20 thoughts on “Is Pluto A Planet?”

  1. The debate rages on.

    As the caption and story show, it’s a Whale of a Tale.

    *ahem*

    And now back to our normal planetary orbital disturbances.

  4. I have always been against the demotion of Pluto for three reasons: a crucial definition of planet used was and still is poorly defined – “clearing the neighborhood”; it doesn’t apply to other star systems – even if we were to attempt to extend the definition (which by definition is not so extended!) the dynamics of the Solar System won’t apply to a fair number of star systems because they will have different dynamics; and finally can you imagine the difficulty of determining whether a protoplanet 500 light-years away has cleared its orbit (even if in a system where a well-defined version of that term makes sense).

    For example of the second point, a Jupiter-sized protoplanet in the L4/5 position of a binary star system will and won’t have cleared its orbit depending on how you define clearing the orbit. In the sense of a shell of space around the main star, it won’t (because the second star is around), but in the sense of anything large sharing its Lagrange point phase-space, it would have.

    Frankly, I think the fundamental driver isn’t pseudoscientific concern over school kids having to memorize 150 planets, but rather that Pluto’s abbreviation is the same as Percival Lowell’s initials, who was the primary sponsor of the telescope site, Lowell Observatory where Pluto was initially discovered. Some astronomers have long memories and axes to grind.

    1. That, and Mike Brown discovered so many planets the IAU would have to acknowledge that a (gasp) American discovered more than half the planets in the solar system.

    2. a Jupiter-sized protoplanet in the L4/5 position of a binary star system …

      Unlikely. Very unlikely. Unless the ratio of the two stellar masses is greater than 25, L4/5 are no more stable than L1/2/3.

      1. Unless the ratio of the two stellar masses is greater than 25,

        Which can be achieved. There are stars (and other objects) more than 25 solar masses, for example. And red dwarfs can range down to about a thirteenth the mass of the Sun. Below that you have brown dwarfs which are thought to mass down to about 50-100 times less mass than the Sun (at least an order of magnitude more massive than Jupiter).

        1. I admit to not following the field closely, but I don’t think you find blue giants and red dwarfs in the same system. At least not until a lot of mass has been exchanged.

          1. There’s no known reason why you couldn’t have a red dwarf orbiting a blue giant, so long as the timing was right. Bellatrix is no longer thought to have a spectroscopic companion, but it wasn’t out of the question. Bellatrix is about 25mln years old, and a main sequence class M could form in that amount of time. It would likely have the same metallicity as the main star, but maybe not.

  6. Shouldn’t the determination be left to top astrologers based on statistical correlations between Pluto’s orbit and aggregated observations of significant events in people’s personal lives?

    1. Our local NPR station during its classical music programming played an orchestral jazz/blues version of Gustav Holst’s The Planets, only this composition was by an American composer.

      Each of the movements was dedicated to American jazz musicians who had that Zodiac sign. The radio announcer explained that the composition had only 8 movements based on only the planets through Neptune being known in 1915.

      I guess not much has changed since 1915 because many people still believe in astrology, and the few people who claim they don’t are scolding us that the last proper planet discovered remains Neptune.

      1. A little searching rarely fails to disappoint.
        New and Improved Holst’s The Planets: now featuring Colin Matthew’s Pluto the Restorer:

        https://www.hyperion-records.co.uk/tw.asp?w=W4771&t=GBAJY0127008&al=W4771_GBAJY0127008

        Took a listen on Spotify. Not bad. Mischievously messing around with Neptune while being elusive and playful. Personally I prefer Neptune with its haunting choir as the final movement. So I would wait to play Pluto until its distance from the Sun is inside Neptune’s orbit to perform.

        But that’s going to be awhile….

        https://starchild.gsfc.nasa.gov/docs/StarChild/questions/question5.html

        1. Also I think the IAU should lighten up and do away with its arcane insistence on Roman nomenclature.

          I much prefer to name it after its discoverer, Planet Clyde.

          3. So, Uranus should shed its unfortunate name and be renamed Planet Bill?

            Anything would be an improvement. There is a lot of speculation of how that planet ended up orbiting the Sun on its side. Including a planetary collision with orbital debris during the formation of the Solar System.

            In other words, something tried to Kill Bill!

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