Saturn's moons Tethys and Dione are flinging great streams of particles into space, according to data from the Cassini mission to Saturn. The discovery suggests the possibility of some sort of geological activity, perhaps even volcanic, on these icy worlds.

The particles were traced to the two moons because of the dramatic outward movement of electrically charged gas, which could be mapped back to the moons' orbits in the magnetic environment of Saturn.

"This new result seems to be a strong indication that there is activity on Tethys and Dione as well,"

http://saturn.jpl.nasa.gov/news/press-rele....cfm?newsID=754

At this rate Rhea is going to become not only the most uninteresting object in the solar system, but also one of the least active moons of Saturn .
Really, this is interesting news. I guess the outgassing is tiny compared to Enceladus, but it's fascinating nonetheless.

Both Dione and Tethys seem to have almost the same tiger-stripey look as Enceladaus. Maybe having some sort of outgassing and residual geological activity is the norm for an airless ice moon in the Saturnian system?

I wonder if Rhea is the exception rather than the rule?

(Hmmm. Now I'm really looking forward to the Iapetus flyby. Wonder what it will reveal?)

-Mike

ROFLMAO, Tethys?!? Umm, yeah, I'm sorry, that moon will be active when pigs fly. Dione, I can believe. Tethys, I'm sorry, no, my brain won't allow that.

Basically, the MAG team found steams of charged particles that appear to originate from the orbits of Tethys and Dione. Now, the question is how those particles came to form plasma tori at these two moons' orbits. One possibility is geological activity leading to H2O outgassing. That is possible, IMHO, on Dione. Not Tethys. Almost certainly, the particle source for Tethys is sputtering or micrometeorite impacts.

Why only Saturn's sattelites? We need a good orbiter around Jupiter (Uranus, Neptune). Will Juno be able to collect such data?

Interesting...

I agree. I feel that adam may eat those words. Some of those cliff walls look just like ones on Dione. Certainly qualifies it for being potential more active than Tethys.

Hehe, I was just joking about that it seems like everyone puts Rhea as their most "boring object in the solar system". I find it amusing that even Tethys is considered to be more active. But I guess, as you say, that this might change.

Well, Tethys' leading hemisphere is the second brightest in the system, after Enceladus. This may be due to E ring particle deposition on it or... internal activity? It's also got a distinct region where the cratering is much lower so it implies a resurfacing at one point in time.

Rhea is in general a lower albedo object, very heavily cratered and doesn't hold much prospects for any activity. Then again, it's got wispy terrain too, just like Dione...