Space weathering effects on the lunar farside revealed by Chang’e-6 samples

Space weathering extensively transforms the materials on the lunar surface due to solar wind irradiation and micrometeorite impact. However, the spatial variability of space weathering across the lunar surface is not yet well understood. The recently returned Chang’e-6 samples from the Apollo Basin provide a new perspective for exploring space weathering on the lunar farside. In this study, we report the space weathering characteristics of the Chang’e-6 samples from the farside of the Moon. All mineral phases exposed on the surface of a single basaltic clast exhibit a typical phase-dependent, solar wind irradiation−damaged zone, but lack a vapor-deposit layer. The nanophase iron (npFe0) particles produced by solar wind H+ are observed as spheres in the pyroxene amorphous rim, elongated in ilmenite, and absent from Fe-poor plagioclase. Compared with samples from the nearside, the Chang’e-6 samples show deeper solar wind damage in a shorter exposure time, while the npFe0 particles are concentrated in the shallow part. Stopping and Range of Ions in Matter (SRIM) ion implantation modeling results indicate that the solar wind on the farside may be dominated by high-energy ion (He+) effects, while the penetration depth of low-energy ions (H+) is limited due to the shielding of local magnetic anomalies. These observations suggest significant differences in space weathering effects between the lunar nearside and farside, which may be attributed to the presence of local magnetic anomalies on the lunar farside.