2025A&A...704A...9B

We investigated the origin and stability of extrasolar satellites orbiting close-in gas giants, focusing on whether these satellites can survive planetary migration within a protoplanetary disk. To address this question, we used POSIDONIUS, an N-Body code with an integrated tidal model, which we expanded to account for the migration of a gas giant within a disk. Our simulations include tidal interactions between a 1 M_⊙ star and a 1 M_Jup planet, and between the planet and its satellite, while neglecting tides raised by the star on the satellite. We adopted a standard equilibrium tide model for the satellite, planet, and star, and additionally explored the impact of dynamical tides in the convective regions of both the star and planet on satellite survival. We systematically examined key parameters, including the initial satellite-planet distance, disk lifetime (which serves as a proxy for the planet's final orbital distance), satellite mass, and satellite tidal dissipation. For simulations incorporating dynamical tides in both the planet and star, we also explored three different initial stellar rotation periods. Our primary finding is that satellite survival is rare if the satellite has nonzero tidal dissipation. Survival is only possible for initial orbital distances of at least 0.6 times the Jupiter-Io separation and for planets orbiting beyond ≈0.1 AU. Satellites that fail to survive are either tidally disrupted, as they experience orbital decay and cross the Roche limit, or dynamically disrupted, where eccentricity excitation drives their periastron within the Roche limit. Satellite survival is more likely for low tidal dissipation and higher satellite mass. Given that satellites around close-in planets appear unlikely to survive planetary migration, our findings suggest that if such satellites do exist (as has been recently suggested), another process should be invoked. In that context, we also briefly discuss the claim of the existence of a putative satellite around WASP-49 A b.