Named after the nineteenth century French solar astronomer Jules Janssen, this large crater whose diameter is nearly 200 km is perhaps best known for its 114 km long rille (Rima Janssen) which spans the western half of the crater and has the unique distinction of representing a rare example of a highland rille. As revealed by the image below, crater Janssen is characterized with low walls, a rough interior floor dominated by the above-named rille and the craterlets Janssen H, K and L north of center and the formations Janssen A and B to the east. Crater Fabricius is the large formation to the northeast whose wall is embedded with that of Janssen.