Jets were discovered on Enceladus in 2005. Enceladus is one of Saturn's icy moons, and the jets are geysers of ice and water vapor. Later study showed that they came from a liquid ocean beneath the icy crust. We know the composition of the jets because Cassini flew through them.
We know there must be an energy source, that there is water, and there are hydrocarbons (organic molecules). This makes Enceladus a promising place to look for life.