Resonance capture and long-term evolution of planets in binary star systems

TL;DR

This study investigates how binary star companions influence the formation, resonance, and long-term evolution of two-planet systems during and after the protoplanetary disk phase, revealing conditions for stable resonances and chaotic outcomes.

Contribution

It introduces a modified symplectic integrator to simulate binary-planet interactions, demonstrating the impact of binary separation and inclination on resonance formation and system stability.

Findings

Wide binaries (1000au) support long-term resonant pairs.

Close binaries (250au) lead to chaotic evolution and planet ejections.

Resonance stability depends on binary separation and planet-planet interactions.

Abstract

The aim of this work is to study the impact of a binary companion on the evolution of two-planet systems during both the type-II migration phase and their long-term evolution after the dissipation of the protoplanetary disk. We use the symplectic integrator SyMBA, modified to include a wide binary companion. We also include the Type-II migration of giant planets during the disk phase with suitable eccentricity and inclination damping as well as the disk gravitational potential acting on the planets and the nodal precession of the disk induced by the binary companion. We consider various inclinations, eccentricities, and separations of the binary companion. Disk migration allows the formation of planet pairs in mean-motion resonances (MMR) despite the presence of the binary companion. When the binary separation is wide (1000au), the timescale of the perturbations it raises on the planets is longer than the disk's lifetime and resonant pairs are routinely formed in the 2:1, 5:2 and 3:1 MMR. Provided the planet-planet interaction timescale is smaller than the binary perturbations timescale, these systems can remain in resonance long after the disk has dissipated. When the binary separation is smaller (250au), only planets in the 2:1 resonance tend to remain in a resonant state and more chaotic evolutions are observed, as well as more ejections. After those ejections, the remaining planet can become eccentric due to the perturbations from the binary companion and for strongly inclined binary companions captures in the von Ziepel-Lidov-Kozai resonance can occur, while in systems with two planets this mechanism is quenched by planet-planet interactions. Our simulations reveal that the interplay between planet-disk, planet-planet and planet-binary interactions can lead to the formation of resonant pairs of planets which remain stable over timescales much longer than the disk's lifetime.