Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR CNRS 7583, Université Paris Est Créteil et Université de Paris, Institut Pierre Simon Laplace, Creteil Cedex, France.
Institut de Chimie Organique et Analytique (ICOA), Université d'Orléans, UMR CNRS 7311, Orléans, France.
Astrobiology. 2020 Nov;20(11):1363-1376. doi: 10.1089/ast.2019.2157.
The search for organic molecules at the surface of Mars is a key objective in astrobiology, given that many organic compounds are possible biosignatures and their presence is of interest with regard to the habitability of Mars. Current environmental conditions at the martian surface are harsh and affect the stability of organic molecules. For this reason, and because current and future Mars rovers collect samples from the upper surface layer, it is important to assess the fate of organic molecules under the conditions at the martian surface. Here, we present an experimental study of the evolution of uracil when exposed to UV radiation, pressure, and temperature conditions representative of the surface of Mars. Uracil was selected because it is a nucleobase that composes RNA, and it has been detected in interplanetary bodies that could be the exogenous source of this molecule by meteoritic delivery to the surface of Mars. Our results show that the experimental quantum efficiency of photodecomposition of uracil is 0.16 ± 0.14 molecule/photon. Although these results suggest that uracil is quickly photodegraded when directly exposed to UV light on Mars, such exposure produces dimers that are more stable over time than the monomer. The identified dimers could be targets of interest for current and future Mars space missions.
在火星表面寻找有机分子是天体生物学的一个主要目标，因为许多有机化合物可能是生物特征，并且它们的存在与火星的可居住性有关。火星表面的当前环境条件非常恶劣，影响有机分子的稳定性。出于这个原因，并且由于当前和未来的火星车从上层表面收集样本，因此评估有机分子在火星表面条件下的命运非常重要。在这里，我们进行了一项实验研究，研究了在代表火星表面的 UV 辐射、压力和温度条件下尿嘧啶的演化。选择尿嘧啶是因为它是构成 RNA 的碱基，并且已经在星际体中检测到了这种分子，这些星际体可能是通过陨石向火星表面输送的这种分子的外源来源。我们的结果表明，尿嘧啶光解的实验量子效率为 0.16±0.14 分子/光子。尽管这些结果表明，当尿嘧啶直接暴露在火星的紫外线下时，它会很快光降解，但这种暴露会产生二聚体，这些二聚体随着时间的推移比单体更稳定。所鉴定的二聚体可能是当前和未来火星太空任务的目标。
