Nanoscale space weathering features in mature lunar soil revealed by TEM and APT

Abstract

Space weathering significantly alters the optical, chemical, and structural properties of lunar regolith at micro‐ and nanoscales; yet detailed nanoscale variability within individual soils remains underexplored. Here we apply transmission electron microscopy (TEM) and atom probe tomography to four mineral grains (olivine, ilmenite, and two agglutinitic grains) from mature Apollo 17 soil 79221, characterizing solar wind‐induced damage, vesiculation, nanophase Fe formation, and volatile retention with nanometer resolution. Our analyses reveal pronounced heterogeneity in vesicle morphology, nanophase Fe abundance, and volatile content that varies with mineralogy and exposure history. Oxygen depletion near grain surfaces indicates sputtering effects. Beyond confirming nanoscale heterogeneity, our coordinated analyses resolve, by APT, the Fe‐depleted halos around npFe ⁰ in mature ilmenite that we previously documented with the same technique in submature Apollo 17 ilmenite. We identify impact‐melt quench textures that contribute non‐weathering npFe ⁰ to agglutinitic grains, and find a thick damage rim with few npFe ⁰ in Mg‐rich olivine accumulates. TEM observations of elongated, linear vesicles aligned parallel to ilmenite blade margins within a bladed agglutinitic grain further suggest crystallographic rather than directional control of vesicles in ilmenite inclusions. We also establish that vesicles distort APT reconstructions and degas during field evaporation, complicating quantitative inventories of npFe ⁰ and volatiles in space‐weathered grains.