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August 27, 2006

The IAU. (Dude. I'm actually posting about the IAU. Wow.)

Until this year, I could never have thought for a moment that I would be especially intrigued by the workings of the International Astronomical Union.

But teaching Astronomy this year (with the absolutely indispensable help of one Joseph McCauley, now now lab coordinator at Georgia Highlands College) slapped my head around something fierce, and offered respect for this astronomy stuff, seeing as it's one of the great ancient sciences and all that. There's something about looking at stars and figuring out that, with a good telescope, you can actually observe the planets move in the sky and see Jupiter's moons that just rocks the world.

And it made me appreciate all the more that there is actually some fundamental understanding about the universe that came out of one of these talks this week.

But more on that in a moment. First, I want to discuss this Pluto thing.

I want to go on the record as saying that I think the IAU made the right call on "demoting" Pluto the way they did, even if their logic was too clever by half. Honestly, I don't know what's so complicated about this. We have these eight planets. Four of them are inside the asteroid belt. They are pretty dang dense, made of rocky matter, metals, minerals, "earthy stuff" if you will. We call these the terrestrial planets. We have for quite some time. Four planets are outside the asteroid belt. They are all huge planets but pretty light as far as huge planets go, tons o' hydrogen and helium running around, all of them have rings and satellites a go-go. We call these the Jovian planets. We have for quite some time.

And then there's Pluto. Pluto's made of rock and ice, closer in density to the terrestrials, but outside of the orbit of even the Jovians. Its own orbit is irregular, out of the plane of the other eight. Its moon is pretty huge in comparison to Pluto's size, and you can even argue that if Pluto's a planet, Charon has to be a planet too. (In fact, the original IAU proposal said as much.)

In short: Pluto doesn't fit.

And science is all about explaining power. All the protest, even from some of the smartest people I read, that because all the astronomy-fascinated little kids have nine glow-in-the-dark planets hanging from the ceiling, there ought to be nine planets, dang it misses the point, in my opinion. (And if that's the argument, I will counter that even my eldest daughter, who has only begun her middle-school astronomy training, can see clearly that Pluto doesn't fit. But I digress.) [1]

In all honesty, Pluto hasn't really been demoted at all. Here's the take from the IAU themselves, conveniently missed by most commentators:

The "dwarf planet" Pluto is recognised as an important proto-type of a new class of trans-Neptunian objects. The IAU will set up a process to name these objects.

What Pluto will be is the standard-bearer for these new "dwarf planets", which we've already started discovering, and not just one of 'em either. One of these, 2003 UB313 (a/k/a Xena), would have been promoted to planetary status had Pluto retained its own status. We honestly don't know how many more of these guys, of Pluto's size and perhaps bigger, might be in the Kuiper belt. They're important, and until I taught Astronomy, I didn't know how important and how well-characterized they were.

So Pluto's not a planet anymore. Yippee. But don't expect Pluto to leave your friendly neighborhood astronomy textbook anytime soon. Pluto's discovery is still a marvelous story, a triumph of observational astronomy, and the first hint that there was a lot more beyond Neptune than any of us had bargained for. In fact, I think it's even worth keeping up in that glow-in-the-dark model of the solar system. (Just find some room for Xena, too.)

One other footnote. The chair of the IAU Planet Definition Committee is a Harvard boy by the name of Owen Gingerich. Gingerich is not only a respected astronomer and historian of science, but he is a Christian and one of the more widely respected philosophers on the interface between science and faith, which is a field I'd dearly love to break into one of these days. Here's some theological perspective on Gingerich's work.

Okay, now, let's get to the real news.

Phooey. It's late. I have no time to get to the real news.

I'll just link back to a previously-cited take on the existence of dark matter and jabber more about what I think that means later.

[1] My eldest daughter has requested the right to weigh in with a her official opinion. I've placed it after the jump.

Pluto cannot be really considered a planet. Most people think that the IAU has gone completely berserk by cancelling out Pluto. I disagree. Pluto is a weirdo in space. It has always been an oddball. There are three reasons why Pluto cannot and will not be a planet:
  1. Pluto and Charon orbit around each other. This, therefore, breaks the rule that moons orbit around planets! If Pluto is considered a planet then Charon has to be a planet too. And Charon is not a planet.
  2. Pluto has an irregular orbit. Well, to some of us, that doesn't matter. But to me it does. Pluto orbits closer sometimes, overlapping with Neptune, Then it goes way out, almost into the Kuiper Belt!
  3. Pluto is tiny. If Jupiter were the size of a quarter, then Pluto would probably be about one one-hundredth the size of the period at the end of this sentence.

As you might see, Pluto doesn't fit. For those of you who use those shortcuts to remember things, start thinking, instead of:

My Very Eager Mother Just Served Us Nine Pizzas

start thinking
My Very Evil Mother Just Served Us Nothing!

(Note: I take the blame for the missing "Mother" in the second mnemonic earlier.)

Posted by Chuck at August 27, 2006 03:52 PM

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