Pluto was discovered in 1930 by an astronomer from the United States. An astronomer is a person who studies stars and other objects in space. Pluto was known as the smallest planet in the solar system and the ninth planet from the sun. Today, Pluto is called a “dwarf planet.” A dwarf planet orbits the sun just like other planets, but it is smaller. A dwarf planet is so small it cannot clear other objects out of its path. On average, Pluto is more than 3.6 billion miles (5.8 billion kilometers) away from the sun. That is about 40 times as far from the sun as Earth. Pluto orbits the sun in an oval like a racetrack. Because of its oval orbit, Pluto is sometimes closer to the sun than at other times. At its closest point to the sun Pluto is still billions of miles away. Pluto is in a region called the Kuiper (KY-per) Belt. Thousands of small, icy objects like Pluto are in the Kuiper Belt. Pluto is only 1,400 miles (2,300 kilometers) wide. That's about half the width of the United States. Pluto is slightly smaller than Earth's moon. It takes Pluto 248 years to go around the sun. One day on Pluto is about 6 1/2 days on Earth. Pluto was named by an 11-year-old girl from England. The dwarf planet has five moons. Its largest moon is named Charon (KER-ən). Charon is about half the size of Pluto. Pluto's four other moons are named Kerberos, Styx, Nix and Hydra.

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