Geological Chronicle
Mare Australe (Latin for 'Southern Sea') is a 997-kilometer-wide lunar mare located in the Moon's southeastern hemisphere. Straddling the boundary between the near side and the far side at 38.9° S, 93.0° E, the eastern half of the mare lies on the lunar far side. Observers on Earth can view the feature during periods of favorable lunar libration. The underlying impact basin formed during the Pre-Nectarian epoch, making it one of the older major impact structures on the Moon.
Unlike continuous basalt sheets such as Mare Imbrium or Mare Serenitatis, Mare Australe has an uneven, fragmented surface. Meteorite impacts degraded and broke down the original Pre-Nectarian basin before major volcanism occurred. During the Upper Imbrian epoch, eruptions of dark volcanic basalt reached the surface and settled into topographic lows, forming isolated dark patches separated by lighter highland material.
Much of the basalt within Mare Australe lines the interiors of pre-existing impact craters. Prominent examples include Jenner crater and Lamb crater, whose floors are submerged beneath flat volcanic lava while their raised rims remain visible. Oblique photography from the Apollo 14 and Apollo 15 missions mapped these flooded craters alongside surrounding features such as Abel, Gernsback, Donner, and Gum, documenting how localized basalt flooding reshaped this ancient portion of the lunar crust.