^1,4Hanwei Wu, ^2,4Qiquan Yang, ¹Yi Xu, ¹Sizhe Zhao, ¹Renrui Liu, ³Tianyi Xu, ¹Xiaoping Zhang, ¹Bohan Zhou
The Astrophysical Journal Letters, 1011, L7
Open Access Link to Article [DOI: 10.3847/2041-8213/aeb028]
¹State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau 999078, People’s Republic of China
²College of Surveying & Geo-Informatics, Tongji University, Shanghai 200092, People’s Republic of China
³Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210034, People’s Republic of China

Space weathering progressively modifies lunar surface regolith, while impact gardening and related processes redistribute weathered materials within the upper regolith, generating depth-dependent variations in maturity. Although surface maturity has been extensively investigated, its variation within the uppermost few centimeters remains insufficiently characterized. In particular, whether shallow maturity profiles differ between nearside and farside, especially at mid-to-high latitudes, has yet to be systematically examined. Here, using multisource orbital and in situ observations together with sampling-derived information, we investigate the depth-dependent distribution of shallow maturity at the Chang’e-5 (CE-5) landing site on the nearside and the Chang’e-6 (CE-6) site on the farside, both located at mid-to-high latitudes. Prelanding orbital spectra characterize the undisturbed surface, whereas in situ spectra acquired after plume-induced erosion (∼0.4/0.7 cm depth) and sampling excavation (∼3.4/3.7 cm depth) provide information on deeper layers, enabling maturity comparisons across three shallow stratigraphic horizons. Maturity indicators consistently indicate that the shallow regolith of CE-6 is more mature than that of CE-5, with the postlanding in situ spectra yielding I_s/FeO values of ∼78.13 and ∼31.40 for CE-6 and CE-5, respectively. Despite this difference in overall maturity, both sites exhibit similar depth-dependent patterns: the regolith becomes fresher with depth, showing relatively small maturity changes following plume erosion and more pronounced changes after sampling excavation. The similarity in these vertical patterns suggests broadly comparable intensities of two sites’ shallow regolith modification. These findings provide new observational constraints on the vertical distribution and evolution of shallow maturity and advance our understanding of regolith modification of CE-5 and CE-6 sites.