The far side of the moon has been revealed to have formed in a different way than the near side. In June last year, China's lunar lander Chang'e 6 became the first in the world to bring back soil samples from the far side of the moon. Chinese researchers confirmed that the soil on the far side has a different composition than that of the near side. This study is expected to expand understanding of the evolution process of the entire moon.
Researchers from the Chinese Academy of Geological Sciences and Shandong University noted, "Analysis of the basalt collected for the first time by Chang'e 6 from the far side of the moon confirmed that it has undergone a different geological formation process" in the international journal Science on the 28th.
As a result of analyzing 33 basalt fragments collected by Chang'e 6, all were identified as low-titanium basalt, created about 2.823 billion years ago. The composition and formation time were similar to the basalt brought back by the United States' Apollo missions.
In contrast, the soil samples from the far side of the moon lacked materials rich in potassium (K), rare earth elements (REE), and phosphorus (P) known as KREEP. KREEP is the residue produced during the final stage of crystallization of the magma ocean in the early formation of the moon. The lunar soil samples brought from the near side in the past contained significant amounts of KREEP. It can be seen that the far side of the moon has a different volcanic activity and geological history than the near side.
Until the transfer of Chang'e 6, lunar exploration had focused on the near side for over half a century. The moon's rotation and revolution cycles are the same, so only the near side is visible from Earth. Therefore, lunar landers had to land on the near side to facilitate communication or observation. The near side of the moon has a smoother surface, making it safer for landers to touch down.
Soil samples brought back from the near side by the United States' Apollo missions, the Soviet Union's Luna missions, and China's Chang'e 5 played a significant role in explaining the lunar magma ocean model (LMO). This model posits that after the moon was formed, its surface was completely molten, creating a magma ocean that cooled and crystallized over time.
However, using only soil samples from the near side of the moon has limited the understanding of the moon's overall geological history. The research team confirmed that the far side of the moon formed in a different manner by analyzing soil collected from the South Pole-Aitken basin by the Chang'e 6 lander.
To clarify the phenomena occurring on the far side of the moon, the research team analyzed the ratio of uranium to lead in the basalt. The samples from the far side contained a higher proportion of uranium compared to those brought back by Apollo missions from the near side. This suggests that the internal mantle forming the basalt had different chemical compositions on the near and far sides of the moon.
Based on the analysis, the research team explained that "the meteorite impacts that created the South Pole-Aitken basin after the crystallization phase, which is the last stage of the lunar magma ocean model, may have significantly affected the internal structure of the moon," adding, "The impact may have melted the mantle on the far side of the moon, causing volatile materials to dissipate and reducing lead components."
The research team stated, "This study expands understanding of the far side of the moon and provides new insights into the moon's early history and the lunar magma ocean model," adding, "Future collection and analysis of soil samples from areas other than the South Pole-Aitken basin may help us understand the entire geological history of the moon."
References
Science (2025), DOI: https://doi.org/10.1126/science.adt3332