Several billion years from now our Sun will become a swollen caricature of itself – a red giant. When that happens the icy moons around the outer planets will warm up. Europa, a satellite of Jupiter which at the present possesses a crust of solid ice, is one such moon that might be thus affected. Its ice might turn into a global ocean of liquid water – perhaps even with primitive life forms swimming in it. Jupiter and another of its moons, Io, hang in the sky in this impression.