Repercussions of thermal atmospheric tides on the rotation of terrestrial planets in the habitable zone

TL;DR

This paper introduces a new analytical model for thermal atmospheric tides on terrestrial exoplanets, accounting for dissipation, which better predicts their influence on planetary rotation states and climate.

Contribution

The authors develop a dissipative analytical model that improves upon previous models by accurately predicting thermal tide effects near spin-orbit synchronization.

Findings

Stable atmospheric stratification can suppress tidal torque and promote synchronization.

Convective atmospheres experience strong tidal torque, leading to non-synchronized rotation.

The model aligns with recent GCM simulation results.

Abstract

Semidiurnal atmospheric thermal tides are important for terrestrial exoplanets in the habitable zone of their host stars. With solid tides, they torque these planets, thus contributing to determine their rotation states as well as their climate. Given the complex dynamics of thermal tides, analytical models are essential to understand its dependence on the structure and rotation of planetary atmospheres and the tidal frequency. In this context, the state of the art model proposed in the 60's by Lindzen and Chapman explains well the properties of thermal tides in the asymptotic regime of Earth-like rapid rotators but predicts a non-physical diverging tidal torque in the vicinity of the spin-orbit synchronization. In this work, we present a new model that addresses this issue by taking into account dissipative processes through a Newtonian cooling. First, we recover the tidal torque recently obtained with numerical simulations using General Circulation Models (GCM). Second, we show that the tidal response is very sensitive to the atmospheric structure, particularly to the stability with respect to convection. A strong stable stratification is able to annihilate the atmospheric tidal torque, leading to synchronization, while a convective atmosphere will be submitted to a strong torque, leading to a non-synchronized rotation state.