The Great Planet Debate conference, August 2008 - Washington DC Options

[surreyguy]

Yeah - asking how the definition (whatever it is) will be used and/or the implications of not having one.

[djellison]

I submitted two

1)

Dr Tyson has said in the past that if you moved Pluto into an Earth-like orbit, it would grow a tail like a comet which, for a planet, would be embarrassing.

However, if we moved Earth to a Pluto-like orbit, under current rules it would cease to be a planet given that Pluto's orbit is considered not to be cleared, and that, surely, is somewhat embarrassing as well.

Given that, does the panel think the definition of a planet should be derived purely from the properties of the body in question, or should the nature and location of it's 'home' contribute to a good planetary definition?



and

2)
Who's job is it to define 'planet' - and what should the purpose of any definition be?

[JRehling]

Good overarching questions.

That discourse of George Lakoff's which I cited, briefly, has something to say about both of them, I think. He takes the example of biologists arguing about whether genetic histories or phenotypes should be used as the basis for classification. He says that there was lengthy and vociferous debate over it, with rival camps. When the "answer" is really a matter of cutting the gordian knot: Have both systems. If one kind of biologist finds it useful to classify things genetically, then by all means, why force the phenotype system upon them? And if the other camp finds it useful to classify things by phenotype, then why force the other system on them? It would be like forcing carpenters to decide between hammer-nail solutions and screwdriver-screw solutions. Each has its use. And while standardizing would make every tool box one tool lighter, it's better to have both.

With planets, per Doug's question (1), this question of WHERE vs WHAT has come up. Cutting the gordian knot is to say that they simply call for two systems of classification (if each is found useful). For a dynamicist, obviously WHERE is important. For someone studying the structure and evolution of planetary bodies, WHAT is the gist, and WHERE matters mainly because temperature has an effect on WHAT.

I think the IAU definition may be really useful to dynamicists (although a dynamicist would have to say). Whether using the term "planet" for that makes more sense than "nucleation site" or whatever is another matter. It would have a lot to say, perhaps, about why the biggest nucleation sites that haven't cleared their orbits are so much lighter than the ones that have.

But for what the rest of planetary scientists do, it has no use. And the question remains, does *any* definition have a real use in planetary science?

And for the layfolk making their 5000 web queries a day on Pluto, would any such definition have any use?

Before they'd tossed around two definitions, the IAU leapt to the conclusion that the three (or more?) groups need one definition.

I think countless examples have shown us that the answer to Doug's (2) question is that when groups need different terms, they end up with different terms. It makes the dictionary 0.0001% bigger, and language 0.0001% more ambiguous, but that ends up being preferred over Group A having to use Group B's word. If the clash is big enough, it won't stay that way unless you have the sort of authority that kept "Stalingrad" in place as a name for sixty-some years.

[nprev]

This is parenthetical (what do I ever say that isn't? ), but it seems to me that the GPD is the first such scientific ruckus over classification outside of biology, at least during the modern era. Geologists see mixtures of rock types every day, for example, and there certainly isn't a dispute on whether a particular specimen (or even a formation) is igneous, sedimentary or metamorphic, or a combination of all the above.

It's odd how emotionally attached we seem to be to some issues but not to others.

[Greg Hullender]

I asked them whether they thought we had enough examples of planets to frame a meaningful definition at all.

--Greg

[alan]

It's started

[Juramike]

I asked why we couldn't just expand the meta-term "planet" to the broadest definition, and let the researchers define their specific subgroups of interest when they publish.

Pity we can't vote on the questions. (I really like Doug's first question)

[nprev]

"Let the Games begin!!!"

(Silent moment of appreciation for the cleaning crew after the meeting; it's really hard to effectively remove blood, sweat, and tears...)

[Juramike]

Whoo-hoo! I'm in!

[Actually, hearing all the startup noises and fumblings is a riot! I swear I heard a "D'oh!" in there]
[Ooops, and I just heard one of the Words You Cant Say on Television]

[alan]

false alarm, they were only practicing the introductions

[djellison]

I hope so - I though it started at half-past

[volcanopele]

Never got confirmation email

[djellison]

It's working, but I'm getting no sound at all.


(I quite the stream and then started it again, and it started working)

[alan]

which one is the 13th?

[djellison]

Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Charon, Eris, and Makemake.