Moonwatch
A pair of double-concentric craters.
There are a number of Moon features with macabre names. The Lake of Death (Lacus Mortis) and the Marsh of Decay (Palus Putredinis) spring to mind, not to mention this month’s Moonwatch target, the Marsh of Epidemics (Palus Epidemiarum).
It lies in the southern gap between the touching maria,
Humorum and Nubium. Its dark lava stands out well against the highland region to the south and although it has irregular boundaries, with a bit of imagination you can visualise a rough, east-west elongated diamond shape.
Its most notable feature is the lava-flooded form of 60km
Capuanus along the southern edge. This crater juts into Epidemiarum, appearing to stretch northwest towards the marsh’s centre. The effect is enhanced by extensions to the western and northwestern ramparts of Capuanus, which give the impression that the crater is evaporating into the marsh material. Impressive lunar domes can be found on the floor of Capuanus, best seen when the lighting is oblique.
Opposite Capuanus, situated on the northern border of the marsh are the twin-like craters
Campanus and Mercator, both 48km. The similarity between these craters is quite striking. They are close enough that their outer ramparts join to form a narrow valley that links Palus Epidemiarum to Mare Nubium. Look out for the impressive concentric grooves of Rimae
Hippalus to the west and northwest of Campanus. These are associated with Mare Humorum and run parallel to its eastern border.
The western part of the marsh is dominated by the flooded 25km crater Ramsden. This is associated with its own set of crevasses known as
Rimae Ramsden. The most obvious section of Rimae Ramsden appears to the north of Ramsden itself, where two sections can be seen running in parallel. Further cracks may be seen between Ramsden and Capuanus. As ever, viewing when the terminator is near is the best strategy as this will emphasise any irregularities in the floor of the marsh.
The eastern border of Palus Epidemiarum is complicated. It’s marked by the 41km crater
Cichus. The residual material littering Epidemiarum’s floor between Cichus and Capuanus hints at two heavily eroded and unnamed ghost craters.
Also in the east of the marsh is the singular but wide crevasse
Rima Hesiodus. This runs for about 275km from a point just north of the northern edge of Capuanus to a point on the edge of 43km crater Hesiodus, on the southern border of Mare Nubium. The 15km Hesiodus A abuts the rim of Hesiodus and is remarkable because it’s a double-concentric crater: it has both an outer and inner rim. Palus Epidemiarum itself boasts a double-concentric crater in the form of 7km Marth, which can be seen between Ramsden and the Campanus-Mercator pair. The inner rims of both these double-concentric craters mentioned are thought to have volcanic origins.
So, despite its decidedly unappealing name, the treasures to be found in and around the Marsh of Epidemics make it worth a closer look.
“Hesiodus A is remarkable because it’s a double concentric crater with both an inner and outer rim”