Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune.
After Pluto was discovered in 1930, it was declared to be the ninth planet from the Sun. Beginning in the 1990s, its status as a planet was questioned following the discovery of several objects of similar size in the Kuiper belt and the scattered disc, including the dwarf planet Eris. This led the International Astronomical Union (IAU) in 2006 to formally define the term planet-excluding Pluto and reclassifying it as a dwarf planet.
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The funny thing is that in all scholarly work, it is still referred to as a planet. Most astronomers still refer to it as a planet. That's because it is a planet. Mike Brown, the chief architect behind behind the "movement" to remove the planet status, even goes by @plutokiller on his Twitter account. It was basically used by one astrophysicist to put a stamp on his career. And what is he doing now? Searching for the "real" planet 9 he says. A vanity project. There is actually some good work being done by a group of astronomers who are trying to re-prove that Pluto is a planet. Either way. It's the oddball. It's even more complex than many of the "real planets".