Origins of Hot Jupiters from the Stellar Obliquity Distribution

TL;DR

This paper investigates the origins of hot Jupiters by analyzing stellar obliquity distributions, concluding that high-eccentricity migration explains their current orbital configurations without needing alternative formation theories.

Contribution

It demonstrates that hot Jupiters' obliquity and eccentricity distributions support high-eccentricity migration as the primary formation mechanism.

Findings

Hot Jupiters with eccentric companions show no obliquity trend with stellar temperature.

Obliquity and eccentricity data align with high-eccentricity migration outcomes.

High-eccentricity migration can explain hot Jupiter properties without other formation mechanisms.

Abstract

The obliquity of a star, or the angle between its spin axis and the average orbit normal of its companion planets, provides a unique constraint on that system's evolutionary history. Unlike the Solar System, where the Sun's equator is nearly aligned with its companion planets, many hot Jupiter systems have been discovered with large spin-orbit misalignments, hosting planets on polar or retrograde orbits. We demonstrate that, in contrast to stars harboring hot Jupiters on circular orbits, those with eccentric companions follow no population-wide obliquity trend with stellar temperature. This finding can be naturally explained through a combination of high-eccentricity migration and tidal damping. Furthermore, we show that the joint obliquity and eccentricity distributions observed today are consistent with the outcomes of high-eccentricity migration, with no strict requirement to invoke the other hot Jupiter formation mechanisms of disk migration or in-situ formation. At a population-wide level, high-eccentricity migration can consistently shape the dynamical evolution of hot Jupiter systems.