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SESK: Stuff Everyone Should Know · sesk.info/astro-dwarf-planet-clearing

What orbital criterion separates an IAU planet from a dwarf planet?

A planet has cleared its orbital neighborhood; a dwarf planet has not.

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  1. Having at least one moon
  2. Having an atmosphere
  3. Clearing the orbital neighborhood ✔

Why: Both categories orbit the Sun and are massive enough to become nearly round. Under the 2006 IAU definition, the key difference is gravitational dominance of the orbital neighborhood.

Huh, didn't know that: The IAU recognizes Ceres, Pluto, Haumea, Makemake, and Eris as dwarf planets.

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Dwarf planets are round, but their neighborhoods are still cluttered.
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References

Answer: Clearing the orbital neighborhood. Both categories orbit the Sun and are massive enough to become nearly round. Under the 2006 IAU definition, the key difference is gravitational dominance of the orbital neighborhood.

  1. Pluto and Dwarf Planets science.nasa.gov/dwarf-planets
    have not been able to clear their orbit of debris.
    Checked 2026-10-10.

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