The stark contrast between the Moon’s near side and far side in topography, volcanic activity and crustal structure provides critical insights into lunar formation and evolution. However, the absence of farside samples has long limited the investigations into the mechanisms driving this hemispherical asymmetry. In new research, scientists looked at fragments of rock and soil scooped up by China’s Chang’e 6 spacecraft last year from a vast crater on the far side of the Moon. They confirmed previous findings that the rock sample was about 2.8 billion years old, and analyzed the chemical make-up of its minerals to estimate that it formed from lava deep within the Moon’s interior at a temperature of about 1,100 degrees Celsius — about 100 degrees Celcius cooler than existing samples from the near side. The findings were published in the 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 side and far side of the Moon are very different at the surface and potentially in the interior,” said Professor Yang Li, a researcher at University College London and Peking University.
“It is one of the great mysteries of the Moon. We call it the two-faced Moon. A dramatic difference in temperature between the near and far side of the mantle has long been hypothesised, but our study provides the first evidence using real samples.”
“These findings take us a step closer to understanding the two faces of the Moon,” said Xuelin Zhu, a Ph.D. student at Peking University.
“They show us that the differences between the near and far side are not only at the surface but go deep into the interior.”
In the study, the authors analysed 300 g of lunar soil allocated to the Beijing Research Institute of Uranium Geology.
“The sample collected by the Chang’e 6 mission is the first ever from the far side of the Moon,” said Dr. Sheng He, a researcher at the Beijing Research Institute of Uranium Geology.
The researchers mapped selected parts of the sample, made up largely of grains of basalt, with an electron probe, to determine its composition.
They measured tiny variations in lead isotopes using an ion probe to date the rock as 2.8 billion years old.
They then used several techniques to estimate the temperature of the sample while at different stages of its past when it was deep in the Moon’s interior.
The first was to analyze the composition of minerals and compare these to computer simulations to estimate how hot the rock was when it formed.
This was compared to similar estimates for near-side rocks, with a difference of 100 degrees Celsius.
The second approach was to go back further in the sample’s history, inferring from its chemical make-up how hot its ‘parent rock’ would have been, comparing this to estimates for near-side samples collected by the Apollo missions.
They again found about a 100 degrees Celesius difference.
As returned samples are limited, they estimated parent rock temperatures using satellite data of the Chang’e landing site on the far side, comparing this with equivalent satellite data from the near side, again finding a difference — this time of 70 degrees Celsius.
On the Moon, heat-producing elements such as uranium, thorium and potassium tend to occur together alongside phosphorus and rare earth elements in material known as KREEP-rich (the acronym derives from potassium having the chemical symbol K, rare-earth elements (REE), and P for phosphorus).
The leading theory of the Moon’s origin is that it formed out of debris created from a massive collision between Earth and a Mars-sized protoplanet, and began wholly or mostly made of molten rock.
This magma solidified as it cooled, but KREEP elements were incompatible with the crystals that formed and thus stayed for longer in the magma.
Scientists would expect the KREEP material to be evenly spread across the Moon. Instead, it is thought to be bunched up in the near side mantle.
The distribution of these elements may be why the near side has been more volcanically active.
Although the present temperature of the far and near side of the Moon’s mantle is not known from this study, any imbalance in temperature between the two sides will likely persist for a very long time, with the Moon cooling down very slowly from the moment it formed from a catastrophic impact.
However, the scientists are currently working on getting a definitive answer to this 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
