Identification of Chlorobenzene in the Viking Gas Chromatograph‐Mass Spectrometer Data Sets: Reanalysis of Viking Mission Data Consistent With Aromatic Organic Compounds on Mars

Abstract

Motivated by the recent detection of chlorobenzene by the Sample Analysis at Mars instrument suite on the Curiosity rover, and the identification of its carbon source as indigenous to the martian sample, we reexamined the original, microfilm preserved, Viking gas chromatograph‐mass spectrometer data sets. We found evidence for the presence of chlorobenzene in Viking Lander 2 (VL‐2) data at levels corresponding to 0.08–1.0 ppb (relative to sample mass), in runs when the sample was heated to 350°C and 500°C. Additionally, we found a correlation between the temperature dependence of the chlorobenzene signal and the dichloromethane signal originally identified by the Viking gas chromatograph‐mass spectrometer team. We considered possible sources of carbon that may have produced the chlorobenzene signal, by reaction with perchlorate during pyrolysis, including organic carbon indigenous to the martian parent sample and instrument contamination. We conclude that the chlorobenzene signal measured by VL‐2 originated from martian chlorine sources. We show how the carbon source could originate from the martian parent sample, though a carbon source contributed from instrument background cannot yet be ruled out.

First Detections of Dichlorobenzene Isomers and Trichloromethylpropane from Organic Matter Indigenous to Mars Mudstone in Gale Crater, Mars: Results from the Sample Analysis at Mars Instrument Onboard the Curiosity Rover

“…Since then, the improvement of our knowledge of the martian surface environment allowed for reinterpretation of these results. For instance, some of the chlorinated hydrocarbons (HCs) (Guzman et al, 2018) detected were likely produced from thermal reactions, occurring in the experiment sample preparation system between oxychlorines, such as those that were detected during the Phoenix (Hecht et al, 2009) and Mars Science Laboratory missions (Glavin et al, 2013) and organic materials potentially present in the martian soil samples (Navarro-González et al, 2010).…”

Radiolysis of Macromolecular Organic Material in Mars‐Relevant Mineral Matrices

“…Other potential indications of indigenous organic matter are indirect and are observed as thermal evolution of CO 2 and CO observed during Sample Analysis at Mars' evolved gas analysis and are in part attributed to decarboxylation and decarbonylation of organics in samples from diverse rocks and aeolian sediments in Gale crater (Ming et al, ; Sutter et al, ), which may also explain CO 2 observed by the Viking GCMS (Biemann et al, ). Chloromethanes (Navarro‐González et al, ) and chlorobenzene (Guzman et al, ) detected in Viking data may also be Martian carbon signals, but terrestrial sources have not been definitively excluded. Additionally, reduced carbon phases including graphite, polycyclic aromatic hydrocarbons, and macromolecular phases with diverse synthesis mechanisms have been detected in Martian meteorites (Steele et al, ).…”

Survivability of 1‐Chloronapthalene During Simulated Early Diagenesis: Implications for Chlorinated Hydrocarbon Detection on Mars

“…This indicates that there must also be a Martian carbon source (Freissinet et al, ; Miller et al, ). A temperature dependence of the chlorobenzene detection recently identified in the Viking Lander 2 data is also indicative of a Martian carbon source (Guzman et al, ). Furthermore, a source of Martian organic carbon has recently been confirmed with the detection of complex macromolecular organic matter by MSL (Eigenbrode et al, ).…”