# Photosynthesis on habitable planets around low-mass stars

## TL;DR

Planets around very low-mass M-dwarfs may lack sufficient photosynthetically active radiation to support Earth-like life, leading to low biosphere productivity and minimal atmospheric oxygen buildup, with most stars unlikely to sustain such biospheres.

## Contribution

This study quantifies the photon flux limitations around low-mass stars and estimates the flaring rates needed to sustain Earth-like biospheres and oxygen accumulation.

## Key findings

- Planets around M-dwarfs with mass less than 0.2 solar masses may not support Earth-like biospheres.
- Most M-dwarfs are unlikely to have flaring activity sufficient to sustain oxygen-producing biospheres.
- Low photon flux limits biological productivity on planets orbiting the smallest M-dwarfs.

## Abstract

We show that planets around M-dwarfs with $M_\star \lesssim 0.2 M_\odot$ may not receive enough photons in the photosynthetically active range of $400$-$750$ nm to sustain Earth-like biospheres. As a result of the lower biological productivity, it is likely that biotic molecular oxygen would not build up to detectable levels in the atmospheres of habitable planets orbiting low-mass stars, consistent with prior work by Lehmer et al. (2018). We also estimate the minimum flaring rate for sustaining biospheres with Earth-like productivity and permitting the build-up of atmospheric oxygen, and find that the overwhelming majority of M-dwarfs are unlikely to exceed this threshold.