The Solar System is becoming increasingly accessible to exploration by robotic missions to search for life. However, astrobiologists currently lack well-defined frameworks to quantitatively assess the chemical space accessible to life in these alien environments. Such frameworks will be critical for developing concrete predictions needed for future mission planning, both to determine the potential viability of life on other worlds and to anticipate the molecular biosignatures that life could produce. Here, we describe how uniting existing methods provides a framework to study the accessibility of biochemical space across diverse planetary environments. Our approach combines observational data from planetary missions with genomic data catalogued from across Earth and analyzed using computational methods from network theory. To demonstrate this, we use 307 biochemical networks generated from genomic data collected across Earth and “seed” these networks with molecules confirmed to be present on Saturn's moon Enceladus. By expanding through known biochemical reaction space starting from these seed compounds, we are able to determine which products of Earth's biochemistry are, in principle, reachable from compounds available in the environment on Enceladus, and how this varies across different examples of life from Earth (organisms, ecosystems, planetary-scale biochemistry). While we find that none of the 307 prokaryotes analyzed meet the threshold for viability, the reaction space covered by this process can provide a map of possible targets for detection of Earth-like life on Enceladus, as well as targets for synthetic biology approaches to seed life on Enceladus. In cases where biochemistry is not viable because key compounds are missing, we identify the environmental precursors required to make it viable, thus providing a set of compounds to prioritize for detection in future planetary exploration missions aimed at assessing the ability of Enceladus to sustain Earth-like life or directed panspermia.

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在其他世界播种生物化学：土卫二作为案例研究

越来越多的机器人任务可以探索太阳系以寻找生命。然而，天体生物学家目前缺乏明确定义的框架来定量评估这些外星环境中生命可进入的化学空间。这样的框架对于制定未来任务规划所需的具体预测至关重要，既可以确定其他星球上生命的潜在生存能力，也可以预测生命可能产生的分子生物特征。在这里，我们描述了如何结合现有方法提供一个框架来研究跨不同行星环境的生化空间的可及性。我们的方法将来自行星任务的观测数据与来自地球各地的基因组数据相结合，并使用网络理论的计算方法进行分析。为了证明这一点，我们使用从地球上收集的基因组数据生成的 307 个生化网络，并将这些网络中的分子“播种”在土星的卫星土卫二上。通过从这些种子化合物开始扩展已知的生化反应空间，我们能够确定地球生物化学的哪些产物原则上可以从土卫二环境中可用的化合物中获得，以及这在地球生命的不同例子中有何不同。生物、生态系统、行星尺度的生物化学）。虽然我们发现分析的 307 个原核生物中没有一个达到生存能力的阈值，但该过程覆盖的反应空间可以提供可能的目标图，用于检测土卫二上的类地生命，以及合成生物学方法的目标。土卫二上的生活。