Astronomers have long called Uranus and Neptune the "ice giants" because models suggested that these outer planets' interiors are largely made of mixtures of water, ammonia and other ices — compounds that freeze easily in deep space. But new research reveals that we actually know very little about what's going on inside these planets, causing researchers to propose that Uranus and Neptune be called "rocky giants" instead.
The problem with Uranus and Neptune is that we have extremely little data available to us. Unlike Jupiter and Saturn, both of which have received dedicated missions like the Cassini probe and the Juno spacecraft, the outer planets have not received any visitors since the Voyager 2 flybys more than 30 years ago.
