Impact-dispersed Fe–Fe1−xS core–shell particles in Chang’e-5 lunar soil impact glass

Abstract

Lunar soil undergoes space weathering and accumulates optically active opaque particles (OAOpq) of different sizes, resulting in a darkening or red shift of the reflectance spectrum. The surfaces of weakly weathered objects exhibit spectral characteristics of strong weathering; these mechanisms are still unclear. The causes of OAOpq in lunar soil are complex, especially for submicrometer particles, which account for the largest mass proportion. We found ubiquitous impact-dispersed Fe–Fe1-xS core–shell particles in Chang’e-5 lunar soil impact glass and splatter. The crystal structure, particle size distribution, and chemical composition of OAOpq in the impact glass indicate that these OAOpq consist of sulfides or metals from multiple sources. Thermodynamic evidence, diffusion behavior, and particle dispersion characteristics indicate that impact dispersion is the most likely formation mechanism of these OAOpq. The proposed impact dispersion provides a reason for the large number of OAOpq and the limited products for in situ reactions. This process explains why lunar soil with a low degree of weathering exhibits substantial spectral modification properties. The results provide insights into space weathering of the lunar surface and also imply that impact-dispersed OAOpq may be the primary modification type on asteroid surfaces. The unique chemical properties of Fe–Fe1-xS OAOpq also indicate that the lunar regolith has the potential for resource utilization.