• Question: why do planets have different names such as gas planet and dwarf planet?

    Asked by Eli H to Heather, Helen, Hugh, Jane, Julian on 14 Nov 2014.
    • Photo: Julian Onions

      Julian Onions answered on 14 Nov 2014:

      Its really just a way of communicating, and as in any field we have our jargon.
      The Gas giant planets are physically different to the rocky planets – you can’t stand on a gas giant for instance, and they tend to be much much bigger too. People like to refer to the major bodies of the solar system, and planets is a convenient term. However someone has to decide what is a planet and what isn’t. Anyway – we’ve come up with some terms that seem to work, and now if we talk about planets everyone should know what we’re talking about.

      Dwarf planets are objects that are quite large, large enough to form a sphere rather than just an irregular lump, but not big enough to be considered a planet.

      We also talk about gas giants (Jupiter and Saturn), Ice giants (Neptune and Uranus) Rocky planets (Mercury Venus Earth and Mars).

    • Photo: Helen Johnson

      Helen Johnson answered on 14 Nov 2014:

      We have rocky planets and gas giants, because the planets in the solar system can be easily split into these two very different categories. The need for the label ‘dwarf planet’ came about in 2006. We discovered there were lots and lots of small planet-like Pluto-sized objects in the outer edges of the solar system, the Kuiper belt, and decided it would be easier to classify all of them as dwarf planets. The two criteria to be a ‘real’ planet over a dwarf planet are a) it must have enough gravity to bring itself into a sphere and b) it must have cleared its orbit.

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