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Thread: Is Pluto about to be reinstated as a planet?

  1. #121
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    Quote Originally Posted by Swift View Post
    Ganymede and Titan mass more than Mercury. Callisto, Io, our Moon, Europa, Triton, and Eris all mass more than Pluto. Are they planets? What is the value for this lower mass limit and what is it based on? Pluto masses 1.3 x 1022 kg, is that the limit, and if so, why that value?

    My understanding of comets and asteroids is that the compositions are highly variable and even the difference between a comet and an asteroid is blurry - how do you define such that Ceres is not a planet, or should it be?

    I'm not picking on you, nor am I favoring or arguing against any of these definitions. But I think a lot of people act like it is easy to come up with some definition, and that the IAU somehow missed some easy, obvious definition. I'm saying it is a lot harder.

    I'm also saying that if your entire goal is to make Pluto a planet (a goal I completely fail to understand), then you are going to have to open it open to a lot of objects that were not traditionally planets.
    My goal is to have a sensible taxonomic classification. The IAU's isn't, as a) it's explicitly limited to the Solar System and b) identical objects would change categories based on location. Pick a mass or a property. Hydrostatic equilibrium, composition, combination of the two all make sense.

    Any classification should be based solely on the body's intrinsic properties.
    Last edited by swampyankee; 2017-May-05 at 10:51 PM.

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  2. #122
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    Quote Originally Posted by swampyankee View Post
    My goal is to have a sensible taxonomic classification. The IAU's isn't, as a) it's explicitly limited to the Solar System and b) identical objects would change categories based on location. Pick a mass or a property. Hydrostatic equilibrium, composition, combination of the two all make sense.

    Any classification should be based solely on the body's intrinsic properties.
    So, is a moon of Jupiter, if it fit this set of properties, a planet?
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  3. #123
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    Quote Originally Posted by Swift View Post
    So, is a moon of Jupiter, if it fit this set of properties, a planet?
    If it would be if it directly orbits a star, certainly.

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    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



  4. #124
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    Quote Originally Posted by swampyankee View Post
    If it would be if it directly orbits a star, certainly.
    But isn't that "b) identical objects would change categories based on location"?
    Quote Originally Posted by swampyankee View Post
    My goal is to have a sensible taxonomic classification. The IAU's isn't, as a) it's explicitly limited to the Solar System and b) identical objects would change categories based on location. Pick a mass or a property. Hydrostatic equilibrium, composition, combination of the two all make sense.
    Titan, for example, is a planet if it orbits the sun, but a moon if it orbits Saturn?

    Again, I'm fine with the classification changing depends on what it orbits (and the nature of that orbit), but I didn't think you were.
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  5. #125
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    Quote Originally Posted by Swift View Post
    But isn't that "b) identical objects would change categories based on location"?
    Titan, for example, is a planet if it orbits the sun, but a moon if it orbits Saturn?

    Again, I'm fine with the classification changing depends on what it orbits (and the nature of that orbit), but I didn't think you were.

    I can't communicate clearly on my tablet

    If something meets some definition of "planet," based on its intrinsic properties when it's orbiting a star (not just the Sun, but any star), it would remain a planet if it orbits a planet or if it's wandering in intergalactic space orbiting nothing.

    Information about American English usage here and here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



  6. #126
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    Quote Originally Posted by swampyankee View Post
    I can't communicate clearly on my tablet

    If something meets some definition of "planet," based on its intrinsic properties when it's orbiting a star (not just the Sun, but any star), it would remain a planet if it orbits a planet or if it's wandering in intergalactic space orbiting nothing.
    It certainly should do. The fact that there are definitions of "planet" that rule out candidates based on what they orbit does, in my opinion, make "planet" a useless term in any scientifically appropriate taxonomy of objects in space.

    First mass, second composition, third surface characteristics, orbit irrelevant, would be my ordering.

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