# The Surface UV Environment on Planets Orbiting M-Dwarfs: Implications for Prebiotic Chemistry & Need for Experimental Follow-Up

## TL;DR

This study models the UV radiation environment on planets orbiting M-dwarfs to assess its potential role in prebiotic chemistry and the origin of life, highlighting the need for experimental follow-up to understand these processes.

## Contribution

It couples radiative transfer models with observed M-dwarf spectra to quantify UV exposure on habitable-zone planets, revealing significantly lower UV levels than early Earth.

## Key findings

- M-dwarf planets receive 100-1000 times less bioactive UV than early Earth.
- Uncertainty remains whether UV-sensitive prebiotic pathways can operate under these conditions.
- Transient UV flares might compensate for low steady-state UV levels, but require further experimental validation.

## Abstract

Potentially-habitable planets orbiting M-dwarfs are of intense astrobiological interest because they are the only rocky worlds accessible to biosignature search over the next 10+ years due to a confluence of observational effects. Simultaneously, recent experimental and theoretical work suggests that UV light may have played a key role in the origin of life on Earth, and especially the origin of RNA. Characterizing the UV environment on M-dwarfs planets is important to understanding whether life as we know it could emerge on such worlds. In this work, we couple radiative transfer models to observed M-dwarf spectra to determine the UV environment on prebiotic Earth-analog planets orbiting M-dwarfs. We calculate dose rates to quantify the impact of different host stars on prebiotically-important photoprocesses. We find that M-dwarf planets have access to 100-1000 times less bioactive UV fluence than the young Earth. It is unclear whether UV-sensitive prebiotic chemistry that may have been important to abiogenesis, such as the only known prebiotically plausible pathways for pyrimidine ribonucleotide synthesis, could function on M-dwarf planets. This uncertainty affects objects like the recently-discovered habitable-zone planets orbiting Proxima Centauri, TRAPPIST-1, and LHS 1140. Laboratory studies of the sensitivity of putative prebiotic pathways to irradiation level are required to resolve this uncertainty. If steady-state M-dwarf UV output is insufficient to power these pathways, transient elevated UV irradiation due to flares may suffice; laboratory studies can constrain this possibility as well.