• Question: What does planet mean? Because Pluto is a planet but then not a planet becuase of it's orbit. So what does planet mean?

    Asked by abichohan to Davie, Gemma, James P, James V, Nuala on 29 Jun 2012.
    • Photo: James Verdon

      James Verdon answered on 29 Jun 2012:

      Hi abichohan,

      There are a number of criteria that have to be filled for something to be called a planet. It must be large enough that the force of its own gravity has made it basically completely round. It must have an orbit around a star, and it must have cleared everything else out of the way around its orbit.

      We used to call Pluto a planet. Then in the last 20 years or so we found loads of ‘space rocks’ orbiting around the same place as Pluto, some of which were even larger than Pluto. So if we were going to call a Pluto a planet, we’d have to call all these other things planets as well. So instead they decided to say that Pluto is not a planet any more – it is too small and there are too many other things around it.

    • Photo: James Pope

      James Pope answered on 29 Jun 2012:

      Hi abichohan,

      A good answer from James V, Pluto is actually smaller than our moon, so it was a very small planet! That said I felt sorry for poor Pluto when they declassified it from Planet, I’d be upset if I was told I could no longer be a planet, because I was too small 🙁

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