Clyde Tombaugh discovered Pluto on Febuary 18, 1930 at the Lowell Observatory, making it the ninth planet found in our Solar System. Pluto is known to be the farthest planet from the Sun, but it is actually closer than Neptune for 20 of its 249 year orbit. Observations of Pluto indicate that the surface is made of methane ice, with a thin atmosphere that freezes to the surface when the planet moves away from the Sun. Pluto has one moon, Charon, which was discovered in 1978. Pluto is the smallest planet in the Solar System with a diameter of only 1,160 kilometers, making it smaller than out Moon. The average distance from the Sun for Pluto is 5,913,520,000 kilometers. Pluto is the only planet not to be visited by any spacecraft, but a mission called the Pluto Express is scheduled for launch in 2001.
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