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

研究甲烷菌产生的微量气体混合物作为火星地下潜在生命的生物特征识别这些生物的光谱生物特征在ExoMars微量气体轨道上的NOMAD光谱仪将进行的观测中寻找这些生物特征寻找地球以外的生命仍然是科学中的基本问题之一。火星，我们最近的邻居，代表了一个潜在的生命栖息地，无论是在其古代历史上，甚至可能是今天，在表面之下。在过去的几年里，我们对火星上可能的可居住环境的了解有所增加;来自蒸发岩沉积物的证据表明，火星过去曾有过富含水的水成矿物质[1，2]，而循环斜坡线（RSL）的发现表明，现代火星上存在短暂的近地表盐水[3]。因此，问题就来了：在火星上的这些环境中是否存在（或曾经存在）生命？在火星上寻找生命的证据需要了解生物特征。目前，我们探测火星上过去或现在生命的最大希望是通过对大气中与生物过程/生命有关的痕量气体进行超高精度测量。显示不平衡的大气可能表明复杂过程的活动，包括生命的存在。挥发性有机化合物（VOC）等气体，其中一些无疑来自生物体，可能是生命的指示剂;这些类型的气体将由痕量气体轨道器（TGO，Patel是共同领导者）上的NOMAD仪器等仪器检测。NOMAD的主要目的是测量大气中的挥发性有机化合物，例如甲烷[4]。火星上甲烷存在的一个可能的解释是它是由产甲烷生物（产甲烷菌）产生的。如果火星上甲烷的来源是生物源，那么我们必须非常精确地了解这种活动排放的痕量气体混合物在火星上的情况。目前已知，生物成因过程导致甲烷与高级烃的高比率，而非生物成因过程导致痕量气体的更平衡的混合物（例如[5]）。高精度地确定在模拟火星条件下产生的气体的确切比例将是解释在火星上观察到的气体（如甲烷）的来源的关键--而且至关重要的是，关于起源是否是生物成因的，这一提议的总体目标是确定可用作火星生命证据的痕量气体生物特征。具体目标如下：描述在陆地条件下从产甲烷微生物中演化出的痕量气体在模拟的火星环境条件下（大气成分、压力和温度以及营养物）重复上述步骤确定产甲烷微生物的痕量气体生物特征将该生物特征应用于从ExoMars痕量气体轨道飞行器任务返回的数据评估在火星上观测到的甲烷是否可能是生物起源的

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