Even with all of the time Cassini spent studying the Saturnian system, many questions remain unanswered. One of the puzzles is the moon Dione
- is it active? There was some inconclusive evidence of cryovolcanism, probably related to the Janiculum Dorsa mountain region where the crust is bent.
A recent paper suggests that Dione could have a subsurface ocean like Enceladus and Jupiter's moon Europa.
Dione gets heated up by being stretched and squeezed as it gets closer to and farther from Saturn in its orbit. With an icy crust that can slide around independently of the moon's core, the gravitational pulls of Saturn get exaggerated and create 10 times more heat.
Certainly if Dione is - or was in the past - active, it doesn't match the activity visible on Enceledus.