Space

June 3, 2013

NASA’s GRAIL mission solves mystery of moon’s surface gravity

NASA’s Gravity Recovery and Interior Laboratory mission has uncovered the origin of massive invisible regions that make the moon’s gravity uneven, a phenomenon that affects the operations of lunar-orbiting spacecraft.

Because of GRAIL’s findings, spacecraft on missions to other celestial bodies can navigate with greater precision in the future. GRAIL’s twin spacecraft studied the internal structure and composition of the moon in unprecedented detail for nine months. They pinpointed the locations of large, dense regions called mass concentrations, or mascons, which are characterized by strong gravitational pull. Mascons lurk beneath the lunar surface and cannot be seen by normal optical cameras.

GRAIL scientists found the mascons by combining the gravity data from GRAIL with sophisticated computer models of large asteroid impacts and known detail about the geologic evolution of the impact craters. The findings are published in the May 30 edition of the journal Science.

“GRAIL data confirm that lunar mascons were generated when large asteroids or comets impacted the ancient moon, when its interior was much hotter than it is now,” said Jay Melosh, a GRAIL co-investigator at Purdue University in West Lafayette, Ind., and lead author of the paper. “We believe the data from GRAIL show how the moon’s light crust and dense mantle combined with the shock of a large impact to create the distinctive pattern of density anomalies that we recognize as mascons.”

The origin of lunar mascons has been a mystery in planetary science since their discovery in 1968 by a team at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. Researchers generally agree mascons resulted from ancient impacts billions of years ago. It was not clear until now how much of the unseen excess mass resulted from lava filling the crater or iron-rich mantle upwelling to the crust.

On a map of the moon’s gravity field, a mascon appears in a target pattern. The bulls-eye has a gravity surplus. It is surrounded by a ring with a gravity deficit. A ring with a gravity surplus surrounds the bulls-eye and the inner ring. This pattern arises as a natural consequence of crater excavation, collapse and cooling following an impact. The increase in density and gravitational pull at a mascon’s bulls-eye is caused by lunar material melted from the heat of a long-ago asteroid impact.

“Knowing about mascons means we finally are beginning to understand the geologic consequences of large impacts,” Melosh said. “Our planet suffered similar impacts in its distant past, and understanding mascons may teach us more about the ancient Earth, perhaps about how plate tectonics got started and what created the first ore deposits.”

This new understanding of lunar mascons also is expected to influence planetary geology well beyond that of Earth and our nearest celestial neighbor.

“Mascons also have been identified in association with impact basins on Mars and Mercury,” said GRAIL principal investigator Maria Zuber of the Massachusetts Institute of Technology in Cambridge.

“Understanding them on the moon tells us how the largest impacts modified early planetary crusts.”

Launched as GRAIL A and GRAIL B in September 2011, the probes, renamed Ebb and Flow, operated in a nearly circular orbit near the poles of the moon at an altitude of about 34 miles (55 kilometers) until their mission ended in December 2012. The distance between the twin probes changed slightly as they flew over areas of greater and lesser gravity caused by visible features, such as mountains and craters,

and by masses hidden beneath the lunar surface.

JPL managed GRAIL for NASA’s Science Mission Directorate in Washington. The mission was part of the Discovery Program managed at NASA’s Marshall Space Flight Center in Huntsville, Ala. NASA’s Goddard Space Flight Center, in Greenbelt, Md., manages the Lunar Reconnaissance Orbiter. Operations of the spacecraft’s laser altimeter, which provided supporting data used in this investigation, is led by the Massachusetts Institute of Technology in Cambridge.

Lockheed Martin Space Systems in Denver built GRAIL.

 




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


 
 

 

Headlines January 28, 2015

News: Panel will propose new military retirement system - The long-awaited report on military compensation set to drop Thursday will propose fundamental changes to military retirement and health care benefits, according to several people familiar with the report. Source: DOD to request $585 billion for fiscal 2016 - The Department of Defense is preparing to submit a...
 
 

News Briefs January 28, 2015

Defense contractor to pay $2 million to settle claims A Northern California defense contractor will pay the federal government $2 million to settle claims about its manufacturing of parts for remote-controlled aircraft. The U.S. Attorney’s Office in Sacramento says Sacramento-based Composite Engineering Inc. agreed to pay the money to end allegations that it artificially inflated...
 
 
Navy photograph

USS Roosevelt marks 200,000 trap

Navy photograph An F/A-18F Super Hornet flown by Capt. Daniel Grieco, commanding officer of the aircraft carrier USS Theodore Roosevelt (CVN 71), and Capt. Benjamin Hewlett, deputy commander of Carrier Air Wing (CVW) 1, complet...
 

 
Navy photograph by PO1 William Larned

USS California returns from maiden deployment

Navy photograph by PO1 William Larned The Virginia-class attack submarine USS California (SSN 781) returns from its maiden deployment to its homeport at Naval Submarine Base New London. Under the command of Cmdr. Shawn Huey, Ca...
 
 
Army photograph

Army proves new watercraft capabilities

Army photograph Marine Corps assets are loaded onto the USNS Sgt. Matej Kocak (T-AK 3005), from an U.S. Army Landing Craft Utility, or LCU, USAV Port Hudson during port operations, at White Beach Naval Base, Jan. 22, 2015. Sold...
 
 

Orbital stockholders approve merger with ATK’s aerospace, defense groups

Orbital Sciences Corporation announced Jan. 27 that at a special meeting, the company’s stockholders voted overwhelmingly to approve the proposed merger with the Aerospace and Defense Groups of Alliant Techsystems Inc., pursuant to the definitive transaction agreement dated April 28, 2014. Approximately 99 percent of the votes cast at the special meeting voted in favor...
 




0 Comments


Be the first to 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>