Aeolian driven oxidant and hydrogen generation in Martian regolith: The role of mineralogy and abrasion temperature

The surface of Mars is a dynamic, cold environment where aeolian abrasion leads to the fracturing of silicate minerals which can produce oxidants upon exposure to water. Here we report results of a series of laboratory experiments where the abrasion of sand sized (125 - 300 sim) quartz, labradorite, forsterite and opal were conducted under a simulated Martian atmosphere at a range of temperatures common to Mars' surface (193 to 273 K). Our results suggest that abrasion rates are controlled by temperature; an observation that may have potential for providing insight into Martian paleo-temperatures. On the addition of water, detectable H2O2 was generated in all abraded experiments with crystalline quartz, labradorite and forsterite, but not amorphous opal - supporting previous inferences that mineral crystal structure plays a role in oxidant production. Dissolved Fe concentrations also indicated a strong additional control on net H2O2 production by Fenton reactions. Detectable H-2 was similarly measured in abraded experiments with crystalline minerals and not for amorphous opal. Labradorite and forsterite generated minimal H-2 and only in more abraded samples, likely due to the reaction of Si center dot & nbsp;& nbsp;with water. In quartz experiments H-2 was only present in samples where a black magnetic trace mineral was also present, and where H2O2 concentrations had been reduced to close to detection. In the quartz samples we infer a mechanism of H-2 generation via the previously proposed model of spinel-surface-promoted-electron transfer to water. The presence of H2O2 & nbsp;may exert an additional control on net H-2 & nbsp;production rates either directly (via reaction of H-2 & nbsp;with OH center dot & nbsp;& nbsp;and H2O2) or indirectly (by the oxidation of H-2 & nbsp;generating sites on mineral surfaces). Overall, our data supports previous inferences that aeolian abrasion can produce additional oxidants within the Martian regolith that can increase the degradation of organic molecules. We further suggest that the apparent control of H2O2 & nbsp;concentrations on net H-2 & nbsp;generation in our experiments may help explain some previous apparently contradictory evidence for mineral-water H-2 & nbsp;generation at low temperatures.(C) 2022 Elsevier B.V. All rights reserved.