The cloud layer has been hypothesized to be the most habitable region of Venus. In the lower clouds, both temperature and pressure fall within bounds that support reproduction of microbial life on Earth, although the water activity of the sulfuric acid cloud droplets makes the clouds uninhabitable to known life. In this study, we carried out an analysis of CHNOPS (carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur) elements and potential redox couples in the cloud layer, and we used a microbial energetic growth model to investigate quantitatively the chemical energy available for microbial growth from methanogenesis, sulfate reduction, and hydrogen oxidation at temperatures between 278 and 350 K. The purpose was to improve knowledge of how far the venusian cloud layer comes from being habitable. Hydrogen oxidation was favorable at all temperatures; however, negative Gibbs free energies for sulfate reduction and methanogenesis depended critically on the assumed concentrations of electron donors, acceptors, and products. Improved measurements and the investigation of new molecules will allow us to better assess quantitatively how far Venus comes from possessing a habitable cloud layer and what would need to be different to make it habitable. We identify specific required measurements. These data will advance our understanding of the habitability of planetary atmospheres on extrasolar greenhouse worlds and the habitability of Earth when the planet eventually enters a greenhouse state.

中文翻译：

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温带但不适宜居住的金星云层中的生物可用化学能：我们想知道什么？

云层被假设是金星最宜居的区域。在较低的云层中，温度和压力都落在支持地球上微生物生命繁殖的范围内，尽管硫酸云滴的水活度使云层不适合已知生命居住。在这项研究中，我们对云层中的 CHNOPS（碳、氢、氮、氧、磷、硫）元素和潜在的氧化还原对进行了分析，我们使用微生物能量生长模型定量研究了可用于在 278 到 350 K 之间的温度下，来自甲烷生成、硫酸盐还原和氢氧化的微生物生长。目的是提高对金星云层距离可居住程度的了解。氢氧化在所有温度下都是有利的；然而，硫酸盐还原和产甲烷的负吉布斯自由能主要取决于电子供体、受体和产物的假定浓度。改进的测量和对新分子的研究将使我们能够更好地定量评估金星距离拥有宜居云层有多远，以及需要什么不同才能使其宜居。我们确定特定的所需测量。这些数据将增进我们对太阳系外温室世界行星大气宜居性以及地球最终进入温室状态时地球宜居性的理解。受体和产品。改进的测量和对新分子的研究将使我们能够更好地定量评估金星距离拥有宜居云层有多远，以及需要什么不同才能使其宜居。我们确定特定的所需测量。这些数据将增进我们对太阳系外温室世界行星大气宜居性以及地球最终进入温室状态时地球宜居性的理解。受体和产品。改进的测量和对新分子的研究将使我们能够更好地定量评估金星距离拥有宜居云层有多远，以及需要什么不同才能使其宜居。我们确定特定的所需测量。这些数据将增进我们对太阳系外温室世界行星大气宜居性以及地球最终进入温室状态时地球宜居性的理解。