Uranus

Uranus is four times wider than Earth. If Earth was the size of a nickel, Uranus would be about as big as a softball. Uranus's diameter is 31,763 miles (51,118 km). Uranus is one of two ice giants in the outer solar system. Most (80% or more) of the planet's mass is made up of a hot dense fluid of "icy" materials – water, methane, and ammonia – above a small rocky core. Near the core, it heats up to 9,000°F(4,982°C). Uranus' atmosphere is mostly hydrogen and helium, with a small amount of methane and traces of water and ammonia. The methane gives Uranus its signature blue color. One day on Uranus takes about 17 hours and it makes a complete orbit around the Sun (a year in Uranian time) in about 84 Earth years. Uranus has 28 known moons. Uranus has two sets of rings. The inner system of nine rings consists mostly of narrow, dark grey rings. There are two outer rings: the innermost one is reddish like dusty rings elsewhere in the solar system, and the outer ring is blue like Saturn's E ring.  It was discovered in 1781 by astronomer William Herschel, although he originally thought it was either a comet or a star. William Herschel tried unsuccessfully to name his discovery Georgium Sidus after King George III. Instead, the planet was named for Uranus, the Greek god of the sky, as suggested by Johann Bode. Uranus's Roman counterpart is Caelus.