Dawn Reveals Secrets of Giant Asteroid Vesta

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Jia-Rui C. Cook 818-354-0850
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Dwayne Brown 202-358-1726
NASA Headquarters, Washington
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News release: 2012-117 April 25, 2012

Dawn Reveals Secrets of Giant Asteroid Vesta

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-117&cid=release_2012-117

PASADENA, Calif. – Findings from NASA's Dawn spacecraft reveal new details about the giant
asteroid Vesta, including its varied surface composition, sharp temperature changes and clues to its
internal structure. The findings were presented today at the European Geosciences Union meeting in
Vienna, Austria, and will help scientists better understand the early solar system and processes that
dominated its formation.

Images from Dawn's framing camera and visible and infrared mapping spectrometer, taken 420
miles (680 kilometers) and 130 miles (210 kilometers) above the surface of the asteroid, show a
variety of surface mineral and rock patterns. Coded false-color images help scientists better
understand Vesta's composition and enable them to identify material that was once molten below the
asteroid's surface.

Researchers also see breccias, which are rocks fused during impacts from space debris. Many of the
materials seen by Dawn are composed of iron- and magnesium-rich minerals, which often are found
in Earth's volcanic rocks. Images also reveal smooth pond-like deposits, which might have formed
as fine dust created during impacts settled into low regions.

"Dawn now enables us to study the variety of rock mixtures making up Vesta's surface in great
detail," said Harald Hiesinger, a Dawn participating scientist at Münster University in Germany.
"The images suggest an amazing variety of processes that paint Vesta's surface."

At the Tarpeia crater near the south pole of the asteroid, Dawn imagery revealed bands of minerals
that appear as brilliant layers on the crater's steep slopes. The exposed layering allows scientists to
see farther back into the geological history of the giant asteroid.

The layers closer to the asteroid's surface bear evidence of contamination from space rocks
bombarding Vesta. Layers below preserve more of their original characteristics. Frequent landslides
on the slopes of the craters also have revealed other hidden mineral patterns.

"These results from Dawn suggest Vesta's 'skin' is constantly renewing," said Maria Cristina De
Sanctis, lead of the visible and infrared mapping spectrometer team based at Italy's National Institute
for Astrophysics in Rome.

Dawn has given scientists a near 3-D view into Vesta's internal structure. By making ultra-sensitive
measurements of the asteroid's gravitational tug on the spacecraft, Dawn can detect unusual densities
within its outer layers. Data now show an anomalous area near Vesta's south pole, suggesting denser
material from a lower layer of Vesta has been exposed by the impact that created a feature called the
Rheasilvia basin. The lighter, younger layers coating other parts of Vesta's surface have been blasted
away in the basin.

Dawn obtained the highest-resolution surface temperature maps of any asteroid visited by a
spacecraft. Data reveal temperatures can vary from as warm as minus 10 degrees Fahrenheit (minus
23 degrees Celsius) in the sunniest spots to as cold as minus 150 degrees Fahrenheit (minus 100
degrees Celsius) in the shadows. This is the lowest temperature measurable by Dawn's visible and
infrared mapping spectrometer. These findings show the surface responds quickly to illumination
with no mitigating effect of an atmosphere.

"After more than nine months at Vesta, Dawn's suite of instruments has enabled us to peel back the
layers of mystery that have surrounded this giant asteroid since humankind first saw it as just a
bright spot in the night sky," said Carol Raymond, Dawn deputy principal investigator at NASA's Jet
Propulsion Laboratory in Pasadena, Calif. "We are closing in on the giant asteroid's secrets."

Launched in 2007, Dawn began its exploration of the approximately 330-mile-wide (530-kilometers)
asteroid in mid-2011. The spacecraft's next assignment will be to study the dwarf planet Ceres in
2015. These two icons of the asteroid belt have been witness to much of our solar system's history.

Dawn's mission 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.

To view the new images and for more information about Dawn, visit: http://www.nasa.gov/dawn .

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