Chemical disequilibrium quantified using the available free energy has previously been proposed as a potential biosignature. However, researchers remotely sensing exoplanet biosignatures have not yet investigated how observational uncertainties impact the ability to infer a life-generated available free energy. We pair an atmospheric retrieval tool to a thermodynamics model to assess the detectability of chemical disequilibrium signatures of Earth-like exoplanets, focusing on the Proterozoic eon when the atmospheric abundances of oxygen–methane disequilibrium pairs may have been relatively high. Retrieval model studies applied across a range of gas abundances revealed that order-of-magnitude constraints on the disequilibrium energy are achieved with simulated reflected-light observations for the high-abundance scenario and high signal-to-noise ratios (50), whereas weak constraints are found for moderate signal-to-noise ratios (20–30) and medium- to low-abundance cases. Furthermore, the disequilibrium-energy constraints are improved by using the modest thermal information encoded in water vapour opacities at optical and near-infrared wavelengths. These results highlight how remotely detecting chemical disequilibrium biosignatures can be a useful and metabolism-agnostic approach to biosignature detection.

使用可用自由能量化的化学不平衡先前已被提议作为潜在的生物特征。然而，遥感系外行星生物特征的研究人员尚未调查观测不确定性如何影响推断生命产生的可用自由能的能力。我们将大气反演工具与热力学模型配对，以评估类地系外行星化学不平衡特征的可检测性，重点关注元古代，当时氧-甲烷不平衡对的大气丰度可能相对较高。应用于一系列气体丰度的反演模型研究表明，通过高丰度场景和高信噪比（50）的模拟反射光观测实现了对不平衡能量的数量级约束，而弱中等信噪比 (20-30) 和中低丰度情况存在限制。此外，通过使用光学和近红外波长的水蒸气不透明度中编码的适度热信息来改善不平衡能量约束。这些结果强调了远程检测化学不平衡生物特征如何成为一种有用且与代谢无关的生物特征检测方法。