Gravity maps of the Moon. Gravity anomaly maps of the Moon as obtained by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission. The gravity anomalies (red) suggest variations in how different lunar features formed, highlighting variations in crustal thickness or crust or mantle density. Red areas have stronger gravity, while blue areas have weaker gravity. The colour-coded key is at top right, with the 'Bouguer gravity' measured in milliGals (mGal). According to theory, magma rose from the Moon's interior to flood low lying areas with lava (molten rock). These images show data from the GRAIL probes which operated in lunar orbit from March to December 2012. Image published in 2012.