FROM: NASA
WASHINGTON -- 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.
Spacecraft images, 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
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 surface bear evidence of contamination from
space rocks bombarding Vesta's surface. 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 ultrasensitive 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 -10 degrees Fahrenheit (-23 degrees Celsius) in the
sunniest spots to as cold as -150 degrees Fahrenheit (-100 degrees
Celsius) in the shadows. This is the lowest temperature measurable by
Dawn. 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 (JPL) 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- (530-kilometer-) wide 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.
