Impacts and Astromaterials Research Centre, Department of Earth Science and Engineering, Imperial College London, London, SW7 2AZ, UK.
NASA Goddard Space Flight Center, Greenbelt, MD, 20771, USA.
Sci Rep. 2018 May 15;8(1):7586. doi: 10.1038/s41598-018-25752-7.
Past life on Mars will have generated organic remains that may be preserved in present day Mars rocks. The most recent period in the history of Mars that retained widespread surface waters was the late Noachian and early Hesperian and thus possessed the potential to sustain the most evolved and widely distributed martian life. Guidance for investigating late Noachian and early Hesperian rocks is provided by studies of analogous acidic and sulfur-rich environments on Earth. Here we report organic responses for an acid stream containing acidophilic organisms whose post-mortem remains are entombed in iron sulphates and iron oxides. We find that, if life was present in the Hesperian, martian organic records will comprise microbial lipids. Lipids are a potential sizeable reservoir of fossil carbon on Mars, and can be used to distinguish between different domains of life. Concentrations of lipids, and particularly alkanoic or "fatty" acids, are highest in goethite layers that reflect high water-to-rock ratios and thus a greater potential for habitability. Goethite can dehydrate to hematite, which is widespread on Mars. Mars missions should seek to detect fatty acids or their diagenetic products in the oxides and hydroxides of iron associated with sulphur-rich environments.
火星上的远古生命可能会产生有机残留物，这些残留物可能保存在现今火星的岩石中。火星历史上最近一段保留了广泛地表水的时期是晚诺亚纪和早赫斯珀里安纪，因此有可能维持最进化和分布最广泛的火星生命。对类似地球酸性和富含硫环境的研究为研究晚诺亚纪和早赫斯珀里安纪岩石提供了指导。在这里，我们报告了一种含有嗜酸生物的酸性溪流的有机反应，其死后的残留物被包裹在硫酸亚铁和氧化铁中。我们发现，如果赫斯珀里安纪时期存在生命，那么火星的有机记录将包含微生物脂质。脂质是火星上潜在的大量化石碳储存库，可用于区分不同的生命领域。脂质的浓度，特别是烷酸或“脂肪”酸，在反映高水岩比的针铁矿层中最高，因此具有更大的宜居潜力。针铁矿可以脱水形成赤铁矿，赤铁矿在火星上广泛存在。火星任务应该设法在与富含硫环境相关的铁的氧化物和氢氧化物中检测脂肪酸或其成岩产物。
