中国科学院地球化学研究所机构知识库

As the first lunar farside landed mission, China’s Chang’E−4 (CE-4) has safely landed on the volcanically resurfaced floor of Von Kármán crater in South Pole-Aitken (SPA) basin. The CE-4 mission will conduct rover exploration by Yutu-2 similar to what Chang’E−3 did in the northern Imbrium basin. Here we present a comprehensive study of the composition, mineralogy, and chronology of the basaltic and nonmare units in this crater, with the intent to provide context for the compositional properties of the landing site. Compositional maps (FeO, TiO₂, Mg#, and Th) demonstrate the heterogeneous distribution of mare and nonmare materials. Using a spectral survey of 1899 small impact craters (<1 km in diameter), we present a mineral map of high-Ca to low-Ca pyroxene ratio that is useful to untangle the effects of spectral mixing of these materials. Mare basalts with low-Ti composition and model ages of ~3.7 Ga and ~3.6 Ga have distinct mineral compositions that differ from the Chang’E−3 landing site, including no olivine enrichment. The non-mare materials have Mg-rich pyroxene, and Finsen crater materials (and Finsen ejecta) have higher Ca/Fe ratios than other parts of the rim of Von Kármán crater, indicating compositional anomaly of the SPA basin. The Von Kármán mare basalts show obvious compositional heterogeneity and complicated mixing effects with non-mare ejecta from subsequent impacts (e.g., the Eratoshenian-aged Finsen impact). We also present a geological map of the landing site, which reveals the geologic history of the landing region and will help to guide the surface exploration route of the CE-4’s Yutu-2 rover. We also put forward some science questions to be answered by Yutu-2, to aid mission planning and scientific research.