After years of debate, NASA researchers have zeroed in on the thickness of the Europa's ice shell. We first discovered that the Jupiter moon's surface looked icy in 1979, when Voyager 2 flew by.

NASA’s Europa Clipper mission will perform 49 close flybys of Jupiter’s icy moon, where radiation levels reach 5,400 milliSieverts per day — lethal within hours. Beneath its frozen crust may lie a ...