Stability of circumbinary multi-planet systems

Circumbinary planets are commonly observed close to the dynamical stability limit of their host binaries, although planet formation is expected to be inefficient in the regions where these planets are currently found. A widely accepted scenario therefore suggests that circumbinary planets formed farther out in a circumbinary disk and migrated inward through planet–disk interactions. During this migration phase, resonant multi-planet configurations may naturally emerge. However, only two multi-planet circumbinary systems orbiting main-sequence binaries have been detected so far, and observational biases are unlikely to fully account for this apparent scarcity. This suggests that the dynamical environment induced by the central binary may strongly affect the long-term stability of such systems.
    
    In this presentation, we investigate the conditions required for the formation of stable circumbinary multi-planet systems through more than 1,000 N-body simulations of migrating super-Earth pairs. We explore the impact of a broad range of binary and migration parameters on the resulting planetary architectures. We first show that planets can be trapped in mean-motion resonance with the central binary, providing the starting point for potential resonant multi-planet chains. We further show that the binary mass ratio and eccentricity strongly influence the long-term stability of these systems, with distinct regions of parameter space leading either to stable configurations or to strong dynamical instability. In addition, for a given binary configuration, the final system architecture can still depend on the adopted migration timescales, related to disk and planet properties. Overall, these results help identify which binary configurations are most favourable for hosting stable circumbinary multi-planet systems. They also provide guidance for future observational surveys and constitute a first step toward studying the stability of circumbinary multi-planet systems in higher-order stellar systems.