Enceladus May Harbor Hydrothermal Activity

Silica detected by the CDA doesn't have a plausible genesis other than water supersaturated with silica cooling.

Methane detected by INMS could be explained by methane being produced faster than it can be bound up in clathrates.

It's noteworthy that we know have at least six icy satellites that are candidates, stronger or weaker, for subsurface liquid water. We have Europa and Enceladus, which are known to vent water into space, Ganymede and Callisto, which may have deep subsurface liquid layers, and Titan and perhaps Triton, which are more speculative possibilities for the same.

It had long been the paradigm that, roughly speaking, terrestrial worlds were the main objects of interest in our solar system and elsewhere, but we now have only four worlds in our solar system that have a solid surface and an appreciable atmosphere, versus four to six worlds with a subsurface ocean (with Titan being in both categories). Moreover, the ocean-bearing icy moons are found circling two or three different gas giants, suggesting the generality of the phenomenon. It might plausibly be found in the majority of gas giant systems and/or majority of exosolar planetary systems.

It might be very difficult to detect or study exosolar icy moon oceans, but at least we have two or more of them to explore in our own system.

Forgive me for responding to your interesting post with a quibble, but isn't it a bit too strong to say that "Europa ... [is] known to vent water into space"? Unless I've missed something, there was a single Hubble observation that hasn't been repeated yet, and some skepticism based on the lack of a good explanation for why, if there are plumes, none of the Jupiter missions detected them.

Follow-up:
https://solarsystem.nasa.gov/news/2015/09/1...ladus-is-global

A global ocean like that of Europa has been confirmed...

On arxiv:

Enceladus's measured physical libration requires a global subsurface ocean

The abstract concludes with this sentence: "The maintenance of a global ocean within Enceladus is problematic according to many thermal models and so may constrain satellite properties or require a surprisingly dissipative Saturn." The paper doesn't enlarge on this.

Wondering about how Saturn might be 'surprisingly' good at dissipating tidal energy a question occurred to me. Might the ring system be a significant site of tidal energy dissipation? Satellite tides acting on the rings must agitate and produce bumping and abrasion of ring particles. maybe this is a factor in maintaining the rings in their current state over astronomically long timescales.
Any thoughts on this? (could be wildly off the mark of course)

Only thing I can think of here is that they mean that Saturn's internal structure (surface--whatever that is--and below) is better at dissipating tidal energy than expected and/or is itself more mobile (less viscous?) than generally thought, else the effects would be stronger on the moons.

Just a guess, of course.

A study on the possible ocean below the surface of Enceladus, and a suggestion to find a common solution to the somewhat different results that have been obtained in a press release from CNRS in France.

Wow - an ocean 45 kilometers deep, with the moon being 40% liquid water by volume? That's pretty incredible.

That'd still place the core at only around 2.5 g/cm³ and a mass fraction of around 60-65%. Given the previously assumed silicate material in the core, even for pure silicates that density level is only within range for low-pressure forms though, which shouldn't be the case in this position. I'd therefore assume the 185 km "core" in the model includes the previously theorized porous zone where ocean water would permeate core material.

Hydrogen (1%) detected in plumes from Enceladus.
This show two things to us, one is that the water have contact with a rocky ocean floor, and that it's very likely to be ongoing hydrothermal activity.
Hydrogen could be an energy source powering secondary processes, then again, according to one hypothesis based on the orbits of Saturn's moons, Enceladus might be a rather young world of an age of about 100 million years.
Sky & Telescope have featured this also.

(Slight edit so one sentence make sense - hurray at least one!)