A Secular Resonant Origin for the Loneliness of Hot Jupiters

TL;DR

This paper proposes that the loneliness of hot Jupiters is caused by a secular resonant interaction with the stellar quadrupole, which tilts the orbits of exterior planets, explaining their observational differences from warm Jupiters.

Contribution

It introduces a unified model explaining hot and warm Jupiter loneliness through stellar quadrupole interactions, challenging previous migration-based theories.

Findings

Hot Jupiters are often lonely due to orbital tilting caused by stellar quadrupole resonance.

Warm Jupiters retain coplanarity because of weaker stellar quadrupole influence.

The model can be tested with upcoming TESS data.

Abstract

Despite decades of inquiry, the origin of giant planets residing within a few tenths of an astronomical unit from their host stars remains unclear. Traditionally, these objects are thought to have formed further out before subsequently migrating inwards. However, the necessity of migration has been recently called into question with the emergence of in-situ formation models of close-in giant planets. Observational characterization of the transiting sub-sample of close-in giants has revealed that "warm" Jupiters, possessing orbital periods longer than roughly 10 days more often possess close-in, co-transiting planetary companions than shorter period "hot" Jupiters, that are usually lonely. This finding has previously been interpreted as evidence that smooth, early migration or in situ formation gave rise to warm Jupiter-hosting systems, whereas more violent, post-disk migration pathways sculpted hot Jupiter-hosting systems. In this work, we demonstrate that both classes of planet may arise via early migration or in-situ conglomeration, but that the enhanced loneliness of hot Jupiters arises due to a secular resonant interaction with the stellar quadrupole moment. Such an interaction tilts the orbits of exterior, lower mass planets, removing them from transit surveys where the hot Jupiter is detected. Warm Jupiter-hosting systems, in contrast, retain their coplanarity due to the weaker influence of the host star's quadrupolar potential relative to planet-disk interactions. In this way, hot Jupiters and warm Jupiters are placed within a unified theoretical framework that may be readily validated or falsified using data from upcoming missions such as TESS.