Origin of Chlorobenzene Detected by the Curiosity Rover in Yellowknife Bay: Evidence for Martian Organics in the Sheepbed Mudstone?

• Main Authors: Dworkin, J., Ming, D., Summons, R., Coll, P., Grotzinger, J., Szopa, C., Glavin, Daniel P., McKay, C., Freissinet, Caroline, Miller, K., Archer, D., Eigenbrode, J., Franz, H., Martin, M., Navarro-Gonzalez, R., Coscia, D., Cabane, M., Sutter, B., Brunner, A., Kashyap, S., Buch, A., Mahaffy, P., Conrad, P., Steele, A., Brinkerhoff, W.
• Format: Other/Unknown Material
• Language: unknown
• Published: 2014
• Subjects: Lunar and Planetary Science and Exploration; Yellowknife; Yellowknife Bay
• Online Access: http://hdl.handle.net/2060/20140017076

The Sample Analysis at Mars (SAM) instrument on the Curiosity rover is designed to determine the inventory of organic and inorganic volatiles thermally evolved from solid samples using a combination of evolved gas analysis (EGA), gas chromatography mass spectrometry (GCMS), and tunable laser spectroscopy. The first solid samples analyzed by SAM, a scoop of windblown dust and sand at Rocknest (RN), revealed chlorinated hydrocarbons derived primarily from reactions between a martian oxychlorine phase (e.g. perchlorate) and terrestrial carbon from N-methyl-N-(tert-butyldimethylsilyl)-trifluoroacetamide (MTBSTFA) vapor present in the SAM instrument background. Chlorobenzene (CBZ) was also identified by SAM GCMS at RN at trace levels (approx.0.007 nmol) and was attributed to the reaction of chlorine with the Tenax polymers used in the hydrocarbon traps. After the RN analyses, Curiosity traveled to Yellowknife Bay and drilled two separate holes designated John Klein (JK) and Cumberland (CB). Analyses of JK and CB by both SAM and the CheMin x-ray diffraction instrument revealed a mudstone consisting of approx.20 wt% smectite clays, which on Earth are known to aid the concentration and preservation of organic matter. In addition, higher abundances and a more diverse suite of chlorinated hydrocarbons in CB compared to RN suggests that martian or meteoritic organic sources may be preserved in the mudstone. Here we discuss the SAM EGA and GCMS measurements of volatiles released from the Sheepbed mudstone. We focus primarily on the elevated CBZ detections at CB and laboratory analog experiments conducted to help determine if CBZ is derived from primarily terrestrial, martian, or a combination of sources.