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posted by on Wednesday February 22 2017, @01:02PM   Printer-friendly
from the i-can-be-a-planet-too! dept.

Scientists against the demotion of objects like Pluto, Eris, Sedna, etc. to "dwarf planet" status have crafted a new definition:

It's no secret that Alan Stern and other scientists who led the New Horizons mission were extremely displeased by Pluto's demotion from planet status in 2006 during a general assembly of the International Astronomical Union. They felt the IAU decision undermined the scientific and public value of their dramatic flyby mission to the former ninth planet of the Solar System.

But now the positively peeved Pluto people have a plan. Stern and several colleagues have proposed a new definition for planethood. In technical terms, the proposal redefines planethood by saying, "A planet is a sub-stellar mass body that has never undergone nuclear fusion and that has sufficient self-gravitation to assume a spheroidal shape adequately described by a triaxial ellipsoid regardless of its orbital parameters." More simply, the definition can be stated as, "round objects in space that are smaller than stars."

From the proposal:

The eight planets recognized by the IAU are often modified by the adjectives "terrestrial," "giant," and "ice giant," yet no one would state that a giant planet is not a planet. Yet, the IAU does not consider dwarf planets to be planets. We eschew this inconsistency. Thus, dwarf planets and moon planets such as Ceres, Pluto, Charon, and Earth's Moon are "fullfledged" planets. This seems especially true in light of these planets' complex geology and geophysics. While the degree of internal differentiation of a given world is geologically interesting, we do not use it as a criterion for planethood in the spirit of having an expansive rather than a narrow definition.

Here's another article about the significance of the New Horizons mission. New Horizons will fly by 2014 MU69 on January 1, 2019.


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  • (Score: 5, Insightful) by theluggage on Wednesday February 22 2017, @02:59PM

    by theluggage (1797) on Wednesday February 22 2017, @02:59PM (#470194)

    Problem is we found SO MANY bodies orbiting the sun... you have to limit them or it ceases to be a useful term.

    Why? Or rather, why does it cease to be a useful term? "Planet" already covers everything from Mercury to Jupiter (even before dragging exoplanets into the argument) so its not scientifically useful without further sub-categories (and it would be ridiculous to have a different set of sub-categories for moons and exoplanets that shared the same planetographical features).

    Whether or not Pluto "is" a planet is non-falsifiable - planet is an arbitrary definition that has already changed several times. The problem with the IAU decision is not that it is "right" or "wrong" but that the whole "must clear your orbit (but only if your name begins with 'P') " thing appears to be a contrivance purely intended to eliminate Pluto. The justification that "we'd have to accept 100 other bodies as planets" is just as much a weak "appeal to tradition" as "but we all learned that Pluto was a planet...".

    If you can't cope with 100 solar planets + a zillion exoplanets, here's my two proposed alternate definitions of "Planet":

    "Planet (1)": One of Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto and "Hypothetical Planet 10/X/Rupert" if it shows up, because we've been calling them bloody planets for years, that's what the textbooks say and there's no scientifically valid way of deciding otherwise. Or:

    "Planet (2)": One of Mercury, Venus, Earth, Mars, Jupiter, Saturn or Uranus (and maybe some of the bigger asteroids). I.e. the planets that were initially identified by observation because they moved against the background of "fixed" stars which was what "planet" originally meant. Sorry, Neptune, Pluto, Rupert - you were only observed after being predicted from the perturbations in the orbits of real planets.

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  • (Score: 2) by tangomargarine on Wednesday February 22 2017, @03:57PM

    by tangomargarine (667) on Wednesday February 22 2017, @03:57PM (#470235)

    "Planet" already covers everything from Mercury to Jupiter

    asteroid belt

    --
    "Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
    • (Score: 2) by theluggage on Wednesday February 22 2017, @04:44PM

      by theluggage (1797) on Wednesday February 22 2017, @04:44PM (#470266)

      asteroid belt

      Sorry - ambiguous - I meant "the range of planet types from Mercury to Jupiter".

      • (Score: 2) by tangomargarine on Wednesday February 22 2017, @05:07PM

        by tangomargarine (667) on Wednesday February 22 2017, @05:07PM (#470278)

        'planet' already covers everything that's already a planet

        Department of Redundancy Department
        If what you mean is "there are no dwarf planets from the Sun out to Jupiter"...

        Ceres (/ˈsɪəriːz/;[18] minor-planet designation: 1 Ceres) is the largest object in the asteroid belt that lies between the orbits of Mars and Jupiter. Its diameter is approximately 945 kilometers (587 miles),[6] making it the largest of the minor planets within the orbit of Neptune. The 33rd-largest known body in the Solar System, it is the only dwarf planet within the orbit of Neptune.[c][19]

        --
        "Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
        • (Score: 2) by maxwell demon on Wednesday February 22 2017, @09:12PM

          by maxwell demon (1608) on Wednesday February 22 2017, @09:12PM (#470430) Journal

          If you engage your brain, it's fairly obvious what was meant: The term "planet" already covers objects of such a wide range of different properties ranging from Mercury (a relatively small rock ball) to Jupiter (a gigantic gas ball).

          --
          The Tao of math: The numbers you can count are not the real numbers.
          • (Score: 2) by tangomargarine on Thursday February 23 2017, @03:44PM

            by tangomargarine (667) on Thursday February 23 2017, @03:44PM (#470731)

            I did engage my brain. The point they were making was totally wrong.

            --
            "Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
            • (Score: 2) by theluggage on Thursday February 23 2017, @05:02PM

              by theluggage (1797) on Thursday February 23 2017, @05:02PM (#470770)

              I'll try again: The term "Planet" already covers a range of bodies as diverse as gas giants (Jupiter) and small, rocky worlds (Mercury) so its never going to be sufficient as a term for classifying objects. That clear enough?

              • (Score: 2) by tangomargarine on Thursday February 23 2017, @05:53PM

                by tangomargarine (667) on Thursday February 23 2017, @05:53PM (#470791)

                Crystal. Thanks.

                --
                "Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"
      • (Score: 2) by FatPhil on Wednesday February 22 2017, @11:13PM

        by FatPhil (863) <pc-soylentNO@SPAMasdf.fi> on Wednesday February 22 2017, @11:13PM (#470506) Homepage
        If he thought that you were implying that the planets stop at Jupiter, and that Saturn..Neptune don't count as planets in your eyes, then he's cleary having a argument with an imaginary opponent.

        It's true you could have worded it in a more spoon-feedy manner, but it was clear enough what you meant, IMHO, as you couldn't have meant the above, and therfore some other range was being expressed by your "from .. to ..".
        --
        Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
        • (Score: 2) by tangomargarine on Thursday February 23 2017, @03:47PM

          by tangomargarine (667) on Thursday February 23 2017, @03:47PM (#470732)

          Oh, range of *properties*? I was reading that as "geographical range," and past Jupiter was excluded because it was common knowledge dwarf planets were in that area.

          Guess my eyes skated over "types" for some reason :P

          --
          "Is that really true?" "I just spent the last hour telling you to think for yourself! Didn't you hear anything I said?"