South Pole–Aitken basin
The South Pole–Aitken basin is a giant, ancient impact basin on the Moon's far side, about 2,500 kilometres across.
The South Pole–Aitken basin is one of the largest known impact structures in the Solar System. It stretches about 2,500 kilometres from near the Moon's south pole to the crater Aitken and reaches depths of roughly 6 to 8 kilometres. It is thought to have formed early in lunar history, perhaps more than 4 billion years ago.
The impact was so large that it may have dug into the Moon's lower crust or even its mantle. Orbital measurements show its floor is richer in iron and in the mineral pyroxene than the surrounding highlands, supporting this idea.
China's Chang'e 4 rover, which landed in 2019, became the first spacecraft to explore the basin's surface, and Chang'e 6 brought back the first samples from inside it in 2024. Dating material from the basin helps pin down when the largest lunar impacts took place, which is key to understanding the bombardment history of the inner Solar System.
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