Characteristics of Space Weathering Modification of Chang'e-5 Lunar Soil: Evidence From the Microanalysis of Anorthite

Due to the lack of an atmosphere and a global magnetic field on the Moon, its surface is extensively subject to space weathering. One of the important products of space weathering is the iron particle, which has significant impacts for planetary exploration. Research on Apollo samples suggests that iron particles primarily form through vapor deposition processes during meteorite impacts. The Chang'e-5 (CE5) samples are the youngest samples collected so far, and the phenomenon of surface vapor deposition has not been studied in depth. Anorthite stoichiometrically free of Fe minerals, is highly suitable for studying the vapor deposition process of iron particles. Five anorthite grains from CE5 were analyzed using transmission electron microscope (TEM). Results show that the iron particle on the surface of anorthite formed from impact sputtering glass, and lack vapor-deposited nanophase iron particles (np-Fe⁰, <100 nm) on its surface. Additionally, residual Fe from Fe-Mg silicate impactors on the anorthite surface did not form np-Fe⁰. The dominant mechanism of np-Fe⁰ formation due to space weathering differs between the CE5 and Apollo landing sites. Impact melting rather than vapor deposition may be the dominant mechanism of np-Fe⁰ formation at the CE5 landing site due to impact. This indicates that the meteorite impact environment of CE5 landing site is weak. It is not possible to generate a large amount of vapor deposition-derived np-Fe⁰ like in Apollo samples.