Poch Olivier, Frey Joachim, Roditi Isabel, Pommerol Antoine, Jost Bernhard, Thomas Nicolas
1 Center for Space and Habitability , Universität Bern, Bern, Switzerland .
2 Institute of Veterinary Bacteriology, University of Bern , Bern, Switzerland .
Astrobiology. 2017 Mar;17(3):231-252. doi: 10.1089/ast.2016.1523. Epub 2017 Mar 10.
To detect signs of life by remote sensing on objects of our Solar System and on exoplanets, the characterization of light scattered by surface life material could complement possible clues given by the atmospheric composition. We reviewed the reflectance spectra of a broad selection of major biomolecules that constitute terrestrial carbon-based life from 0.4 to 2.4 μm, and we discuss their detectability through atmospheric spectral windows. Biomolecule features in the near-infrared (0.8-2.4 μm) will likely be obscured by water spectral features and some atmospheric gases. The visible range (0.4-0.8 μm), including the strong spectral features of pigments, is the most favorable. We investigated the detectability of a pigmented microorganism (Deinococcus radiodurans) when mixed with silica sand, liquid water, and water-ice particles representative of diverse surfaces of potentially habitable worlds. We measured the visible to near-infrared reflectance spectra (0.4-2.4 μm) and the visible phase curves (at 0.45 and 0.75 μm) of the mixtures to assess how the surface medium and the viewing geometry affect the detectability of the microorganisms. The results show that ice appears to be the most favorable medium for the detection of pigments. Water ice is bright and featureless from 0.4 to 0.8 μm, allowing the absorption of any pigment present in the ice to be well noticeable. We found that the visible phase curve of water ice is the most strongly affected by the presence of pigments, with variations of the spectral slope by more than a factor of 3 with phase angles. Finally, we show that the sublimation of the ice results in the concentration of the biological material onto the surface and the consequent increase of its signal. These results have applications to the search for life on icy worlds, such as Europa or Enceladus. Key Words: Remote sensing-Biosignatures-Reflectance spectroscopy-Exoplanets-Spectroscopic biosignatures-Pigments. Astrobiology 17, 231-252.
为了通过遥感探测太阳系天体和系外行星上的生命迹象，对表面生命物质散射光的特征描述可以补充大气成分给出的可能线索。我们回顾了构成地球碳基生命的多种主要生物分子在0.4至2.4微米范围内的反射光谱，并讨论了通过大气光谱窗口对它们的可探测性。近红外（0.8 - 2.4微米）波段的生物分子特征可能会被水的光谱特征和一些大气气体所掩盖。包括色素强烈光谱特征的可见光范围（0.4 - 0.8微米）是最有利的。我们研究了一种有色素的微生物（耐辐射球菌）与代表潜在宜居世界不同表面的硅砂、液态水和水冰颗粒混合时的可探测性。我们测量了混合物的可见光至近红外反射光谱（0.4 - 2.4微米）以及可见光相位曲线（在0.45和0.75微米处），以评估表面介质和观测几何形状如何影响微生物的可探测性。结果表明，冰似乎是检测色素最有利的介质。水冰在0.4至0.8微米范围内明亮且无特征，使得冰中存在的任何色素的吸收都能很容易被注意到。我们发现水冰的可见光相位曲线受色素存在的影响最大，光谱斜率随相位角变化超过3倍。最后，我们表明冰的升华会导致生物物质在表面浓缩，从而使其信号增强。这些结果适用于在冰卫星上寻找生命，如木卫二或土卫二。关键词：遥感 - 生物特征 - 反射光谱学 - 系外行星 - 光谱生物特征 - 色素。天体生物学17，231 - 252。
