NASA Twin Spacecraft Create Most Accurate Gravity Map Of Moon

        NASA Twin Spacecraft Create Most Accurate Gravity Map Of Moon

PR Newswire

WASHINGTON, Dec. 5, 2012

WASHINGTON, Dec. 5, 2012 /PRNewswire-USNewswire/ -- Twin NASA probes orbiting
the moon have generated the highest resolution gravity field map of any
celestial body.

(Logo: http://photos.prnewswire.com/prnh/20081007/38461LOGO)

The new map, created by the Gravity Recovery and Interior Laboratory (GRAIL)
mission, is allowing scientists to learn about the moon's internal structure
and composition in unprecedented detail. Data from the two washing
machine-sized spacecraft also will provide a better understanding of how Earth
and other rocky planets in the solar system formed and evolved.

The gravity field map reveals an abundance of features never before seen in
detail, such as tectonic structures, volcanic landforms, basin rings, crater
central peaks, and numerous simple, bowl-shaped craters. Data also show the
moon's gravity field is unlike that of any terrestrial planet in our solar
system.

These are the first scientific results from the prime phase of the mission,
and they are published in three papers in the journal Science.

"What this map tells us is that more than any other celestial body we know of,
the moon wears its gravity field on its sleeve," said GRAIL principal
investigator Maria Zuber of the Massachusetts Institute of Technology in
Cambridge. "When we see a notable change in the gravity field, we can sync up
this change with surface topography features such as craters, rilles or
mountains."

According to Zuber, the moon's gravity field preserves the record of impact
bombardment that characterized all terrestrial planetary bodies and reveals
evidence for fracturing of the interior extending to the deep crust and
possibly the mantle. This impact record is preserved, and now precisely
measured, on the moon.

The probes revealed the bulk density of the moon's highland crust is
substantially lower than generally assumed. This low bulk crustal density
agrees well with data obtained during the final Apollo lunar missions in early
1970s, indicating that local samples returned by astronauts are indicative of
global processes.

"With our new crustal bulk density determination, we find that the average
thickness of the moon's crust is between 21 and 27 miles (34 and 43
kilometers), which is about 6 to 12 miles (10 to 20 kilometers) thinner than
previously thought," said GRAIL co-investigator Mark Wieczorek of the Institut
de Physique du Globe de Paris. "With this crustal thickness, the bulk
composition of the moon is similar to that of Earth. This supports models
where the moon is derived from Earth materials that were ejected during a
giant impact event early in solar system history."

The map was created by the spacecraft transmitting radio signals to define
precisely the distance between them as they orbit the moon in formation. As
they fly over areas of greater and lesser gravity caused by both visible
features, such as mountains and craters, and masses hidden beneath the lunar
surface, the distance between the two spacecraft will change slightly.

"We used gradients of the gravity field in order to highlight smaller and
narrower structures than could be seen in previous datasets," said Jeff
Andrews-Hanna,a GRAIL guest scientist with the Colorado School of Mines in
Golden. "This data revealed a population of long, linear, gravity anomalies,
with lengths of hundreds of kilometers, crisscrossing the surface. These
linear gravity anomalies indicate the presence of dikes, or long, thin,
vertical bodies of solidified magma in the subsurface. The dikes are among the
oldest features on the moon, and understanding them will tell us about its
early history."

While results from the primary science mission are just beginning to be
released, the collection of gravity science by the lunar twins continues.
GRAIL's extended mission science phase began Aug. 30 and will conclude Dec.
17. As the end of mission nears, the spacecraft will operate at lower orbital
altitudes above the moon.

When launched in September 2011, the probes were named GRAIL A and B. They
were renamed Ebb and Flow in January by elementary students in Bozeman, Mont.,
in a nationwide contest. Ebb and Flow were placed in a near-polar,
near-circular orbit at an altitude of approximately 34 miles (55 kilometers)
on Dec. 31, 2011, and Jan. 1, 2012.

NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the mission for
NASA's Science Mission Directorate in Washington. GRAIL is part of the
Discovery Program managed at NASA's Marshall Space Flight Center in
Huntsville, Ala. Lockheed Martin Space Systems of Denver built the spacecraft.

To view the lunar gravity map, visit:
http://bit.ly/grailtour

For more information about the mission, visit:
http://www.nasa.gov/grail

SOURCE NASA

Website: http://www.nasa.gov
Contact: Dwayne Brown, Headquarters, Washington, +1-202-358-1726,
dwayne.c.brown@nasa.gov; D.C. Agle, Jet Propulsion Laboratory, Pasadena,
Calif., +1-818-393-9011, agle@jpl.nasa.gov; Sarah McDonnell, Massachusetts
Institute of Technology, Cambridge, +1-617-253-8923, s_mcd@mit.edu