Influence of magnesium perchlorate on the pyrolysis of organic compounds in Mars analogue soils

The Mars Organic Molecule Analyzer (MOMA) onboard the ExoMars-2018 rover shall apply thermal volatilization (TV), gas chromatography (GC) and mass spectrometry (MS) in order to search for organic compounds in the Martian soil. Here we describe a series of TV–GC–MS experiments on powdered basalt containing known organic compounds (benzoic acid or mellitic acid) at different concentrations (500 and 0.5 ppm). With reference to the discovery of perchlorate in Martian soils by the Phoenix Wet Chemistry Laboratory (WCL) all pyrolysis experiments were performed both in presence of 0.6 wt% magnesium perchlorate and in absence of perchlorate. We find that benzoic acid (BA) is detectable at both concentrations, while mellitic acid (MA) is only detectable at high concentration (500 ppm). In both cases perchlorate strongly affects type and number of organic fragments generated during pyrolysis.