We've got 12 Planets!

It’s official!

The voting membership of the IAU has accepted the draft definition of “Planet.”

This means that we’ve got three new planets, with many many more to come. Ceres, the planet formerly known as an asteroid, takes the coveted fifth planet position away from Jupiter. Charon, the planet formerly known as Pluto’s satellite, is a part of the Pluto-Charon double planet system. 2003 UB313 a.k.a. Xena, is the first of the new Plutons, other than Pluto itself. (Will “pluton” be capitalized or not? Hmmm…)

What do I think this means. Diddly! I think a lot of people will talk about the 8 “classical” planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune) plus the 9th “discovered” planet of Pluto, and then lump all the rest into “those other things.”

I think Ceres is going to get the small end of the stick here. Not big enough to be considered a planet for 120 years, it’s not even going to be classified as a Pluton. Red-headed step-child syndrome if there ever was one.

Of course, whether we have 9 planets or 8 or 12 or (soon) a gazillion, it’s all very arbritraryarbitrary. See my last post.

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5 Responses to We've got 12 Planets!

  1. Amy says:

    So do we expect elementary school curriculums to change and have several generations of confused parents, or will kids still learn we have 9 planets and to hell with the IAU?

    I wonder.

  2. Bill says:

    I was thinking about that on the way in today. Not so much what will be done “from now on,” but what will be done this coming school year. Will teachers adhere or will they ignore the topic or will they touch on it, but revert to the nine-planet-dogma?

    Thinking about it some more this weekend, I think the IAU should have included another category for planet: Planetary System. That way, any system with two (or more, but this isn’t scifi) bodies revolving around a common center which is in orbit around a star (thusly satisfying IAU criteria 2) would be a single planetary system, and not counted into the total by an increment of more than one. This would fix what a lot of people are bitching about, namely that Charon gets planetary status.

  3. Tenner says:

    any system with two (or more, but this isn’t scifi) bodies revolving around a common center

    That doesn’t really happen; maybe I’m wrong, but I’d imagine the point(s) at which the third (fourth, fifth, etc) objects would have to exist would be unstable equilibria, and a passing hydrogen atom which bumps into it a little too hard is enough to send it crashing into one of the other bodies (or off into space if the bombarding particle has enough kinetic energy). That’s why there are tons of binary stars, but few (or no) ternary stars. In the case of orbits, the central body has to have a mass significantly greater than the orbiting bodies; that’s what distinguishes a two-body system (two objects orbiting around the barycenter) versus a central body with an associated (or, in the case of Saturn, 47 confirmed) orbiting bodies.

    I don’t know why Charon’s promotion is drawing complaints. The problem here is just one of semantics. When Charon was discovered in 1979, our imaging was so poor little was known about the object. It seems to me that the public wants Charon to be a satellite for historical reasons — just because it always has been. Using that argument, Pluto’s discovery in 1930 elevated it to planet status then because we didn’t know what else to call it — Gerard Kuiper was still in Leiden working on his dissertation then.

    But then again, I always learned that when observations change, the science changes, whether we’re speaking of physical laws or mere taxonomy. That’s science, no?

  4. Tenner says:

    What will happen this school year?

    Nothing. “Nine planets” in 98% of classrooms.

    With all due respect to the work that they do (I could never do it), elementary school teachers don’t at all care about science. The vast majority of them became elementary school teachers because they liked kids, and liked to teach reading and (maybe) math. Social studies is a subject that naturally most people with barely-triple-digit IQs can get their head around. However, science is the subject that is not only “hard”, but is socially permissible to be “hard” — as I tell my students, no one will ever laugh at you for saying you don’t understand a concept in physics. Elementary school teachers are generally afraid of science, and naturally it goes to the bottom of the priority list when they prepare their lesson plans.

    This is one of the main reasons I’d argue that our scientific preparation in this country is poor — kids get at most six years of good science education in middle and high school, compared with 13+ years in English and social studies.* If you asked most first- or second-graders what they would like to be when they grow up, I’ll bet more than half would say “doctor” or “dinosaur scientist” or “veterinarian” or some other science-based career track. Good science education would help to keep at least some of them, whereas it’s perfectly politically allowable for students (sadly, especially girls) to abandon science because it’s “hard”. Yes, it’s hard, but that doesn’t mean it’s not worth studying. Good teachers will help their students rise to the challenge and ensure they have fun the whole way along.


    *Yes, I’ve omitted math. I can’t speak well on why this is the case, but I’d suspect it’s because math is treated like a recipe class rather than a number-theory class, and the vast majority of math teachers don’t understand the practical nature of what they’re teaching. The (excellent) calculus teacher in my school can’t even tell the kids why they’re learning what they are. And honestly, as a physicist by training I don’t see much point in math for math’s sake, other than as an exercise in logic or mental gymnastics.

  5. sarah beth says:

    werent u and dad saying this lieka few yrs ago

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