Many of the moons of Saturn and Jupiter possess subterranean oceans, which are huge bodies of water located under the surface or in the case of Europa, the ice sheet, of the planet.
Subterranean oceans cannot receive sunlight, but could still be bastions of life, per some scientists. Microorganisms discovered on earth feed off the minerals and heat sources from volcanic activity and water volcanic activity is more long lasting and powerful than magma volcanism, given that it takes a lower temperature to melt water than magma.
This phenomenon creates the possibility of a variety of seafloor microorganisms and larger organisms. The likelihood of a fish species developing is low, and photosynthesis for algae is nigh impossible. That said, the discoveries open the possibility of life on Europa and other moons with subsurface oceans on the sea floor.
Given these theories, the decision to crash space probes into gas giants instead of onto moons on which there may be life may appear obtuse, but are correct for protecting alien life forms. Some scholars have pointed out the potential medical value of alien life, and their importance of studying diverse species on extraterrestrial worlds.