Star Hoppers: Planet Instability and Capture in Evolving Binary Systems

TL;DR

This study explores how stellar evolution in binary systems can destabilize planetary orbits, leading to collisions, exchanges between stars, ejections, and potential captures that may influence habitable zones around white dwarfs.

Contribution

It introduces a new model analyzing the impact of binary stellar evolution on planetary dynamics, including planet capture and exchange mechanisms.

Findings

Stellar evolution can induce planetary orbital chaos.

Planets can be captured during stellar envelope collisions.

Binary evolution can lead to planet ejections and exchanges.

Abstract

Many planets are observed in stellar binary systems, and their frequency may be comparable to that of planetary systems around single stars. Binary stellar evolution in such systems influences the dynamical evolution of the resident planets. Here we study the evolution of a single planet orbiting one star in an evolving binary system. We find that stellar evolution can trigger dynamical instabilities that drive planets into chaotic orbits. This instability leads to planet-star collisions, exchange of the planet between the binary stars ("star-hoppers"), and ejection of the planet from the system. The means by which planets can be recaptured is similar to the pull-down capture mechanism for irregular solar system satellites. Because planets often suffer close encounters with the primary on the asymptotic giant branch, captures during a collision with the stellar envelope are also possible. Such capture could populate the habitable zone around white dwarfs.