• Question: Why isn't Pluto a planet anymore

    Asked by jessiemooney to Angela, Gabriele, Karen, Maria, Shane on 11 Nov 2013.
    • Photo: Shane Mc Guinness

      Shane Mc Guinness answered on 11 Nov 2013:


      Great question. And I’ve just asked a person in my office who works on space research! So pluto is a “dwarf planet”. It turns out that there are a couple of reasons for this. Firstly, it’s thought that pluto is actually mainly made of ice and is much smaller than most planets. Secondly it actually does’t just orbit around the sun but also orbit around another tiny planet somewhere out there, making it kind of a moon too! There are actually several really big asteroids in our solar system which are closer to being planets than pluto is. However, the verdict is still out on Pluto, and some people don’t argee with “dwarf planet”, which shows the beauty of science; nothing is ever fact!

    • Photo: Karen McCarthy

      Karen McCarthy answered on 11 Nov 2013:


      Poor Pluto, I think everyone misses it as a planet!

      Originally Pluto was thought to be the largest object past the orbit of Neptune, and that anything else past it’s orbit was too small to be considered a planet. However with all the fancy new telescopes and space equipment we have now, it was noticed that Pluto actually belongs to a group of smaller objects and moons called the Kuiper Belt. Within this group, there are about 70,000 other objects which have the same dimensions and make-up as Pluto so unfortunately that meant Pluto got kicked off the planet list!

    • Photo: Angela Stevenson

      Angela Stevenson answered on 11 Nov 2013:


      Pluto was my favourite planet 🙁 now I guess it’s my favourite dwarf planet 🙂 It’s all just down to planetary terminology really: apparently, in order to be called a ‘planet’ it needs to (1) be in orbit around the sun… Pluto is, but so are asteroids, etc… so we ll move on to the next requirement, (2) have sufficient mass to assume hydrostatic equilibrium… which basically means that it has to be spherical in shape – Pluto is! but asteroids aren’t. and last but not least: (3) it must have cleared the neighborhood around its orbit, which means that it needs to be gravitationally dominant in its orbit… Pluto orbits within Neptunes orbit! so it fails at this last point. Sigh. Dwarf planet it is. Great question Jessie! thanks for asking 🙂

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