Hemispheric Variations and Isotopic Signatures of Lunar Noble Gases: Insights from Chang’e-5 and Chang’e-6 Soils

The origin, distribution, and isotopic fractionation of lunar volatiles remain debated. Lunar soils, lacking a substantial atmosphere and long-term global magnetic field, preserve volatiles mainly from solar wind implantation and exogenous meteorites and comets. Analyses of Chang’e-5 (nearside) and Chang’e-6 (farside) lunar soils offer a unique opportunity to compare these processes across hemispheres. Comprehensive measurements of noble gases (He, Ne, Ar, Kr, Xe) in Chang’e-5 and Chang’e-6 soils both show that the regolith cannot be explained as a simple binary mixture of solar wind and cosmogenic components. Kr and Xe isotopes indicate admixtures from cometary and meteoritic sources. Correlations between Kr and Xe isotopes distinguish Chang’e-5 samples from Apollo soils affected by atmospheric contamination, suggesting early Xe escape from Earth and underscoring the interconnected Earth–Moon system. In Chang’e-6 farside soils, Ne isotopes reflect highly fractionated solar wind compositions, while solar wind-derived Kr and Xe distinguish from meteoritic and cometary components. Compared with Chang’e-5 results, these data indicate deeper solar wind implantation on the farside, likely due to nearside deceleration by Earth’s magnetosphere. This hemispheric difference highlights the role of Earth’s magnetosphere in modulating solar wind velocity and shaping the distribution and isotopic diversity of lunar volatiles. Together, Chang’e-5 and Chang’e-6 findings provide new insights into the temporal and spatial evolution of lunar volatiles, mechanisms of Kr and Xe fractionation, and broader Sun–Earth–Moon interactions, with important implications for early Xe escape from Earth, the origin of lunar volatiles, and volatile redistribution in the inner solar system.