The largest and oldest impact feature on the Moon, and one of the largest in the Solar System. It is centred at −56° lat., 180° E long., on the lunar farside. It takes its name from the fact that the lunar south pole is on its southern rim and the 130-km crater Aitken is on its northern rim. The Basin consists of three main rings with a maximum diameter of some 2400 km and is up to 13 km deep. It is overlain with more recent impacts and contains smoother mare regions resulting from volcanic flooding. The Basin’s surface is enriched in mafic minerals (enhanced amounts of iron and magnesium), perhaps derived from the Moon’s lower crust. The Basin may have been formed by a glancing blow over 4 billion years ago, before the other lunar basins.

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