On the oxidation ability of the NASA Mars‐1 soil simulant during the thermal volatilization step: Implications for the search of organics on Mars

[1] The search for organic molecules on Mars has been a major goal in planetary science. Viking performed the first analyses of the Martian soil in 1976, but was unable to detect organics at the ppb level using the thermal volatilization (TV) method. Three decades later, the Phoenix lander conducted analyses of Martian soil samples by TV, and found the release of CO2 from 400 to 680°C that was attributed to Mg or Fe carbonate, adsorbed CO2, or organic molecules. We have previously reported that high levels of iron species present in the soil efficiently oxidize the organics to CO and CO2 by TV. Here we explore in detail the oxidation ability of the organic-free NASA Mars-1 soil simulant during TV in molecular hydrogen or in the presence of stearic and mellitic acids. Our results imply that there are two sources of strong oxidizers in palagonite soils: (1) hydroxyl radicals originating from the dehydroxylation of the silica layer matrix at 320°C to 600°C and (2) oxygen atoms released by the reduction of iron(III) to iron(II) species at 320°C to 600°C and of iron(II) to metallic iron at 850–1150°C. These strong oxidizers completely decompose stearic or mellitic acids to carbon dioxide when they are present at low levels (<0.05% wt) in the NASA Mars-1 soil simulant. Since organics are expected to be present at very low levels on Mars, future space missions utilizing TV will face the challenge of determining if any CO2 released is of inorganic or organic origin.