论文标题
过渡金属丰度作为寻找宇宙生活的关键参数
Transition metal abundance as a key parameter for the search of Life in the Universe
论文作者
论文摘要
在宇宙中寻找生命通常具有三个基本的生命需求：i）基础元素（即chnops），ii）生命反应的溶剂（通常是液态水）和iii）热力学不平衡。假定类似的要求在宇宙中可能是普遍的。在我们的星球上，生命能够从多种热力学不平衡中收获能量，通常是以氧化还原不平衡的形式收获。据估计，生活系统使用的不同氧化还原夫妇的数量在数千个反应范围内。这些能量反应中的每一个都需要一种称为氧化还原酶的专门蛋白质，它们具有一个或多个金属辅因子，充当催化中心以交换电子。事实上，这些金属是生命用来利用助力代谢所需的热力学不平衡的发动机的关键组成部分。这些过渡金属的可用性在宇宙中并不统一，它是复杂动力学的分布（时间和空间）的函数。尽管如此，到目前为止，在识别天体生物学目标时，生活需要特定金属进入热力学不平衡的需求被完全忽略了。我们认为，至少某些过渡元素的可用性似乎是可居住性的基本特征，应被认为是在寻找生命中选择系外行星目标的主要必要条件。
The search for Life in the Universe generally assumes three basic life's needs: I) building block elements (i.e., CHNOPS), II) a solvent to life's reactions (generally, liquid water) and III) a thermodynamic disequilibrium. It is assumed that similar requirements might be universal in the Cosmos. On our planet, life is able to harvest energy from a wide array of thermodynamic disequilibria, generally in the form of redox disequilibrium. The amount of different redox couples used by living systems has been estimated to be in the range of several thousands of reactions. Each of these energy yielding reactions requires specialised proteins called oxidoreductases, that have one or more metal cofactors acting as catalytic centres to exchange electrons. These metals are de facto the key component of the engines that life uses to tap into the thermodynamic disequilibria needed to fuel metabolism. The availability of these transition metals is not uniform in the Universe, and it is a function of the distribution (in time and space) of complex dynamics. Despite this, Life's need for specific metals to access thermodynamic disequilibria has been so far completely overlooked in identifying astrobiological targets. We argue that the availability of at least some transition elements appears to be an essential feature of habitability, and should be considered a primary requisite in selecting exoplanetary targets in the search for life.
