Like Earth, the Moon has been struck by numerous asteroids and comets, creating craters and basins. However, determining the exact timing of these impacts, especially the age of the Moon's oldest and largest basin, has been challenging - until now.
A team of researchers from The University of Manchester, studying a lunar meteorite named Northwest Africa 2995, has suggested that the Moon's massive South Pole-Aitken (SPA) basin was formed over 4.32 billion years ago. This enormous basin, located on the Moon's far side, spans more than 2,000 kilometers, making it the Moon's oldest confirmed impact site.
The team's proposed date pushes the basin's formation back about 120 million years earlier than previously believed, during what was thought to be the Moon's most intense period of asteroid bombardment.
Their findings, published in 'Nature Astronomy', offer new insights into the Moon's early impact history.
Dr. Joshua Snape, a Royal Society University Research Fellow at The University of Manchester, commented, "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.
"For several decades, there has been general agreement that the most intense period of impact bombardment was concentrated between 4.2-3.8 billion years ago. 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 there was a more gradual process of impacts over a longer period."
The meteorite, found in Algeria in 2005, is classified as a regolith breccia, meaning it contains fragments of different rock types fused together during an impact event. By analyzing the uranium and lead content in the meteorite's mineral and rock fragments, the researchers estimated the materials to date between 4.32 and 4.33 billion years ago.
Collaborating with institutions like the Chinese Academy of Sciences in Beijing, the Swedish Museum of Natural History, and the University of Portsmouth, the team compared their results with data from NASA's Lunar Prospector mission. This comparison confirmed chemical similarities between the meteorite and rocks in the SPA basin, providing a new estimate for the basin's age.
Dr. Romain Tartese, a Senior Lecturer at The University of Manchester, explained, "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 learnt about the Moon to provide us with clues about the conditions on Earth during the same period of time."
This discovery paves the way for future lunar exploration.
Professor Katherine Joy from The University of Manchester added, "The proposed ancient 4.32 billion year old age of the South Pole-Aitken basin now needs to be tested by sample return missions collecting rocks from known localities within the crater itself."
Research Report:Evidence of a 4.33 billion year age for the Moon's South Pole-Aitken basin
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