Just like Earth, the Moon was heavily bombarded by meteorites, asteroids, comets, and planetesimal debris that shaped the lunar surface. The large collisions formed giant impact basins (>150 km), meanwhile, the smaller impact craters caused the rock at the impact site to melt and become superheated. The force of the impact distributed the debris all across the Moon’s surface.
Among these impacts, the South Pole – Aitken (SPA) basin is the largest and oldest impact crater on the far side of the moon. Researchers believe that the SPA could have brought materials from the lower crust and upper mantle to the lunar surface. Therefore, studying this 2,000 × 1,500 km wide dimension offers clues on the crustal and volcanic history of the lunar farside and the basin formation.
Researchers analyzed the samples collected from the Chang’e–6 robotic mission, Apollo, and Luna. Astronomers believe that apart from these samples, recent impactors could’ve naturally delivered the SPA debris back to Earth. Investigating these materials will open up new avenues for future lunar explorations.
“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 us with clues about the conditions on Earth during the same period of time,” said Dr. Romain Tartese.
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The lunar meteorite Northwest Africa (NWA) 2995 is one such sample, believed to be part of SPA. The Northwest Africa 2995 meteorite was found in Algeria in 2005. The mineral chemistry of this sample supports a lunar origin.
By analyzing the amount of uranium and lead found within the meteorite, the researchers determined the age of the material, dating between 4.32 and 4.33 billion years ago. This proposed date is 120 million years earlier than the previously assumed timing of the bombardments on the Moon.
“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,” says Dr Joshua Snape.
“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 – 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 there was a more gradual process of impacts over a longer period.” Dr. Snape continued.
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Journal Reference:
Joy, K. H., Wang, N., Snape, J. F., Goodwin, A., F., J., Whitehouse, M. J., Liu, Y., Lin, Y. T., Darling, J. R., Tar, P., & Tartèse, R. (2024). Evidence of a 4.33 billion year age for the Moon’s South Pole–Aitken basin. Nature Astronomy, 1-11. DOI: https://doi.org/10.1038/s41550-024-02380-y