spaceSpace and Physics

Saturn's Moon Dione Might Have An Ocean Under Its Surface


Jonathan O'Callaghan

Senior Staff Writer

Dione, as seen by Cassini. NASA

A study from researchers at the Royal Observatory of Belgium has found that Saturn’s moon Dione might be one of the growing number of worlds in the Solar System we know to have a subsurface ocean.

The discovery, published in Geophysical Research Letters, was made using gravity data from the Cassini spacecraft. They found that the data was consistent with a liquid layer underneath the moon’s icy shell.


The ocean appears to be about 65 kilometers (40 miles) deep, surrounded by the moon’s 100-kilometer-thick (62-mile-thick) icy shell. The crust would float on top like an iceberg immersed in water, with the ocean also surrounding the moon’s rocky core.

The method used to make the finding, observing the oscillations (libration) of the moon, was similar to how a subsurface ocean was found on another of Saturn’s moons, Enceladus. This latest study also indicates that Enceladus’ ocean is closer to its surface than thought in places, being just a few kilometers deep at the south pole.

“For Dione, we did a similar gravity-topography analysis as was done for Enceladus in 2014, but with improved techniques,” lead author Mikael Beuthe told Gizmodo. “Thus that’s the best evidence we have now for a present-day ocean on Dione.”

Unlike Enceladus, Dione, which is 1,123 kilometers (698 miles) across, does not appear to have geysers of water shooting from its surface in places. But its broken surface suggests it was once more active, with the ocean thought to have survived for the moon’s entire history.


The researchers said that future missions to Saturn (of which there are none in the works) could help confirm this prediction. At the moment, gravity data from Cassini is not accurate enough to say for sure if there is an ocean, but the evidence is pointing in that direction.

If confirmed, Dione would join a prestigious group of worlds that includes Enceladus and Europa that we know to have a subsurface ocean, with more evidence recently confirming the latter. As always, the discovery of an ocean also raises the tantalizing prospect of finding life, too.

“The contact between the ocean and the rocky core is crucial,” said study co-author Attilio Rivoldini in a statement. “Rock-water interactions provide key nutrients and a source of energy, both being essential ingredients for life.”

Add one to the tally of ocean worlds. Our Solar System continues to surprise us, in the most unusual of places.


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