The Potential for Tidally Heated Icy and Temperate Moons around Exoplanets

Moons of giant planets may represent an alternative to the classical pictureof habitable worlds. They may exist within the circumstellar habitable zone ofa parent star, and through tidal energy dissipation they may also offeralternative habitable zones, where stellar insolation plays a secondary, orcomplementary, role. We investigate the potential extent of stable satelliteorbits around a set of 74 known extrasolar giant planets located beyond 0.6 AUfrom their parent stars - where moons should be long-lived with respect toremoval by stellar tides. Approximately 60% of these giant planets can sustainsatellites or moons in bands up to $\sim 0.04$ AU in width. For comparison, theGaliean satellites extend to $\sim 0.013$ AU. We investigate the stellarinsolation that moons would experience for these exoplanet systems, and theimplications for sublimation loss of volatiles. We find that between 15 and 27%of {\em all} known exoplanets may be capable of harboring small, icy, moons. Inaddition, some 22-28% of all known exoplanets could harbor moons within a``sublimation zone'', with insolation temperatures between 273 K and 170 K. Asimplified energy balance model is applied to the situation of temperate moons,maintained by a combination of stellar insolation and tidal heat flow. Wedemonstrate that large moons ($>0.1 $M$_{\oplus}$), at orbital radiicommensurate with those of the Galilean satellites, could maintain temperate,or habitable, surface conditions during episodes of tidal heat dissipation ofthe order 1-100 times that currently seen on Io. (Abridged).Comment: 28 pages, 8 Figures, AASTex, Accepted for publication in the Astrophysical Journa