Oxygenic photosynthesis unlikely around red dwarf stars, warns expert

In the context of extraterrestrial life, research led by Chris Duffy, a theoretical biophysicist at Queen Mary University in London, has drawn attention to the limitations of oxygenic photosynthesis around M-dwarf stars. These red dwarf stars are the most common type in the universe, but their faint light poses challenges for complex life forms to develop. Duffy explains that planets orbiting these stars would receive significantly less visible light, resulting in conditions similar to shaded environments on Earth. This reduced light limit the efficiency of photosynthesis, which on Earth takes place within a specific spectrum of visible light. Oxygenic photosynthesis is critical for producing oxygen-rich atmospheres, which facilitate aerobic respiration—a key process for supporting multicellular and intelligent life. Duffy elaborates that plants and photosynthetic organisms utilize a complex system that requires visible light for converting water and carbon dioxide into essential nutrients and oxygen. However, the light available around red dwarf stars is mostly outside of the optimal range for these processes, leading to the conclusion that the evolution of oxygenic photosynthesis may be significantly hindered. Moreover, although photosynthetic organisms rely on visible light, they are also vulnerable to damage from ultraviolet light, which can harm DNA and proteins in the cells. Because water absorbs much UV radiation, the damage is primarily a concern for surface organisms. In relation to these findings, the concept of the 'red edge'—coined by Carl Sagan—refers to the reflectance of the Earth as seen by space probes, indicating how terrestrial life might differ on other planets. In summary, Duffy stresses that the prospects for oxygenic photosynthesis to develop around M-dwarf stars look bleak. Given the prevalence of these stars in the universe, this could be a key factor limiting not only the existence of complex life within our galaxy but also beyond. This understanding highlights the critical conditions necessary for life as we know it and may influence future explorations for habitable exoplanets.