About 4.3 billion years ago, an asteroid collided with the Moon’s far side in a glancing blow which left behind an oblong basin as deep as 8.2km.

Now, new research has revealed the giant asteroid that created the South Pole-Aitken basin (SPA), the Moon’s largest crater, slammed into the lunar surface from a northerly direction.

The team compared SPA’s oblong shape to other giant impact basins in the solar system which have independent evidence about the motion of the projectile which created them.

Their new analysis reveals that SPA’s shape narrows toward the south, indicating the impact came from the north.

This means the down range end of the basin, closer to the Moon’s South Pole, should be covered by a thick layer of material which was kicked up from the lunar interior by the impact.

The South Pole-Aitken basin on the Moon (left), the Hellas basin on Mars (centre) and the Sputnik basin on Pluto (right) all formed in oblique impacts. Their outlines get narrower in the down-range direction (bottom) like a raindrop or an avocado. Elevations range from low (blue) to high (orange). Credit: Jeff Andrews-Hanna/University of Arizona/NASA

When humans return to the Moon again for NASA’s Artemis III mission, they will be the first humans to explore the lunar South Pole region.

“This means that the Artemis missions will be landing on the down-range rim of the basin – the best place to study the largest and oldest impact basin on the Moon where most of the ejecta, material from deep within the Moon’s interior, should be piled up,” says Jeffrey Andrews-Hanna, a planetary scientist at the University of Arizona, USA who led the study published in Nature.