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The Great Planet Debate conference, August 2008 - Washington DC
surreyguy
post Aug 11 2008, 09:00 PM
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Ah, that'll be good, if so. Keep me out of (or in) mischief for the weekend.
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surreyguy
post Aug 11 2008, 09:09 PM
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QUOTE (Greg Hullender @ Aug 11 2008, 09:57 PM) *
That's actually a very powerful argument I haven't really heard before -- that the scientific definition of planet should correspond to "worlds that have geology," because that's what Planetary Scientists study.


Well, only if you accept that geology is what planetary scientists study in the first place. Presumably dynamicists think they study planets, too, and opt for the dynamical definition. I'd agree with you, though, that if supporters of the hydrostatic definition pressed to abolish the satellite, their position would be a lot more clear.

I think if planetary scientists manage to define their own profession, that'll be a world first. In my own, erm, 'profession', operations research, it's a standing joke that if you put two OR people in a room, you'll get three definitions of OR. Now let's just ask the biologists for a definition of 'life'...
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Greg Hullender
post Aug 11 2008, 10:01 PM
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QUOTE (surreyguy @ Aug 11 2008, 02:09 PM) *
Well, only if you accept that geology is what planetary scientists study in the first place.


No, I said they study worlds that have geology. Now if, in fact, they actually study the stars and the dust and everything in between then it's much harder to argue that they need a scientific definition of "planet".

--Greg
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djellison
post Aug 11 2008, 10:20 PM
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I was worried this would turn into another 'define-a-body' argument, because we've really had enough of that here. But wow - we've got a new one, define-a-debate. Debating who can debate it is a nice new twist...I like it.

Doug
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surreyguy
post Aug 11 2008, 10:20 PM
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OK, I get you. We seem to be straying off 'Dwarf Planet Eris' so I'd better stop.
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JRehling
post Aug 11 2008, 10:41 PM
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The "authority" issue is a relevant one. If you like a particular kind of music, and a panel of experts convened and came out saying that the term you'd always used to describe it was invalid, would you stop using it? If there were a cartographical definition that discriminated between hills and mountains and you saw a protuberance whose height was unknown to you, would you pause mid-sentence out of uncertainty which term was correct?

Part of the issue here is the relationship between folk uses of terms and expert uses. Look up "star" in any dictionary and, besides the terms referring to actors, you find one astronomical definition denoting large gaseous spheroids heated by fusion and another denoting small, twinkling lights in the sky. By the latter definition, the percept Jupiter makes in the night sky is aptly labeled a "star".

One of the things that concerns me most is when a naive viewer of the night sky asks a question about a "star" and is told snippily that they just displayed their ignorance -- that what they are looking at is not a star. I don't think many people get very far in life without having some encounters like that, and the take-home lesson is that science equals pedantry and poor manners to boot. And I think the whole notion of the IAU defining "planet" gives that perception a giant shot in the arm.

When it comes right down to it, the "twinkling pointlike source of light" is *a* perfectly fine definition of the word "star" that doesn't supplant the scientific one, but exists for another context. And my perspective on that hypothetical encounter is that the pedant is actually the one displaying ignorance.

Cue the "planet" debate: While the lay-experience with planets is much less frequent than with stars, I'd say the folk experience (in schools, in backyards, watching science fiction movies) is still extensive enough to consider the term to have a folk sense. Meanwhile, it has absolutely no useful scientific sense. Saturn and Mars obviously have less in common than Pluto and Triton.

So I find the whole thing to be that backyard experience writ large: There's a kind of arrogance behind it, and it says to the world that pedantry is really what science is up to. If some jazz counsel had a vote on whether or not Miles Davis played jazz, I wouldn't care if the vote were 51-49 or if it were 100-0 -- I'd still keep calling it jazz. Far from caring about which side of which line Pluto is placed, I consider this a battle against pedantry, which, if won unbloodily, might mean more people who care about science.
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alan
post Aug 11 2008, 11:19 PM
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QUOTE (Greg Hullender @ Aug 11 2008, 10:43 AM) *
I'm still liking Mike Brown's thinking on the matter:
http://www.mikebrownsplanets.com/ (scroll down to "Ground rules for debating the definition of 'planet'")
There's a lot of good stuff here, but this struck me as new information:

-Greg

I found this quote about Nature and Science from his latest post interesting
QUOTE
along with publishing important ground-breaking papers appears to come the requirement that a larger than usual fraction of the conclusions published in these journals turn out to be incorrect. This leads to the semi-joking line that you often hear amongst astronomers: “Just because it is published in Nature doesn’t necessarily mean that it is wrong.”
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Greg Hullender
post Aug 11 2008, 11:50 PM
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QUOTE (JRehling @ Aug 11 2008, 02:41 PM) *
One of the things that concerns me most is when a naive viewer of the night sky asks a question about a "star" and is told snippily that they just displayed their ignorance -- that what they are looking at is not a star. I don't think many people get very far in life without having some encounters like that, and the take-home lesson is that science equals pedantry and poor manners to boot. And I think the whole notion of the IAU defining "planet" gives that perception a giant shot in the arm.


I think we definitely need to restrict the debate to exclude people who can't tell the difference between planets and stars. I realize this will hurt their feelings, but I just don't think it can be helped.

--Greg :-)
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Alan Stern
post Aug 12 2008, 12:56 AM
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QUOTE (Greg Hullender @ Aug 11 2008, 09:19 PM) *
Gee . . . they seem so nice on TV!

--Greg :-)


I really need to learn to type, it's going to limit my career if I don't.
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Alan Stern
post Aug 12 2008, 12:59 AM
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QUOTE (Greg Hullender @ Aug 11 2008, 09:57 PM) *
That's actually a very powerful argument I haven't really heard before -- that the scientific definition of planet should correspond to "worlds that have geology," because that's what Planetary Scientists study. That means, though, that our Solar System has about thirty planets, since this includes our moon and about seventeen other moons on top of the magic eight and the four dwarves. (Or am I completely confused? You're the real Planetary Scientist here.) :-)

Sometimes it does seem that all the counterarguments to this definition really boil down to "but what will we tell the children?" A fair point could be made that the definition should serve scientists -- not school kids -- given that there are in fact scientists to whom it's useful.

--Greg


30, 300, 3000-- it's whatever Nature tells us. No one limits the numbers of rivers, streams, elements, mountains, stars, etc. just for the convenience of memory. That argument is anti-scientific, and, I think, a dodge.

Alan
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Juramike
post Aug 12 2008, 01:07 AM
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QUOTE (Greg Hullender @ Aug 11 2008, 07:50 PM) *
I think we definitely need to restrict the debate to exclude people who can't tell the difference between planets and stars. I realize this will hurt their feelings, but I just don't think it can be helped.

--Greg :-)


Uhhhmmmm....Brown dwarf? smile.gif smile.gif

Is the Lithium test a widely known thing among most people?

My point is that there is a continuum between all things. The minute you define something, you will find yourself with an exception or special case that is difficult to assign. As our detection methods get better, these special cases can multiply beyond control and you get real cumbersome definitions and special rules that don't help very much - I kinda think we're there now with the whole "planet" definition thing. We probably do need an extensive series of categories that span the whole range of things we know about, and of things we probably haven't even discovered yet.

What will you call a world that orbits an unassociated brown dwarf
What will you call a world that orbits a gas cloud?
What will you call co-orbital worlds?
What will you call twinned worlds that orbit each other?
What will you call worlds that switch orbits periodically?

For all we know, these things could be more common than our own solar system.

For the Great Debate whether Pluto is a "planet" or not, I'm not vehement one way or the other. It will work itself out over the years as we get a better idea of the spectrum of "object relationships" from both observational (extrasolar detections) and theoretical modelling (since there will be limits on what we can detect).

Heck, I'm still struggling with the definition of "terrestrial world". Which is more similar to Earth: Mercury or Titan?

-Mike


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Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
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nprev
post Aug 12 2008, 01:19 AM
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Totally agree, Mike; said it before & I'll say it again, natural things exist along a continuum.

(I call this the "Platypus Argument"). tongue.gif


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A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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Greg Hullender
post Aug 12 2008, 01:38 AM
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QUOTE (Alan Stern @ Aug 11 2008, 05:59 PM) *
30, 300, 3000-- it's whatever Nature tells us. No one limits the numbers of rivers, streams, elements, mountains, stars, etc. just for the convenience of memory. That argument is anti-scientific, and, I think, a dodge.

Alan


Oh I didn't mean to appear to be arguing that 30 was too many. Just making sure we agreed that "orbiting a star" wasn't a reasonable part of the definition as far as "what planetary science studies" goes.

I am right on that part? The "planets" that planetary science studies are exactly those bodies in hydrostatic equilibrium, right? Not dust and not stars, but definitely including moons, if they're big enough. It's all about what they are -- not where they are.

--Greg
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Alan Stern
post Aug 12 2008, 01:42 AM
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QUOTE (Greg Hullender @ Aug 12 2008, 02:38 AM) *
Oh I didn't mean to appear to be arguing that 30 was too many. Just making sure we agreed that "orbiting a star" wasn't a reasonable part of the definition as far as "what planetary science studies" goes.

I am right on that part? The "planets" that planetary science studies are exactly those bodies in hydrostatic equilibrium, right? Not dust and not stars, but definitely including moons, if they're big enough. It's all about what they are -- not where they are.

--Greg


Greg--

I completely agree and will argue so in my invited talk at GPD. Whether bound to a star, bound to another planet, or just floating through the ISM, I am good with it as a planet so long as it has the central attributes of planethood-- large enough to be in HSE but not so massive that it does/never did fusion in its interior. An Earth in orbit around a Jupiter or escaped from its sun is still a planet, just as much a star is a star whether orbiting another star or even escaped from a galaxy.

-Alan
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Greg Hullender
post Aug 12 2008, 01:54 AM
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QUOTE (nprev @ Aug 11 2008, 06:19 PM) *
Totally agree, Mike; said it before & I'll say it again, natural things exist along a continuum.

(I call this the "Platypus Argument"). tongue.gif


But the logical conclusion of this argument is that there's no such thing as science; everything is unique, and studying patterns is wrong. You SURE you want to ride this train? :-)

--Greg
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