Why do people say there may be life on Jupiter's moons?

A moon in our own solar system might support life, according to scientists. Europa ... Jupiter's moon Europa could support alien life, scientists announce after finding activity under its shell ... Researchers say they have found evidence that there are sliding tectonic plates underneath the moon's ice shell. read more

Well, they only theorize that 2 Galilean moons, Europa and Ganymede, may have life because of the immense oceans of salt water (very similar in makeup to our own oceans) under their icy crusts. IIRC they also found amino acids in one of the geysers from Ganymede. They theorize that there is life in these oceans. read more

Looking for life Just as a layer of ice over a pond allows the water beneath it to stay liquid through the freezing winter, Europa's icy crust shields its enormous ocean despite the moon's great distance from the sun. read more