• Question: do you think it was right that the International Astronomical Union decided that pluto was no longer a planet //

    Asked by zmzmzm to Allan, Diva, Harriet, Nathan on 4 Jul 2012. This question was also asked by hannahroberts.
    • Photo: Allan Pang

      Allan Pang answered on 4 Jul 2012:

      Well, up to now, there are still some disagreements among astronomers on that issue. The IAU considered Pluto as “minor planet”/”dwarf planet”, so it is still classified as a planet, but not one of the major planets like Mars, Jupiter, etc.

      Problem with Pluto is, the mass of Pluto did not fit in the category set by IAS. So that’s the reason why they downgraded the poor planet into dwarf planet.

      But for me, my question is, does it matter? Pluto is still going to be Pluto, it will still be part of our universe, so it doesn’t really matter if we call it a planet, dwarf planet or minor planet. Humans love classifying and naming things, but at the core of things, naming and classification don’t really matter much.

    • Photo: Nathan Langford

      Nathan Langford answered on 4 Jul 2012:

      Well, this is an interesting question. How do you decide if something’s a planet or not? Should we call Halley’s comet a planet? Should we call the asteroids in the asteroid belt a planet? As scientists discover new things, they have to come up with new words to describe them. And at some point they need to decide on a set of rules to define the words they use. The problem is that we’re always learning new things, and sometimes that new information is going to change what we thought we knew before. And if that changes how things fit into the rules, then that might change how we need to name things.

      After all, Pluto was first discovered in around 1930. Since then, we’ve built huge telescopes, launched satellites and rocket ships into space and even put telescopes up on satellites in space. With all of this new technology, I guess it’s not surprising that we learnt enough new stuff that we need to change a few names here and there. For example, they discovered that, although Pluto is big enough to be a planet, it’s still floating around in amongst a whole bunch of other stuff, including a number of other planet-sized objects. Did you know they even found one that’s bigger than Pluto?

      So I don’t mind that they don’t call Pluto a planet any more, but I’m glad they still call it a dwarf planet. If you’re interested, you can read about the exact definition of a planet here:

      http://www.iau.org/public_press/news/release/iau0603/questions_answers/

      or here:
      http://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf

    • Photo: Diva Amon

      Diva Amon answered on 5 Jul 2012:

      Hey zmzmzm,

      You ask some great questions!
      I agree that Pluto should have been downgraded to a dwarf planet. The definition of a planet now is, ‘an object that orbits the sun and is large enough to have become round due to the force of its own gravity. In addition, it must dominate the neighborhood around its orbit’.

      Pluto has been demoted to dwarf planet because it does not dominate its neighborhood. Charon, its large “moon,” is only about half the size of Pluto, while all the true planets are far larger than their moons. There are around 40 other dwarf planets known so far and it was a case of either excluding Pluto from being a planet or including the other 40. Also, planets that dominate their neighborhoods, “sweep up” asteroids, comets, and other debris, clearing a path along their orbits. Pluto’s orbit isn’t clean, it’s quite untidy.

      Though I do agree with the move, it is sad because we can’t say the rhyme to remember the planet order anymore – My Very Elegant Mother Just Cooked Us Nine Pizzas. Instead of making nine pizzas, maybe she could make nachos now…… 🙂

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