Saturday, September 02, 2006

Pluto-nium

One cannot make an omelette without breaking eggs – but it is amazing how many eggs one can break without making a decent omelet. ~ Prof. Charles P. Issawi

The revolt has begun. The metaphorical gates of the IAU are being stormed by angry astronomers, all because of a ball of ice and dirt called Pluto.

I first mentioned that the International Astronomical Union was going to take up the issue of what makes a body a planet here in a passing matter-of-fact reference. Before too long, I penned a more expansive piece dealing with the increasing emotionalism that seemed to swirl around the first proposed definition. This initial definition, developed by a committee chaired by Owen Gingerich, who is no slouch of an astronomer, increased the number of planets to 12. The trouble is that this definition had multiple categories (both official and unofficial) including “plutons”, a term that turned out to already be in use by geologists. The definition also promoted Charon to planethood, which didn't seem like such a good idea.

Another astronomer, Julio Fernandez, was so displeased with the committee's effort that he offered his own proposal for discussion. A press conference to present his idea practically turned into a revolution itself.

Finally, as I chronicled here, the IAU came up with and passed yet another proposal that demoted Pluto to something called a “dwarf planet”, dropping the number of “real” planets to eight but adding a flock of “dwarf” planets, led by Pluto and including Ceres (but not Charon), and the recently-discovered Xena (as it is unofficially named). This resulted in howls from many astronomers, who are now in open revolt against the IAU.

I tell you, this has been a blogging bonanza.

There have been stories all over about this, but my favorite headline came from the New Scientist site: "Astronomers Plot To Overturn Planet Definition". Can't you just picture a bunch of white-coated astronomers meeting in the middle of the day (they work nights, remember?) to concoct a scheme to pull a coup d'etat against the evil overlords of the IAU. Can't you imagine a crack team of mutant ninja astronomers sneaking into IAU headquarters to steal the definition?

Well, no, neither can I, but it would be pretty funny.

What astronomers are doing is going very public about their dissatisfaction with the IAU. In the lead, as if he hasn't caused enough trouble (I'm joking, already), is Owen Gingrich, who, if you can recall a few paragraphs back chaired the committee that created one of the definitions that wasn't accepted. Led by Mr. Gingerich, astronomers will have a new conference to once again tackle the issue of what a planet is. This guys are serious; they have also prepared a petition , by golly, to show the IAU that they mean business.

All right, perhaps I'm a little overboard here (so what else is new?), but there is something comical about the fuss. I am reminded of the quote I used in one of the earlier articles from an astronomer at Johns Hopkins: "I think the whole debate is absurd. The fact (in my opinion) that Pluto is in a different class from the eight planets does not make it less interesting." Well said, sir.

Instead of solving anything, the IAU has create chaos. Some scientists are saying they will simply ignore the definition; some museums and planetaria are saying they will not change displays or presentations to conform with Pluto's devalued status. And, we are liable to be looking at a competing definition in 2007 when the conference organized by Mr. Gingerich occurs. All of this distracts astronomers from the real work they should be doing, and that is a bad thing.

At the root of this whole brouhaha is the way the voting happened in Prague. While the IAU has thousands of members, only between 400 and 500 actually were left at the conference by the time the proposal came to a vote on the last day of the session. Even Mr. Gingerich had been forced to leave because of other commitments. He has called loudly for Internet voting to avoid such controversies in the future, which is a sensible enough concept.

The trouble is that, even if thousands of astronomers had voted, they would have had poor choices. Any vote would have been very close, ensuring even more controversy. I also suspect that, like me, there would have been a lot of astronomers who didn't like any of the definitions, for reasons I have discussed previously (see those links above, if you're curious). To make matters worse, as far as the IAU is concerned, the next meeting is in 2009. No one wants to wait that long to achieve some sort of consensus.

So, essentially, we're right back where we were before the IAU meeting in that there is no clear agreed-upon definition of a planet. What bothers me is that we will soon have at least two, if not more, definitions to choose from. This is also not a good thing.

We can make light of it, but teachers are going to have a genuine problem here, trying to explain to students how a concept as seemingly obvious as a “planet” can get so completely muddled. Textbook writers are going to have to waste time and effort explaining the same thing or, worse, taking one definition over another. Now this isn't earthshakingly serious; no one will build bridges that fall down because they haven't got a clear concept of what Pluto is. But, it demeans science itself if its practitioners can't settle an issue this basic.

At the bottom of this, the fundamental problem is that science took a back seat to politics. The idea of voting on what constitutes a planet is like voting on what constitutes a photon. This is not some legalistic exercise; it's a description of real objects that impacts how we define theories of planetary formation. We don't need committee meetings, conferences or votes. We need for astronomers (and perhaps astrophysicists and physicists) to step forward with definitions that are backed up with data. Let's have none of this “largest by far” and “cleared the neighborhood” nonsense.

Use things like size, shape of orbit, distance from the sun, physical makeup, and so on to put a specific set of parameters on the table for what a planet is. Publish it, and let the comments flow. Will we get bunches of definitions and even bigger bunches of comments? Probably, but that's basically the way most of our definitions have come about. Someone says that a certain class of stars has common qualities, so we say they're all of a type. Perhaps later we learn more about them that causes us to subdivide the classification or dispense with it altogether.

When Clyde Tombaugh discovered Pluto, we didn't know Kuiper Belt objects existed; now we do. Should all of them be planets or should Pluto be one of them? Personally, I lean toward the latter view (yes, that would mean eight planets; deal with it), but I could live with either if someone defines the difference between planets and the Kuiper Belt objects.

Or did I just start a whole new argument?

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