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 results are reported of a series of laboratory experiments where the abrasion of sand sized (125 – 300 µm) 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). These 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 H₂ was similarly measured in abraded experiments with crystalline minerals and not for amorphous opal. Labradorite and forsterite generated minimal H₂ and only in more abraded samples, likely due to the reaction of Si^• with water. In quartz experiments H₂ was only present in samples where a black magnetic trace mineral (possibly magnetite) was also present, and where H₂O₂ concentrations had been reduced to close to detection. In the quartz samples a mechanism of H₂ generation is inferred via the previously proposed model of spinel-surface-promoted-electron transfer to water. The presence of H₂O₂ may exert an additional control on net H₂ production rates either directly (via reaction of H₂ with OH^• and H₂O₂) or indirectly (by the oxidation of H₂ generating sites on mineral surfaces). Overall, the data supports previous inferences that aeolian abrasion can produce additional oxidants within the Martian regolith that can increase the degradation of organic molecules. It is further suggested that the apparent control of H₂O₂ concentrations on net H₂ generation in these experiments may help explain some previous apparently contradictory evidence for mineral-water H₂ generation at low temperatures.