[meteorite-list] Dawn Mission Discovers Hydrogen on Giant Asteroid Vesta
From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 20 Sep 2012 13:12:25 -0700 (PDT)
NEWS RELEASE FROM THE PLANETARY SCIENCE INSTITUTE
Public Information Officer
Planetary Science Institute
fischer at psi.edu
Dawn mission discovers hydrogen on giant asteroid Vesta
Sept. 20, 2012, Tucson, Ariz. -- The first measurements of the elemental
composition of the surface of the giant asteroid Vesta indicate that
hydrogen was brought to the body by impactors, research by a team led by
Planetary Science Institute Senior Scientist Thomas H. Prettyman has shown.
Using data collected by the NASA Dawn mission's spacecraft's gamma ray and neutron
detector instrument - GRaND - as it circled the giant asteroid, researchers
also confirmed the elemental composition of the surface of Vesta matches
meteorites found on Earth believed to have originated from Vesta.
The hydrogen content of Vesta's regolith, or rocky surface materials, is
consistent with delivery of hydrogen-bearing, carbonaceous chondrite materials
to Vesta, Prettyman and co-authors report in a paper titled "Elemental
Mapping by Dawn Reveals Exogenic H in Vesta's Regolith" that appears
The highest concentrations of hydrogen were found in equatorial
regions, where water ice is not stable. The lowest amounts were found
within the giant, south-polar Rheasilvia impact basin. The amounts of
hydrogen and its association globally with broad, low albedo - low
reflective - regions on Vesta indicate the infall of carbonaceous chondrites
bearing hydrated minerals as the likely origin. A companion paper by
Brett Denevi of Johns Hopkins University Applied Physics Laboratory shows
pitted regions within young craters that formed due to high velocity impacts
into volatile-rich material.
"Where did the hydrogen from Vesta's surface come from? We ruled out the wind
of charged hydrogen particles streaming off the sun as a source, as well as
water ice within the top few feet of Vesta's surface," Prettyman said. "The
hydrated minerals appear to be delivered by carbon-rich space rocks that
collided with Vesta at speeds slow enough to preserve their volatile content."
GRaND's first elemental measurements of Vesta's surface showed the composition
matches howardite, eucrite and diogenite (HED) meteorites believed to
have been blasted off of Vesta, Prettyman said.
"The Vesta-HED connection was established long ago by comparing the spectrum of
reflected light for the HED meteorites with telescopic measurements of Vesta,"
he said. GRaND confirms this by showing that the abundances of iron and silicon
are consistent with HEDs.
Dawn orbited within 210 kilometers of Vesta, allowing GRaND a unique opportunity
to analyze the asteroid. "From a broader perspective, we are reporting the first
direct measurements of Vesta's elemental composition, which can only be
accomplished by getting very close to Vesta," Prettyman said. "It is unlikely
these measurements will be repeated any time soon."
Dawn left Vesta's orbit Sept. 4 and is making its way to a rendezvous with the
dwarf planet Ceres in early 2015.
The data acquired by GRaND are available to the public through the NASA
Planetary Data System.
Prettyman is lead author on the Science paper, which includes PSI co-authors
Naoyuki Yamashita, William C. Feldman, Pasquale Tricarico, Robert C. Reedy and
GRaND is operated and managed by the Planetary Science institute under the
leadership of Prettyman, who is also the lead for Geochemistry on Dawn. This
work is supported by NASA under a subcontract from the Jet Propulsion Laboratory
to the Planetary Science Institute. GRaND was built by Los Alamos National
Laboratory under Prettyman???s direction and supervision.
The Dawn mission to Vesta and Ceres 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.
Thomas H. Prettyman
prettyman at psi.edu
Mark V. Sykes
sykes at psi.edu
Received on Thu 20 Sep 2012 04:12:25 PM PDT