Dione could be Saturn’s third moon with a subsurface ocean

Three years ago, researchers found evidence that Saturn’s moon Dione was home to an ocean located deep beneath its surface when it originally formed, and now, a new study appearing in Geophysical Research Letters suggests that said body of water might still be there.
Research published in the journal Icarus in March 2013 used images collected from the NASA Cassini spacecraft to hypothesize that the moon’s topography suggested that a subsurface ocean caused Dione’s crust to become cracked and stressed early on during the satellite’s lifespan.
Now, researchers from the Royal Observatory of Belgium and their colleagues used computer modeling techniques to demonstrate that gravitational data observed during Cassini’s flybys of the moon can be explained if its crust is floating above an ocean located roughly 62 miles (100 km) below its surface, the American Geophysical Union (AGU) explained in a blog post.
If confirmed, this would make Dione the third of Saturn’s moons found to harbor oceans under their surface, joining Titan and Enceladus in that increasingly less-exclusive group. It would also suggest that the subsurface waters have likely persisted throughout the moon’s history, meaning that Dione may be home to a long-term habitable zone for microbial life.

Computer model also sheds new light on Enceladus

In a statement, the authors explain that this newfound ocean is likely “tens of kilometers” deep and surrounds “a large rocky core” in the heart of the moon. From within, they explained, Dione is similar to but smaller than Enceladus, suggesting that both of the satellites have icy shells that are made up of global icebergs immersed in water and supported by deep keels.
Similar models have been used by scientists in the past, but that research suggested that Dione lacked an ocean and Enceladus was home to an extremely thick crust. According to lead author Mikael Beuthe, the researchers “assumed that the icy crust can stand only the minimum amount of tension or compression necessary to maintain surface landforms,” as additional stress “would break the crust down to pieces.”
Based on this model, Beuthe’s team determined that Enceladus’ ocean is closer to the surface than Dione’s, especially near the moon’s south pole, where geysers have been spotted erupting through a thin layer of crust. The findings support the discovery made by Cassini last year that the moon undergoes extensive back-and-forth oscillations or libration during its orbit.
Dione, on the other hand, is home to a much deeper ocean located between its crust and core, according to the new study. It too undergoes libration, co-author Antony Trinh explained, but it does so at levels that the Cassini probe is unable to detect. Of course, this is only a prediction, Trinh noted, and will need to be confirmed or disproven by sending a future orbiter to analyze Saturn’s moons – one with more sensitive instruments than Cassini.
The study provides “the first clear evidence for a present-day ocean within Dione,” the authors wrote. With this discovery, there are now three “ocean worlds” orbiting Saturn, along with three orbiting around Jupiter and at least one believed to be in the Pluto system based on observations made recently by the New Horizons spacecraft. In light of these observations, Beuthe said that he believes future missions should be sent to explore the Uranus and Neptune systems.
Image credit: NASA/JPL