Organic molecules in the Sheepbed Mudstone, Gale Crater, Mars

Abstract

The Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration, and long-term preservation. This will guide the future search for biosignatures. Here we report the definitive identification of chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2 to C4 dichloroalkanes (up to 70 ppbw) with the SAM gas chromatograph mass spectrometer (GCMS) and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs, and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of Martian chlorine and organic carbon derived from Martian sources (e.g., igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets, or interplanetary dust particles.Key PointsFirst in situ evidence of nonterrestrial organics in Martian surface sediments Chlorinated hydrocarbons identified in the Sheepbed mudstone by SAM Organics preserved in sample exposed to ionizing radiation and oxidative condition

Low Hesperian P CO2 constrained from in situ mineralogical analysis at Gale Crater, Mars

“…In particular, the organic molecules observed by the Sample Analysis at Mars (SAM) instrument suite are extremely localized and restricted to simple structures (e.g., C1-C4 alkyl and single-ring aromatic hydrocarbons and chlorohydrocarbons; ref. 24) that lack source information. As such, they may be derived from meteoritic, abiogenic, or geologically reworked biological inputs to the sediments.…”

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“…However, the amount and forms of organics present on the surface of Mars remains an open question because harsh surface conditions, such as UV radiation and the production of oxidants are most likely a key factor determining their evolution and/or destruction (Stalport et al 2008(Stalport et al , 2009Ten Kate et al 2005;Poch et al 2015). A combination of both environmental factors and alteration during in situ sample analysis may explain why only few chlorinated compounds have been detected in Martian soil to date (Freissinet et al 2015;Leshin et al 2013). …”