Mystery of the moon’s far side explained by ancient giant impact

Schematic illustration of how the SPA basin-forming impact modified the lunar crust and mantle and led to volatile loss during the event. Credit: Image by Prof. Hengci Tian

doi.org/10.1073/pnas.2515408123
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One of the biggest differences between the two sides of the Moon has always intrigued scientists: the side we see from Earth (the near side) has vast dark plains formed by solidified lava, a sign of intense volcanic activity in the past, while the far side shows far fewer of these dark regions and almost no traces of significant volcanism

Now, recent analyses of lunar rocks brought back by the Chinese Chang’e-6 mission, which collected samples directly from the enormous South Pole-Aitken Basin-one of the largest impact scars in the Solar System-have provided a compelling explanation for this contrast.

Researchers from the Chinese Academy of Sciences examined with great precision the potassium isotopes present in these basaltic rocks.

Potassium is an element that evaporates easily at extreme temperatures, and its isotopic composition acts as a kind of natural thermometer of violent past events.

Samples from Chang’e-6 showed potassium isotopes that were “heavier” than those found in rocks collected by the Apollo missions and in lunar meteorites, which represent the Moon’s middle mantle.

After ruling out minor causes such as cosmic radiation or contamination, scientists concluded that the cause of this special signature was the gigantic impact that formed the South Pole-Aitken Basin itself, billions of years ago.

This colossal shock released so much energy that it vaporized and expelled large quantities of volatile elements, including potassium, from the affected region.

With fewer of these elements inside, magma production decreased drastically on the far side of the Moon, reducing or even halting volcanic activity there.

Computer simulations reinforce this idea: the impact excavated material deep from the crust and possibly the mantle, while simultaneously generating enough heat to stir the lunar interior through convection.

Thus, a single massive collision not only opened a gigantic crater, but also altered the chemical and thermal evolution of the Moon’s interior, leaving permanent marks that explain why the two sides of our satellite appear so different.

This study, published in the journal Proceedings of the National Academy of Sciences, shows how catastrophic events from the distant past continue to reveal secrets about the history of the Moon and other planetary bodies.

Published in 03/19/2026 03h18

Portuguese version

Text adapted by AI (Grok) and translated via Google API in the English version. Images from public image libraries or credits in the caption. Information about DOI, author and institution can be found in the body of the article.

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