  Exomoon detections might be feasible with NASA's Kepler or ESA's upcoming
PLATO mission or the ground-based E-ELT. To use observational resources most
efficiently we need to know where the largest, most easily detected moons can
form. We explore the possibility of large exomoons by following the movement of
water (H2O) ice lines in the accretion disks around young super-Jovian planets.
We want to know how different heating sources in those disks affect the H2O ice
lines. We simulate 2D rotationally symmetric accretion disks in hydrostatic
equilibrium around super-Jovian exoplanets. The energy terms in our
semi-analytical model -- (1) viscous heating, (2) planetary illumination, (3)
accretional heating, and (4) stellar illumination -- are fed by precomputed
planet evolution tracks. We consider planets accreting 1 to 12 Jupiter masses
at distances between 1 and 20 AU to a Sun-like star. Accretion disks around
Jupiter-mass planets closer than ~4.5 AU to Sun-like stars do not feature H2O
ice lines, but the most massive super-Jovians can form icy satellites as close
as ~3 AU to Sun-like stars. Super-Jovian planets forming beyond ~5 AU can host
Mars-mass moons. We study a broad range of disk parameters for planets at 5.2
AU and find that the H2O ice lines are universally between ~15 and 30 Jupiter
radii when the last generation of moons is forming. If the abundant population
of super-Jovian planets at ~1 AU formed in situ, then they should lack giant
icy moons because their disks did not host H2O ice in the final stages of
accretion. In the more likely case that these planets migrated to their current
locations from beyond a few AU, they might be orbited by large, H2O-rich moons.
In this case, Mars-mass ocean moons might be common in the stellar habitable
zones. Future exomoon searches can provide powerful constraints on the
formation and migration history of giant exoplanets.
