Large Impact Caused the "Evaporation" of the Moon's Mantle? New Discoveries from Chang'e-6 Samples
Source: Xinhua News Agency
The evolutionary differences between the near and far sides of the Moon have long been an unresolved scientific mystery.
Chinese researchers, through high-precision potassium isotope analysis of samples from the far side of the Moon collected by Chang'e-6, have revealed for the first time that the impact event in the South Pole-Aitken Basin caused the loss of moderate volatile elements in the lunar mantle. This provides important evidence for understanding the effects of large impacts on lunar evolution and revealing the causes of the Moon's "dichotomy."
"High-precision isotope analysis is like a 'geological detective,' capable of reconstructing the traces left by impact events by capturing subtle changes in isotope ratios," said Tian Hengci, a researcher at the Institute of Geology and Geophysics, Chinese Academy of Sciences. Potassium, zinc, and gallium, which are moderate volatile elements, tend to volatilize and fractionate under the high temperatures generated by impacts. Their isotope composition acts like a "biometric fingerprint," sensitively recording information about temperature, energy, and material sources during the impact.
Since the formation of the Moon, asteroid impacts have shaped the countless impact craters and basins on the lunar surface and significantly altered its topography and chemical composition. However, whether and how large early lunar impact events affected the deep interior of the Moon remains to be explored. In 2024, the Chang'e-6 mission successfully retrieved samples from the largest impact basin on the Moon, the South Pole-Aitken Basin, providing critical physical evidence to solve this question.
Illustration of the South Pole-Aitken Basin impact event. (Provided by the Institute of Geology and Geophysics, Chinese Academy of Sciences)
Tian Hengci's research team conducted high-precision potassium isotope analysis on milligram-level basaltic grains from Chang'e-6 samples. The results showed that the potassium isotope ratio of the Chang'e-6 basalt differs from that of samples from the Moon's near side, confirming the impact event's effect on the lunar mantle.
During the instantaneous high temperature and pressure generated by the impact, lighter isotopes tend to escape first. The loss of these volatile elements may suppress the formation of deep magmas and volcanic activity on the far side of the Moon, providing new clues for understanding the asymmetric geological evolution of the Moon's near and far sides.
The relevant findings were published in the international academic journal "Proceedings of the National Academy of Sciences of the United States of America" on January 13, 2024, at 12:00 Beijing Time. (Reporter: Liu Zhen)
Original article: toutiao.com/article/1854161592880202/
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