Kepler-16b: safe in a resonance cell

Abstract

The planet Kepler-16b is known to follow a circumbinary orbit around a system of two main-sequence stars. We construct stability diagrams in the "pericentric distance - eccentricity" plane, which show that Kepler-16b is in a hazardous vicinity to the chaos domain - just between the instability "teeth" in the space of orbital parameters. Kepler-16b survives, because it is close to the stable half-integer 11/2 orbital resonance with the central binary, safe inside a resonance cell bounded by the unstable 5/1 and 6/1 resonances. The neighboring resonance cells are vacant, because they are "purged" by Kepler-16b, due to overlap of first-order resonances with the planet. The newly discovered planets Kepler-34b and Kepler-35b are also safe inside resonance cells at the chaos border.