Rimae Mersenius is seen here stretching from the centre of the image
downwards into a network of parallel rilles. Mersenius Rille is actually
nearly 140 miles long, but only 1 mile wide. Mersenius (51 mi) is the
crater near the south-western end of the rille, seen here near the bottom
of the image, left of the centre. Towards the north-east (top-right) are
craters Mersenius P (25 mi) and Mersenius S (9 mi) which appears to have
quite high crater walls illuminated brightly by the rising Sun in this
image. Just South of it, near the Mersenius Rille, is similar-sized
Mersenius C appearing very bright here.
The large crater in the centre-right is Gassendi (67 mi) featuring a double central mountain 1,200 metres high. Gassendi A (20 mi) overlaps its crater walls to the North.
Eastwards (right of the image) is Mare Humorum.
The following image was taken a month later. The use of a narrowband red filter helped in revealing some more detail in the same region: