Pluto, usually the ninth planet from the Sun, is the smallest planet in the solar system. Some scientists believe that Pluto once was one of Neptune’s moons. It pulled out of Neptune’s atmosphere and made its own orbit.
After the discovery of Neptune in 1846, scientists believed that there still might be a ninth planet, and they set out to find it. Finding Pluto was difficult. Pluto is very small, it is a long way from the Sun, and it is very dim in the sky. The planet moves very slowly, taking 248 years to complete its orbit around the Sun, so it took many years before Pluto’s motion could help identify it. An amateur American astronomer, Clyde Tombaugh, finally found Pluto in 1930.
Missions to Pluto
Pluto is the only planet that has not been visited by a spacecraft from Earth. The Pluto Express probe has been delayed.
Interesting Facts About Pluto
Unless otherwise noted, all images courtesy of NASA. Permission for use at http://www.nasa.gov/gallery/photo/guideline.html.
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