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. Known as plasma, the gas is composed of negatively charged electrons and positively charged ions, which are atoms with one or more electrons missing. Because they're charged, the electrons and ions can become trapped inside a magnetic field.
Saturn rotates in just 10 hours and 46 minutes. This sweeps the magnetic field and the trapped plasma through space. Just like a child on a fast-spinning merry-go-round, the trapped gas feels a force trying to throw it outwards, away from the center of rotation.
Soon after the Cassini spacecraft reached Saturn in June 2004, its instruments revealed that the planet's hurried rotation squashes the plasma into a disc, and that great fingers of gas are being thrown out into space from the disc's outer edges. Hotter, more tenuous plasma then rushes in to fill the gaps.
For More Information go to http://www.nasa.gov/cassini
