Localized Alteration and Contamination of Lunar Regolith Particles upon Exposure to Earth Atmosphere

Abstract Microstructures on surfaces of lunar regolith particles record intricate processes during regolith formation and evolution. To acquire the complete morphology and composition of microstructures on surfaces of Chang'e‐5 and Chang'e‐6 regolith particles, the selected particles were rotated, cleaned using anhydrous ethanol, and loaded into electron microscopes for multiple rounds of analysis. During sample analysis, we noticed a few unusual features on the surfaces of the particles, including ferric‐rich iron oxides and NaCl and KCl crystals. These features exhibit overlapping relationships with other microstructures, similar to those formed on the Moon. By comparing the before and after scanning electron microscope (SEM) images, we confirmed that these features resulted from the oxidation of metallic iron particles in the Earth atmosphere and the adhesion of terrestrial contaminants. Our results demonstrate that localized alteration and contamination of lunar regolith samples, although rare, may occur during a limited exposure to the Earth atmosphere, which might hamper interpretations of sample analysis. This work highlights the importance of full‐process environmental protection (e.g., inert gas, constant temperature) for pretreatment, transfer and analysis of extraterrestrial samples.