Oblique Impact Adjacent to Chang'E−5 Sampling Site: Fine-Scale Analysis and Implication on the Provenance of Returned Samples

Abstract

Impact ejecta is a major source of lunar regolith. Symmetric ejecta thickness models are widely used to estimate ejecta distribution. However, they cannot accurately describe the asymmetric distributions from oblique impacts. Here, the Xu Guangqi crater provides an example for the study of oblique impacts. High-resolution data from this crater, acquired during the Chang'E−5 mission, has facilitated studies of a potential oblique impact, the development of a correction model for asymmetric ejecta distribution, and a detailed analysis of regolith provenance at the sampling site. The results show that the Chang'E−5 returned samples mainly originate from the Xu Guangqi crater formed by an oblique impact at 25°–45°, and its corrected ejecta thickness at the sampling site is about 80 cm, an increase of about 30% over the estimate from the original symmetric ejecta thickness model. Within the uppermost 5 cm, the Chang'E−5 returned regolith is modeled to consist mainly of Xu Guangqi ejecta (∼99%) and a small number of local materials (∼1%), but both are similar in composition composed of local mare basalts. Although small quantities (∼0.7%) of nonlocal mare components from Sharp B, Copernicus, Harpalus, and Aristarchus occur at the bottom of the drilled samples (80–90 cm), the samples are still dominated by Xu Guangqi ejecta (∼88%) and local materials (∼11%). Our study demonstrates the possible effect of an oblique impact to be considered when discussing the sample provenance for a lunar sample returning mission.