Mare Humorum. Several connections exist to Oceanus Procellarum to the north. The rather large crater to the north of the mare is Gassendi. The crater on the southwestern rim of the basin is Doppelmayer. The light grey feature that protrudes into the mare from the southeast is Promontorium Kelvin.
It was not sampled by the Apollo program, so a precise age has not been determined. However, geological mapping indicates that it is intermediate in age between the Imbrium and Nectaris Basins, suggesting an age of about 3.9 billion years. Humorum Basin is filled with a thick layer of mare basalt, believed to exceed 3 kilometers in thickness at the center of the basin.
A mass concentration (mascon), or gravitational high, was identified in the center of Mare Humorum from Doppler tracking of the five Lunar Orbiter spacecraft in 1968. The mascon was confirmed and mapped at higher resolution with later orbiters such as Lunar Prospector and GRAIL.