Structures, compositions, and origins of glass beads in the lunar Chang'e-5 samples reveal the complexity of local regolith

Abstract Glass beads formed from impact melt and vapor are extensively distributed in lunar regolith samples, containing much information about protolith composition, regolith formation, and reworking. However, their understanding is often controversial due to the diversity of their sources and the complexity of later modifications. Recently returned regolith samples from the Chinese Chang'e-5 mission to the Moon provide a unique opportunity to understand microscopic mechanisms of regolith reworking and the contribution of exotic components because of their shorter gardening history and exposure time. In this study, we present 256 glass beads selected from 1700 mg of Chang'e-5 regolith and characterize their representative microstructures. A series of textures such as microcraters, linear scratches, and bonded silicate are observed on the surface of impact glass beads, which mainly originate from low-speed impacts of micrometeorites and their sputtered products onto in situ materials. The major and trace elements data of two sample groups of Chang'e-5 local glass beads with different textures show that homogeneous glass beads are mainly characterized by linear element loss while heterogeneous glass exhibits element redistribution with certain minerals. Based on relatively stable elements, 71 exotic glass beads were identified and divided into seven subtypes, which are associated with impact and transported materials from other regions on the Moon, tens to hundreds of kilometers away from the Chang'e-5 landing site. These results indicate that the influence of large-scale impacts might be the major factor for regolith transformation including the addition of exotic materials or alterations in elements. In contrast, the small-scale impacts mainly transformed the morphology of in situ regolith particles.