This still image features a free-air gravity map of the Moon's southern latitudes developed from data returned by the Gravity Recovery and Interior Laboratory (GRAIL) mission. If the Moon were a perfectly smooth sphere of uniform density, the gravity map would be a single, featureless color, indicating that the force of gravity at a given elevation was the same everywhere. But like other rocky bodies in the solar system, including Earth, the Moon has both a bumpy surface and a lumpy interior. Spacecraft in orbit around the Moon experience slight variations in gravity caused by both of these irregularities. The free-air gravity map shows deviations from mean gravity, measured in milliGals, a unit of acceleration. On the map, purple is at the low end of the range, at around -400 mGals, and red is at the high end near +400 mGals. Yellow denotes the mean. This image illustrates the very good correlation between the gravity map and topographic features such as peaks and craters, as well as the mass concentration lying beneath the large Schr繹dinger basin in the center of the frame. The terrain in the image is based on Lunar Reconnaissance Orbiter (LRO) altimeter and camera data.