Comment on Sad Ganymede noises

• nexguy@lemmy.world ⁨2⁩ ⁨days⁩ ago

  If the definition of a planet is that it has cleared is orbit then how is Neptune a planet? It shares its orbit with the dwarf planet pluto therefore they should both be dwarf planets correct?

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  • sp3ctr4l@lemmy.dbzer0.com ⁨2⁩ ⁨days⁩ ago

    You could just look up the actual astronomical or mathematical definition of a ‘cleared orbit’ if you wanted to, you know that right?

    en.wikipedia.org/wiki/Clearing_the_neighbourhood

    As a consequence it does not then share its orbital region with other bodies of significant size, except for its own satellites, or other bodies governed by its own gravitational influence.

    This latter restriction excludes objects whose orbits may cross but that will never collide with each other due to orbital resonance, such as Jupiter and its trojans, Earth and 3753 Cruithne, or Neptune and the plutinos.[3]

    As to the extent of orbit clearing required, Jean-Luc Margot emphasises “a planet can never completely clear its orbital zone, because gravitational and radiative forces continually perturb the orbits of asteroids and comets into planet-crossing orbits” and states that the IAU did not intend the impossible standard of impeccable orbit clearing.

    Pluto and other plutinos are bodies whose orbits are significantly governed by Neptune.

    Go look at all the numerical values provided by various algorithms that measure essentially the extent to which a celestial body is locally gravitationally dominant, the extent to which it has ‘cleared its orbit’.

    You may notice that everything considered a dwarft planet scores orders of magnitude less, by literally all the metrics.

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    • nexguy@lemmy.world ⁨1⁩ ⁨day⁩ ago

      I understand the exception created for Neptune. But they had to create this exception… for their own brand new rule… in order to classify 8 things. Notice the exception is written very specifically just to keep pluto from “clearing” is orbit.

      Another IAU rule is that the body must assume hydrostatic equilibrium(nearly round). Mercury does NOT assume hydrostatic equilibrium. They knew this.

      Guess what? They just…decided…Mercury doesn’t have to follow that rule.

      It was all done very unscientifically.

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      • mnemonicmonkeys@sh.itjust.works ⁨1⁩ ⁨day⁩ ago

        Notice the exception is written very specifically just to keep pluto from “clearing” is orbit.

        There are tons of other Kuiper Belt objects in Pluto’s orbit. This wasn’t an exception written to spite Pluto. If you can attribute any malice to the definition, it comes from not wanting to include Eris, Sedna, Makemake, Quorua, and 200+ other Kuiper Belt objects as planets. Pluto was just caught in the crossfire because it fits with the other Kuiper Belt objects because it is one.

        “orbit the Sun”. Not a star but very specifically the Sun.

        This is a level of knitpicking that is completely childish. Grow up.

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