Estimation of the tidal heating in the TRAPPIST-1 planets. Influence of the internal structure

TL;DR

This study assesses the tidal heating of TRAPPIST-1 planets using a new method that accounts for internal structure, revealing some planets may have significant volcanic activity driven by tidal forces, detectable by JWST.

Contribution

It introduces a simple, structure-dependent model for tidal heating profiles across TRAPPIST-1 planets, considering internal composition and eccentricity uncertainties.

Findings

Tidal heat flux in T-1b and c can surpass Io's, possibly detectable by JWST.

Tidal heating in T-1f and g is below Earth's geothermal flux, unlikely to dominate.

Planets d and e likely have tidal heating that influences their geological activity.

Abstract

With the arrival of JWST observations of the TRAPPIST-1 planets, 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 calculate the tidal heating contributions for all T-1 planets, with a particular focus on the impact of internal structure 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. For volatile-poor planets of silicate-rock compositions, we investigate the role of core iron content by exploring a range of core sizes. For each structure, we compute the degree-two gravitational Love number, $k_2$, and the corresponding tidal heating profiles. We assume sub-solidus temperatures 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 T-1b and c can exceed Io's heat flux, with uncertainties primarily driven by eccentricity. These high fluxes may be detectable with JWST. For T-1f 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.