Scientists Propose a New Twist on the Moon’s Largest Crater
For decades, the South Pole-Aitken (SPA) basin has stood as a giant, enigmatic scar on the Moon. Measuring more than 1,200 miles across, it is the planet’s largest known impact structure. A recent paper published in Nature challenges long-held assumptions about how this colossal crater formed, suggesting a southward, glancing blow rather than a direct, head-on collision. If confirmed, the idea could help explain why the Moon’s far side is peppered with large basins while the near side has a relatively smoother landscape.
The Shape Clue: A Teardrop Crater from a Glancing Hit
The study team examined the SPA’s peculiar teardrop shape and compared it with other giant basins across the solar system. Their conclusion: the crater’s asymmetric form points to a southward impact that gouged through the Moon’s crust and exposed heavier minerals beneath. This nuanced view of the event could alter how scientists interpret the Moon’s crustal structure and its thermal history in the early days of the Solar System.
Why This Matters for Lunar Interior and Evolution
Understanding the SPA’s formation is not just a matter of naming a historic impact. It ties into big questions about the Moon’s magma ocean era — a period when a largely molten mantle and crust defined the early Moon. Heavier minerals settled toward the interior, while lighter materials formed the crust. Yet a reservoir of KREEP material (potassium, rare earth elements, and phosphorus) lingered in the fading magma ocean, concentrating in pockets that eventually hardened into a patchwork crust. The new interpretation helps explain a striking asymmetry: KREEP-enriched material is far more abundant on the near side than on the far side.
Near-Side vs. Far-Side Asymmetry: A Clue to the Moon’s Hidden History
Researchers propose that, as the Moon cooled, the crust thickened more on the far side, while the magma ocean below was squeezed outward toward the near side—an effect likened to toothpaste being squeezed from a tube. The result: the near side accumulated more of the deeper, radioactive elements and KREEP-rich material, while the far side retained a thinner crust with a different internal layout. The latest findings suggest the SPA lies at a boundary where these contrasting regions met, potentially holding keys to how the Moon’s interior has evolved over billions of years.
Implications for Artemis and Human Exploration
With NASA’s Artemis program targeting the Moon’s south polar region, these insights arrive at a timely moment. The down-range rim of the SPA basin is a prime landing area for early crewed missions, described as a natural laboratory where ejecta from deep within the Moon’s interior could be sampled. Artemis missions are expected to bring back material that helps scientists decode the Moon’s volcanic past and interior dynamics. The study’s authors argue that the SPA region could yield more about the Moon’s early evolution than previously anticipated, offering context for how the interior and crust interacted as the magma ocean cooled.
What Comes Next: Samples, Tests, and Open Questions
Astute observers note that scientific knowledge remains provisional. The new thesis invites further modeling, more comparative data from other giant basins, and, crucially, lunar samples that Artemis will help obtain. Analyzing material from the SPA region on Earth could illuminate the exact composition and distribution of KREEP and other rock types, refining our view of the Moon’s interior structure and crustal development. As Jeffrey Andrews-Hanna, the study’s lead author from the University of Arizona, emphasizes, these samples may reveal more about the Moon’s early evolution than previously thought.
A Moment of Discovery for Moon Science
The Moon has long invited speculation about its origin and evolution. This latest work illustrates how new interpretations of existing structures can reshape our understanding of planetary formation. If the South Pole-Aitken basin is indeed the product of a southward impact that uncovered deeper materials, the SPA may become a central piece of the puzzle about how our nearest celestial neighbor came to look the way it does today — and why the Artemis era could transform our knowledge of the Moon more quickly than anticipated.
