In 2005, the Cassini orbiter discovered huge, 125-mile-high geysers spraying from the south pole of Enceladus, a small and icy moon that orbits Saturn. Since then, scientists have speculated where the geysers draw from—and whether that water source might be home to some form of life. The most intriguing idea was that the geysers indicated the presence of a subsurface ocean. Later, the discovery that the plumes contain water vapor, nitrogen, methane, carbon dioxide and other chemicals associated with life made the geysers even more exciting.

Now, new data has confirmed that Enceladus does indeed have an ocean, and it’s buried beneath 25 miles of ice at the south pole. The ocean appears to be about six miles deep and may be as large or larger than Lake Superior.

“These are very exciting findings about one of the most habitable places in the solar system,” says Steven Desch, an astrophysicist at Arizona State University, who was not involved in the new study.

Cassini found the ocean while mapping the gravitational field of Enceladus. As the orbiter circled the moon, its flight path dipped or rose depending on the strength of gravity at each location. The gravitational field was weaker around Enceladus’ south pole. That was expected: Enceladus’ south pole is dented in, and where there’s less mass, there’s less gravity. But the anomaly was a lot smaller than scientists expected, suggesting that something with a lot of mass was compensating for the depression. The most likely solution turned out to be a large mass of liquid water. (Liquid water is more dense than ice—that’s why ice cubes float.)

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