The photolytic degradation and oxidation of organic compounds under simulated Martian conditions

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Abstract
Cosmochemical considerations suggest various potential sources for the accumulation of organic matter on Mars. However the Viking Molecular Analysis did not indicate any indigenous organic compounds on the surface of Mars. Their disappearance from the top layer is most likely caused by the combined action of the high solar radiation flux and various oxidizing species in the Martian atmosphere and regolith. In this study the stability of several organic substances and a sample of the Murchison meteorite was tested under simulated Martian conditions. After adsorption on powdered quartz, samples of adenine, glycine and naphthalene were irradiated with UV light at various oxygen concentrations and exposure times. In the absence of oxygen, adenine and glycine appeared stable over the given irradiation period, whereas a definite loss was observed in the case of naphthalene, as well as in the volatilizable and pyrozable content of the Murchison meteorite. The presence of oxygen during UV exposure caused a significant increase in the degradation rate of all samples. It is likely that similar processes have led to the destruction of organic materials on the surface of Mars.

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