Scientists pinpointed the age of the largest and oldest impact basin on the Moon

A long time ago, before 3.8 billion years ago, the Moon was hit a lot by asteroids, comets, and debris. These impacts created big holes and smaller craters on its surface. They also caused some areas to heat up and spread material around. Figuring out when these significant impacts happened helps us learn more about what happened in the early Solar System.

Scientists from the University of Manchester studied a lunar meteorite called Northwest Africa 2995 to learn more about the South Pole-Aitken (SPA) basin. This basin is the Moon’s oldest known impact site and is over 2,000 kilometers wide, located on the far side of the Moon. Their research suggests that the SPA basin formed about 120 million years earlier than previously thought, during a time of heavy impacts on the Moon.

The Northwest Africa 2995 meteorite was discovered in Algeria in 2005. It’s called a regolith breccia because it has pieces of various rock types that were once part of lunar soil, all fused together by the heat and pressure from an impact. By studying the amounts of uranium and lead in different minerals within the meteorite, researchers found that these materials are about 4.32 to 4.33 billion years old.

Dr. Joshua Snape, Royal Society University Research Fellow at The University of Manchester, said: “Over many years, scientists across the globe have been studying rocks collected during the Apollo, Luna, and Chang’e 5 missions, as well as lunar meteorites, and have built up a picture of when these impact events occurred.”

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“For several decades, there has been general agreement that the most intense period of impact bombardment was concentrated between 4.2 and 3.8 billion years ago, in the first half a billion years of the Moon’s history. But now, constraining the age of the South-Pole Aitken basin to 120 million years earlier weakens the argument for this narrow period of impact bombardment on the Moon and instead indicates a more gradual process of impacts over a longer period.”

Dr Romain Tartese, Senior Lecturer at The University of Manchester, said: “The implications of our findings reach far beyond the Moon. We know that the Earth and the Moon likely experienced similar impacts during their early history, but rock records from the Earth have been lost. We can use what we have learned about the Moon to provide clues about Earth’s conditions during the same period of time.”

Journal Reference:

1. Joy, K.H., Wang, N., Snape, J.F. et al. Evidence of a 4.33 billion year age for the Moon’s South Pole–Aitken basin. Nat Astron (2024). DOI: 10.1038/s41550-024-02380-y

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