Tatooine's Future: Dynamical Evolution of Planets Orbiting Two Stars

Science fiction has long teased our imaginations with tales of planets with two suns. How these planets form and evolve, and their survival prospects, are active fields of research. Expanding on previous work, four new Kepler candidate circumbinary planet systems were evolved through the complex common-envelope phase. The dynamical response of the planets to this dramatic evolutionary phase was simulated using open-source binary star evolution and numerical integrator codes. All four systems undergo at least one common-envelope phase; one experiences two and another, three. Their planets tend to survive the common-envelope phase, regardless of relative inclination, and migrate to wider, more eccentric orbits; orbital expansion can occur well within a single planetary orbit. During the secondary common-envelope phases, the planets can gain significant eccentricity to be ejected from the system. Depending on the mass-loss rate, the planets either migrate adiabatically outward within a few orbits, or non-adiabatically to much more eccentric orbits. Their final orbital configurations are consistent with those of post-common-envelope circumbinary planet candidates, suggesting a possible origin for the latter. The results from this work provide a basis for future observations of post-common-envelope circumbinary systems.