Degradation of Organics in a Glow Discharge under Martian Conditions

Introduction: The primary objective of this project is to understand the consequences of glow electrical discharges on the chemistry and biology of Mars. The possibility was raised some time ago that the absence of organic material and carbonaceous matter in the Martian soil samples studied by the Viking Landers might be due in part to an intrinsic atmospheric mechanism such as glow discharge. The high probability for dust interactions during Martian dust storms and dust devils, combined with the cold, dry climate of Mars most likely results in airborne dust that is highly charged. Such high electrostatic potentials generated during dust storms on Earth are not permitted in the low-pressure CO2 environment on Mars; therefore electrostatic energy released in the form of glow discharges is a highly likely phenomenon. Since glow discharge methods are used for cleaning and sterilizing surfaces throughout industry, the idea that dust in the Martian atmosphere undergoes a cleaning action many times over geologic time scales appears to be a plausible one. Although free radicals and UV light are present on Mars and available for reactions with organics,[1-3] a plasma introduces new and different reactive species. Chemistry in a plasma is driven by reactions due to the ‘four horsemen’ of the plasma: free ions, UV irradiation, free radicals and chemically reactive neutral species. This provides very different reactive conditions than would otherwise be found on Mars. Free ions would either be nonexistent or in very low concentrations. UV radiation created in the plasma is different than solar radiation and could exist in areas where UV solar radiation does not reach; for example, a dust storm would attenuate most solar radiation but discharges from the plasma would still provide light. Different free radicals would be expected in a plasma on Mars, than would be formed by other means. Finally, there are high energy neutral species in the plasma (excited states of N2 for example), that would not otherwise be expected. Procedure: Glow discharge (GD) experiments were performed in a vacuum chamber using a Mars gas mixture composed of 95.5% CO2, 2.7% N2, 1.6% Ar, 0.13% O2 and 0.07% CO. The apparatus built to perform the GD experiments is shown in Fig. 1. Slide