Obliquity Variation of Circumbinary Planets

Planet spin-axis variations play an important role in the stability of a planet’s climate. For planets around a single star, perturbations from planetary companions could drive spin-orbit resonances and create large variations in the planetary spin-axis orientations. Here, we investigate the spin-axis variations of circumbinary planets — planets that orbit around stellar binaries. We find that the large quadrupole potential of the stellar binary could speed up the planetary orbital precession, and detune the system out of spin-orbit resonances. This leads to very small obliquity variations for planets that reside near the same plane as the stellar binaries. Thus, habitable zone planets around the stellar binaries may hold higher potential for stable climate comparing to their single star analogues.