When Voyager 2 flew by Uranus and Neptune 40 years ago, astronomers were surprised that it detected no global dipole magnetic fields, like Earth's. The explanation: the ice giants are layered and unmixed, which prevents large scale convection to create a dipole field. But what substances would remain immiscible? A scientist modeled the interiors and found that water-rich and hydrocarbon-rich layers naturally form at extreme pressure and temperature, and they do not mix.