read this great article that gives very valid observation and math to extrapolate that the moon of jupiter, titan may have a subsurface ocean like europa is thought to have. titan is like our own moon in that it always has one face towards it's home planet. but, unlike our moon there is an odd fluctuation in titan's inertia and scientists now think the cause is an ocean below the surface. very exciting! this is exciting to me because if there is an ocean, there is a much greater chance of having primitive life forms in that ocean! read the article here:
http://www.technologyreview.com/blog/arxiv/26662/