Rock fragments returned by Chang’e-6 preserve different histories of exposure to cosmic rays. A peer-reviewed isotope study separates relatively recent excavation from prolonged surface exposure and points to possible origins for unusual fragments. Its reconstruction suggests wider dispersal of potassium-rich material across the lunar farside, while the proposed source regions remain candidates.
Rock fragments brought back by the Chang’e-6 lunar mission did not all spend the same length of time exposed to cosmic rays. A single peer-reviewed study used changes in samarium, hafnium and chromium isotopes to reconstruct how impacts exposed and mixed material in the South Pole-Aitken basin, a large impact basin on the lunar farside.[1]
The soil’s average cosmic-ray exposure age was about 500 million years. This estimates irradiation history rather than the time the rocks formed. Most low-titanium basalt fragments showed prolonged exposure; two had been excavated more recently. Combining isotope systems helped distinguish the effects of exposure duration from burial and shielding, which can alter the signal in different ways.[1]
Three fragments containing KREEP, material rich in phosphorus, potassium and rare-earth elements, fell into two compositional groups with different exposure ages. Their chemistry and remote observations point to possible source regions including a magnesium-rich pyroxene ring and buried volcanic terrain. Those origins remain tentative. The findings suggest that KREEP material may be more widely distributed across the farside than previously recognised.[1]
