Ice giants likely have cores of rock and metal similar to those of the gas giants. Beyond that lie oceans of water, ammonia, and methane, squeezed by intense pressures into semi-solid states. Electric currents flowing through their icy-hot oceans may be responsible for powering the ice giants’ magnetic fields.
Like Jupiter and Saturn, the ice giants’ atmospheres consist mostly of hydrogen and helium, with the addition of water and ammonia as well as methane that absorbs red light, giving them their deep blue hues. The only actual ices in ice giants are found in clouds in their upper atmospheres.
Exoplanets
When it comes to composition, planets outside our Solar System may follow the same general groupings as our home planets. Exoplanet surveys have found rocky worlds similar to the terrestrial planets, as well as gas giants and ice giants like those we know here (though sometimes in exotic locations). There are also exoplanets that may have surfaces covered entirely by water, perhaps representing a whole new category of planetary composition.
The more we discover about the worlds in our Solar System and beyond, the better we understand the mechanics of the Universe. And by searching for worlds in other star systems, we may even someday find one that has a feature we’ve only seen once: life.