Cassini first studied Enceladus in 2005, and mission scientists expected to find a cold dead world, like it’s neighbour Mimas.  They were astonished to find it active, marked with fissures (the famous tiger strips) which were constantly blowing puffs of steam, icy particles and organic compounts into space.  This is what led to the idea that the might be liquid water below the surface, to provide the material for the geysers, but it was remarkably fresh – massive oceans should be very salty.  It wasn’t until 2009 when Cassini found the salt trapped within the icy particles, which helped to confirm the theory.

Cassini’s latest studies include thermal measurements of the tiger stripes, showing them to be unexpectedly warm at 190 Kelvins (-83 °C).  Such high temperatures so far from the Sun, and without any insulating atmosphere, must come from tidal forces at work on the core of Enceladus.  Tidal flexing warms the core, which keeps the oceans liquid.  Dissolved gasses start to fizz with the high temperatures, and the water forces its way up through tens of kilometers of ice (several times thicker than the height of Mount Everest) till it nears the surface.  The warm water forms a fissure with a thin shell of about 100 meters thick, which ocassional cracks, releasing the pressurized water and gas.  The spray shoots high up from Enceladus’s weak gravity, but eventually falls back to the surface to freeze solid and renew the thick icy crust.