“Is there an Outer Circumplanetary Habitable Edge? Further Adventures with Exomoon Climate Models”

Duncan Forgan (St. Andrews)
Wednesday, 1510, Lecture Room 106

Simple calculations of the orbit averaged flux received by Earth-like exomoons orbiting giant planets suggest that the circumplanetary region has an inner habitable edge defined by tidal heating, and no discernible outer edge (at least, until the orbital stability limit is reached at around a third of the planet's Hill Radius). In previous work using 1D climate models that account for atmospheric circulation and ice-albedo feedback processes, we identified an outer circumplanetary habitable edge that is present if the moon's orbit is coplanar to the planet's. Eclipses appear to produce a sufficiently long drop in stellar radiative flux that the moon transitions to a snowball state from which it cannot escape.

I will present our recent attempts to improve the climate model, by adding the carbonate-silicate cycle and viscoelastic tidal heating. Will the snowball state be avoided by allowing the moon to regulate its CO2 partial pressure? Will temperature-dependent rigidity/tidal dissipation extend the circumplanetary habitable region to the orbital stability limit? I will address these questions, and consider some routes for future work in exomoon climate modelling.