These maps of the moon show the "Bouguer" gravity anomalies as measured by NASA's GRAIL mission. Bouguer gravity is what remains from the gravity field when the attraction of surface topography is removed, and therefore represents mass anomalies inside the moon due to either variations in crustal thickness or crust or mantle density.
Red areas have stronger gravity, while blue areas have weaker gravity.
NASA's Jet Propulsion Laboratory in Pasadena, Calif., manages the GRAIL mission for NASA's Science Mission Directorate in Washington. The Massachusetts Institute of Technology, Cambridge, is home to the mission's principal investigator, Maria Zuber. GRAIL is part of the Discovery Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems in Denver built the spacecraft. The California Institute of Technology in Pasadena manages JPL for NASA.
For more information about GRAIL, please visit http://grail.nasa.gov.