Pluto is there, but is not considered as a planet. Pluto has been the ninth planet in our solar system ever since it was discovered. However, as a small rocky planet with a very strange orbit, it doesn't really fit in with the rest of the gaseous outer planets. Pluto is much more similar to a group of objects called Trans-Neptunian Objects (TNOs), or asteroids.The definition that the IAU came up with for a planet was that it must revolve around a star and not something else like a planet. It must be basically round, and there must not be anything else near its size within its orbit. Because of this last parameter Pluto could no longer be considered a planet.
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