Tuesday, July 12, 2016

Circumbinary Exoplanets get Scattered, not Collide

Planet Scattering Around Binaries: Ejections, Not Collisions


Smullen et al


Transiting circumbinary planets discovered by Kepler provide unique insight into binary 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. Aside from the absence of very close-in planets, which are unstable around a binary, dynamical evolution alone does not introduce systematic differences in the final planet populations. Thus, we suggest that any intrinsic differences in the populations are imprinted by formation.

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