Mersenius (Moon)

Named after Mersenne, Marin Mersenius - French mathematician, physicist (1588-1648).

Mersenius is a lunar crater that is located to the west of the Mare Humorum, in the southwestern part. To the southwest is the crater Cavendish, and to the south-southeast lies Liebig. Mersenius is 84 kilometers in diameter and 2.3 kilometers deep. It is from the Nectarian period, 3.92 to 3.85 billion years ago. (wikipedia entry)

A crater is a circular depression likely created by an impact event. On the Moon they are named after deceased scientists, polar explorers, astronauts or cosmonauts.