Multi-Planet Destabilisation and Escape in Post-Main Sequence Systems

TL;DR

This paper investigates how stellar mass loss combined with planet-planet interactions can destabilize multi-planet systems around evolved stars, leading to planetary escape through chaos-driven close encounters.

Contribution

It introduces a dynamical framework showing how mass loss and mutual planetary interactions induce chaos, causing planetary escape in post-main sequence systems.

Findings

Mass loss triggers transition from stable to chaotic configurations.

Chaos leads to close encounters and planetary ejection.

Non-adiabatic effects are significant for massive progenitors.

Abstract

Discoveries of exoplanets orbiting evolved stars motivate critical examinations of the dynamics of $N$-body systems with mass loss. Multi-planet evolved systems are particularly complex because of the mutual interactions between the planets. Here, we study the underlying dynamical mechanisms which can incite planetary escape in two-planet post-main sequence systems. Stellar mass loss alone is unlikely to be rapid and high enough to eject planets at typically-observed separations. However, the combination of mass loss and planet-planet interactions can prompt a shift from stable to chaotic regions of phase space. Consequently, when mass loss ceases, the unstable configuration may cause escape. By assuming a constant stellar mass loss rate, we utilize maps of dynamical stability to illustrate the distribution of regular and chaotic trajectories in phase space. We show that chaos can drive the planets to undergo close encounters, leading to the ejection of one planet. Stellar mass loss can trigger the transition of a planetary system from a stable to chaotic configuration, subsequently causing escape. We find that mass loss non-adiabatically affects planet-planet interaction for the most massive progenitor stars which avoid the supernova stage. For these cases, we present specific examples of planetary escape.