这篇论文用机器学习推翻了以往对光合作用宜居带的认知，发现M矮星周围行星的宜居潜力比我们想的大得多，而且可能产生近红外的生物特征信号。
研究团队基于热力学和氧化还原化学提出一个无参考生物的光合作用宜居带(agnostic PHZ)模型。该模型使用遗传算法优化光吸收特性和CO2还原速率，以匹配主序星周围系外行星的辐照光谱。模拟显示，光合生物通过演化更大的捕光结构来补偿光通量下降，使得光合可行性仅随轨道距离线性下降而非平方反比，因此agnostic PHZ远超以往基于地球生物的估计。对于M矮星，可见光氧光合作用在宜居带外缘受限，但无氧光合作用和近红外驱动的氧光合作用在整个宜居带均可行，表明M矮星系外行星可能维持不同于地球的氧光合作用。
An Agnostic Machine Learning Model of Photosynthetic Habitability
The search for exoplanet biosignatures is guided by whether planetary environments can sustain photosynthesis. As such, the Photosynthetic Habitable Zone (PHZ) was recently proposed, as the overlap between the canonical habitable zone and the orbital range where stellar irradiance is sufficient to drive photosynthesis. Existing PHZ estimates rely on empirical light-response curves from Earth phytoplankton, and thus include implicit Earth-centric biases. We introduce an agnostic PHZ derived from a generalized model of photosynthesis grounded in thermodynamics and redox chemistry, without reference to model organisms. The model is built on a generic photochemical reaction in which photon capture couples oxidation of a donor molecule to the reduction of CO2. The optical properties and CO2 reduction rate are optimized against irradiance spectra for exoplanets orbiting main-sequence stars, using a genetic algorithm that mimics evolution by natural selection. Our simulations predict that photosynthetic organisms compensate for reduced flux by evolving larger light-harvesting structures. As a result, photosynthetic viability declines only linearly with orbital distance, despite stellar flux falling off quadratically. As such, the agnostic PHZ expands well beyond previous Earth-based estimates. Earth-like (visible light) oxygenic photosynthesis is flux-limited at the outer habitable zone for cool M-dwarf stars; however, both anoxygenic photosynthesis and a hypothetical, NIR-driven oxygenic photosynthesis are viable across the entire habitable zone for M, K, and G stars. This implies that M-dwarf exoplanets could sustain robust oxygenic photosynthesis, though it would be different to that found on Earth, presenting reflectance biosignatures in the NIR band rather than the visible.