1 School of Earth and Space Exploration, Arizona State University , Tempe, Arizona.
2 Current address: Geophysical Laboratory, Carnegie Institution of Washington , Washington, District of Columbia.
Astrobiology. 2018 Apr;18(4):431-453. doi: 10.1089/ast.2017.1716. Epub 2018 Apr 6.
The Mars 2020 mission will analyze samples in situ and identify any that could have preserved biosignatures in ancient habitable environments for later return to Earth. Highest priority targeted samples include aqueously formed sedimentary lithologies. On Earth, such lithologies can contain fossil biosignatures as aromatic carbon (kerogen). In this study, we analyzed nonextracted kerogen in a diverse suite of natural, complex samples using colocated UV excitation (266 nm) time-gated (UV-TG) Raman and laser-induced fluorescence spectroscopies. We interrogated kerogen and its host matrix in samples to (1) explore the capabilities of UV-TG Raman and fluorescence spectroscopies for detecting kerogen in high-priority targets in the search for possible biosignatures on Mars; (2) assess the effectiveness of time gating and UV laser wavelength in reducing fluorescence in Raman spectra; and (3) identify sample-specific issues that could challenge rover-based identifications of kerogen using UV-TG Raman spectroscopy. We found that ungated UV Raman spectroscopy is suited to identify diagnostic kerogen Raman bands without interfering fluorescence and that UV fluorescence spectroscopy is suited to identify kerogen. These results highlight the value of combining colocated Raman and fluorescence spectroscopies, similar to those obtainable by SHERLOC on Mars 2020, to strengthen the confidence of kerogen detection as a potential biosignature in complex natural samples. Key Words: Raman spectroscopy-Laser-induced fluorescence spectroscopy-Mars Sample Return-Mars 2020 mission-Kerogen-Biosignatures. Astrobiology 18, 431-453.
“火星 2020 任务”将对样本进行就地分析，并识别出那些可能在古代宜居环境中保存生物特征的样本，以便以后送回地球。具有最高优先级目标的样本包括水成沉积岩性。在地球上，这种岩性可以包含化石生物特征，如芳香碳（干酪根）。在这项研究中，我们使用共置的紫外激发（266nm）时间门（UV-TG）拉曼和激光诱导荧光光谱法，对一系列自然、复杂样本中的非提取干酪根进行了分析。我们在样本中对干酪根及其宿主基质进行了探测，以（1）探索 UV-TG 拉曼和荧光光谱学在探测火星上可能生物特征的高优先级目标中的干酪根的能力；（2）评估时间门和紫外激光波长在减少拉曼光谱中荧光的有效性；（3）确定可能会对基于漫游车的紫外-TG 拉曼光谱学鉴定干酪根造成挑战的样本特定问题。我们发现，未门控的紫外拉曼光谱适用于在无荧光干扰的情况下识别诊断性干酪根拉曼带，而紫外荧光光谱适用于识别干酪根。这些结果突出了共置拉曼和荧光光谱学的价值，类似于“火星 2020”任务中的 SHERLOC 可获得的光谱学，可增强在复杂自然样本中探测干酪根作为潜在生物特征的置信度。关键词：拉曼光谱学-激光诱导荧光光谱学-火星样本返回-火星 2020 任务-干酪根-生物特征。天体生物学 18，431-453。
