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Why is Pluto now classified as a dwarf planet? Why was it downgraded?

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James VardiniI have recently graduated from Imperial College London with an Upper Second Class degree in Biochemistry17.5k students helped

The International Astronomical Union (IAU) had a vote which was very close. They defined three criteria which a planet must satisfy. - It must be large enough for gravity to overcome structures of materials and make it spherical. Most bodies are flattened spheroids due to rotation. - It must orbit the Sun. - It must have cleared its orbit of other bodies other than moons. The IAU created a new definition of an object called a dwarf planet which only satisfies the first two criteria. Pluto fails the third criterion, so it was demoted to a dwarf planet. Much more detail can be found here: https://www.loc.gov/rr/scitech/mysteries/pluto.html

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