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.

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模拟火星紫外线辐射环境中尿嘧啶的二聚化

在火星表面寻找有机分子是天体生物学的一个关键目标，因为许多有机化合物可能是生物特征，而且它们的存在对火星的宜居性很重要。目前火星表面的环境条件恶劣，影响了有机分子的稳定性。出于这个原因，并且由于当前和未来的火星探测器从上表面层收集样本，因此评估火星表面条件下有机分子的命运非常重要。在这里，我们展示了尿嘧啶在暴露于代表火星表面的紫外线辐射、压力和温度条件下的演变的实验研究。选择尿嘧啶是因为它是构成 RNA 的核碱基，并且已经在行星际天体中检测到它可能是通过陨石输送到火星表面的这种分子的外源。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。尽管这些结果表明尿嘧啶在火星上直接暴露在紫外线下时会迅速光降解，但这种暴露会产生比单体更稳定的二聚体。确定的二聚体可能是当前和未来火星太空任务的目标。尽管这些结果表明尿嘧啶在火星上直接暴露在紫外线下时会迅速光降解，但这种暴露会产生比单体更稳定的二聚体。确定的二聚体可能是当前和未来火星太空任务的目标。尽管这些结果表明尿嘧啶在火星上直接暴露在紫外线下时会迅速光降解，但这种暴露会产生比单体更稳定的二聚体。确定的二聚体可能是当前和未来火星太空任务的目标。