Researchers have developed an agnostic model for the Photosynthetic Habitable Zone (PHZ) based on thermodynamics and redox chemistry, eliminating Earth-centric biases found in previous estimates. By optimizing a generic photochemical reaction against exoplanet irradiance spectra using a genetic algorithm, the study predicts that photosynthetic viability declines linearly with orbital distance rather than quadratically.
- The model uses a generalized photochemical reaction coupling photon capture to CO2 reduction without reference to specific Earth organisms.
- Simulations indicate that organisms evolve larger light-harvesting structures to compensate for reduced stellar flux.
- Photosynthetic viability declines linearly with orbital distance, expanding the PHZ well beyond previous estimates.
- Anoxygenic and hypothetical NIR-driven oxygenic photosynthesis are viable across the entire habitable zone for M, K, and G stars.
- Earth-like visible light oxygenic photosynthesis is flux-limited at the outer habitable zone for cool M-dwarf stars.
This implies that M-dwarf exoplanets could sustain robust oxygenic photosynthesis distinct from Earth's, potentially presenting reflectance biosignatures in the near-infrared band rather than the visible spectrum.