The widespread presence of perchlorate (ClO4-) has significant implications for the destruction of indigenous organic compounds that may have been or still be present on Mars. The intermediary products of the UV-driven production of ClO4- include oxychlorines (ClOx) such as chlorite (ClO2-), chlorate (ClO3-), and chlorine-dioxide (ClO2) gas. Using ClO2- or ClO3- as the starting oxychlorines, the temperature, humidity, and UV wavelengths were varied in order to isolate the reaction pathways leading to ClO4- and their ability to destroy amino acids under Mars ambient conditions. By monitoring the intermediary products, we showed that the production of ClO4- from ClO2- and ClO3- proceeds through different pathways. We observed that temperature affects the reaction products and that different oxychlorines can utilize different regions of the UV spectrum. We have also shown that adding TiO2 to the SiO2/ClOx mixture has a catalytic effect in the production of ClO4- under terrestrial conditions but shows primarily a shielding effect under Mars ambient conditions. We have also shown that although UV light only penetrates ~ 1 mm into the martian regolith, the UV driven oxychlorine reactions produce a reactive gaseous intermediate (ClO2) that can penetrate deeper into the regolith and thus destroy subsurface organics compounds even though they are protected from direct UV exposure and that water vapor facilitates the generation of ClO2(g) during perchlorate production. Finally, we report on the ability of a series of chlorine salts from NaCl to NaClO4 to destroy buried amino acids (Glycine, Proline, Tryptophan) and the role of water vapor in these reactions. We also compare how destructive the reaction products of each salt are and the effects of the structure of the amino acids on their survival.

UV-driven production of perchlorate (ClO4–) from chlorite (ClO2–) and chlorate (ClO3–) on Mars and its implications in the destruction of organic compounds on and below the surface

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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