  With dozens of Jovian and super-Jovian exoplanets known to orbit their host
stars in or near the stellar habitable zones, it has recently been suggested
that moons the size of Mars could offer abundant surface habitats beyond the
solar system. Several searches for such exomoons are now underway, and the
exquisite astronomical data quality of upcoming space missions and ground-based
extremely large telescopes could make the detection and characterization of
exomoons possible in the near future. Here we explore the effects of tidal
heating on the potential of Mars- to Earth-sized satellites to host liquid
surface water, and we compare the tidal heating rates predicted by tidal
equilibrium model and a viscoelastic model. In addition to tidal heating, we
consider stellar radiation, planetary illumination and thermal heat from the
planet. However, the effects of a possible moon atmosphere are neglected. We
map the circumplanetary habitable zone for different stellar distances in
specific star-planet-satellite configurations, and determine those regions
where tidal heating dominates over stellar radiation. We find that the
`thermostat effect' of the viscoelastic model is significant not just at large
distances from the star, but also in the stellar habitable zone, where stellar
radiation is prevalent. We also find that tidal heating of Mars-sized moons
with eccentricities between 0.001 and 0.01 is the dominant energy source beyond
3--5 AU from a Sun-like star and beyond 0.4--0.6 AU from an M3 dwarf star. The
latter would be easier to detect (if they exist), but their orbital stability
might be under jeopardy due to the gravitational perturbations from the star.
