Geological Chronicle
Located to the west of Mare Humorum in the southwestern part of the Moon, Mersenius spans 84.46 kilometers in diameter and is 2.3 kilometers deep. Formed during the Nectarian period between 3.92 and 3.85 billion years ago, the crater has a heavily worn rim that is especially low along its northern section. The crater Mersenius N lies across the southwestern rim.
Basaltic lava flooded the interior of Mersenius, bulging upward into a convex dome with an estimated height of 450 meters relative to the floor edges. This domed profile most likely formed by lava upwelling beneath the surface. Several tiny craters and at least two faint rilles cross the floor, which features little in the way of a central peak.
To the east of the crater on the surface and edges of Mare Humorum lies a rille system designated Rimae Mersenius. These rilles run generally parallel to the north-northeast for about 230 kilometers. Nearby, the satellite feature Mersenius M forms a concentric, double-walled crater.
The crater was named after the seventeenth-century French mathematician and physicist Marin Mersenne. Its designation was formally adopted by the International Astronomical Union in 1935.