Cassini Spacecraft Finds Ocean May Exist Beneath Titan's Crust

[News]

NASA's Cassini spacecraft has discovered evidence that points to the existence of an underground ocean of water and ammonia on Saturn's moon Titan.

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[Nokton]

Ocean translates as a sea, as we know it, liquid water, so to speak.
With Titan being so far from our sun, how is it a liquid. Has Titan an
internal heat source? If so, how has Titan kept it over millenia when other moons lost theirs. Know Europa does it with Jupiters gravity kicking it.
Titan not in the same situation.
Nokton.