Big Impact, Big Consequences: Rethinking the Moon’s oldest scar
For decades, scientists have grappled with the South Pole–Aitken basin, the Moon’s colossal imprint that stretches nearly 2,000 kilometres across. A landmark study led by planetary scientist Jeffrey Andrews-Hanna from the University of Arizona, published in Nature, offers a fresh view: the asteroid that carved this massive crater may have approached from the north rather than the south. This shift in perspective helps explain why the Moon’s near side and far side look so different, and why certain radioactive materials are enriched in specific regions.
The shape that tells a story: teardrop, not a flat scar
The research hinges on the basin’s distinctive teardrop geometry, which narrows toward the south. By analyzing the crater’s outline and subsurface structure, the team deduced an northern approach for the impacting body. This single detail reshapes how scientists think about early lunar bombardment and how the Moon’s crust responded to the collision.
What the impact revealed: radioactive clues from the Moon’s interior
One of the most intriguing consequences of the giant crash is the exposure and redistribution of radioactive-rich materials known as KREEP — potassium, rare earth elements and phosphorus. These elements formed in the Moon’s molten past and settled unevenly as the surface cooled. The impact effectively created a “window” into the interior, concentrating heat-producing KREEP materials on one side. The result, researchers propose, was a kick-start to volcanic activity that left dark, mare-like plains on the near side while leaving the far side thick, rugged, and densely cratered.
Why KREEP matters for lunar science
KREEP-enriched zones hold clues about the Moon’s thermal evolution. The presence and distribution of these elements help scientists reconstruct the timing of volcanic episodes, heat flow, and differentiation within the lunar crust. If the northern origin hypothesis holds, it could also explain why the Moon’s two hemispheres exhibit pronounced geological and mineralogical contrasts today.
The study’s implications for future missions
NASA’s Artemis program plans to land astronauts near the South Pole, not far from the South Pole–Aitken basin rim. This proximity makes the region a tantalizing target for sampling ancient debris blasted into space by the colossal impact. By bringing back rocks and soils rich in KREEP and other trace elements, missions may reveal how heat and material moved through the Moon after the collision. Such findings could refine models of lunar formation and the Earth–Moon relationship, shedding light on solar system evolution as a whole.
What this means for our picture of the Moon
The discovery adds a new layer to the Moon’s complex history. The northern origin of the giant impact provides a plausible mechanism for the Moon’s asymmetric crust and its long-running volcanic legacy. In short, the Moon’s greatest crash was not just a deep crater — it was a driver of geologic processes that shaped the Moon we study today.
Looking ahead: a reimagined map of lunar history
As researchers continue to refine their models and analyze samples from future missions, the new interpretation invites a more nuanced view of how early impacts sculpt planetary bodies. The Moon’s ancient scars remain powerful records of a dynamic and violent youth, offering insights not only into lunar science but also into the violent beginnings shared by rocky planets across the cosmos.
