The pronounced disparities in terrain, volcanic activity, and crustal architecture between the Moon’s near and far hemispheres offer invaluable insights into its genesis and evolutionary trajectory. Nonetheless, the scarcity of samples from the lunar farside has historically constrained investigations into the underlying mechanisms driving this hemispheric asymmetry. In a recent scientific endeavor, researchers meticulously examined rock and regolith fragments retrieved by China’s Chang’e 6 mission last year from a substantial impact basin on the Moon’s far side. Their analysis corroborated prior estimations, establishing the rock sample’s age at approximately 2.8 billion years. Furthermore, a detailed analysis of the mineralogical composition indicated that the material originated from magma that ascended from considerable depths within the lunar interior, solidifying at roughly 1,100 degrees Celsius—a temperature approximately 100 degrees Celsius lower than that of comparable samples procured from the near side. These groundbreaking discoveries have been formally documented in the esteemed journal Nature Geoscience.
Global map of the albedo from the 750 nm filter of the UV-VIS camera onboard NASA’s Clementine spacecraft. The image shows the near side and far side of the Moon in Lambert, equal-area projection. Image credit: NASA.
“The near and far hemispheres of the Moon exhibit marked differences both at their surfaces and, presumably, within their interiors,” stated Professor Yang Li, an esteemed researcher affiliated with University College London and Peking University.
“This represents one of the Moon’s profound enigmas, often referred to as the ‘two-faced Moon.’ While a significant thermal gradient between the near and far sides of the lunar mantle has long been theorized, our current study presents the inaugural empirical evidence derived from actual terrestrial samples.”
“These findings advance our comprehension of the Moon’s dual nature,” remarked Xuelin Zhu, a doctoral candidate at Peking University.
“They unequivocally demonstrate that the divergences between the near and far sides are not confined to the superficial layers but extend deep into the lunar interior.”
Within the scope of this investigation, the research team undertook the analysis of 300 grams of lunar regolith that had been allocated to the Beijing Research Institute of Uranium Geology.
“The sample obtained by the Chang’e 6 mission holds the distinction of being the very first ever collected from the Moon’s far side,” commented Dr. Sheng He, a senior researcher at the Beijing Research Institute of Uranium Geology.
Employing an electron probe, the scientists meticulously mapped specific sections of the sample, which was predominantly composed of basaltic grains, to ascertain its precise elemental composition.
Utilizing an ion probe, they precisely measured minute variations in lead isotopes, thereby accurately dating the geological specimen to 2.8 billion years.
Subsequently, employing a suite of advanced techniques, the researchers endeavored to reconstruct the thermal conditions of the sample during various phases of its existence when it resided deep within the Moon’s interior.
The initial methodology involved scrutinizing the precise composition of the constituent minerals and cross-referencing these findings with sophisticated computational simulations to extrapolate the temperature at which the rock originally formed.
This inferred formation temperature was then juxtaposed with analogous estimations derived from near-side rock samples, revealing a thermal discrepancy of approximately 100 degrees Celsius.
A secondary analytical approach involved delving further back into the sample’s geological history. By discerning its chemical makeup, the researchers inferred the thermal characteristics of its ‘parent rock,’ a process that was subsequently compared with established estimates for near-side samples acquired during the Apollo missions.
This comparative analysis again yielded a significant difference of roughly 100 degrees Celsius.
Given the limited quantity of returned samples, the inferred temperatures of the parent rocks were further refined by leveraging satellite data from the Chang’e landing zone on the far side. This data was then contrasted with equivalent satellite observations from the near side, a comparison that consistently indicated a temperature variance, this time measuring approximately 70 degrees Celsius.
Within the lunar environment, elements that generate heat, such as uranium, thorium, and potassium, tend to co-locate with phosphorus and rare earth elements. This specific assemblage of elements is categorized as KREEP-rich, an acronym derived from the chemical symbol for potassium (K), rare-earth elements (REE), and phosphorus (P).
The prevailing scientific hypothesis regarding the Moon’s origin posits that it coalesced from debris resulting from a colossal impact event between Earth and a protoplanet roughly the size of Mars, initiating its existence as a largely or entirely molten celestial body.
As this primordial magma gradually cooled, it solidified. However, the KREEP elements, being incompatible with the crystalline structures that formed, remained in a molten state for a considerably extended period.
It would logically be anticipated that KREEP material would be distributed uniformly across the lunar surface. Instead, current theory suggests that these elements are concentrated within the mantle of the near side.
The uneven distribution of these specific elements is theorized to be a causal factor in the enhanced volcanic activity observed on the near side.
While this study does not provide definitive data on the current thermal state of the lunar mantle on both the far and near sides, any pre-existing thermal imbalance between these hemispheres is likely to have persisted over immense geological timescales, given the Moon’s slow rate of cooling since its formation from a cataclysmic impact.
Nevertheless, the scientific team is actively pursuing avenues to ascertain a conclusive answer to this particular question.
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S. He et al. A relatively cool lunar farside mantle inferred from Chang’e-6 basalts and remote sensing. Nat. Geosci, published online September 30, 2025; doi: 10.1038/s41561-025-01815-z
