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B Shouldn't dwarf planets be a subset of planets?

  1. May 18, 2016 #1
    After all, dwarf stars are a subset of stars and dwarf galaxies are a subset of galaxies, shouldn't a dwarf planet be a type of a planet?
     
  2. jcsd
  3. May 18, 2016 #2

    russ_watters

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    I suppose the powers that be could call all of them "planets" and add a category of "major planets", but they don't really need to: for scientific consensus purposes, definitions are decided on by the people who write them and can be whatever they want them to be.
     
  4. May 18, 2016 #3
    Dwarf main sequences stars are not a subset of main sequence stars, nor are dwarf galaxies a subset of galaxies. They are simply smaller stars, smaller galaxies, and smaller planets. Red dwarf (spectral type M) stars should not be confused with degenerate white dwarf stars. While they are both very small stars, one still fuses hydrogen (the red dwarf), whereas the other is a dead star (the white dwarf) and no longer fuses hydrogen.

    Every stellar classification also has "dwarf" stars. Our own sun, for example, is a spectral type G2V and more imprecisely called either a "yellow dwarf" or a "G dwarf" star. "Dwarf" in this case merely refers to its size.

    Besides there is already a subset of stars. Every main sequence star has a spectral type (O, B, A, F, G, K, M) and a subset number that refers to its effective surface temperature (0 through 9).
     
    Last edited: May 18, 2016
  5. May 18, 2016 #4

    ogg

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    Why "should" they? Would that change in structure of the categorization lead to a change in their physical properties? Of course not. The utility of a categorization is to enable generalization (abstraction) and/or improve communication. Which purpose would that change address and how? Your question seems to me to be equivalent to asking whether the word "planet" should be capitalized. What possible difference would it make? Many (if not most) of their similarities with the planets are known, so there seems to be no good reason to invent a more general category which includes both planets and dwarf planets and nothing else. You may want to read more about the criticisms of the IAU definition of planet - Wikipedia article of that name discussed it, iirc.
     
  6. May 18, 2016 #5
    If dwarf planets are not planets, they should call them by some other name, not "dwarf planets". Dwarf stars are stars and dwarf galaxies are galaxies. They're not something different from stars and galaxies, they're a type of stars and galaxies.
     
  7. May 18, 2016 #6

    russ_watters

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    Why? What difference does it make?
     
  8. May 18, 2016 #7

    D H

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    This is a red herring argument. Interestingly, red herrings are almost always neither red nor herrings.
     
  9. May 21, 2016 #8

    Ken G

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    Actually, I quite agree with Jupiter60. I don't know of a single other case in all of astronomy where a "X Y" is not a type of Y, except for "dwarf planet." I think it's quite a silly way to build a category and I hope they come to their senses soon. But it's rather moot, because most actual practitioners of planetary astronomy certainly do consider dwarf planets to be planets, indeed they consider moons to be planets also. They just don't care what the official designation of planet is, they care about the physics and geology that unifies these obects. That's why you will find moons within the general field of "planetary astronomy." The definition for "planet" is only used outside planetary science, it's for elementary schools.
     
  10. May 21, 2016 #9

    D H

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    Every science has its oxymoronic terms, including astronomy. For example, neutron star and Martian geology.

    Not amongst dynamicists. Your hopes are most likely as moot as were those of the discoverers of the first four asteroids, which were categorized as planets for the first half of the 19th century.
     
  11. May 21, 2016 #10

    Ken G

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    All the same, neither of those are counterexamples to my point.
    So your logic is, if you can cite a subset of astronomers who care about the official meaning of "planet", and I can cite a subset who don't care at all what other people regard as "planets", that makes my point moot? I don't follow that logic. What I'm saying is, there is an entire subfield of astronomy called "planetary astronomy" which, in general, includes essentially zero interest in the IAU classification of "planet", but a whole lot of interest in the common physics, and contrasts, among objects that are of interest to "planetary astronomy." In that latter camp, a "dwarf planet" is very much a subclass of "planet", expressly because of the interesting physics they share with what the IAU might wish to call a "planet." For them, it makes no difference at all how many planets we count in the solar system, it is their physics that they care about.
     
    Last edited: May 21, 2016
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