Regolith at Chang'E-5 landing site: mature lunar soils from Fe-rich and young mare basalts

Abstract Space weathering process on airless bodies produces metallic iron (Fe 0 ) particles widely existing in the rim and interior of mineral grains, which complicate visible and near-infrared spectra of surface materials. Although these space weathering products and their spectroscopic effects on the Moon have been extensively investigated based on returned Apollo samples and orbital datasets, the Chang’E-5 (CE-5) mission provides an unprecedent opportunity to couple information gained from newly returned CE-5 samples with in situ observations and investigate space weathering process on extremely Fe-rich basalts. The in situ detections, returned soils, and orbital measurements of soil maturity at CE-5 landing site are cross-validated and provide a new ground truth (I s /FeO value of 66.4) for lunar surface. The age of Xu Guangqi crater was determined to be 240 ~ 300 Ma and its ejecta is the main source of CE-5 soils. Further, abundant larger-sized Fe 0 particles were observed in the regolith at CE-5 landing site, which indicates that the inherited Fe 0 particles from late-stage mare basalts and dense clustering of oversaturated Fe 0 in extremely FeO-rich (> 17 wt.%) basalts both contribute to observed Fe 0 abundances. We suggest that space weathering of Fe-richer basalt generates Fe 0 particles with larger grain size and faster production rate.