1 Department of Physics and Astronomy, University of Leicester , Leicester, UK .
2 Laboratory of Inorganic Analytical Chemistry, Department of Chemistry, University of Liège , Liège, Belgium .
Astrobiology. 2017 Nov;17(11):1123-1137. doi: 10.1089/ast.2016.1512. Epub 2017 Oct 17.
In 2020, the ESA ExoMars and NASA Mars 2020 missions will be launched to Mars to search for evidence of past and present life. In preparation for these missions, terrestrial analog samples of rock formations on Mars are studied in detail in order to optimize the scientific information that the analytical instrumentation will return. Desert varnishes are thin mineral coatings found on rocks in arid and semi-arid environments on Earth that are recognized as analog samples. During the formation of desert varnishes (which takes many hundreds of years), organic matter is incorporated, and microorganisms may also play an active role in the formation process. During this study, four complementary analytical techniques proposed for Mars missions (X-ray diffraction [XRD], Raman spectroscopy, elemental analysis, and pyrolysis-gas chromatography-mass spectrometry [Py-GC-MS]) were used to interrogate samples of desert varnish and describe their capacity to sustain life under extreme scenarios. For the first time, both the geochemistry and the organic compounds associated with desert varnish are described with the use of identical sets of samples. XRD and Raman spectroscopy measurements were used to nondestructively interrogate the mineralogy of the samples. In addition, the use of Raman spectroscopy instruments enabled the detection of β-carotene, a highly Raman-active biomarker. The content and the nature of the organic material in the samples were further investigated with elemental analysis and methylated Py-GC-MS, and a bacterial origin was determined to be likely. In the context of planetary exploration, we describe the habitable nature of desert varnish based on the biogeochemical composition of the samples. Possible interference of the geological substrate on the detectability of pyrolysis products is also suggested. Key Words: Desert varnish-Habitability-Raman spectroscopy-Py-GC-MS-XRD-ExoMars-Planetary science. Astrobiology 17, 1123-1137.
2020 年，欧空局的 ExoMars 任务和美国宇航局的 Mars 2020 任务将被发射到火星，以寻找过去和现在生命的证据。为了准备这些任务，详细研究了火星上岩石地层的地球模拟样本，以优化分析仪器将返回的科学信息。沙漠漆是在地球上干旱和半干旱环境中的岩石上发现的薄矿物涂层，被认为是模拟样本。在沙漠漆的形成过程中（需要数百年的时间），有机物质被掺入，微生物也可能在形成过程中发挥积极作用。在这项研究中，提出了四种用于火星任务的互补分析技术（X 射线衍射 [XRD]、拉曼光谱、元素分析和热解-气相色谱-质谱联用 [Py-GC-MS]），用于探测沙漠漆样本并描述其在极端情况下维持生命的能力。首次使用相同的样本集描述了与沙漠漆相关的地球化学和有机化合物。XRD 和拉曼光谱测量被用于非破坏性地探测样品的矿物学。此外，拉曼光谱仪的使用能够检测到β-胡萝卜素，这是一种高度拉曼活性的生物标志物。使用元素分析和甲基化 Py-GC-MS 进一步研究了样品中有机材料的含量和性质，并确定了细菌来源的可能性。在行星探索的背景下，我们根据样品的生物地球化学组成描述了沙漠漆的宜居性。还提出了地质基质对热解产物可检测性的可能干扰。关键词：沙漠漆-宜居性-拉曼光谱-Py-GC-MS-XRD-ExoMars-行星科学。天体生物学 17,1123-1137。
