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.

Europa is one of Jupiter’s 95 moons, and, perhaps, among the planet’s most famous orbiters. It’s covered in a shell of ice that likely sits atop a global saltwater ocean that’s estimated to be around ...