Uranus is composed largely of hydrogen and helium like the other gas giants. It also has water ice, methane ice and ammonia ice. There are also tiny amounts of carbon monoxide, carbon dioxide and hydrocarbons such as ethane, acetylene, diacetylene and methylacetylene.
The pale blue, somewhat featureless appearance of Uranus is due to layers of ice clouds. Clouds made of water ice are thought to be on the bottom layer, while methane clouds make up the top layer. These methane clouds are what give the planet its blue color. The planet's atmosphere is also extremely cold and windy. Minimum temperatures can sink to minus 372 degrees Fahrenheit, and the speed of the winds can reach 560 miles per hour.
Scientists also believe that the core of Uranus is made of ice and silicate iron/nickel rock. This rocky core is believed to be less than half the mass of Earth. The mantle is made not of cold ice but of a dense, electrically conductive fluid that is actually hot. Some scientists believe that the pressures and heat inside the mantle might lead to the formation of liquid diamond on which float "icebergs" made of pure diamond. There might also be superionic water with hydrogen ions floating about in crystals of oxygen.