Stability of circumbinary planets: The role of binary properties and migration scenarios

Abstract

Of the thousands of exoplanets detected to date, only a very small fraction are classified as circumbinary planets. When considering only low-mass planets, their number becomes negligible. This rarity may be partly explained by observational biases, but also by the challenging dynamical environment that often prevents the long-term stability of planetary orbits in binary systems. It is therefore essential to investigate the conditions that enable the formation and survival of stable circumbinary planets, with particular attention to the case of low-mass planets. To this end, we performed N-body simulations coupled with a planet migration prescription to study the post-formation dynamics of two circumbinary planets of 10 Earth masses in a protoplanetary disc. This approach allowed us to estimate whether, for a given set of binary and planetary parameters, planets remain bound to their stars or become unstable and ejected. Based on more than 1,000 simulations, our results indicate that two-planet inward migration can, in some cases, be halted through resonance capture with the binary. In contrast to some previous purely N-body studies, such configurations appear to remain stable over long timescales. We further find that the binary parameters q_B and e_B play a key role in shaping the stability landscape of multi-planet systems. Within the explored parameter space, some regions support long-term stability, whereas others appear highly unstable. These stability regions are also highly sensitive to the migration timescales (i.e. to disc properties and planetary masses). Finally, our simulations suggest that systems in which two planets enter resonance while migrating together are more likely to form stable multi-planet configurations, particularly around highly eccentric binaries. This constitutes a first step towards identifying the most promising binary star systems likely to host multiple low-mass circumbinary planets. They may serve as valuable guidelines for future observational campaigns, such as those of PLATO and . Gaia