Gassendi 17.6°S, 40.1°W

The crater Gassendi is a prominent example of a crater that was altered after the impact, over a long period of time by post-impact volcanism and lava flows. It lies on the northern edge of Mare Humorum and has a diameter of 101 km and a depth of about 1.9 km. Dating the formation of the basin from measurements made by the European Moon probe Smart-1 gives a value of about 3.6 billion years. When the lava flows flooded the Humorum impact basin, large parts of the crater floor were also filled with lava. The crater wall and a few peaks of the central mountains are still visible. The whole floor of the crater is crossed by Rimae Gassendi, a complicated system of rilles, fissures and grabens. Located on the floor are the craterlets Gassendi P (2 km, in the northwest) and Gassendi M (3 km, in the southeast). The northern crater wall is breached by Gassendi A (33 km). The western wall shows a triangular landslip (similar to the one in the crater Plato).

The Helmet 16.7°S, 31.5°W

The Helmet is a low rise in the lunar crust with a diameter of about 60 km and a very low height of less than 200 metres. The structure is classified as a volcanic megadome. The surface is covered in rocky ridges and exhibits a few small craters. On colour-coded multispectral images of the region the structure stands out strinkingly like a ‘beacon’ from the surrounding mare lava through its brilliant colours.