On the Tidal Dissipation of Obliquity

TL;DR

This paper examines how tidal dissipation affects the obliquity of hot Jupiters, finding that it does not lead to alignment as observed, challenging existing theories about their orbital evolution.

Contribution

It demonstrates that tidal dissipation alone cannot explain the observed alignment of hot Jupiters around cool stars, questioning its role in obliquity evolution.

Findings

Obliquity evolves to prograde, retrograde, or 90° orbits.

Tidal dissipation does not produce alignment in hot Jupiters.

Observed alignment around cool stars is inconsistent with model predictions.

Abstract

We investigate tidal dissipation of obliquity in hot Jupiters. Assuming an initial random orientation of obliquity and parameters relevant to the observed population, the obliquity of hot Jupiters does not evolve to purely aligned systems. In fact, the obliquity evolves to either prograde, retrograde or 90^{o} orbits where the torque due to tidal perturbations vanishes. This distribution is incompatible with observations which show that hot jupiters around cool stars are generally aligned. This calls into question the viability of tidal dissipation as the mechanism for obliquity alignment of hot Jupiters around cool stars.