Animal Life Unlikely Around a Third of Stars in the Galaxy, Study Says

Why It Matters

The finding narrows the pool of stellar targets for searching extraterrestrial animal life, reshaping astrobiology priorities and mission designs.

Key Takeaways

• Late M-stars emit insufficient PAR for oxygenic photosynthesis
• Oxidation event would require tens of billions of years
• Non‑oxygenic microbes would dominate ecosystems around late M-stars
• 35% of stars are late M, limiting animal life

Pulse Analysis

Late‑type M dwarfs dominate the Milky Way, making up roughly a third of all stars and offering the most accessible signals for small, rocky planets. Their low mass and cool temperatures produce a spectral output heavily weighted toward infrared wavelengths, leaving the 400‑700 nm band—crucial for Earth‑like photosynthesis—severely depleted. This mismatch means that even if a planet resides in the conventional habitable zone, the photon flux required to drive oxygenic photosynthesis is orders of magnitude lower than on Earth, challenging traditional habitability metrics.

Oxygenic photosynthesis is the engine behind atmospheric oxygen accumulation, a prerequisite for aerobic metabolism and, by extension, complex multicellular life. The study’s models show that the Great Oxidation Event, which on Earth took roughly 700 million years, would stretch to tens of billions of years under the dim red light of a late M star. Likewise, the Cambrian‑type diversification of animal forms would be delayed by hundreds of billions of years, effectively outlasting the stable main‑sequence lifetime of these stars. In contrast, non‑oxygenic phototrophs thrive on longer‑wavelength photons, likely establishing ecosystems dominated by simple, anaerobic microbes.

For exoplanet hunters, these insights shift focus toward earlier‑type M dwarfs or Sun‑like stars where sufficient PAR can sustain oxygenic pathways. Future telescopes targeting biosignatures—such as O₂, O₃, or methane disequilibrium—must account for stellar spectral constraints to avoid false negatives. By refining target selection, the astronomical community can allocate resources more efficiently, improving the odds of detecting truly Earth‑analog biospheres rather than microbial shadows on red dwarf worlds.