KEPLER-16b: SAFE IN A RESONANCE CELL

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.