In June of 2024, China made history as the Chang’e-6 mission successfully returned lunar material to Earth for the first time ever, bringing back 1935.3 grams (around 4.25 pounds) of regolith and rock samples from the Moon. Scrutinizing these samples has already yielded substantial insights into the Moon’s makeup and geological heritage, revealing significant divergences between its two hemispheres. This information is paramount because China, alongside NASA, ESA, and other space agencies and commercial partners, is actively preparing for the establishment of future lunar outposts, specifically targeting the far side of the Moon.
All these forthcoming endeavors focus on the South Pole-Aitken Basin as a prime site for development, given its abundance of permanently shadowed regions believed to harbor vast reserves of water ice. Moreover, examining these returned samples aids researchers in resolving long-standing enigmas concerning the Moon’s geological development. Among these uncertainties is how massive impact events—such as the colossal impact that sculpted the South Pole-Aitken Basin approximately 4.25 billion years ago—affected the Moon’s deeper interior structure and reshaped its surface.
In a recent piece of research, Chinese scientists from the Institute of Geology and Geophysics (IGG) of the Chinese Academy of Sciences (CAS) conducted a fresh analysis of basalt samples collected by the Chang’e-6 lander. Their findings indicate that the enormous impact responsible for creating this basin also generated considerable heat deep within the Moon, leading to the depletion of certain volatile elements. Utilizing high-precision isotopic analysis, the researchers managed to detect subtle variations in isotope ratios, thereby precisely cataloging the evidence left by the impact.
Understanding the consequences of impacts on the Moon holds immense significance for scientists, as impacts are recognized as the dominant external force that sculpted the lunar surface over eons. This contrasts sharply with Earth, where surface features and geological transformation are primarily driven by tectonic activity. The research team reported that the intense heat radiated by the massive impact measurably altered moderately volatile elements such as potassium, zinc, and gallium. These specific elements were of particular interest because they are prone to vaporization and isotopic fractionation when subjected to extreme heat.
Essentially, these “isotopic fingerprints” serve as proxies for measuring the thermal and barometric conditions imposed by impact events, thus providing context on how impacts modified both the lunar crust and mantle. Another compelling discovery involved the discrepancies observed between the materials brought back by Chang’e-6 from the far side and the samples collected by Apollo astronauts from the near side. The basalts retrieved from the far side exhibit a notably higher proportion of the heavier isotope, Potassium-41. To pinpoint the precise cause, the research group investigated several possible influences, including cosmic ray exposure, internal volcanism, and the deposition of impact ejecta.
Ultimately, they concluded that the isotopic difference stemmed from an early, massive collision that fundamentally altered the potassium isotopic composition within the Moon’s deep mantle reservoirs. This collision forged conditions so extreme they caused a loss of the lighter isotope, Potassium-39, concomitantly enriching the material in the heavier Potassium-41 isotope. Furthermore, they deduced that the resulting loss of volatile compounds suppressed later volcanic activity on the Moon’s far side.
These findings constitute the most recent contribution to a growing body of evidence that is reshaping our comprehension of how large-scale collisions influenced the geological evolution of the lunar far side. They also serve to reinforce the conclusion that the near and far sides of the Moon have followed distinct evolutionary paths over the past several billion years. Moreover, this work underscores the substantial contribution that Chinese missions and their associated scientific community are making to the ongoing endeavor of deciphering the shared evolutionary story of the Moon and Earth.
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