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Saturn's third largest moon is a 300-mile snowball, which has been spraying icy snot all over its mother planet for about as long as we've been able to observe it. Enceladus' southern polar region is dotted with active geysers (NASA counts more than 100 individual "cryovolcanoes"), which eject plumes of water and organic material far above the moon's frozen surface.

After analyzing seven years' worth of photos and data, NASA researchers now think they know the source of those ice spurters: A globe-spanning ocean hidden below the frozen surface.

Utilizing data collected by the Cassini space probe, which has been orbiting Saturn since 2004, researchers have been able to indirectly determine what lies below Enceladus' surface—or so they claim in a study published in the journal Icarus.

"This was a hard problem that required years of observations, and calculations involving a diverse collection of disciplines, but we are confident we finally got it right," said Peter Thomas, a Cassini imaging team member at Cornell University in a NASA blog post.

Researchers measured a slight "wobble" in Enceladus's orbit (known as a libration), which led them to conclude that buried far below the moon's frozen crust is a global ocean of water that sits atop a rocky core.

"If the surface and core were rigidly connected, the core would provide so much dead weight the wobble would be far smaller than we observe it to be," said Matthew Tiscareno, a Cassini participating scientist at the SETI Institute, and a co-author of the paper. "This proves that there must be a global layer of liquid separating the surface from the core."

Scientists are still not entirely sure what mechanism has stopped the subsurface of Enceladus from freezing solid (not to mention the observable geological features on the surface). It may be that Saturn's gravitational pull generates more internal heat than previously suspected, or perhaps it's hidden hydrothermal activity, as was suggested by a separate research team earlier this year. Project scientists are already considering studies that may be able to resolve that question.

In the immediate future, scientists will get a close-up view of the moon when Cassini performs a flyby only 30 miles above the moon's surface on Oct. 28.