Giant northern asteroid crash made the Moon's surface radioactive, new study suggests

Moon’s Biggest Crash Came from the North, Leaving a Radioactive Mark (Image: Canva)

Billions of years ago, there was a huge impact that transformed the Moon permanently. Researchers now think that the asteroid which created its largest crater originated from the north rather than the south originally believed.

How did the giant crash shape the Moon?
A new study led by planetary scientist Jeffrey Andrews-Hanna from the University of Arizona, published in Nature, traces the origin of the South Pole–Aitken basin. This colossal crater, stretching about 1,931 kilometres from north to south and 1,600 kilometres east to west, remains the biggest and oldest known impact site in the solar system.

The team found that the basin’s teardrop shape, which narrows toward the south, reveals the direction of the ancient strike. The asteroid’s northern approach reshaped the lunar surface and played a crucial role in forming the Moon’s uneven crust.

The South Pole-Aitken basin on the Moon’s far side was created by an asteroid striking from the north. (Image: Jeff Andrews-Hanna / University of Arizona / NASA / NAOJ)

What secrets lie beneath the lunar surface?
The impact carved deep into the Moon’s crust, exposing radioactive-rich materials known as KREEP — short for potassium, rare earth elements and phosphorus. These elements once floated in the molten layers of the Moon’s early surface and later settled unevenly.

As Andrews-Hanna explains, the impact created a “window” into the Moon’s interior. The heat-producing KREEP materials concentrated on one side, sparking volcanic activity that formed the dark plains visible from Earth. The far side, meanwhile, remained thick, rugged and heavily cratered.

Why does this matter for future lunar missions?
NASA’s Artemis programme is set to land astronauts on the lunar south pole, right along the rim of the South Pole–Aitken basin. Scientists believe this area holds vital debris and materials thrown up by the ancient collision.

These upcoming missions may reveal radioactive minerals and other traces from the Moon’s violent formation, offering new clues about how both the Moon and Earth evolved. Researchers say samples collected there could confirm how heat and materials moved through the Moon after the impact.

What does the study mean for lunar science?
The research offers fresh insight into why the Moon’s two sides look so different and how early impacts influenced its geology. As Andrews-Hanna and his team suggest, the Moon’s greatest crash didn’t just shape its surface — it may have fuelled the volcanic forces that made it what it is today.

The discovery now guides the next steps in lunar exploration, as scientists prepare to revisit the Moon’s ancient scars in search of answers to its fiery past.