Europa’s ocean is interesting. It’s most likely a liquid ocean, warm and very deep. Europa’s the second satellite out from Jupiter. The inner satellite, Io, is blazing hot; it has volcanoes. The other satellites are frozen solid. In between there’s Europa, which has a thin layer of cracked ice. If you want to find creatures living in Europa’s ocean, you can do it the hard way – send a huge spacecraft carrying a submarine, dig through the ice, then launch the submarine to explore the ocean. Or you can do it the easy way. We know the other satellites have huge numbers of craters from being close to the asteroid belt. So what happens when Europa is hit with a huge asteroid? It will splash out immense quantities of water into space. If there are any fish present, they will be kicked out and freeze dried, and you’ll find them orbiting around Jupiter. There is already a ring of debris orbiting Jupiter, but nobody has gone to see if there are any freeze-dried fish. It’s a clever way to explore.
Freeman Dyson here some years ago.