From “Squishiness of Saturn’s moon suggests salty ocean below surface” (Associated Press Posted: Jun 30, 2012), we learn, “Measurements from Cassini spacecraft best evidence yet of water on giant moon Titan”:
Scientists did not delve into the characteristics of the ocean, but previous estimates suggested it could be 50 to 100 kilometres deep and contain traces of ammonia. Titan is one of the few worlds in the solar system with a significant atmosphere, and the presence of an underground ocean could help explain how Titan replenishes methane in its hazy atmosphere.
Having an internal body of water would also make Titan an attractive place to study whether it would be capable of supporting microbial life. Other moons on the shortlist: Jupiter’s Europa, where an underground ocean is thought to exist and another Saturn moon, Enceladus, where jets have been seen spewing from the surface.