  Jupiter and Saturn play host to an impressive array of satellites, making it
reasonable to suspect that similar systems of moons might exist around giant
extrasolar planets. Furthermore, a significant population of such planets is
known to reside at distances of several Astronomical Units (AU), leading to
speculation that some moons thereof might support liquid water on their
surfaces. However, giant planets are thought to undergo inward migration within
their natal protoplanetary disks, suggesting that gas giants currently
occupying their host star's habitable zone formed further out. Here we show
that when a moon-hosting planet undergoes inward migration, dynamical
interactions may naturally destroy the moon through capture into a so-called
"evection resonance." Within this resonance, the lunar orbit's eccentricity
grows until the moon eventually collides with the planet. Our work suggests
that moons orbiting within about 10 planetary radii are susceptible to this
mechanism, with the exact number dependent upon the planetary mass, oblateness
and physical size. Whether moons survive or not is critically related to where
the planet began its inward migration as well as the character of inter-lunar
perturbations. For example, a Jupiter-like planet currently residing at 1AU
could lose moons if it formed beyond 5AU. Cumulatively, we suggest that an
observational census of exomoons could potentially inform us on the extent of
inward planetary migration, for which no reliable observational proxy currently
exists.
