Looking for evidence of past life on mars: clues from vera rubin ridge and glen torridon, gale crater, mars

Introduction: Organic biosignatures have a record of up to 3.8 billion years old on Earth in the form of ancient refractory organic matter. [1]. This 3.8Ga time period corresponds to a time of potential habitability on Mars, which could therefore enable a similar detection of ancient life on Mars, if it was present. Examination of organic matter also allows an assessment of both exogenous and endogenous abiotic sources of organic carbon. Exogenous sources of organic carbon include meteorites and interplanetary dust [2-3]. Endogenous sources that were potentially present in the past include hydrothermal environments, organic synthesis in the atmosphere, and life [4-5]. Organic molecules have been previously detected in Gale crater, Mars by the MSL Curiosity rover in variable concentrations and compositions [4]. In particular, results from the analysis of the Glen Torridon (GT) samples indicated the presence of Sbearing organic compounds including aliphatics: dimethylsulfide (DMS) (or ethanethiol), dithiapentane and aromatics: thiophenes, dithiolane and trithiane [7]. Vera Rubin Ridge (VRR) is believed to be stratigraphically equivalent to parts of the GT trough, but has likely encountered multiple fluids with different pH, salinity and temperatures during late diagenesis [8]. The comparison between these two locations therefore allows an examination of the impacts of diagenetic conditions on the preservation of organic matter, and the potential identification of signatures of high organic preservation potential. To assess possible signatures of organic preservation potential, we are examining the geochemical and Evolved Gas Analysis (EGA) data of samples from the Vera Rubin ridge (VRR) and Glen Torridon (GT) sites. We are focused on (1) H2 and SO2, because low-temperature SO2 release may indicate sulfide minerals [9], and H2 is a reduced gas and (2) Fe and Mn concentrations because they can be valuable indicators of oxidation state [10]. Methods: To observe S-containing gas release from relevant sulfide minerals, we synthesized rambergite (MnS) using protocol B of [11] and purchased alabandite (MnS) from Minerals Unlimited. A Proto AXRD Powder Diffraction System was used to confirm the structure of these two minerals. Using an agate mortar and pestle, rambergite and alabandite were each powdered before being sieved to <150-μm. A Setaram Labsys EVO connected to a Pfeiffer ThermoStar mass spectrometer at NASA JSC, configured to operate similarly to SAM on MSL, was used to measure evolved gases from the manganese sulfide minerals. We then compared the evolved gases from the manganese sulfide minerals to evolved gases from Gale crater samples [9] and examined Alpha Particle X-ray Spectrometer (APXS) data for Fe and Mn concentrations for comparison. Results: