Planet Scattering Around Binaries: Ejections, Not Collisions

TL;DR

This study uses N-body simulations to compare how planet-planet scattering affects planetary systems around binary stars versus single stars, revealing that ejections dominate planet loss in binaries and that initial conditions influence final system configurations.

Contribution

It provides the first detailed comparison of dynamical evolution in circumbinary versus single-star planetary systems, highlighting the role of ejections and initial conditions.

Findings

Most circumbinary planets are lost via ejections.

Binary presence mainly affects planet loss mechanisms, not final distributions.

Systems like Kepler-47 can form from tightly packed, unstable initial configurations.

Abstract

Transiting circumbinary planets discovered by Kepler provide unique insight into binary star and planet formation. Several features of this new found population, for example the apparent pile-up of planets near the innermost stable orbit, may distinguish between formation theories. In this work, we determine how planet-planet scattering shapes planetary systems around binaries as compared to single stars. In particular, we look for signatures that arise due to differences in dynamical evolution in binary systems. We carry out a parameter study of N-body scattering simulations for four distinct planet populations around both binary and single stars. While binarity has little influence on the final system multiplicity or orbital distribution, the presence of a binary dramatically effects the means by which planets are lost from the system. Most circumbinary planets are lost due to ejections rather than planet-planet or planet-star collisions. The most massive planet in the system tends to control the evolution. Systems similar to the only observed multi-planet circumbinary system, Kepler-47, can arise from much more tightly packed, unstable systems. Only extreme initial conditions introduce differences in the final planet populations. Thus, we suggest that any intrinsic differences in the populations are imprinted by formation.