[meteorite-list] NASA Dawn Mission Reveals Secrets of Large Asteroid

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 10 May 2012 12:11:49 -0700 (PDT)
Message-ID: <201205101911.q4AJBnDU003947_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.cfm?release=2012-132

NASA Dawn Mission Reveals Secrets of Large Asteroid
Jet Propulsion Laboratory
May 09, 2012

PASADENA, Calif. - NASA's Dawn spacecraft has provided researchers with
the first orbital analysis of the giant asteroid Vesta, yielding new
insights into its creation and kinship with terrestrial planets and
Earth's moon.

Vesta now has been revealed as a special fossil of the early solar
system with a more varied, diverse surface than originally thought.
Scientists have confirmed a variety of ways in which Vesta more closely
resembles a small planet or Earth's moon than another asteroid. Results
appear in today's edition of the journal Science.

"Dawn's visit to Vesta has confirmed our broad theories of this giant
asteroid's history, while helping to fill in details it would have been
impossible to know from afar," said Carol Raymond, deputy principal
investigator at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"Dawn's residence at Vesta of nearly a year has made the asteroid's
planet-like qualities obvious and shown us our connection to that bright
orb in our night sky."

Scientists now see Vesta as a layered, planetary building block with an
iron core - the only one known to survive the earliest days of the solar
system. The asteroid's geologic complexity can be attributed to a
process that separated the asteroid into a crust, mantle and iron core
with a radius of approximately 68 miles (110 kilometers) about 4.56
billion years ago. The terrestrial planets and Earth's moon formed in a
similar way.

Dawn observed a pattern of minerals exposed by deep gashes created by
space rock impacts, which may support the idea the asteroid once had a
subsurface magma ocean. A magma ocean occurs when a body undergoes
almost complete melting, leading to layered building blocks that can
form planets. Other bodies with magma oceans ended up becoming parts of
Earth and other planets.

Data also confirm a distinct group of meteorites found on Earth did, as
theorized, originate from Vesta. The signatures of pyroxene, an iron-
and magnesium-rich mineral, in those meteorites match those of rocks on
Vesta's surface. These objects account for about 6 percent of all
meteorites seen falling on Earth.

This makes the asteroid one of the largest single sources for Earth's
meteorites. The finding also marks the first time a spacecraft has been
able to visit the source of samples after they were identified on Earth.

Scientists now know Vesta's topography is quite steep and varied. Some
craters on Vesta formed on very steep slopes and have nearly vertical
sides, with landslides occurring more frequently than expected.

Another unexpected finding was that the asteroid's central peak in the
Rheasilvia basin in the southern hemisphere is much higher and wider,
relative to its crater size, than the central peaks of craters on bodies
like our moon. Vesta also bears similarities to other low-gravity worlds
like Saturn's small icy moons, and its surface has light and dark
markings that don't match the predictable patterns on Earth's moon.

"We know a lot about the moon and we're only coming up to speed now on
Vesta," said Vishnu Reddy, a framing camera team member at the Max
Planck Institute for Solar System Research in Germany and the University
of North Dakota in Grand Forks. "Comparing the two gives us two
storylines for how these fraternal twins evolved in the early solar
system."

Dawn has revealed details of ongoing collisions that battered Vesta
throughout its history. Dawn scientists now can date the two giant
impacts that pounded Vesta's southern hemisphere and created the basin
Veneneia approximately 2 billion years ago and the Rheasilvia basin
about 1 billion years ago. Rheasilvia is the largest impact basin on Vesta.

"The large impact basins on the moon are all quite old," said David
O'Brien, a Dawn participating scientist from the Planetary Science
Institute in Tucson, Ariz. "The fact that the largest impact on Vesta is
so young was surprising."

Launched in 2007, Dawn began exploring Vesta in mid-2011. The spacecraft
will depart Vesta on August 26 for its next study target, the dwarf
planet Ceres, in 2015.

Dawn's mission to Vesta and Ceres is managed by JPL 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. 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 images and videos related to the findings, visit:
http://www.nasa.gov/mission_pages/dawn/news/dawn20120510.html .

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

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

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown at nasa.gov

2012-132
Received on Thu 10 May 2012 03:11:49 PM PDT