A new map of the Moon's gravity field, created by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, provides a detailed view of the Moon's many impact craters, evidence for ancient volcanic structures, and new estimates of the thickness of the lunar crust. Scientists announced the results from the first phase of the GRAIL mission at the AGU Fall Meeting; the results are also reported in three papers in the journal Science. GRAIL, launched in September 2011, consists of two satellites that send signals to each other. When a region of stronger gravity pulls on one satellite more than the other, the distance between the two changes. By measuring changes in the distance between the two satellites, researchers can create a map of the Moon's gravity field. The same method is used by the twin satellites of NASA's Gravity Recovery and Climate Experiment mission to measure Earth's gravity field.