Spin-orbit coupling for close-in planets

TL;DR

This paper develops a comprehensive framework for understanding the spin evolution of close-in planets, accounting for multi-body interactions, and demonstrates how perturbations can lead to complex spin states, with applications to Mercury and exoplanet systems.

Contribution

It introduces a general formulation of the spin-orbit problem, including new methods for analyzing spin dynamics, librations, and tidal effects in multi-planet systems.

Findings

Planet-planet perturbations can cause asynchronous or chaotic spins.

The framework applies to Mercury and exoplanet systems like KOI-1599.

Perturbations significantly influence spin states even in nearly circular orbits.

Abstract

We study the spin evolution of close-in planets in multi-body systems and present a very general formulation of the spin-orbit problem. This includes a simple way to probe the spin dynamics from the orbital perturbations, a new method for computing forced librations and tidal deformation, and general expressions for the tidal torque and capture probabilities in resonance. We show that planet-planet perturbations can drive the spin of Earth-size planets into asynchronous or chaotic states, even for nearly circular orbits. We apply our results to Mercury and to the KOI-1599 system of two super-Earths in a 3/2 mean motion resonance.