Saturn's moon Dione: The ocean is several tens of kilometres deep and surrounds a large rocky core

According to new data from the Cassini mission, Saturn moons Titan and Enceladus are already known to hide global oceans beneath their icy crusts, but a new study suggests an ocean exists on Dione as well.The ocean is several tens of kilometres deep and surrounds a large rocky core, researchers said. Researchers from the Royal Observatory of Belgium show gravity data from recent Cassini flybys can be explained if Dione's crust floats on an ocean located 100 kilometres below the surface. 

Dione is very similar to its smaller but more famous neighbour Enceladus, whose south polar region spurts huge jets of water vapour into space. 

Dione seems to be quiet now, but its broken surface bears witness of a more tumultuous past. 

"As an additional principle, we assumed that the icy crust can stand only the minimum amount of tension or compression necessary to maintain surface landforms," said Mikael Beuthe, lead author of the study."More stress would break the crust down to pieces," Beuthe said. 
Ocean is much closer to the surface, especially near the south pole where geysers erupt through a few kilometres of crust.  

Dione's ocean has probably survived for the whole history of the moon, and thus offers a long-lived habitable zone for microbial life. 

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

With PTI inputs