• Question: how small does a planet have to be, to a dwarf planet?

    Asked by holliebob to Reka on 8 Nov 2016.
    • Photo: Reka Nagy

      Reka Nagy answered on 8 Nov 2016:

      Pluto-sized, apparently.. The more official definition is not all about size, though. It says that a dwarf planet has to:
      1. be in orbit around the sun (that is why the Moon is not a dwarf planet – it is in orbit around the Earth, not the Sun)

      2. be large enough to cause itself to take the shape of a sphere due to its own gravity pulling itself in (so weird-shaped asteroids aren’t dwarf planets)

      3. have other things free floating around its orbit – ‘real’ planets tend to have stronger gravity and pull things towards themselves that either crash onto the planet, or start revolving around it (such as the Earth pulling the Moon into its orbit). Dwarf planets are too weak to do this so they still have things near them that neither orbit them, nor have they crashed onto its surface yet.

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