Influence of Calcium Perchlorate on Organics under SAM‐like Pyrolysis Conditions: Constraints on the Nature of Martian Organics

Abstract : Most of the organics detected on Mars so far are aliphatic and aromatic organo‐chlorine compounds. The smallest were first identified by the thermal treatment of the solid samples by Viking in 1976, although at the time, they were attributed to contamination. Since 2012, a larger variety of structures have been identified by the Sample Analysis at Mars (SAM) experiment aboard the Curiosity rover. Evidence suggests that the chlorohydrocarbons formed during pyrolysis of sedimentary materials. Laboratory experiments show that heating of samples containing oxychlorines, such as chlorates (ClO₃^‐) and perchlorates (ClO₄^‐), along with organic matter present at Mars’ surface is the logical source of these compounds. Nevertheless, this discovery of indigenous organic matter in the Mars regolith raises important questions: How do the oxychlorines influence the pyrolysis of organics? What are the organics precursors of the organo‐chlorinated molecules detected on Mars? Is there a way to identify the parent molecules in a sample after pyrolysis? This paper presents the results of systematic laboratory experiments of the products formed during the pyrolysis of organic compounds from three chemical families—polycyclic aromatic hydrocarbons (PAHs), amino acids and carboxylic acids—in presence of calcium perchlorates. Results show that the PAH parent molecules and most of the carboxylic acids are still detectable after pyrolysis in presence of calcium perchlorate and that the degradation and/or evolution of all parent molecules mostly depends on their chemical nature. In addition, we demonstrate that the chlorohydrocarbons detected on Mars by the SAM instrument could come from the three chemical families studied.