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Stargazing [just for fun] Planet Definition

  1. Feb 22, 2017 #1
    So I'm reading in the news and a group of scientists from the New Horizons missions
    appear to be reopening "The Pluto Debate" with yet another new definition of planet
    at the Lunar and Planetary Science Conference in March:rolleyes:. If accepted their definition
    of planet would increase the number of planets in Solar System to about 110.
    ( http://www.popsci.com/pluto-might-be-planet-again )

    So, just for fun, I'm trying to figure out a set of rules that would:
    1 - define Pluto as a "Planet" (to quell the nostalgic masses)
    2 - define Ceres as a "Dwarf Planet"
    3 - permit rouge planets to be "Rouge Planets"
    and 4 - permit multiple planets in the same orbit (eg: if Mars and Earth shared the same orbit but on opposite sides of the sun then they can still be planets with moons)

    I enjoy brain puzzles like these and also wonder if the PhysicsForums.com community
    can actually manage to come up with a set of definitions that would out-do what was
    accepted 10 years ago and what will be proposed by the New Horizon's team in March.

    So here is my attempt, debug it for some fun (if you, too, enjoy these types of brain puzzles)

    Planet:
    A sub-stellar mass body that is not currently undergoing nuclear fusion, has sufficient gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid, and is the main gravitational object of it's own system.
    A planet may or may not orbit a star or stars, may or may not have other objects in it's own system.
    (Eg: Martian System, Jovian system, Mercury)

    Moon / Moon-Type Planetary Satellite:
    A Sub-stellar mass body that is not currently undergoing nuclear fusion,
    and has a mass equal to or greater than 10*1015 kg, and orbits a non-star object.

    non Moon-Type Satellite:
    A sub stellar mass body that is not currently undergoing nuclear fusion,
    and has a mass less than 10*1015 kg

    Dwarf Planet:
    A sub-stellar mass body that is not currently undergoing nuclear fusion, has sufficient gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid, is the main gravitational object of it's own system, and has more than 0.06 G (0.61 m/s2) of gravity. A Dwarf Planet may or may not have other objects in it's system.


    This is not intended as personal theory or speculation that go beyond or counter to generally-accepted science, but instead just a fun brain challenge and fully expect other people to make better definitions than my own or teach me a new word (like triaxial ellipsoid!)
    :partytime:

    You must admire Clyde Tombaugh. After years of hard work to accomplish what should of been impossible, his discovery of Pluto keeps pulling people to astronomy and science still today. If for no other reason than because some people still wonder "what the heck is that???"
     
  2. jcsd
  3. Feb 22, 2017 #2
    We can't say the mass of these far-out, massive bodies with a high degree of accuracy yet (mostly just estimations I believe), so maybe it might be better to focus more on their orbits around the sun. Just a suggestion though
     
  4. Feb 22, 2017 #3
    Good point. Scientists' approximation of far-off bodies - especially Exo-Solar System bodies - is
    just a best scientific guess with available data that may be revised in the future when a probe finally
    reaches the object or when more accurate methods of measurement are devised.

    I suppose you could say that moons and satellites orbit a planet, but what's to differentiate between
    a full-on planet and a dwarf planet such as Ceres if not the mass?

    The current definition of "has cleared the neighborhood around its orbit" may likely be revised in the
    future because even the Earth has a lot of asteroids and comets that crosses it's orbit, does it not?

    ______________________________________________________
    What you call a "theory" I call a "hypothesis".
    What you call a "fact" I call a "theory".
    You think two plus two equals four and that is a "fact"?
    That is a theory because one day we may learn that one of the twos are negative.
    THAT is why we call gravity, relativity, and even the contents of our bologna sandwiches "Theories".
    Not because it's a guess, but because there is always room to discover new knowledge.
     
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