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Twelve Planets?

August 16, 2006 pm31 1:48 pm

It’s out of my normal range, but the International Astronomers Union is preparing to vote on adding 3 planets to our current 9: Ceres (the largest rock in the asteroid belt), Charon (Pluto’s moon), and 2003 UB313 (which would get a letters name to replace its numbers name, soon. Xena is an early favorite. Whatever happened to Gabrielle?)

Bigger than Texas, smaller than Canada? Meet our new planets.

Images of the Asteroid Ceres As It Rotates One Quarter
Mug Shots of the New Planet (former Asteroid?) Ceres

Click for ———>
Does this bother you? Doesn’t make me happy.

Pluto’s orbit is not really the right shape for a planet; I thought they would exclude it. Instead, they have a new definition of a planet: A planet is round, has enough gravity to hold itself together, orbits the sun, and is at least one eighth of one percent the mass of the Earth, and with a diameter of 500 or more miles.

Kuiper Belt Object 2003 UB313
The Warrior Princess?

Do you see anything after Neptune?

Where will it end?  These are additional candidates for planethooddom.

Part of me says, add them all. And they are establishing a special class of small planets, called Plutons.  (the word is stolen from geology/vulcanology, click to see what it means). Let us keep 8 big planets, and as many plutons as they can number.

But part of me really wants to keep the 8 or 9 that we memorized in a special category.

10 Comments leave one →
  1. James Fox permalink
    August 16, 2006 pm31 2:32 pm 2:32 pm

    I would agree with you about keeping the ‘classical eight’ in a special, superior category. When it comes to the dividing line, however, things get rather fuzzy. Where is the orbital dividing line between a classical planet and a non-classical planet? How low does the inclination have to be, and why? What percentage of the mass in it’s are does the object need to have, and why? It becomes rather hard to come up with something that does not look like assuming Pluto isn’t a planet, and working from there.

  2. Kombiz permalink
    August 16, 2006 pm31 7:37 pm 7:37 pm

    Correct me if I’m wrong but the whole exercise is predicated on the common agreement by Astronomers that Pluto should never have been a planet in the first place. So they’re creating a new category of large rocks in which to cateogrize Pluto, and a few other large rocks.

    I’m a child of the 80’s, and 90’s, and I’m a deep believer in the ability of scientists to do as science demands but emotionally I don’t want to lose Pluto.

  3. August 17, 2006 am31 12:47 am 12:47 am

    The category of large rocks will be subsumed within planets, so no, they are not excluding Pluto. They are just being more inclusive. And James makes a very important point: Opponents of counting Pluto as a planet begin by making a definition of a planet that excludes Pluto. I think I’ve done that, and it’s not good science.

    (to define a race of humans one needs to start with a sense of which group one wants to count as separate, and then create criteria which enforce this preconception. It is the same kind of bad science.)

  4. August 17, 2006 am31 1:52 am 1:52 am


    Pluto has always been a planet since the 1930s and just because a minority (not majority) of Astronomers wants to eliminate Pluto as a planet does not make it so. If Kombiz was not asleep in his Earth Science class, he would know that Pluto was always considered a planet. Further, the Earth Science Reference Table has pluto as a planet.

    Being young is no excuse for being ignorant of scientific facts and Kombiz has further proved that Edwiz is clueless when it comes to the classroom.

  5. August 17, 2006 am31 2:09 am 2:09 am

    There has been a fairly vocal anti-Pluto caucus, for quite some time. I recall, and you may correct me, that there is a nice polynomial expression for predicting the distance of our planets from the sun. (Maybe 3rd or 4th degree???). Pluto is the only one of the nine that doesn’t fit the data. Now, this is a pretty hazy recollection; it goes back to a middle school science class in the mid – late 70’s. But I was forever convinced that including Pluto among the planets was a mistake.

    John’s post above, about setting criteria in order to exclude Pluto, that is the first thing that has led me to reconsider. Reading a handful of articles today, I accept that whatever definition is chosen is going to be somewhat arbitrary, but better to have an arbitrary objective definition than a subjective one.

  6. August 17, 2006 am31 2:25 am 2:25 am


    Kombiz comments here on his own behalf, not on behalf of Edwize. If you want to call him an idiot, you are welcome to do so. But please be aware:
    1. it’s not very nice
    2. it’s not really deserved
    3. it is an attack on a programmer/blogger who is speaking only for himself.

    You know more about this stuff than we do. How would you explain this to a kid with similar misconceptions? I’d rather see an exchange of science than of insults.

  7. August 20, 2006 pm31 1:37 pm 1:37 pm


    Sorry to insult Kombiz on your blog even if he allows people to insult me and then deletes my response on Edwiz. However, it is still no excuse for his being ignorant about the facts since he runs an educational blog.

    As for your comments about Pluto. The way I explain it to the students is that Pluto is different from the other planets due to its more elliptical orbit and a 17 degree inclination relative to the other planets. However, Pluto is defined as a planet based upon its revolution around the sun, its spherical shape, its methane atmosphere, and a moon that revolves around it.

    While Pluto may be part of the Kuiper belt it still should be considered a planet. Xena would also classify as a planet, based upon the recent findings. Ceres & Charon would and should not be considered planets since Charon revolves around Pluto (they think) and Ceres is not truely spherical.

  8. August 21, 2006 am31 1:39 am 1:39 am


    they are claiming that Charon and Pluto jointly orbit the sun. They are calling the two together a “double planet.” And they are claiming that Ceres is close enough to spherical.

  9. east_coast_john permalink
    April 14, 2007 pm30 8:49 pm 8:49 pm

    I don’t claim to be an expert on the topic here but it does seem that a set of criteria for what does or does not constitute a planet has to be in place. In addition, it seems that as we learn more about geology, ecology, astronomy, and a host of other associated topics that the criteria will evolve. When I first heard about pluto being demoted from its planetary status, I was not happy. I’m still not sure that I like it, but I do recognise the fact that the criteria will evolve as it must. As far as I can tell, the vast majority of scientists in this field still say that Pluto is a planet. The original argument was that pluto was too small to be a planet but that did not come into play until an argument started comparing Pluto to the newly discovered object to debate its status. If the discussion had been more geared toward defining a find and less about a minority of scientists getting their own way, I would probably take it more seriously.

  10. tynesshia permalink
    July 10, 2008 pm31 8:05 pm 8:05 pm


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