Characteristics of Weak Space Weathering in Chang'e-5 Lunar Soil: Evidence From Microcraters Formed by Low-Speed Impacts

Micrometeoroid impacts play a key role in space weathering during the evolution of lunar regolith. The micro-cratering morphology and material transformation of common lunar phases are effective ways to understand the interaction between the space environment and matter, but there are few systematic studies. Micro-analysis is conducted on the microcraters in the Chang'e-5 lunar soil to evaluate the microscale impact effects. Here, our study reveals the different morphological characteristics and internal microstructure of microcraters across five typical components (pyroxene, olivine, plagioclase, ilmenite, and glass). The impact effects include planar defects like dislocation slip, amorphization, and the formation of np-Fe⁰ and vesicles. Key parameters, including the microcrater depth to diameter ratio and microcrater diameter to impactor diameter ratio, are calculated to quantify microcrater morphology. The formation process of microcraters is reproduced with the smoothed-particle hydrodynamic method. The results suggest that the microcraters retain transient characteristics, likely from low-speed micrometeoroids or secondary impact events. These microscale impacts exhibit lower intensity compared to microcraters from Apollo samples, indicating weak space weathering processes on young basalt. The exploratory work tries to provide a comprehensive summary of low-speed impact-induced microcraters in lunar soil and outlines the theoretical frameworks for understanding microscale impact processes.