[meteorite-list] Dawn Reality-Checks Telescope Studies of Asteroids

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 27 Sep 2013 11:00:06 -0700 (PDT)
Message-ID: <201309271800.r8RI06lq024028_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2013-293

Dawn Reality-Checks Telescope Studies of Asteroids
Jet Propulsion Laboratory
September 27, 2013

Tantalized by images from NASA's Hubble Space Telescope and ground-based
data, scientists thought the giant asteroid Vesta deserved a closer
look. They got a chance to do that in 2011 and 2012, when NASA's Dawn
spacecraft orbited the giant asteroid, and they were able to check
earlier conclusions. A new study involving Dawn's observations during
that time period demonstrates how this relationship works with Hubble
and ground-based telescopes to clarify our understanding of a solar
system object.

"Since the vast majority of asteroids can only be studied remotely by
ground-based and space-based facilities, confirming the accuracy of such
observations using in-situ measurements is important to our exploration
of the solar system," said Vishnu Reddy, the lead author of a paper
published recently in the journal Icarus. Reddy is based at the
Planetary Science Institute in Tucson, Ariz., and the Max Planck
Institute for Solar System Research in Katlenburg-Lindau, Germany.

In the paper, Reddy and other members of Dawn's framing camera team
describe how up-close observations of Vesta have confirmed and provided
new insights into more than 200 years of Earth-based observations.

Vesta, the second most massive asteroid in the main asteroid belt,
differs from most garden-variety asteroids in having a crust, mantle and
core like our Earth. Early ground-based observations of Vesta, which was
discovered in 1807, showed that Vesta's color and surface composition
changed as it rotated around its axis. Astronomers using NASA's Infrared
Telescope Facility at Mauna Kea in Hawaii saw distinct compositional
units. It wasn't until Dawn arrived at Vesta that scientists determined
the fine details and the exact distribution of these color variations,
and the difference in composition between these regions.

"A generation of scientific questions framed on the basis of
lower-resolution data have been resolved by visiting Vesta with Dawn,"
said Dawn Principal Investigator Christopher Russell, who is based at
the University of California, Los Angeles. "We chose to go to Vesta
because the ground-based telescopes and, later, Hubble told us it was an
interesting place. That was true, but we needed Dawn to discern the
mineral distribution and history of Vesta's surface. We now know how
these data sets tie together and complement each other. This will help
us in our telescopic studies of other members of our solar system."

One particularly useful comparison for future work on asteroids or other
solar system objects involves comparing Dawn's framing camera data to
data from Hubble. With Hubble, astronomers first saw the giant impact
basin near the south pole of Vesta and also identified numerous bright
and dark features on Vesta that correspond to different compositional
units. It wasn't until Dawn's framing camera provided high-resolution
views of Vesta that scientists were able to see the detailed contours of
the giant impact basin that came to be called Rheasilvia and saw how
bright the brightest materials were and how dark the dark materials
were. Dawn's observations also showed that there was an older,
overlapping giant impact basin under Rheasilvia. The bright materials
appear to be pristine rocks native to Vesta, while the carbon-rich dark
material appears to have been brought to Vesta from afar.

"When Dawn got to Vesta, it showed us how accurate Hubble's data were
about Vesta," said Planetary Science Institute research scientist
Jian-Yang Li, the Dawn participating scientist who mapped out the
surface of Vesta using Hubble data. "And it also showed us how Vesta was
so much more interesting up-close."

Other paper co-authors include Robert Gaskell and Lucille Le Corre of
the Planetary Science Institute.

Launched in 2007, Dawn orbited Vesta for more than a year, departing in
September 2012. Dawn is now on its way to the dwarf planet Ceres and
will arrive there in early 2015.

The Dawn mission to Vesta and Ceres is managed by NASA's Jet Propulsion
Laboratory, a division of the California Institute of Technology in
Pasadena, for NASA's Science Mission Directorate, Washington. The
University of California, Los Angeles, is responsible for overall Dawn
mission science. The Dawn framing cameras were developed and built under
the leadership of the Max Planck Institute for Solar System Research,
Katlenburg-Lindau, Germany; with significant contributions by DLR German
Aerospace Center 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.

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

Alan Fischer 520-382-0411
Planetary Science Institute, Tucson, Ariz.
fischer at psi.edu

2013-293
Received on Fri 27 Sep 2013 02:00:06 PM PDT