The Influence of Oxychlorine Phases on the Flash Pyrolysis of Polycyclic Aromatic Hydrocarbons and Implications for Mars - INSU - Institut national des sciences de l'Univers Access content directly
Journal Articles Journal of Analytical and Applied Pyrolysis Year : 2024

The Influence of Oxychlorine Phases on the Flash Pyrolysis of Polycyclic Aromatic Hydrocarbons and Implications for Mars

Abstract

A variety of chlorine-bearing hydrocarbons have been detected in the chemical analyses of soil and rock samples performed on Mars with the GCMS instruments onboard the Viking landers and the SAM instrument suite onboard the Curiosity rover. These aromatic and aliphatic chlorohydrocarbons are most likely produced by chemical reactions between salts (e.g., perchlorates, chlorates) and organic molecules of martian origin either during the thermal processing of the samples in flight or generated through radiation processes happening in Mars’ near surface. To understand the influence of salts on the organic molecules during pyrolysis and identify the potential precursors of the chlorohydrocarbons detected on Mars, we performed a systematic study and pyrolyzed three polycyclic aromatic hydrocarbons (PAHs)—naphthalene, phenanthrene, and benzanthracene—in the presence of six perchlorate and chlorate salts that have been identified or are most likely present on Mars—calcium perchlorate, iron perchlorate, sodium perchlorate, magnesium perchlorate, sodium chlorate, and potassium chlorate. Iron perchlorate had the strongest (oxy)chlorination power on the PAHs of all the salts tested whereas magnesium perchlorate and potassium chlorate were the most destructive ones. Despite the presence of these caustic salts, PAHs were highly chemically and thermally stable, suggesting they would likely be detectable natively if present in a martian sample. In addition, chlorohydrocarbons that are characteristic of the parent PAH were formed and could be used to help identify the nature of a PAH. This investigation underlines that PAHs could be the precursors of aromatic chlorohydrocarbons detected on Mars, but a definitive identification will require the detection of the parent PAHs and their respective pyrolyzates, molecules that were not yet detected on Mars likely because of the flight operating constraints of the SAM instrument.
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insu-04612978 , version 1 (15-06-2024)

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Maëva Millan, Cyril Szopa, A Buch, P R Mahaffy, S S Johnson. The Influence of Oxychlorine Phases on the Flash Pyrolysis of Polycyclic Aromatic Hydrocarbons and Implications for Mars. Journal of Analytical and Applied Pyrolysis, In press, ⟨10.1016/j.jaap.2024.106578⟩. ⟨insu-04612978⟩
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