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