The habitable zone for Earth-like exomoons orbiting Kepler-1625b

The recent announcement of a Neptune-sized exomoon candidate orbiting the Jupiter-sized object Kepler-1625b has forced us to rethink our assumptions regarding both exomoons and their host exoplanets. In this paper, I describe calculations of the habitable zone for Earth-like exomoons in the orbit of Kepler-1625b under a variety of assumptions. I find that the candidate exomoon, Kepler-1625b-i, does not currently reside within the exomoon habitable zone, but may have done so when Kepler-1625 occupied the main sequence. If it were to possess its own moon (a 'moon-moon') that was Earth-like, this could potentially have been a habitable world. If other exomoons orbit Kepler-1625b, then there are a range of possible semi-major axes/eccentricities that would permit a habitable surface during the main sequence phase, while remaining dynamically stable under the perturbations of Kepler-1625b-i. This is however contingent on effective atmospheric CO₂ regulation.