Abstract
AbstractAll missions to Mars which have attempted to detect organic molecules have detected simple chlorohydrocarbons, the source of which has yet to be firmly established. This study assessed the likelihood of these chlorinated molecules being indigenous to the sedimentary units in which they were detected or if they were chlorinated during analysis. The survivability of 1‐chloronapthalene was examined via hydrous pyrolysis experiments and its dechlorination kinetics were determined. The results of these experiments were used to model the survivability of this simple chlorohydrocarbon under Mars‐relevant diagenetic conditions using the Sheepbed mudstone unit as a case study. It was found that 1‐chloronapthalene was rapidly dechlorinated under Noachian conditions, and thus, the detected Martian chlorohydrocarbons are unlikely to be ancient and probably formed within the rover's sample handling chain during analysis.
Highlights
All three landed missions to Mars which have attempted to detect organic compounds have found chlorinated organic molecules
This study examined the ability of simple chlorinated organic molecules to survive the high pressures and temperatures associated with burial over geological time scales
Chloromethane and chloromethylpropene detected by Sample Analysis at Mars (SAM) have been attributed to Martian chlorine from perchlorate decomposition reacting with terrestrial organic carbon from MTBSTFA, a chemical known to have leaked from a derivatization cup inside the SAM instrument suite (Glavin et al, 2013)
Summary
All three landed missions to Mars which have attempted to detect organic compounds have found chlorinated organic molecules. The Viking data were thought to show terrestrial contamination from residual cleaning products, as chlorinated solvents had been used in the cleaning of the spaceflight hardware (Biemann et al, 1976, 1977) This conclusion did not sufficiently explain the absence of these compounds in the blanks, nor why the two landers detected different compounds. Chlorobenzene was detected above instrument background levels during Evolved Gas Analysis, where samples do not pass through the Tenax® hydrocarbon trap. This indicates that there must be a Martian carbon source (Freissinet et al, 2015; Miller et al, 2015). A source of Martian organic carbon has recently been confirmed with the detection of complex macromolecular organic matter by MSL (Eigenbrode et al, 2018)
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