetual contamination of Vesta with material native to elsewhere
in the solar system is a dramatic example of an apparently common
process that changes many solar system objects," said Tom McCord, the
other lead author and a Dawn team member based at the Bear Fight
Institute, Winthrop, Wash. "Earth likely got the ingredients for life -
organics and water - this way."

Launched in 2007, Dawn spent more than a year investigating Vesta. It
departed in September 2012 and is currently on its way to the dwarf
planet Ceres.

JPL manages the Dawn mission 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. The
University of California at Los Angeles (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. The California Institute of Technology in Pasadena
manages JPL for NASA.

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.
jccook at jpl.nasa.gov

2012-342
Received on Wed 31 Oct 2012 03:17:18 PM PDT


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