It’s official: Pluto is a planet!

well, nearly official, there’s still some rubber stamping to be done, but this week the proposal was made at the IAU conference, which is expected to be unanimously passed, that a planet is defined as follows:

  • A body that orbits a star but is not itself a star or a satellite of another planet
  • Such a body that has sufficient mass that its own gravity causes it to take an approximately spherical shape
  • Where a body is orbiting another body that has been defined as a planet, the orbiting body is defined as a satellite if the barycenter of the two bodies lies within the primary body; else, the secondary body is not a satellite but also a planet.

By this definition, Pluto is absolutely a planet. But so are at least three other bodies in the solar system, and potentially several more! As of this week, we have at least 12 planets!

The Bad Astronomer has a detailed explanation of what this all means, and what some of the loopholes could be, but essentially we now have three classes of planets: Terrestrials, Jovians, and Plutons. The first two kinds are collectively referred to as the ‘classical planets’.

Now here’s some of the weirdness that arises from this definition: firstly, the asteroid Ceres, which orbits between Mars and Jupiter, is classified as a planet. This means plutons aren’t necessarily trans-neptunian. Secondly, Pluto’s moon Charon is also a planet. This makes Pluto-Charon a binary planet system. Thirdly, due to tidal interactions our moon is steadily moving away from us. Eventually, it will be distant enough that the barycenter of our system is outside the surface of the earth, making the Moon a planet!

Another of our additional planets is UB313, which is yet to be given an official name. The nickname given to it by its discoverers is Xena, but I doubt that’ll stick. This is the planet that finally pushed the IAU into redefining the term, because it’s bigger than Pluto, which pretty much meant that the IAU had to either declare Xena the 10th planet or remove planetary status from Pluto. Frankly, I think they went in the more interesting, but less scientifically accurate direction. It’ll sell papers, that’s for sure, and it’s not bruising any egos.

So get used to it: soon schoolbooks may be teaching kids that the planets are Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon and (Something). Well, except for the fact that sometimes Charon is closer to the sun than Pluto. And sometimes both of them are closer to the sun than Neptune…And then there are all the other bodies under review, like Sedna and Quaoar, and all the many bodies thought to be just beyond the reach of our telescopes… exciting times for the solar system, indeed. Granted, this is all semantics and taxonomy, and has nothing to do with the science of solar system formation. But it certainly is fun.

I can’t wait for the astrologers to start falling over themselves to explain why their horoscopes don’t reflect the fact that there are more planets. They can’t argue size – Xena is bigger than Pluto. They can’t argue proximity – Ceres is closer. This is going to be hilarious.

11 Responses to “It’s official: Pluto is a planet!”

  1. Er yes, this does present a conundrum for astrologers. Oh well. Science will always push us forward and ultimately it’s all about adaptability.

  2. I’m still waiting for astrologers to adapt to precession, and recognize Ophiacus as a sign of the Zodiac. As long as they continue to ignore the actual heavens in favour of star charts that are 2000 years out of date, i doubt they’ll be doing much adapting.

  3. and i doubt that it’ll have any meaning anyway, but that’s only because i let you influence my susceptible little mind.

  4. In one of Linda Goodman’s books (circa the 70s, I believe) she mentions that there are two planets that are still to be discovered, which, when their influence is eventually understood, will mean forecasting will need to be adapted.

  5. wait, so what she’s saying is that the planets only start affecting your birth chart once an astronomer announces they’ve found them? What, do they only pop into existance on the astrological plane of influence once a scientist has released a press release?

    Surely if astrology is as accurate as people like Linda claim, she should be able to tell us exactly where the two planets are, based on the difference between a chart and the actual person? Besides, people have known for decades that Pluto has a moon that is almost the same size as it, and that moon Charon is now one of the planets. How are the astrologers going to explain their ommision of Charon for so long? And Ceres? It’s also been known for many decades. It’s only Xena, Sedna and Quaoar that are new.

  6. No, no. She’s saying because they haven’t been discovered it isn’t completely understood how they affect an individual because you need to be able to calculate angles between planets and such to work out what the influences are.

    She did, however, nickname the one planet “Pan Horus” (and, and I really am dredging my memory here) I think she did say that the planet was between either Mars and Jupiter or Jupiter and Saturn (if the former, then, it would be Ceres). She worked referencecs of “Pan Horus” into some of the texts she produced about at least one astrological sign that she figured it influenced.

    Also, and I really don’t want to get into a huge (and probably neverending, LOL) astrology debate here anymore than a scientific one (except to say that I agree with you about the omission of Charon and Ceres), the chart is just an indicator of “built-in” tendencies (as well as info about past-life experiences), which can be “tweaked”, although not completely changed, due to environment and self-awareness of one’s tendencies. You can’t really work backwards from tendencies to produce a chart, especially since more than one aspect/angle/whatever could produce a tendency.

    As a side note, when I was a kid and there were “only” 9 planets I used to get very upset when astronomers would claim, with immense conviction, that it’s absolutely not possible that there are more planets in our solar system, or that there could be more outside of our solar system.

    And then they found one.

    And then hundreds.

  7. Argh! I’ve misremebered somewhat.

    I think she said there was a planet beyond Pluto (that may have been what she called “Pan Horus”), and she claimed that the asteroid belt (that’s where my Mars/Jupiter slash Jupiter/Saturn slash Ceres confusion came in) was originally a planet and it exerted influence.

    Sorry – it’s been decade(s) since I read the books and, beyond astrology (Aries etc) facts I mainly took away the information that there were and are other planets (partly because it so goes against what other astrologers say).

  8. hmm, you’ve been listening to some strange astronomers then. As far as i know it’s always been expected that there would be planets around other stars. No astronomer worth his salt expects our solar system to be in any way special.

    We’ve been through this with the discovery of Uranus, Neptune and Pluto. We all know astrology will scramble for a few years and then quietly integrate, as they have done at least three times before. Eventually, people will assume that astrology always included all the major heavenly bodies.

    Anyway, it’s a moot point. Astrology doesn’t work, and i’ve already said all there is to say about it.

  9. just as an extra, people have been claiming for many many decades that there was a planet beyond pluto, not for any scientific or logical reasons, but for totally crazy ones. Just google ‘Planet X’ for a whole smorgasbord of crazy. Nancy Lieder is a particularly amusing example.

  10. I got the distinct impression as a kid (I was very into astronomy then) that general scientific opinion was there are no other planets.

    Is that not why Carl Sagan’s Cosmo series was so sensational, in that he was arguing that there are, in terms of mathematical probability (there was an equation, of sorts), millions of planets in the universe and, therefore, probably thousands of planets that support life (currently)?

    Anyway, I wasn’t trying to argue that astrology does work (I know where you stand on that and respect that you feel that way), I just wanted to point out that not all astrologers are the same, especially when astronomical facts “change”, and some were/are not steadfast on the “9 planets, that’s it, you’re all wrong about everything, don’t argue with us” mindset.


  11. I’m willing to believe that astonomers said that they haven’t (and couldn’t have) seen any other planets, but to say that there just weren’t any: it’s mind-boggling.

    But then again, science, much as any religion, is good as re-editing their past.

Comments are closed.

%d bloggers like this: