NASA's Grail Mission Solves Mystery of Moon's Surface Gravity

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Source:  NASA RELEASE 13-164
Excerpt: ...NASA's Gravity Recovery and Interior Laboratory (GRAIL) 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 ... pinpointed the locations of large, dense regions called mass concentrations, or mascons, which are characterized by strong gravitational pull. ...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 (JPL) 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. ..."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. ...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.... 

 http://www.nasa.gov/home/hqnews/2013/may/HQ_13-164_Grail.html

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