Impact-induced ultra-high melting point oldhamite discovered in Chang’E-6 lunar soil

Abstract

Chang’E-6 lunar soil was the first sample collected on the lunar farside. It provides insights into impact history and thermodynamic evolution of the Moon. Here we show the discovered widespread oldhamite (CaS) in lunar regolith samples. Analysis of the microscopic composition and crystal structure showed that the oldhamite has a cubic structure and presence at the interface of glass and iron on the surface of the impact glass beads, suggesting a interface thermochemical reaction. Thermodynamic calculations show that the formation of chemical reactions requires a reducing atmosphere and high temperature to ensure reducing environment and high iron activity for promoting the interaction. Such environment suggests a potential large-scale, high-energy impact event with a S-rich asteroid or involving lunar S-rich mantle-core excavation. Oldhamite has never been observed in other lunar samples from near side. Our findings reveal a unique evolution history of the South Pole-Aitken basin, which is distinct from nearside.