UV Surface Habitability of the TRAPPIST-1 System

TL;DR

This study models the UV surface environments of TRAPPIST-1's habitable zone planets, assessing how stellar activity and atmospheric conditions influence potential habitability and the possibility of surface life.

Contribution

It provides the first detailed UV surface environment models for TRAPPIST-1 planets, highlighting the importance of atmospheric composition in habitability assessments.

Findings

Dense atmospheres with ozone could shield planets from harmful UV.

Eroded or anoxic atmospheres would expose surfaces to high UV levels.

Detection of ozone would make planets promising targets for life searches.

Abstract

With the discovery of rocky planets in the temperate habitable zone (HZ) of the close-by cool star TRAPPIST-1 the question of whether such planets could harbour life arises. Habitable planets around red dwarf stars can orbit in radiation environments that can be life-sterilizing. UV flares from these stars are more frequent and intense than solar flares. Additionally, their temperate HZs are closer to the star. Here we present UV surface environment models for TRAPPIST-1's HZ planets and explore the implications for life. TRAPPIST-1 has high X-ray/EUV activity, placing planetary atmospheres at risk from erosion. If a dense Earth-like atmosphere with a protective ozone layer exists on planets in the HZ of TRAPPIST-1, UV surface environments would be similar to present-day Earth. However an eroded or an anoxic atmosphere, would allow more UV to reach the surface, making surface environments hostile even to highly UV-tolerant terrestrial extremophiles. If future observations detect ozone in the atmospheres of any of the planets in the HZ of TRAPPIST-1, these would be interesting targets for the search for surface life. We anticipate our assay to be a starting point for in-depth exploration of stellar and atmospheric observations of the TRAPPIST-1 planets to constrain their UV-surface-habitability.