The plan to resume robotic and manned missions to the Moon in the next decade has led to a renewed interest in the properties of lunar soils, ranging from geological to chemical to toxicological. As an approximation of the effects of crushing and weathering on the Moon, previous work (W. T. Wallace et al. (2009) Meteor. Planet. Sci. 44: 961–970) demonstrated that freshly ground lunar soil is extremely active, as measured by the production of hydroxyl radicals in solution. The present study was performed in order to understand the origin of this reactivity. We have ground 8 lunar soils of varying maturity and source (highland or mare) and measured the hydroxyl-radical production and decay of the reactivity. It was determined that there is a direct correlation between the reactivity and the amount of nanophase metallic iron particles (as a function of soil maturity) in the samples; thus, the highland soils, with their lower total FeO contents, and less nanophase iron, are less reactive than ground mare soils. However, there was no obvious correlation between maturity and source (highland or mare), with respect to the amount of time required for deactivation to a non-reactive state. These results provide the first chemical reactivity values as an important property of lunar soils, necessary data for returning humans to the Moon.

Abstract— NASA plans to resume human exploration of the Moon in the next decade. One of the pressing concerns is the effect that lunar dust (the fraction of the lunar regolith <20 μm in diameter) will have on systems, both human and mechanical, due to the fact that various problems were caused by dust during the Apollo missions. The loss of vacuum integrity in the lunar sample containers during the Apollo era ensured that the present lunar samples are not in the same condition as they were on the Moon; they have been passivated by oxygen and water vapor. To mitigate the harmful effects of lunar dust on humans, methods of “reactivating” the dust must be developed for experimentation, and, ideally, it should be possible to monitor the level of activity to determine methods of deactivating the dust in future lunar habitats. Here we present results demonstrating that simple grinding, as a simple analog to micrometeorite crushing, is apable of substantially activating lunar dust and lunar simulant, and it is possible to determine the level of chemical activity by monitoring the ability of the dust to produce hydroxyl radicals in aqueous solution. Comparisons between ground samples of lunar dust, lunar simulant, and quartz reveal that ground lunar dust is capable of producing over three times the amount of hydroxyl radicals as lunar simulant and an order of magnitude more than ground quartz.