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Ocean Inside

This illustration shows what astronomers think the interior of Saturn's moon Enceladus looks like. There's a big rocky core, an icy exterior, and a large liquid sea in the south, between the core and the exterior. The illustration also shows jets of water vapor discovered on Enceladus's southern surface in 2005.

Image courtesy of NASA/JPL-Caltech

Buried under miles of ice, astronomers have detected a liquid water sea on one of Saturn's moons, Enceladus. The sea is about the size of Lake Superior and it touches Enceladus' silicate core… which means it could have minerals dissolved in it that are necessary for life. "It makes, in fact, the interior of Enceladus a very attractive potential place to look for life," Jonathan Lunine, a Cornell University astronomer who worked on the study determining Enceladus has an ocean, said during a teleconference for reporters.

This extraterrestrial sea could also be the source of water for those funny jets Enceladus has geysering out of its south pole, but scientists don't yet have data linking the two phenomena.

This new announcement comes from a team of Italian and U.S. scientists, who analyzed gravity data from the Cassini spacecraft. Cassini has been flying around Saturn for almost ten years now, passing close to the surfaces of Saturn's moons and taking sexy photos of Saturn itself.

Scientists had previously suspected Enceladus may have an underground ocean. This latest study calculated the density of material in different parts of Enceladus after three gravity-measuring flybys. Those measurements revealed there's something underneath Enceladus' ice in the south that's denser than the ice. Liquid water is the most likely explanation, says David Stevenson, a planetary scientist at the California Institute of Technology who also worked on the study.

Enceladus

In this image, you can see the fissures on Enceladus' southern region from which its jets of water vapor emerge.

Image courtesy of NASA/JPL/Space Science Institute

"When you interpret data like this, gravity, of course, doesn't tell you what kind of material [is there]," he says. However, because scientists know the most common materials in the outer solar system are rock and ice, they're assuming the density of material on Enceladus must be explained by rock and water in different forms, Stevenson explains. Later, the study's lead author, Luciana Iess of the Sapienza University of Rome, says the team is "very comfortable" with its results.

Scientists weren't always this excited about Enceladus, which is just one of Saturn's more than 50 known moons. It's small, with a diameter about one-seventh that of Earth's moon's. So at first, scientists thought it was likely inactive. Small objects like Enceladus cool quickly after they form, so they don't have warm, active cores. They also don't have enough gravity to hold an atmosphere. But in 2005, Cassini spotted plumes of ice erupting from Enceladus' southern surface, revealing this little moon has more up its sleeve than anyone suspected.

The secret to little Enceladus' activity is the strong tidal force it feels from Saturn's gravitational pull. Its parent planet pulls Enceladus' ice out of shape, creating friction and heat and melting ice into water. The liquid water then acts as a lubricant, encouraging more ice blocks to rub against each other and create more water. It's even possible that the moon's ice plumes come only from water created by flexing ice, not from the newly discovered under-ice sea. So far, scientists have no way of checking whether there's any interior plumbing connecting the sea to the plumes.

Cassini's immediate next plans are to make repeated flybys of the Saturnian moons Titan and Dione, which may also have underground oceans.

You can read about Enceladus' underground sea in Iess, Stevenson, Lunine and their colleagues' paper in the journal Science.