August 26, 2006

My Very Easy Method Just Speeds Up Naming…

Writing about web page http://news.bbc.co.uk/1/hi/world/5282440.stm

…well, nothing actually; Pluto's not a planet anymore.

Apparently, after discovering a random block of ice in the Kupier Belt (think Asteroid Belt, but ice and out past Pluto – which is still there, of course, it's just not a planet) that was bigger than Pluto, Scientists decided that the definition of a planet needed tighteing. So, for something to be classed as a planet:

  • it must be in orbit around the Sun
  • it must be large enough that it takes on a nearly round shape
  • it has cleared its orbit of other objects

Since Pluto's orbit crosses Neptune's, it therefore doesn't fulfil these criteria…

So, remember: There are only 8 planets in the Solar System.

It's not a very suprising decision, really; some moons are bigger than Pluto…


- 4 comments by 2 or more people Not publicly viewable

  1. Mathew Mannion

    But some moons are also bigger than Earth, are they not? And Earth, Neptune and a couple of other planets don't clear it's orbit (particularly Neptune, because Pluto crosses it)

    27 Aug 2006, 09:22

  2. But some moons are also bigger than Earth, are they not?

    True, but the Earth is huge. Plus, Pluto's moon (Charon?) is nearly as big as Pluto

    And Earth, Neptune and a couple of other planets don't clear it's orbit

    How so for Earth?
    And it's not Neptune's fault that Pluto crosses it's orbit; I'm pretty sure the other eight (well the eight, now, I suppose…) all orbit in the same plane and don't cross each other.

    27 Aug 2006, 15:28

  3. Mathew Mannion

    Earth has a meteor belt that it doesn't clear, plus some other things. I'm not a physicist, but I read it somewhere. Pluto and Charon's centre of mass is between them, so they orbit around themselves, so Charon isn't really a natural satellite – they are a binary planet system (or at very least a binary dwarf planet system!)

    The definition is vague and crap, when applied literally half of the regular planets wouldn't be planets. Also, saying that it's "not Neptune's fault" isn't really a valid argument – the fact of the matter is that it doesn't clear it's orbit and therefore by the definition isn't a planet.

    Dr. Alan Stern, of the NASA New Horizons mission to Pluto, argues that Earth, Mars, Jupiter and Neptune have also not completely cleared their orbital neighbourhoods, which would technically make them qualify as dwarf planets. Earth co–orbits with 10,000 near–Earth asteroids, and Jupiter has 100,000 Trojan asteroids in its orbital path. "If Neptune had cleared its zone, Pluto wouldn't be there," he has said. A contrary view is that having 'cleared the neighborhood' refers to an object being the dominant mass in its vicinity, e.g. Earth is many times more massive than all of the NEAs combined.

    28 Aug 2006, 14:53

  4. Well I didn't create the guidlines, so I'm going to stop defending them; you're right, they are a bit too vague to be practical.
    Yes, the asteroids do tend to be all over the place; I hadn't thought of that. I think they were probably thinking "being the dominant mass in its vicinity", but I don't know why they didn't say that; it's much more sensible than "clearing the orbit".
    To be fair to my "not Neptune's fault" argument, Neptune and the other 7 do pretty much orbit in vague circles in the same plane, whereas Pluto's at a definite angle which might mean it came along after the other planets; so Neptune didn't have much (if anything; I don't know what there is floating around that far out) in it's way until Pluto came along…
    But it is still a bit crap…

    28 Aug 2006, 16:31


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