Eight? Nine? Ten? Fifty-three?

reminds me that the International Astronomical Union is set to rule soon on the status of 2003 UB313 (provisionally known as ‘Persephone’ and unofficially/informally as both ‘Xena’ and ‘Lila’)–which means making a final ruling on whether or not Pluto should still be a planet.

Possible outcomes are as follows:

  1. Pluto–and anything larger–will be declared a planet, but Pluto becomes the bottom end of the planet scale, and we have ten planets for the time being.
    I find this acceptable, but sloppy, as it’s becoming clearer and clearer that both Pluto and ‘Persephone’ (to say nothing of Quaoar and Sedna) are just the largest known members of an icy trans-Neptunian asteroid belt.
  2. Pluto gets demoted, and we have eight planets.
    Personally, this is the solution I like best. Pluto doesn’t have a nearly circular orbit like the other eight, it’s not in the same orbital plane as the other eight… in short, one of these things is not like the others.
  3. Pluto remains a planet, but only by being grandfathered in, and ‘Persephone’ is cut out by the new definition, for nine planets.
    Bleah! These are supposed to be scientists! Just take a decision and stick to it! After all, Ceres was called the (then) eighth planet when it was discovered, but as it became clearer that it was just a member of a large class of objects between Mars and Jupiter, that status was revoked and Ceres was not grandfathered in.
  4. Every object that is gravitationally forced into a spherical shape and directly orbits the Sun is declared a planet.
    I like this one because it relies on a strictly scientific definition. The downside? It doesn’t add one new planet, it adds forty-four. Although watching the astrological community cope with that would provide me with amusement. ;)

And if it is declared a planet and named Persephone, I shall immediately begin calling it Rupert. :D

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12 comments so far

  1. surakofb5 on

    Actually, I vote for #3. I realize it’s unscientific to grandfather Pluto, but there are a lot of things in astronomy that are unscientific or arbitrary.

    More importantly, tradition is a powerful force, and demoting Pluto after 76 years would cause lots of problems outside the scientific community.

    • The Rev Dr Sherwood Forrester on

      Oh, I couldn’t disagree more. Otherwise, we’d still refer to the Andromeda Nebula (known as that for about a hundred and fifty years or so before it was shown to be a glaxy by Hubble et al.) and the planet Ceres rather than the asteroid Ceres (as mentioned above).

  2. chilayse on

    I vote for #4.

    ^_^ You know that’d be fun.

  3. jayteeone on

    I vote for #2. Yeah Pluto gets demoted, but it establishes distinct and definite rules for describing planets. It’s clean, scientific, and such things are a joy to all geekdom, so kiss my ass if you don’t like it. Ohh sorry, a little residual angst left over from high school geek days. Of course my nephew has declared me a nerd with geek tendencies, so what are you gonna do?

    By the by, you like 2 and 4, but which one will you stick with?

    • The Rev Dr Sherwood Forrester on

      Anything but #3. I already consider this system to consist of eight planets plus debris; if they redefine ‘planet’ to include Pluto et al., I can live with that, because at least it’d be consistent.

  4. jamess_fox on

    My information…

    From what I have heard, it may very well be option #4. However, some people seem to feel from rumours that this will a demotion. One thing that almost everything seems to forget is that everything that directly orbits the sun (except for comets), is already called a planet! You see, asteroids, centaurs, and TNO’s are collectivly called minor planets. The Minor Planet Center is in charge of tracking them.

    The rumours talk of a new category of dwarf planets. Some take this to mean minor planets < dwarf planets < major planets. Others focus on the term planet, and interpret things as planets = terrestrial planets + gas giant planets + dwarf planets. Perhaps this ambiguity is deliberate.

    • The Rev Dr Sherwood Forrester on

      Re: My information…

      Well, not quite. We refer to Ceres, Eros, Toutatis et al. as asteroids, sometimes planetoids, but never as planets. I can see adding a sub-planet class, but that’s an additional layer that I’m not sure is really necessary.

      That said, I have no objection to a physical definition of planet = directly orbits Sun + gravitationally made spherical, although I personally would prefer to see another term in the equation for low eccentricity–but I’m not particularly fiercely wedded to that last.

      My main point–or at least one of the reasons I’m particular about this–is that ambiguity belongs in astrology, not in a real science like astronomy. If Pluto isn’t a planet, it isn’t a planet, regardless of what we’re used to thinking about it. If it is, then anything its size or larger in direct orbit must also be.

      • jamess_fox on

        Re: My information…

        Umm, no. Ceres, Eros, all of the Asteroids, are frequently referred to as minor planets. You can look it up if you don’t beleive me. Now if the term dwarf planet means some sort of planet, then why wouldn’t the term minor planet also mean some sort of planet?

        I know that the general public uses terms like Asteroid, and so on, but in official, IAU parlance, asteroids are a type of minor planet. For some reason, most of the planet definitions seem to ignore this, perhaps because these objects are never referred to without the ‘minor’. Taking this into account, however, means we already have at least two groupings of planets, major and minor. So why not a third?

        In any case, the official defintion proposal will be presented to the IAU tomorrow.

        • The Rev Dr Sherwood Forrester on

          Re: My information…

          Minor planet, yes, but they’re never referred to as planets. Myself, I don’t see a need for a third category, myself. Pluto (and 2003 UB313 for that matter) are trans-Neptunian asteroids–or minor planets, if you insist. In any case, regardless of the terminology, they’re really not in the same category as the eight planets. Even leaving matters of size out, both bodies have very eccentric orbits (at least compared to the eight planets) and neither one is in the same orbital plane.

          Long and short, they really don’t share many characteristics with Mercury through Neptune. They’re the grit, rubble and debris left over from the formation of the solar system. Find me a gravitationally rounded body in a low-eccentricity direct solar orbit close to the ecliptic plane, I’ll be happy to call it a planet.

          • jamess_fox on

            Re: My information…

            Mercury has an eccentricity of 0.205, and an inclination of ~7 degrees. Quaoar, estimated at 1260 km across (certainly spherical), has an eccentricity of 0.034, and an inclination of around 8 degrees. The inclination of Ceres is around 10.5 degrees (eccentricity of 0.08).

            In any case, if one insists of focusing only on the solar system, then Pluto does appear not like the others. But there are plenty of extrasolar objects in orbit around various stars, that have Jupiter-sized or more masses, and high eccentricities (see http://www.extrasolar.net/charts.asp?w=640&h=480&x=Eccentricity&y=Mass&names=0&showcounts=1).

            Also, if you insist that calling something a minor planet is not calling it a planet, then I don’t see why calling something a dwarf planet also makes it a planet.

            • The Rev Dr Sherwood Forrester on

              Re: My information…

              I don’t have a problem with calling Quaoar a planet, as long as it’s brought in by a consistent definition of what a planet is. Heck, I don’t have a problem with Mercury not being a planet as long as the definition’s consistent.

              Good point about extrasolars. Probably best to dispense with eccentricity as a measure of planethood, then. I’d forgotten about those.

              No, I don’t think calling an object a ‘minor planet’ is the same as calling it a planet. Nor do I think we need a third tier. But, if that’s the way the IAU wants to do it, as long as they’re consistent with what’s what.


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