Drifts of the sub-stellar points of the TRAPPIST-1 planets

TL;DR

This study models the tidal interactions of TRAPPIST-1 planets, revealing they are not fully synchronized but exhibit oscillations and drifts in their sub-stellar points, affecting their thermal and surface conditions.

Contribution

Introduces a new tidal model implementation in Posidonius to analyze the rotational states and sub-stellar point drifts of TRAPPIST-1 planets considering their internal structures.

Findings

Planets oscillate around synchronization rather than being fully synchronized.

Planet-planet interactions cause significant variations in mean motion and tides.

Sub-stellar points drift over long timescales, affecting habitability considerations.

Abstract

Accurate modeling of tidal interactions is crucial for interpreting recent JWST observations of the thermal emissions of TRAPPIST-1~b and c and for characterizing the surface conditions and potential habitability of the other planets in the system. Indeed, the rotation state of the planets, driven by tidal forces, significantly influences the heat redistribution regime. Due to their proximity to their host star and the estimated age of the system, the TRAPPIST-1 planets are commonly assumed to be in a synchronization state. In this work, we present the recent implementation of the co-planar tidal torque and forces equations within the formalism of Kaula in the N-body code Posidonius. This enables us to explore the hypothesis of synchronization using a tidal model well suited to rocky planets. We studied the rotational state of each planet by taking into account their multi-layer internal structure computed with the code Burnman. Simulations show that the TRAPPIST-1 planets are not perfectly synchronized but oscillate around the synchronization state. Planet-planet interactions lead to strong variations on the mean motion and tides fail to keep the spin synchronized with respect to the mean motion. As a result, the sub-stellar point of each planet experiences short oscillations and long-timescale drifts that lead the planets to achieve a synodic day with periods varying from $55$~years to $290$~years depending on the planet.