On Europa and Callisto especially, it is thought that there may exist liquid water under their icy exteriors. The interiors of the moons are heated by friction caused by the constant pushing and pulling of Jupiter and its moons. Simple organisms have been discovered deep within Earth's oceans, far from any sunlight, and grouped around heat vents in the ocean floor. It is possible that similar life may exist under Europa or Callisto's icy surface. Saturn's moon Titan, may also have conditions that may support life.
Titan has a thick atmosphere of mostly nitrogen that contains complex hydrocarbon molecules.
These hydrocarbons are the building blocks of life.