The Moon: South Pole-Aitken Basin

Steven Dutch, Professor Emeritus, Natural and Applied Sciences, University of Wisconsin - Green Bay

This view of the Moon is full of extremes: the biggest, oldest and deepest impact basin on the Moon, the highest elevations and lowest depressions, and the coldest spots found not only on the Moon, but the entire Solar System.

The South Pole-Aitken Basin is named for two landmarks on opposite sides of the basin: the lunar south pole and the crater Aitken. It is the huge depression in the center of the view. The topography near the lunar south pole is too complex to plot the pole with a symbol, but it is midway between the left and right edges of the moon and one quarter of the way from bottom to top. There is very little in this view that a terrestrial observer might find familiar. Only the bottom quarter of the view is visible from Earth and none of the familiar dark plains, or maria, are visible.

Some of the highest points on the Moon are near the lunar south pole. The moon's axis has very little tilt so the sun does not appear to move north and south in the lunar sky as it does on earth. Some of the lunar peaks may be "peaks of eternal light," or peaks that are almost always in sunlight. However, as the Moon goes around the Earth, different parts of the peak are sunlit so that there is no one point that is permanently lit.

Craters near the lunar south pole, however, never get sun at all. The only source of heat in those craters is sunlight reflected from distant peaks, light reflected from the Earth and other planets, light reflected by fine dust orbiting the Sun, and heat from the moon's interior. Some of the deepest spots in those craters are as cold as Pluto. There has been speculation that, if there is any water on the Moon at all, it may be ice in those eternally dark craters.

Possible Coloring

Labeled Features

The very large circle approximately outlines the South Pole-Aitken Basin. The craters Clavius, Tycho and Schickard are visible from Earth. Bailly is on the extreme edge of the Moon as seen from Earth. Mare Orientale (Eastern Sea) is on the extreme eastern edge of the Moon as seen from Earth.

Many craters on the far side rival some of the maria on the near side in size but are not filled by lava. The names commemorate:

The large circle labeled Unnamed is obvious on the topographic map but has not yet been identified as an impact basin. It may be a very old and heavily degraded basin.

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Created 20 September 2009, Last Update 15 January 2020