Objects recognized by the IAU as dwarf planets:
Dwarf planets are worlds that are too small to be considered full-fledged planets, but too large to fall into smaller categories.
Name
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Region of Solar System
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Ceres
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Asteroid belt
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Pluto
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Kuiper belt
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Haumea
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Kuiper belt
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Makemake
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Kuiper belt
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Eris
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Scattered disc
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Pluto:
Pluto
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- It is the largest object in the Kuiper belt,
- The tenth-most-massive known body directly orbiting the Sun,
- The second-most-massive known dwarf planet, after Eris.
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Discovered
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1930
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Natural satellites
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Pluto has five known moons:
- Charon (the largest, with a diameter just over half that of Pluto),
- Nix,
- Hydra,
- Kerberos, and
- Styx.
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Why it's not a planet now?
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- Starting in 1977 with the discovery of the minor planet Chiron, numerous icy objects similar to Pluto with eccentric orbits were found.
- The scattered disc object Eris, discovered in 2005, is 27% more massive than Pluto.
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The understanding that Pluto is only one of several large icy bodies in the outer Solar System prompted the International Astronomical Union (IAU) to formally define "planet" in 2006.
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This definition excluded Pluto and reclassified it as a member of the new "dwarf planet" category (and specifically as a plutoid).
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