Uranus, Neptune may be magma worlds, not ice giants

Uranus and Neptune remain two of the most mysterious objects in the solar system, primarily because they have been visited only by NASA's Voyager 2 spacecraft in 1986 and 1989, respectively. Their "ice giant" moniker comes from longstanding hypotheses that their interiors are comprised of an icy mantle beneath their hydrogen-helium atmospheres. While Jupiter and Saturn are also composed primarily of hydrogen and helium, Uranus and Neptune are hypothesized to have a layered structure composed of icy elements in their interiors.