Estimation of the tidal heating in the TRAPPIST-1 planets

Influence of the internal structure

¹ Observatoire de Genève, Université de Genève, Chemin Pegasi 51, 1290 Sauverny, Switzerland
² Centre pour la Vie dans l’Univers, Université de Genève, Geneva, Switzerland
³ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV Groningen, The Netherlands
⁴ Laboratoire de Planétologie et Géosciences, UMR-CNRS 6112, Nantes Université, 44322 Nantes cedex 03, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 14 March 2025
Accepted: 6 January 2026

Abstract

With the arrival of JWST observations of the TRAPPIST-1 planets – particularly secondary transit depths and phase curves – it is timely to reassess the contribution of tidal heating to their heat budget. JWST thermal phase curves could reveal endogenic heating through an anomalously high nightside temperature, providing an opportunity to estimate tidal heating. In this study, we revisit the tidal heating of these planets and propose a simple method to compute the tidal heating profile across a broad range of parameters. Our approach leverages a known formulation for synchronously rotating planets on low-eccentricity orbits and the fact that the profile shape depends solely on internal structure. We recalculate the tidal heating contributions for all TRAPPIST-1 planets, with a particular focus on the impact of internal structure (core size and viscosity profile) and eccentricity uncertainties on their total heat budget. Although the masses and radii of these planets are well constrained, degeneracies remain in their internal structure and composition. We investigate the role of core iron content for volatile-poor planets of silicate-rock compositions by exploring a range of core sizes. For each structure, we compute the degree-two gravitational Love number, k₂, and the corresponding tidal heating profiles. We assume sub-solidus temperature profiles that are decoupled from interior heat production, which means our estimates are conservative and likely represent minimum values. We find that the tidal heat flux for TRAPPIST-1 b and c can exceed Io’s heat flux, with uncertainties primarily driven by eccentricity. These high fluxes may be detectable with JWST. For planets f to g, the tidal flux remains below Earth’s geothermal flux, suggesting that tidal heating is unlikely to be the dominant energy source. For planets d and e, however, tidal heating likely dominates their heat budget, potentially driving intense volcanic and tectonic activity, which could enhance their habitability prospects.