Because it was way too small to be a real planet.
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Some may be annoyed by my nit-picking. It is not that Pluto was singled out and redefined as a dwarf planet (and by the way it is not Pluto's size that is at issue). A definition of planet was decided upon, and according to the definition Pluto does not meet criteria to be considered a major planet. Pluto has not cleared its neighborhood (the Kuiper Belt) of debris. It may well be that Pluto's then-disputed place among the major planets fueled the need for a definition, but the definition was needed and the current one seems reasonable to most.
This is Pluto.
Pluto has been nicknamed the Dwarf Planet.
pluto was found as a dwarf planet by the international astronomical union on august 24th 2006
Ceres was reclassified from a planet to a dwarf planet in 2006 by the International Astronomical Union. This decision was made during the same time that Pluto was also reclassified as a dwarf planet.
Pluto, Xena, Ceres are some examples of dwarf planets.
Pluto
Pluto, it was reclassified as a dwarf planet
This is Pluto.
Pluto, it is now a dwarf planet or planetoid.
Pluto has been nicknamed the Dwarf Planet.
Pluto was originally called a planet, it is now reclassified as a dwarf planet.
Pluto was reclassified as a dwarf planet in 2006, after being known as a major planet for 76 years.
A concensus of astronomers at a convention in Prague of the International Astronomical Union reclassified Pluto as a minor or dwarf planet, in 2006.
Five such bodies were reclassified as "dwarf planets" in 2006. The most famous, or infamous, has been the demotion of Pluto.
No, it was only reclassified as a dwarf planet
Pluto is a rocky world. Pluto is now reclassified as a dwarf planet.
Scientists concluded that Pluto is to small to be a normal planet. It is more of a ball of ice. I think this was established in 2008.