Solar System/134340 Pluto
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Pluto is a dwarf planet in the Solar System. Its formal name is 134340 Pluto, and its planetary symbol or . Pluto is the ninth largest body that moves around the Sun. Upon first being discovered, Pluto was considered a planet but was reclassified to a dwarf planet in 2006. It is the largest body in the Kuiper belt.
Like other members of the Kuiper belt, Pluto is mainly made of rock and ice. It is quite small. It is about a fifth (⅕) of the weight of the Earth's Moon. It is only a third (⅓) of its volume. Pluto is very far from the Sun, so its temperature is very low. The average temperature on Pluto is -226 to -240 degrees Celsius. It has an odd orbit and this orbit is very sloped. It takes Pluto to 30 to 49 AU (4.4–7.4 billion km) from the Sun. This causes Pluto to sometimes go closer to the Sun than Neptune.
Since it was discovered in 1930, Pluto was thought to be the Solar System's ninth planet. In the late 1970s, the minor planet 2060 Chiron was found and people learned that Pluto had a small size. Later, in the early 21st century, the scattered disc object Eris and other objects like Pluto were discovered. Eris was initially believed to be 27% larger than Pluto, but was later found to be slightly smaller. On August 24, 2006, the International Astronomical Union (IAU) gave a definition to the word "planet" for the first time. By this definition, Pluto was not a planet anymore. It became a "dwarf planet" along with Eris and Ceres. After this, Pluto was put on the list of minor planets and was downgraded in 2006 by astronomer Michael E Brown. It was given the number 134340. Some scientists still think that Pluto should be classified as a planet.