Space

December 5, 2012

NASA twin spacecraft create most accurate gravity map of Moon

Twin NASA probes orbiting the moon have generated the highest resolution gravity field map of any celestial body.

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.

 




All of this week's top headlines to your email every Friday.


 
 

 

Ninth Boeing GPS IIF reaches orbit, sends first signals

Boeing Global Positioning System (GPS) IIF satellites are steadily replenishing the orbiting constellation, continuing to improve reliability and accuracy for users around the world. The ninth GPS IIF reached orbit about three hours, 20 minutes after launching today aboard a United Launch Alliance (ULA) Delta IV rocket from Cape Canaveral Air Force Station, Fla., and...
 
 
NASA/JPL-Caltech photograph

NASA asteroid hunter spacecraft data available to public

NASA/JPL-Caltech photograph The NEOWISE spacecraft viewed comet C/2014 Q2 (Lovejoy) for a second time on January 30, 2015, as the comet passed through the closest point to our sun along its 14,000-year orbit, at a solar distanc...
 
 
NASA and ESA image

NASA’s Hubble, Chandra find clues that may help identify dark matter

NASA and ESA image Here are images of six different galaxy clusters taken with NASA’s Hubble Space Telescope (blue) and Chandra X-ray Observatory (pink) in a study of how dark matter in clusters of galaxies behaves when t...
 

 
SOFIA

SOFIA finds missing link between supernovae, planet formation

NASA/CXO/Herschel/VLA/Lau et al SOFIA data reveal warm dust (white) surviving inside a supernova remnant. The SNR Sgr A East cloud is traced in X-rays (blue). Radio emission (red) shows expanding shock waves colliding with surr...
 
 
NASA/JPL-Caltech/Univ. of Arizona

NASA’s Opportunity Mars Rover finishes marathon

NASA/JPL-Caltech/Cornell Univ./USGS/Arizona State Univ. This illustration depicts some highlights along the route as NASA’s Mars Exploration Rover Opportunity drove as far as a marathon race during the first 11 years and ...
 
 
NASA/MSFC/Emmett Given

NASA announces teams for 2015 Human Exploration Rover Challenge

NASA/MSFC/Emmett Given Pedaling across a simulated alien landscape of rock, craters and shifting sand is one of the nearly 90 teams of high school, college and university students from across the United States and around the wo...
 




One Comment



Leave a Reply

Your email address will not be published. Required fields are marked *

You may use these HTML tags and attributes: <a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <strike> <strong>