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Uranus and its rings. Computer artwork of Uranus, the seventh planet from the Sun, and its rings. Uranus is a gas giant, composed mostly of hydrogen and helium with some methane. It has a diameter four times that of the Earth. The planet's blue colour is thought to result from absorption of red light by the methane in its atmosphere. It rings, which are formed of rocks and ice, are very thin, each being only a few kilometres wide and around 100 metres thick. (KEYSTONE/SCIENCE PHOTO LIBRARY/CHR 366 FRIEDRICH SAURER/SCIENCE PHOTO LIBRARY) === ===