On 24 August 2006, the International Astronomical Union reclassified Pluto from a planet to a “dwarf planet”. Under their new definition, a full planet has to meet three conditions: it must orbit the Sun, be large enough to pull itself into a nearly round shape, and must be large enough to clear the neighbourhood surrounding its orbit . Pluto meets the first two but fails the third: it orbits within the Trans-Neptunian region, a region beyond Neptune full of other icy bodies of similar size, so it never became the dominant object in its own orbital path.

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