Carbon Isotopes of CO2 From Mineral Catalyzed Organic Oxidation Processes Under Martian Conditions

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2016-05

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Abstract

Organic molecules have not been positively identified by spacecraft missions on Mars. The extent of indigenous or meteoric contributions to organic molecules observed in Martian meteorites is also not well understood. The reason has been mostly attributed to the potential presence of oxidizing agents in Martian soil, degradation, and photocatalytic reactions by UV radiation. Given the presence of strong UV radiation, hydrogen peroxide, perchlorates, and chlorates create an extremely oxidizing environment. It is possible that oxidation reactions have diminished the concentrations of organic molecules, if present, on Martian surface. Oxidation of organic matter can proceed through a series of pathways under different conditions, such as temperature, mineral catalysts, and residence time. Carbon isotope measurement has long been used as an effective tool to identify reaction mechanisms. However, the effects of variables on carbon isotope fractionations between products and reactants during kinetic-controlled oxidation reactions are poorly understood. Previous laboratory experiments on the δ13C values of CO2 generated by hydrogen peroxide reacting with short chain carboxylic acids have shown that organic intermediates and reaction pathways may be different with different mineral catalysts, which control the isotope values of CO2. To get a better understanding of the effects of oxidizing agents and mineral catalysts on reaction pathways of organic oxidation reactions and corresponding carbon isotope values of CO2, a series of experiments were performed under Martian conditions. The simple carboxylic acid, acetic acid, was used as an organic reactant, with hydrogen peroxide, which is believed to be present on Martian surface as an oxidizer. The mineral catalysts in each experiment includes magnetite (NiFe2O4), hematite (Fe2O3), olivine ([Mg+2, Fe+2]2SiO4.), akaganéite (Fe3+O[OH,Cl]), and goethite (FeO(OH)). Experiments were conducted at 30 o C with carbon isotope measurements taken at reaction times of 1 hour, 4 hours, 24 hours, 72 hours, and 144 hours. The carbon isotope values obtained from the experiments give insights into reaction mechanisms of organic oxidation processes, provide fundamental data which is critical for understanding the results returned by the Mars Science Laboratory rover and future missions, and help elucidate the origin and evolution of organics, if present, on Mars.

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Keywords

Organic, Oxidation, Carbon, Isotopes, Mars, Conditions, Catalyzed, Mineral

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