# Tidal Heating and the Habitability of the TRAPPIST-1 Exoplanets

## TL;DR

This study models tidal heating and insolation effects on TRAPPIST-1 planets, suggesting that planets e and d could be habitable, while others are too hot or cold for life, based on their heat fluxes and surface conditions.

## Contribution

It applies a Maxwell viscoelastic rheology to accurately estimate tidal heating, improving understanding of habitability conditions for TRAPPIST-1 planets.

## Key findings

- Planets e and d may support habitable conditions with Earth-like temperatures.
- Planets b and c likely experience runaway greenhouse effects, making them uninhabitable.
- Planets f, g, and h probably have icy surfaces with potential subsurface oceans.

## Abstract

Context. New estimates of the masses and radii of the seven planets orbiting the ultracool M-dwarf TRAPPIST-1 star permit improved modelling of their compositions, heating by tidal dissipation, and removal of tidal heat by solid-state convection. Aims. Here, we compute the heat flux due to insolation and tidal heating for the inner four planets. Methods. We apply a Maxwell viscoelastic rheology to compute the tidal response of the planets using the volume-weighted average of the viscosities and rigidities of the metal, rock, high-pressure ice and liquid water/ice I layers. Results. We show that TRAPPIST-1d and e can avoid entering a runaway greenhouse state. Planet e is the most likely to support a habitable environment, with Earth-like surface temperatures and possibly liquid water oceans. Planet d also avoids a runaway greenhouse, if its surface reflectance is at least as high as that of the Earth. Planets b and c, closer to the star, have heat fluxes high enough to trigger a runaway greenhouse and support volcanism on the surfaces of their rock layers, rendering them too warm for life. Planets f, g, and h are too far from the star to experience significant tidal heating, and likely have solid ice surfaces with possible subsurface liquid water oceans.