The evidence for a Europa ocean is strong, but all indirect. Cracks in surface ice where 'new' ice appears to well-up from below. Induced magnetic field could be created in the salty ocean. Gravitational measurements indicate a layer of water or slushy ice. internal heating from tidal forces could keep the water liquid. Its scientifically acceptable to believe that Europa has an ocean, as long as one retains an open mind to the possibility theres just mushy ice. Although we can't test this hypothesis, I wouldn't call it a belief with current technology, in principle, it is something we can empirically test. This is a scientific belief since it explains already observed phenomena as well as predicts new observations that can be made to test the hypothesis. Please respond to discussion post. What do you think? Must be 80 words exact..