We take water for granted on Earth because of its abundance, but it’s something special out in space, where its very presence could suggest life. And it seems that there's more water out there than we ever thought: we’ve found evidence of water on Mars, we’ve seen the jet plumes of Europa (one of Jupiter’s moons), and we’ve even found ice on our own moon. And now, thanks to NASA’s Cassini mission, we know that a huge underground ocean of liquid water exists beneath the surface of Saturn moon Enceladus.
Enceladus, the 6th largest of Saturn’s 62 moons, has shown hints of having water under its icy surface. Its south pole has regularly active water jets that shoot water vapor and ice crystals into its atmosphere. Until now, however, there was no definitive proof that oceans existed under its icy exterior. NASA’s Cassini spacecraft, which has been studying Saturn and its moons for the past decade, found proof when a recent flyby brought it within 62 miles of Enceladus. After looking over the data sent back by Cassini, scientists estimated that Enceladus’ mass at its south pole wasn’t large enough to account for its gravity field. This suggests that something underneath the surface of the planet was denser than ice, which is all that's visible on the surface. This something is probably a lot of liquid water: an underground ocean. Scientists estimate that the ocean lies under something like 18 to 24 miles of ice. Finding an ocean on this moon is exciting due to the possibility that it harbors (or once harbored) life.
Data from Cassini’s Enceladus flyby also suggests that the moon’s composition includes a small core, mantle, and crust. This, along with the presence of the underground ocean, explains the jets of water vapor that often occur on that region of the moon. As it stands with our current knowledge, Enceladus and Jupiter’s moon Europa are the only two celestial bodies in the outer Solar System that have liquid water. If we’re going to find signs of life away from Earth, both might be worth further study.