Migration and Stability of Multi-Planet Circumbinary Systems

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The Ohio State University

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Of the known circumbinary planets, most are single planets observed just outside of the zone of instability caused by gravitational interactions with the binary. Migration is the preferred mechanism of getting circumbinary planets to these positions, as the turbulent conditions in these zones make in situ planetary formation unlikely. Only one con firmed multi-planet circumbinary system is known in Kepler-47. In order to understand the stability and likelihood of multi-planet circumbinary systems, we have modeled currently known systems with synthetic outer planets using varying starting parameters. Our simulations indicate long-term stable resonant locking occurring most reliably for mass ratios (outer/inner) less than 0.1, with some exception up to 0.4. Systems below this threshold lock primarily in the 2:1 resonance, with occasional exception to the 3:2 resonance. Mass ratios greater than one and up to ten are probed, but these cases cause the inner planet to be pushed interior to the realm of instability, resulting in the ejection of the inner planet, and occasionally also the outer planet. Our results have implications on the potential discovery of additional planets in known single-planet circumbinary systems, an understanding of the transition between stable and unstable multi-planet architectures, and a source for free-floating exoplanets.



exoplanets, binary stars, circumbinary planets, planetary migration