Spin evolution of Earth-sized exoplanets, including atmospheric tides and core-mantle friction

TL;DR

This study investigates the long-term spin evolution of Earth-sized exoplanets, emphasizing the roles of atmospheric tides, core-mantle friction, eccentricity, and obliquity, revealing that planets tend to settle into specific non-synchronous equilibrium states.

Contribution

The paper extends previous models by incorporating eccentric orbits and obliquity effects, providing a more comprehensive understanding of exoplanet spin dynamics and habitability implications.

Findings

Obliquity evolves to 0 or 180 degrees.

Planets reach a limited set of equilibrium rotations.

Atmospheric tides significantly influence habitability assessments.

Abstract

Planets with masses between 0.1 - 10 M_earth are believed to host dense atmospheres. These atmospheres can play an important role on the planet's spin evolution, since thermal atmospheric tides, driven by the host star, may counterbalance gravitational tides. In this work we study the long-term spin evolution of Earth-sized exoplanets. We generalize previous works by including the effect of eccentric orbits and obliquity. We show that under the effect of tides and core-mantle friction, the obliquity of the planets evolve either to 0 or 180 degrees. The rotation of these planets is also expected to evolve into a very restricted number of equilibrium configurations. In general, none of this equilibria is synchronous with the orbital mean motion. The role of thermal atmospheric tides becomes more important for Earth-sized planets in the habitable zones of their systems, so they cannot be neglected when we search for their potential habitability.