Why Red Dwarfs Have Fewer Chances for Photosynthesis ⚡ экспресс
A radiation-thermodynamic model has been constructed to quantitatively estimate the maximum useful work of stellar radiation for a given star–planet configuration. Based on exergy, upper limits on photosynthetic power and long-wavelength absorption thresholds are obtained. Kinetically limited red limits are derived for photochemistry with a high free energy change (ΔG) and applied to Earth-like planets with equal bolometric flux from blackbody sources of FGK and M spectral classes. Calculation of photon threshold flux and truncated exergy below the red limit of photosystem II showed that single-photon oxygenic photosynthesis is limited to the near-infrared range for solar-type stars and a bluer region for late M-dwarfs. Spectrum-integrated reserves of threshold photons and exergy for the water oxidation stage are ~5 times greater for FGK stars than for M-dwarfs with T≈3000 K. For the Sun–Earth system, the exergy limit of O₂ production exceeds the observed flux by several orders of magnitude, consistent with the actual efficiency of photosynthesis.
Oxygenic photosynthesis requires splitting water. It's kind of like a water wheel: to make it spin, you need a strong current. Light acts as the current, and light particles are the streams. For red dwarfs, the most common stars, the light is "cool" and weak — the streams barely move the wheel.
But even on Earth, with its bright Sun, the wheel uses only a drop of the available energy. The theoretical maximum oxygen output is thousands of times higher than what's actually produced. So complex life might be hiding unnoticed — and we should search for it around stars similar to ours.
🎯 The upper theoretical limit for oxygen production on Earth is thousands of times higher than what plants actually produce.