Topography (top) and surface gravity (bottom) for
Mare Serenitatis. The gravity shows a plateau and thus a substantial
near-surface contribution to the mascon. Also apparent is the smaller
mascon Mare Vaporum in the lower left and center part of the figure.
Data from Lunar Prospector
A mascon is a region on the surface of the Moon where the gravitational
pull is slightly higher than normal due to the presence of dense rock. "Mascon"
is short for "mass concentration." Mascons were first detected by spacecraft
orbiting the Moon and are associated with basalt-filled impact basins such as Mare Imbrium.