Dynamical constraints on the origin of hot and warm Jupiters with close friends

TL;DR

This study investigates the dynamical history of hot and warm Jupiters with outer companions, finding that secular migration processes are unlikely to explain their current positions, suggesting alternative formation pathways.

Contribution

The paper combines numerical and analytical methods to demonstrate that secular migration cannot account for most observed hot and warm Jupiters with companions, challenging existing migration theories.

Findings

Most observed Jupiter pairs are dynamically unstable if the inner planet started beyond 1 AU.

Unstable systems tend to lead to ejections or star collisions, not tidal migration.

Secular migration explains less than 10% of hot and warm Jupiters between 0.1-1 AU.

Abstract

Gas giants orbiting their host star within the ice line are thought to have migrated to their current locations from farther out. Here we consider the origin and dynamical evolution of observed Jupiters, focusing on hot and warm Jupiters with outer friends. We show that the majority of the observed Jupiter pairs (twenty out of twenty-four) will be dynamically unstable if the inner planet was placed at >~1AU distance from the stellar host. This finding is at odds with formation theories that invoke the migration of such planets from semi-major axes >~1AU due to secular dynamical processes (e.g., secular chaos, Lidov-Kozai oscillations) coupled with tidal dissipation. In fact, the results of N-body integrations show that the evolution of dynamically unstable systems does not lead to tidal migration but rather to planet ejections and collisions with the host star. This and other arguments lead us to suggest that most of the observed planets with a companion could not have been transported from further out through secular migration processes. More generally, by using a combination of numerical and analytic techniques we show that the high-e Lidov-Kozai migration scenario can only account for less than 10% of all gas giants observed between 0.1-1 AU. Simulations of multi-planet systems support this result. Our study indicates that rather than starting on highly eccentric orbits with orbital periods above one year, these "warm" Jupiters are more likely to have reached the region where they are observed today without having experienced significant tidal dissipation.