The conventional observables to identify a habitable or inhabited environment in exoplanets, such as an ocean glint or abundant atmospheric O₂, will be challenging to detect with present or upcoming observatories. Here we suggest a new signature. A low carbon abundance in the atmosphere of a temperate rocky planet, relative to other planets of the same system, traces the presence of a substantial amount of liquid water, plate tectonics and/or biomass. Here we show that JWST can already perform such a search in some selected systems such as TRAPPIST-1 via the CO₂ band at 4.3 μm, which falls in a spectral sweet spot where the overall noise budget and the effect of cloud and/or hazes are optimal. We propose a three-step strategy for transiting exoplanets: detection of an atmosphere around temperate terrestrial planets in about 10 transits for the most favourable systems; assessment of atmospheric carbon depletion in about 40 transits; and measurements of O₃ abundance to disentangle between a water- versus biomass-supported carbon depletion in about 100 transits. The concept of carbon depletion as a signature for habitability is also applicable for next-generation direct-imaging telescopes.

用于识别系外行星中宜居或有人居住环境的传统可观测物体，例如海洋闪烁或丰富的大气 O ₂，​​将很难用现有或即将建成的天文台进行探测。在这里我们建议一个新的签名。相对于同一系统的其他行星，温带岩石行星大气中的碳丰度较低，这表明存在大量液态水、板块构造和/或生物量。在这里，我们表明 JWST 已经可以在某些选定的系统中执行此类搜索，例如通过 4.3 μm 处的 CO ₂波段的 TRAPPIST-1，该波段处于光谱最佳位置，其中总体噪声预算以及云和/或雾霾的影响是最优的。我们提出了凌日系外行星的三步策略：在大约 10 次凌日中探测温带类地行星周围的大气层，以获得最有利的系统；对大约 40 个过境的大气碳消耗进行评估；并测量 O ₃丰度，以区分大约 100 次凌日中水与生物质支持的碳消耗。碳消耗作为宜居性标志的概念也适用于下一代直接成像望远镜。