Re: OK! Europa, Ganymede & Callisto likely have subsurface liquid water, but...
My understanding is that Enceladus must have been active to account for its smooth surface, but its small size seems to make this unlikely. I believe the leading candidate is some form of tidal interaction similar to those for Io and Europa that no longer exists. Saturns ring's are also believed to be fairly recent (roughly 100 MYA if I remember correctly) so we know Saturns system has not been stable long term.
Regards,
Mark