The Moon’s oldest wound may trace back to a northern strike
Billions of years ago, a colossal asteroid plowed into the Moon, carving out the South Pole–Aitken basin—the solar system’s biggest and oldest known impact site. A new study led by planetary scientist Jeffrey Andrews-Hanna of the University of Arizona, published in Nature, argues that the hit approached from the Moon’s north rather than from the south as previously thought. This single event didn’t just sculpt a crater; it helped forge the Moon’s geological and volcanic character that persists today.
The basin stretches roughly 1,931 kilometers from north to south and about 1,600 kilometers east to west. Its teardrop shape curves toward the south, a telltale sign that the asteroid struck from a northern trajectory. This insight reframes how scientists understand the Moon’s crust and its uneven geological evolution in the wake of one monumental collision.
How the crash revealed the Moon’s hidden interior
The impact excavated deep into the lunar crust, exposing material concentrated with heat-producing elements known as KREEP—potassium, rare earth elements, and phosphorus. KREEP materials congregated in the Moon’s early molten layers and later settled unevenly, forming a kind of chemical “window” into the interior. The researchers argue that this redistribution helped drive volcanic activity along the near-side’s dark, smooth plains. In contrast, the far side retained a thicker, more rugged crust speckled with craters, highlighting how a single event can shape planetary asymmetry.
Why radioactive clues matter for future missions
NASA’s Artemis program plans to land astronauts near the lunar south pole, right along the rim of the South Pole–Aitken basin. Scientists expect this region to hold debris and volcanic material ejected during the ancient collision, including potentially radioactive minerals tied to KREEP. By returning samples from this area, future missions could confirm how heat and materials moved through the Moon after the impact, offering clues about both lunar evolution and Earth’s own early environment.
Implications for lunar science and exploration
The study strengthens a narrative in which the Moon’s two sides diverge markedly in appearance and composition due to early, violent events. The northern-origin crash didn’t just write a large scar across the lunar surface; it likely fueled the volcanic and magmatic processes that generated the Moon’s near-side plains and far-side ruggedness.
As researchers plan further investigations, revisiting the Moon’s ancient scars may reveal more about how heat, material, and celestial dynamics shaped Earth’s neighbor. The South Pole–Aitken basin stands as a natural archive—one whose contents could answer longstanding questions about planetary formation, differentiation, and the intertwined fate of the Earth–Moon system.
Looking ahead
With Artemis and other lunar missions targeting the south pole, scientists anticipate a wave of samples and observations that could verify the northern-origin crash hypothesis and uncover the role of early impacts in setting the Moon’s long-term geology. Each new specimen has the potential to illuminate how a single, colossal collision can influence a world for billions of years.
