• Question: How small does a planet have to be before it is classified as a dwarf planet?

    Asked by igloo23 to Adam, Catherine, Karen, Leila, Nazim on 16 Mar 2012.
    • Photo: Adam Stevens

      Adam Stevens answered on 16 Mar 2012:

      The size isn’t actually used in the definition.

      To be a planet you have to:

      Be in orbit around the sun
      Have sufficient gravity to become rounded in shape
      Clear your orbit – meaning that another other bits or bodies along your orbit have been pulled in by your gravity

      A dwarf planet:
      Orbits the sun
      Doesn’t have to be round
      Doesn’t have to have cleared its orbit
      But can’t be orbiting a larger body

    • Photo: Karen Masters

      Karen Masters answered on 16 Mar 2012:

      That depends on its orbit – a classic planet has to be the main thing orbiting around the Sun at its distance.

    • Photo: Leila Battison

      Leila Battison answered on 17 Mar 2012:

      The main thing that makes a planet a dwarf is that it’s not big enough to have cleared the space around it from other things like meteors yet. It’s not really clear how small a planet has to be to have not done this, but Mercury is a real planet, and is only (!) 1000 km bigger than the biggest dwarf planet Eris.

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