Why is Pluto considered a dwarf planet?

According to IAU, a planet is a celestial body that satisfies the following criteria: 1. it has an elliptical orbit around the sun; 2. it has enough mass to overcome rigid body forces and take on the shape of a hydrostatic equilibrium (round in shape); 3. it has cleared the area around its orbit (dominant object in its orbit).

However, a dwarf planet satisfies the following criteria: 3. it has not left its orbit's surrounding area; 4. it is not a satellite of any other planet.

Furthermore, the other planets in the Kuiper belt must also be major planets if Pluto is not regarded as a dwarf planet.

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Pluto is classified as a dwarf planet because, unlike the other eight planets in our solar system, it has not cleared its orbit of other debris and does not meet all three of the criteria set forth by the International Astronomical Union (IAU) for a full-fledged planet.