Instability from high-order resonant chains in wide-separation massive planet systems

TL;DR

This study investigates how high-order resonant chains influence the long-term stability of wide-separation massive exoplanet systems, revealing that such resonances can induce chaos and instability despite predominantly secular evolution.

Contribution

It demonstrates that high-order mean-motion resonant chains significantly contribute to instability in planetary systems, expanding understanding beyond first-order resonance effects.

Findings

High-order resonances can cause chaos and instability.

Secular evolution remains mostly regular over long timescales.

Resonant chains impact angular momentum deficit and system stability.

Abstract

Diversity in the properties of exoplanetary systems arises, in part, from dynamical evolution that occurs after planet formation. We use numerical integrations to explore the relative role of secular and resonant dynamics in the long-term evolution of model planetary systems, made up of three equal mass giant planets on initially eccentric orbits. The range of separations studied is dominated by secular processes, but intersects chains of high-order mean-motion resonances. Over time-scales of $10^8$ orbits, the secular evolution of the simulated systems is predominantly regular. High-order resonant chains, however, can be a significant source of angular momentum deficit (AMD), leading to instability. Using a time-series analysis based on a Hilbert transform, we associate instability with broad islands of chaotic evolution. Previous work has suggested that first-order resonances could modify the AMD of nominally secular systems and facilitate secular chaos. We find that higher-order resonances, when present in chains, can have similar impacts.