Comparison of noble gas characteristics of lunar soil 61220 grain‐size fractions: Implications for exploration‐supportive volatile resources

Abstract

This study examined the noble gas inventories of different grain size fractions of lunar soil 61220 as a proxy for solar wind‐implanted volatiles of in situ resource utilization (ISRU) interest (e.g., H ₂ O and noble gases). Sample 61220 is representative of a “dry” highland regolith, comparable to those that may be sampled by missions exploring the lunar polar regions. All grain size fractions were mineralogically homogenous, except for the finest <25 µm fraction, which showed increased glass and pyroxene abundances and decreased feldspar abundance compared with the >25 µm fractions. Solar wind derived gases dominated the measured gases and yielded similar concentrations across the 25–63, 63–125, and 125–250 µm fractions, while the <25 µm fraction showed higher concentrations, possibly as a result of greater glass abundance in this fraction. Xe concentrations suggest a present‐day equivalent surface solar wind exposure duration of ∼1000 years. Cosmic ray exposure ages were comparable between all grain size fractions (average T21 = 181.0 ± 70.3 Ma and average T38, T83, and T126 = 415.6 ± 54.4 Ma). Diffusive loss of cosmogenic components was indicated in the T21 ages of the <25 µm fraction. Much of soil 61220 likely formed from a common comminution event(s) (e.g., impacts). For ISRU on an immature feldspathic soil, such as 61220, there is no substantive increase in volatile yield by selective grain size separation. Furthermore, the soil had not reached saturation of solar wind implanted noble gas volatiles, which could prove significant for the replenishment rate of extracted ISRU volatiles.