Searching for biogenic trace gases on Mars using laboratory experiments and the ExoMars NOMAD instrument

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Investigate the cocktail of trace gases produced by methanogens as biosignatures for potential life in the martian subsurfaceIdentify the spectral biosignature of these organismsSearch for these biosignatures in observations that will be made by the NOMAD spectrometer on the ExoMars Trace Gas OrbiterThe search for life beyond Earth remains one of the fundamental questions in science. Mars, our closest neighbour, represents a potential habitat for life, either in its ancient history or possibly even present-day, below the surface. Our understanding of possible habitable environments on Mars has increased over the last few years; evidence from evaporite deposits indicates that Mars had a water-rich evaporitic past [1, 2], and the discovery of Recurring Slope Lineae (RSL) suggests the presence of transient near-surface brines on modern-day Mars [3]. Thus the question arises: could life exist (or have existed) within these environments on Mars?Finding evidence of life on Mars requires an understanding of bio-signatures. At present, our best hope of detecting past or present life on Mars is through ultra-high precision measurements of trace gases relating to biological processes/life in the atmosphere.Atmospheres that display a disequilibrium are a potential indication of the action of complex processes including the presence of life. Gases such as volatile organic compounds (VOCs), some of which are unequivocally derived from organisms, could be an indicator of life; these types of gases will be detected by instruments such as the NOMAD instrument on-board the Trace Gas Orbiter (TGO, Patel is co-lead). A primary objective of NOMAD is to measure atmospheric VOCs, such as methane (among many others) [4].One possible explanation for the presence of methane on Mars is that it was (or is) being produced by methane-producing organisms (methanogens). If the source of methane on Mars is biogenic, it is imperative that we understand with great precision exactly what the emitted trace gas mixture of such activity would be in the context of Mars. It is currently known that biogenic processes result in a high ratio of methane to higher hydrocarbons, with abiogenic process resulting in a more balanced mixture of trace gases (e.g. [5]). Determining with high precision the exact ratios of gases produced under simulated martian conditions will be key to interpreting the origin of the gases, such as methane, that are observed on Mars - and crucially, as to whether the origin is biogenic or not.The overall aim of this proposal is to identify trace gas bio-signatures that could be used as evidence of life on Mars. The specific aims are as follows:Characterise the trace gases evolved from methanogenic Archaea under terrestrial conditionsRepeat the above under simulated Mars environmental conditions (atmospheric composition, pressure and temperature and nutrients)Determine a trace gas biosignature for methanogensApply this biosignature to data returned from the ExoMars Trace Gas Orbiter missionAssess whether the methane observed on Mars could be of biogenic origin