The search for organic biosignatures on Mars will depend on finding material protected from the destructive ambient radiation. Solar ultraviolet can induce photochemical degradation of organic compounds, but certain clays have been shown to preserve organic material. We examine how the SHERLOC instrument on the upcoming Mars 2020 mission will use deep-ultraviolet (UV) (248.6 nm) Raman and fluorescence spectroscopy to detect a plausible biosignature of adenosine 5′-monophosphate (AMP) adsorbed onto Ca-montmorillonite clay. We found that the spectral signature of AMP is not altered by adsorption in the clay matrix but does change with prolonged exposure to the UV laser over dosages equivalent to 0.2–6 sols of ambient martian UV. For pure AMP, UV exposure leads to breaking of the aromatic adenine unit, but in the presence of clay the degradation is limited to minor alteration with new Raman peaks and increased fluorescence consistent with formation of 2-hydroxyadenosine, while 1 wt % Mg perchlorate increases the rate of degradation. Our results confirm that clays are effective preservers of organic material and should be considered high-value targets, but that pristine biosignatures may be altered within 1 sol of martian UV exposure, with implications for Mars 2020 science operations and sample caching.

中文翻译：

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深紫外光谱法检测和降解高氯酸盐尖刺火星风化层类似物中的单磷酸腺苷

在火星上寻找有机生物特征将取决于找到免受破坏性环境辐射保护的材料。太阳紫外线可以诱导有机化合物的光化学降解，但某些粘土已被证明可以保存有机材料。我们研究了即将到来的2020 年火星上的 SHERLOC 仪器如何任务将使用深紫外 (UV) (248.6 nm) 拉曼光谱和荧光光谱来检测吸附在钙蒙脱石粘土上的 5'-单磷酸腺苷 (AMP) 的合理生物特征。我们发现 AMP 的光谱特征不会因粘土基质中的吸附而改变，但会随着紫外线激光的长时间暴露而改变，剂量相当于环境火星紫外线的 0.2-6 溶胶。对于纯 AMP，紫外线照射会导致芳香腺嘌呤单元的断裂，但在粘土存在的情况下，降解仅限于轻微改变，新的拉曼峰和荧光增加与 2-羟基腺苷的形成一致，而 1 wt % 高氯酸镁增加降解率。我们的结果证实粘土是有机材料的有效保护者，应被视为高价值目标，火星 2020科学操作和样本缓存。