Research from the Chinese Academy of Sciences (CAS) has shed light on the notable differences between the near and far sides of the Moon. A study examining samples collected by the Chang’e-6 mission indicates that these discrepancies in chemical composition and volcanic activity are likely linked to the massive impact event that formed the South Pole-Aitken Basin (SPA).
The near side of the Moon is characterized by vast volcanic plains, while the far side is dominated by rugged terrain and fewer maria. According to researchers, the analysis of iron and potassium isotopes in four lunar samples has revealed that the unique composition of the SPA region plays a crucial role in this asymmetry. The findings were published in the *Proceedings of the National Academy of Sciences*.
Launched on May 3, 2024, the Chang’e-6 mission successfully returned samples from the SPA, a basin estimated to be between 4.2 and 4.3 billion years old. This mission follows China’s significant achievements in lunar exploration, including the Chang’e-4, which made history in 2019 as the first spacecraft to land on the Moon’s far side.
In their analysis, scientists discovered that the ratio of potassium-41 to potassium-39 is higher in the SPA samples than in those collected from the near side by both Chang’e-5 and NASA’s Apollo missions. Study leader Heng-Ci Tian explained that this ratio reflects the extreme conditions generated by the impact that created the basin.
“The intense temperatures and pressures resulted in the evaporation of many volatile elements, including potassium, from the Moon’s crust and mantle,” said Tian. He noted that the lighter potassium-39 isotope would evaporate more readily than the heavier potassium-41 isotope, leading to the observed higher ratio in the SPA samples.
This research offers vital insights into the impact event’s role in shaping the Moon’s geological landscape. The findings suggest that the depletion of volatiles could limit volcanic activity on the far side, contributing to its stark differences compared to the near side.
“The loss of moderately volatile elements likely suppressed magma generation and volcanic eruptions on the far side,” Tian stated. “We propose that the SPA impact contributed, at least partially, to the observed hemispheric asymmetry in volcanic distribution.”
The team undertook a detailed investigation to rule out other potential explanations for the isotopic differences. They examined whether cosmic ray irradiation or processes related to magma melting could have influenced the isotopic ratios. Ultimately, these alternatives were deemed to have minimal impact.
While the current results are preliminary, researchers plan to analyze additional isotopes of moderately volatile elements to further validate their conclusions. Tian highlighted the technical challenges faced during this study, particularly due to the fine-grained nature of the Chang’e-6 samples.
To address this, the team developed an ultra-low-consumption potassium isotope analytical protocol, which enabled high-precision measurements.
Moving forward, the researchers intend to combine their findings with numerical modeling to assess the broader implications of the SPA impact on the Moon’s geology. This work emphasizes the ongoing significance of lunar exploration in understanding not only the Moon itself but also the history of planetary bodies in our solar system.
