http://www.slate.com/articles/video/video/2015/09/enceladus_surface_ocean_cassini_finding_could_suggest_possibility_of_life.html

In 2005, scientists observed a water-rich plume venting from the south polar region on Enceladus, suggesting a subsurface ocean on the Saturnian moon, but they didn’t have enough information to estimate its size. Observational data collected over the past seven years from the Cassini spacecraft noted the moon’s wobble as it rotates around Saturn, is too large for a solid crust frozen to its rocky core. Instead, the wobble suggests a global ocean that reaches depths of 25 to 31 kilometers below the icy surface.