Nature of space-weathered rims on Chang'e-5 lunar soil grains

The space weathering processes modify the microstructure and physicochemical properties of the surface of regolith mineral grains. We report microcraters and space-weathered rims on the surface of plagioclase, pyroxene, olivine, ilmenite and troilite grains in Chang'e-5 scooped lunar soil by electron microscopy. Microanalysis shows that low-speed secondary impact events indicated by microcraters dominated the evolution of Chang'e-5 regolith materials, which may have driven the formation of a potential microscale redox environment under a special mineral combination. Solar wind and cosmic ray irradiation lead to significant differences in space-weathered rims of mineral surfaces. This indicates the correlation between the nature of different spaceweathered rims and the inherent structure and composition of minerals. According to the statistical correlation between space-weathered rim width and track density, the average exposure ages of plagioclase and olivine in Chang'e-5 lunar soil are 2.180(- 0.222)(+0.229) Ma and 0.842(-0.469)(+1.120) Ma, respectively. This rule applies to regolith materials with short exposure time. The in situ mineralogical evidence clarifies that compared with Apollo mature lunar soil, Chang'e-5 lunar soil seems to have undergone weaker space weathering modification and shorter exposure history, and the essence is a weakly space-weathered lunar soil from young basalt. The nature of the space-weathered rims on the mineral surface of Chang'e-5 lunar soil reflects the response of regolith material to space weathering in a short exposure history, which is of great significance for the interpretation of spectral data of returned samples.