The evolutionary differences between the near and far sides of the moon are a long-standing scientific mystery. Chinese researchers have revealed for the first time that the South Pole Aitken Basin impact event caused the loss of medium volatile elements in the lunar mantle through high-precision potassium isotope analysis of samples from the far side of the moon by Chang'e-6. This provides important evidence for understanding the impact of large-scale impacts on lunar evolution and revealing the cause of the moon's "binary" nature. High precision isotope analysis is like a 'geological detective', able to reconstruct the traces left by impact events by capturing small changes in isotope ratios. ”Tian Hengci, a researcher at the Institute of Geology and Geophysics of the Chinese Academy of Sciences, said that such moderately volatile elements as potassium, zinc and gallium are easy to volatilize and fractionate in the high temperature environment generated by impact, and their isotope composition is like "identity fingerprint", which can sensitively record the temperature, energy and material source information at the time of impact. Since the formation of the moon, asteroid impacts have shaped impact craters and basins throughout the lunar surface, significantly altering its morphology and chemical composition. However, it remains to be explored whether and how the early large-scale impact events on the moon affected its deep regions. In 2024, the Chang'e-6 mission successfully retrieved samples from the South Pole Aitken Basin, the largest impact basin on the Moon, providing key physical evidence to unravel this question. The research team led by Tian Hengci conducted high-precision potassium isotope analysis on single particles of Chang'e-6 basalt at the milligram level. The results showed that the potassium isotope ratio of Chang'e-6 basalt was different from that of samples from the near side of the moon, confirming the changes in the lunar mantle caused by the impact event. During the instantaneous high temperature and pressure process generated by the impact, lighter isotopes often preferentially escape, and the loss of such volatile elements is likely to suppress the formation of deep-seated magma and volcanic activity on the far side of the moon, providing new clues for understanding the asymmetric geological evolution of the moon's front and back. The relevant results were published in the international academic journal Proceedings of the National Academy of Sciences on the early morning of January 13th Beijing time. (New Society)