Why is pluto a dwarf planet?
Pluto is no longer a planet. The 2006 definition of planet defined Pluto not as planet, but as dwarf planet, because it have not cleared its neighbourhood. Pluto (unlike all other planets in our Solar system) does not orbit the Sun alone, but as part of a population of similarly sized objects.
In 2006 the International Astronomical Union (IAU) defined planets with Resolution 5A-a, Orbits the Sun, b, a nearly round shape, c, has cleared the neighborhood around its orbit. Resolution 6A defines Pluto as a Dwarf Planet, since it has not cleared its neighborhood (5A-c).
A dwarf planet is a celestial body that is in orbit around the sun, has sufficient mass to achieve hydrostatic equilibrium, is not a satellite, and has cleared its orbit of smaller objects. Unfortunately for Pluto, it is yet to clear it's orbit of debris, so has been downgraded to a dwarf planet.
Because it has not cleared the neighborhood around its orbit, Pluto is considered a dwarf planet. It orbits in a disc-like zone beyond the orbit of Neptune called the Kuiper belt, a distant region populated with frozen bodies left over from the solar system's formation.
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