Saturn's moon Titan happens to be my favorite moon, even more so than our own. I find it unbearably fascinating, because it has permanent liquid of the surface. My favorite celestial body of all is the dwarf planet Eris. Why, you may ask? Eris is the Greek goddess of strife and discord, and its discovery did exactly that to the astronomical community.
Yes, I'm aware I'm a nerd for even having a favorite celestial body. There are worse hobbies.
By measuring how much Titan 'flexes' due to Saturn's gravity, astronomers can determine how rigid the structure is. Since Titan seems to flex quite a bit, this implies a good portion of it is in fact a liquid ocean. However, this ocean is most likely made of methane rather than water, and thus not as good for life.
For more information on Titan, click here.