This image from the Cassini probe shows an ice volcano erupting on the surface of Saturn's moon Enceladus. Scientists have suggested that these volcanoes might come from water beneath the moon's surface, and new evidence makes this theory more plausible.
Not only are these ice volcanoes massive - you can see from this image how high their plumes get - but researchers believe that ejected material from them makes up most of Saturn's "E" ring. Today Nature has published a paper written by researchers who have analyzed the chemical composition of the volcanoes, which burst from cracks in Enceladus' south pole. According to the journal:
[Author] William Lewis and colleagues . . . find that ammonia and various organic compounds are present, together with deuterium - 'heavy' hydrogen that is abundant in the oceans of Earth. Ammonia, together with methanol and salts, acts as an antifreeze, allowing liquid water to exist at temperatures of nearly −100 degrees Celsius. The authors suggest that preserving even a residual oceanic layer during cooling episodes would maintain conditions necessary for tidal heating and geologic activity.
In other words, yes, there might be an underground ocean on Enceladus, complete with tides. You know what that means? Subterranean floating colonies.