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

Abstract

China's Chang'e-4 mission has carried out the first ever lunar farside landing exploration on the floor of the Von Kármán 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 ~80 m with a mean value of ~41 m. The ejecta at the Chang'e-4 landing site is ~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.