Fine and ultrafine Martian dust presents additional risks for future crewed missions to Mars

Surface dust poses a fundamental challenge to extraterrestrial human exploration, a reality demonstrated by the operational hazards encountered during Apollo lunar missions. On Mars, this challenge is compounded by regional and global dust cycles that coat sensitive hardware. While previous Mars missions have constrained the bulk geochemistry of coarser particulates (≳3 µm), the properties of the fine (≲2.5 µm) and ultrafine (≲0.1 µm) fractions remain largely uncharacterized. This knowledge gap is critical as these respirable particles, defined by their ability to bypass upper respiratory defenses, possess the mobility to penetrate deep into the alveolar regions of biological systems, presenting a systemic toxicity risk to future crews. Here, we report on direct examination of these fine and ultrafine Martian dust fractions using X-ray fluorescence through the analysis and modeling of data acquired by the Perseverance rover. We observe particulates measuring as small as 100 to 200 nm on spacesuit samples and calibration targets. Compositionally, this dust is a phosphorus-, iron-, and sulfur-enriched mafic silicate accumulating on materials analogous to the planned external layers of potential crew systems. Our results emphasize the importance of a thorough characterization of Martian dust properties in terrestrial laboratories to better prepare future crews and crew support systems destined for the surface of Mars.