Rima Hyginus 7.4°N, 7.8°E

Rima Hyginus is an extraordinary feature and, together with Rimae Triesnecker, is the best-known of all rilles. It consists of two linear sections, each of about 11 km in length, and is interrupted in the centre by the crater Hyginus (11 km, 7.8°N, 6.3°E). Hyginus is extended on the north by an unnamed small crater of about 4 km in diameter.

Both sections of the rille are about 400 m deep. The eastern section runs nearly parallel to Rima Ariadaeus, whereas the western section bends at the crater Hyginus by about 35° towards the north. This section is interrupted by nine craterlets, which lie directly in the rille. Rima Hyginus is probably an old lava channel and the craterlets may have been responsible for repeated eruptions of volcanic ash. This suspicion is strengthened by the fact that there are many nearby areas that are coated with dark volcanic ash (they are DMD regions). The crater Hyginus itself also appears to be of volcanic origin, because there is no form of crater wall and the floor is absolutely flat and level – it appears as if it were a cylinder punched out of the lunar surface.

About 35 km north of the crater Hyginus lies a small mountain, that appears spiral, rather like the letter ‘e’. The mountain has the former official name of ‘Schneckenberg’ (‘Snail Mountain’, at 9.0°N, 6.5°E).