Study suggests moon's largest crater formed from northern impact
A new analysis indicates that the moon's South Pole-Aitken basin, its oldest and largest crater, likely formed from an asteroid impact originating from the north rather than the south. This finding challenges previous assumptions about the moon's early history. The discovery could enhance the value of NASA's upcoming Artemis III mission to the basin's rim.
The South Pole-Aitken (SPA) basin, located on the moon's far side, formed about 4.3 billion years ago, shortly after the moon itself. Previously, astronomers believed a massive asteroid struck from a southerly direction below the south pole, creating a crater thousands of kilometers wide and 12 kilometers deep, with thicker piles of ancient rubble toward the northern rim.
However, researchers led by Jeffrey Andrews-Hanna at the University of Arizona have analyzed the basin's shape and found it tapers southward in a teardrop pattern, suggesting the impact came from the north. "We traced the outline of the South Pole-Aitken basin in every way we could," Andrews-Hanna said. "We used topography, gravity, models of the thickness of the crust. We tried different choices of how to trace the basin and no matter how we traced it, it was always a shape that’s tapering towards the south."
To support this, the team compared the SPA basin to craters on Mars, such as Hellas and Utopia, where impact directions are better known. This northern origin would alter understandings of how the moon's interior material scattered during its cooling from a magma ocean, exposing deep interior rocks around the basin's rim that are otherwise inaccessible.
The finding adds significance to NASA's Artemis III mission, which plans to send astronauts to the SPA basin rim to search for water ice. Mahesh Anand at the Open University, UK, noted, "It can tell you more about the interior of the moon, of which we don’t have many samples at all. It’s a bonus." Confirmation will require returning samples from the basin to Earth, Anand added.
The research appears in Nature (DOI: 10.1038/s41586-025-09582-y).