Geochemistry of the Von Karman crater floor and thickness of the non-mare ejecta over the Chang'e-4 landing area

China's Chang' e-4 mission has carried out the first ever lunar farside landing exploration on the floor of the Von Karmen crater, a geologically complex region located in the most ancient and deepest South Pole-Aitken (SPA) basin. In order to demonstrate the characteristics of materials in the landing area, we investigated the regional geochemistry and thickness of non-mare ejecta overlaying the mare basalts. Comparative analyses of FeO, TiO2 and Th concentrations suggest that the landing site surface is dominated by non-mare ejecta from nearby craters (e.g., Finsen crater) with part of basaltic materials. The ejecta thickness is estimated based on the excavation depth of dark-haloed and non-dark-haloed craters by using support-vector machine, a supervised machine learning method for classification. The results show that the ejecta thickness in the region of 40 km across the landing site varies from near zero to similar to 80 m with a mean value of similar to 41 m. The ejecta at the Chang' e-4 landing site is similar to 40 m thick, which is comparable to the in situ observations by the Lunar Penetrating Radar onboard the Yutu-2 rover. Our results provide valuable information for interpretation of the on-going returned data and geologic analysis of the Chang' e-4 exploration region.

Automated summary

China's Chang' e-4 mission successfully conducted the first lunar farside landing exploration in the Von Karmen crater region, revealing the geological characteristics and thickness of ejecta in the landing site. The ejecta at the landing site is approximately 40 meters thick, dominated by non-mare ejecta from nearby craters, providing valuable information for interpreting ongoing data and geological analysis of the region.