Basalt samples returned by the Chang'e-6 mission have provided unprecedented insights into the volcanic history of the lunar farside, revealing significant volcanic events that occurred 2.8 billion years ago (Ga) and 4.2 Ga. This groundbreaking research was conducted by Prof. Li Qiuli's lab at the Institute of Geology and Geophysics of the Chinese Academy of Sciences and has been published in the prestigious journal, Nature.

The Significance of the Chang'e-6 Mission

The Chang'e-6 mission marks a pivotal event in lunar exploration, as it is the first to return samples from the moon's farside. This area has long been shrouded in mystery, particularly concerning its geological history and composition. Prior to Chang'e-6, knowledge about the moon's farside was limited primarily to data gathered through remote sensing and prior missions, which focused on the more accessible nearside. The unique opportunity presented by the Chang'e-6 mission allows scientists to investigate the geological processes that shaped this region of the moon.

Distribution of distinct volcanic episodes on the moon's farside

A Groundbreaking Discovery

Upon analyzing the retrieved 1,935.3g of lunar soil, particularly focusing on 108 basalt fragments, the research team determined that 107 of these samples dated to approximately 2,807 ± 3 million years ago. This finding suggests that significant volcanic activity occurred at the Chang'e-6 landing site during this time, an event that remains undocumented in samples obtained from the lunar nearside.

Volcano Age Analysis

One basalt fragment, characterized as a high-aluminum basalt, provided an even older date of 4,203 ± 4 million years, indicating its origin from a cryptomare region located south of the landing site. This specific sample has been identified as the oldest lunar basalt whose age has been rigorously determined, further enhancing our understanding of the moon's geological timeline.

Volcanic Activity Timeline

The chronological data indicates that the lunar farside experienced volcanic activity over an extended timespan, approximately 1.4 billion years, from 4.2 Ga to 2.8 Ga. Initial analyses suggest these basalts originate from distinct mantle sources:

The 4.2 Ga basalt is derived from a KREEP-rich source—with potassium (K), rare earth elements (REE), and phosphorous (P)—while
The 2.8 Ga basalt originates from a KREEP-poor mantle source.

Research and Implications

According to Prof. Li, "Unraveling the volcanic history of the lunar farside is crucial for understanding the hemispheric dichotomy of the moon." This asymmetry between the nearside and farside encompasses various geological attributes, including differences in basalt distribution, topography, crustal thickness, and thorium concentration.

Impact on Lunar Crater-Counting Chronology

Another significant finding pertains to the correlation between the 2.8 Ga basalt age and preexisting crater-counting estimates. This alignment suggests that models of cratering chronology, which were initially established based on observations of the lunar nearside, may also apply to the lunar farside. The radioisotope ages of the Chang'e-6 basalts are thus pivotal in refining lunar crater-counting chronology, marking a substantial advancement in lunar geology.

Table 1: Summary of Basalt Sample Ages

Sample ID	Composition	Age (Ma)	Source Region
Fragment 1	Low-Alumina Basalt	2807 ± 3	Chang'e-6 Landing Site
Fragment 2	High-Alumina Basalt	4203 ± 4	Cryptomare Region

Future Research Directions

The findings from the Chang'e-6 mission open numerous avenues for future exploration and research. One immediate line of inquiry involves refining methods of isotope analysis to further discern the characteristics of the mantle sources from which these basaltic samples originated. Additionally, comparative studies with nearside samples can elucidate the contrasts in volcanic activity and geological processes between the two hemispheres of the moon.

Another important aspect is assessing how the findings from the Chang'e-6 mission influence our understanding of lunar history and its evolution over billions of years. Insights gained may also contribute to the broader field of planetary sciences by providing comparative data for understanding other celestial bodies with volcanic histories, such as Mars and Venus.

Conclusion

In conclusion, the analysis of basalt samples from the Chang'e-6 mission significantly enriches our understanding of the lunar farside's geological history. The concrete evidence of volcanic activity spanning over 1.4 billion years, along with the determination of distinct mantle sources, highlights the complexities involved in lunar formation and evolution. The implications of these findings extend beyond lunar geology, offering broader insights relevant to planetary science as a whole.

For more information

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These findings and ongoing research demonstrate the enduring intrigue of lunar exploration and its capacity to inform our understanding of planetary science.

Published in Nature on November 15, 2024, this research profoundly impacts our grasp of the moon's geological history. Future missions will no doubt examine other regions and contribute further to our knowledge base.