That’s no planet… it’s a space station

Thursday, 24 August 2006 — 1:46pm | Science

The big news at this hour, in the unlikely event you haven’t heard, is Pluto’s demotion to “dwarf planet” status, in a stunning (but appreciated) reversal from the twelve-planet proposal that raised such a brouhaha in the mainstream press.

It’s about bloody time.

Let me begin by saying that I have no sympathies for Pluto as a planet. I haven’t thought of it as one since the day I discovered it was even up for debate. I don’t think I’m wholly uninformed: I’ve had an amateur interest in astronomy since the age of six months. My first book was about space, and appropriately entitled My First Book About Space. I noticed early on that something was off, and that Pluto’s behaviour was markedly different from the rest of the objects that were considered planets: its sheer puniness, its erratic orbit, its mass relative to Charon’s, the mere realization that we haven’t observed it long enough to validate the orbital path that was extrapolated in all of those pretty picture books – the list goes on and on.

It is interesting and aggravating to me that a lot of the coverage about the planetary redefinition cites, as a major source of resistance to change, the inertia of public opinion and the tendency of the ignorant masses to stick to obsolete schoolbooks as eternal, axiomatic truths.

Public opinion is bollocks. The public is inadequately educated on the basic tenets of scientific method and still thinks in terms of epistemological facts and non-facts. Don’t believe me? Take a good look at one of those science textbooks in the States with the utterly idiotic disclaimer that “Evolution is a theory, not a fact,” which is true of everything that we consider science (excluding mathematics, which is founded on abstract definitions and axioms and does not by itself adhere to real-world empirical observations).

Scientists aren’t out of touch with the public consensus. The public consensus is out of touch with science.

As for the scientific opposition to Pluto’s demotion – which is at least based on argumentation and not dogma, but is objectionable for linguistic reasons – I get the sense that what the IAU aimed to do was retain some kind of observable distinction between the eight planets and trans-Neptunian objects (plus the usual oddballs like Ceres), other than some arbitrary statement about where they lie. And let’s face it: Pluto’s planetary status was a legacy concession, and the nine-planet definition was pretty arbitrary to begin with.

On principle, drawing a line around the eight classical planets is no different from how we currently distinguish between the inner planets and the four gas giants. The new “dwarf planet” category (not subcategory) is sufficiently accommodating in spite of some outstanding quirks (Charon, anyone?), as it correctly classifies Pluto as “not quite as much of a planetary object as the other ones” and even provides a useful distinction that separates Ceres from the rest of the asteroid belt.

Given what we know about our solar system and its outskirts today, there’s hardly a Pluto-inclusive definition that wouldn’t be a slippery slope. You might even say that the rejected twelve-planet proposal was jury-rigged to include Pluto for sentimental reasons, and one of the concerns about it was that it would open the door to at least ten other candidate planets, and almost certainly more in the future. The dilution would eventually necessitate a special term for the eight planets up to Neptune anyway, since those objects fall into two very distinguishable taxonomic classes. I like the term “classical planet”, which was bandied about at one point, but “planet” alone is more in keeping with the intuitive connotations of the term.

In the article I linked to above, Alan Stern from NASA’s New Horizons mission complains that a vote of 424 astronomers out of over 10,000 professionals worldwide is insufficiently representative. This is tantamount to saying that international relations are invalid unless you sit all the governing politicians of one country down with all the governing politicians of another. Furthermore, I’m not sure a direct democracy would have made any difference with respect to the outcome. Science is not a democracy, and I do not think there is any indication that the IAU voters – all professional astronomers – were grossly unrepresentative of the astronomical community at large.

Last week, maverick descriptivist Geoff Pullum of Language Log fame made an entertaining comparison between planetary status and the rules of grammar. I think he illustrates my point pretty well.

Now I’m going to listen to Gustav Holst. He got it right the first time.


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