Astrophysicist: Pluto's Planet Demotion Justified

NT: It can influence how you think about a problem. One example that ... I will give at the debate is William Herschel, who is an unimpeachably great astronomer. He is credited for discovering what came to be known as the planet Uranus. But no one had ever discovered a planet before. So what's that like: To discover something that no one has ever discovered before?

You know what the title of his research paper is? Something like "A report of an unusual comet in orbit beyond Saturn." And you read his paper and it says, "This is an unusual comet, it shows no fuzz. It shows - yes it orbits the sun... but its orbit is not elliptical like other comets. It's kind of round, like the planets. And so a curious comet, this is."

He didn't have the brain to accept the possibility that there could be planets beyond Saturn. His brain was shut off to that. It's like someone from 100 years ago thrust into modern times and they see a car. How are they going to describe a car? They're going to say it's a horse-drawn carriage without the horse. To Herschel, Uranus was a comet without fuzz.

DM: Let's go back to the Great Planet Debate, which you don't sound too enthusiastic about the title.

NT: It puts great pressure on Mark Sykes and me to solve all the problems of the universe. (laughs)

DM: Speaking of Mark Sykes, you're about to do this throw-down with him. Are you nervous?

NT: Not in the least, I've been doing this for eight years.

DM: Have you been doing anything special to prepare for this debate?

NT: Well, it depends on what you call special. Coincidentally, I am putting the final edits on the galley of my next book, which is called "The Pluto Files: The Rise and Fall of America's Favorite Planet." And in that book it contains all of my files that contains hate mail from third-graders back when we first reclassified Pluto.

DM: Have you ever been in any sort of scuffle with Pluto lovers?

NT: Completely! Because we did this at the museum. ... We struck first blood as the first public institution to actually take a stand on what the future of Pluto should be.

Because I'm director of the planetarium and head of the universe part of the museum ... I got all the mail and all of the correspondence. So this book is a celebration of the public's reaction to the reclassification of Pluto, with this historical stuff in there as well but also right on back to Herschel and right on back to the search for Planet X with Percival Lowell and Clyde Tombaugh, and right on up through modern times.

So I'm fresh. I got -- Everything is there. It's all there. It's at my fingertips.

DM: So you're ready?

NT: Oh yeah.

DM: You're ready to take Mark?

NT: Oh yeah.

DM: Is he going down?

NT: (laughs) He's going down!

But I don't think of it that way. I have high confidence that the arguments I will present are the scientific and pedagogical high road. Anything else -- in my judgment -- will be mudslinging and strongly influenced by hidden bias. So this will be a test of who's more biased [in the scientific community].

DM: Sykes recently told us at Discovery Space, and I quote, "In writing up the definition, [the IAU] failed to craft one that made sense to the public and even most scientists." Any thoughts on that?

NT: Yeah. He's wrong because the vote was 420-something to 15 ... So for him to say that it didn't make sense to scientists is ... simply false. It's not my opinion that it's false. If it really didn't make sense to scientists ... they would have said, "this doesn't make sense, rewrite it, do it again."

DM: By the way, here's the rest of his quote "... a simple examination of Jupiter's orbit, for instance, would seem to disqualify the gas giant. So, people rely on the IAU's ex cathedra listing of planets. An unfortunate consequence is that science is misrepresented as the promulgation of 'truth' by an 'authoritative' body." Do you agree with that, or what are your thoughts?

NT: The IAU is to the astronomical community what the American dictionary is to the English language as spoken in America. Its goal is not to legislate. Its goal is to codify trend lines in the scientific community so that everyone can end up speaking the same language.

And so sometimes the IAU can be a little ahead of itself because it sees a trend line and it's excited, it looks like there's consensus. ... They're actually responding to the scientific community. There's not some "Science Pope" up on high decreeing divine commentary -- that's not how it works. Hence the vote. And the vote was an attempt to understand if there was a prevailing consensus. Had the vote been 50/50 or even 60/40 they would have said, "you know, this is not a strong enough consensus for us to declare this."And I'm convinced that they wouldn't have.

IAU sets the standards for how you name stars, how you name planets, how you name comets. Nobody complains about that because it's sensible, we all agree and we move on. ... We shouldn't turn to the IAU and blame them. They are us. They are the expression of our collective wisdom.

If Mark Sykes can gather enough resistance to the IAU vote, then that becomes the new consensus. I don't have a problem with that. He just hasn't. I'm not here to blockade or lobby ... Iin spite of how I've been characterized -- I'm actually quite passive in all of this. If you want to define the word planet in some way that serves your needs, fine. I don't have to teach it that way. Keep the definition of planet.

If your definition of planet [is] "anything spherical that's not manufacturing its own source of energy," ok -- fine. But give me a word that then describes objects that orbit in the habitable zone, objects that orbit that have rings, objects that orbit that are gaseous, objects that orbit that have magnetic fields, objects that orbit that have water. Why not have a classification scheme that teases out of our database interesting things about objects that orbit a star that they have in common? That's what classification schemes are all about. Yes it means a more complex scheme. So? Biology is accustomed to that.

DM: Like kingdom, phylum, class, order, family, genus, species...

NT: Thank you! Yes! (picks up microphone and shouts) YES!

This is a point I will bring up. Why are we dwelling on the word planet like that has some kind of sacred meaning? It lost its sacred meaning in ... 1543. We lost the meaning of the word planet with Copernicus. We were just lazy thereafter. Because we weren't actually challenged to have to do something fundamentally different.

DM: What's the most important thing to take away from this whole thing?

NT: ...As an astrophysicist, we should feel charmed that the public would take such great interest in the work that we do. There would never be a "Great Debate" on the naming of some subatomic particle with the public clamoring to attend. There'd be no "Great Debate" over chemists thinking of a name for a new molecule or a new classification scheme.

So I'm charmed and heartened that the work that we do has such a following and such strong and passionate interest expressed by the public.

Article posted August 13, 2008.

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