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

[Alan Stern]

You probably already know about The Great Planet Debate meeting coming this week near DC, if not, see:
gpd.jhuapl.edu.

To register for Great Planet Debate conference web participation, click: http://tinyurl.com/6xcqec
Watch the talks and debate on line!

-Alan

[ElkGroveDan]

Thanks Alan. The whole issue hit home with me this week when I was talking to my kids about planets and my five-year-old daughter corrected me and and said "Pluto is not a planet. My teacher told me that." I'll be glad to see the discussion opened up again in a serious forum.

[Hungry4info]

Forgive the, perhaps ignorant question... but do the people at this coming debate have the authority to change the status of Pluto? i.e. change what objects are planets, and what objects are dwarf planets? I'm guessing "No.", but am not sure.

[djellison]

Nobody can change what these planets 'are'.

But they can try and come up with a better way of categorizing them - the current system is utterly broken (and that's coming from someone who doesn't care if Pluto is a planet or not,I just want a definition that makes sense)

Doug

[ngunn]

I just want a definition that makes sense

Unfortunately that might just be 'pie in the sky' (that would cover pizza moons as well).

[Greg Hullender]

But they can try and come up with a better way of categorizing them - the current system is utterly broken (and that's coming from someone who doesn't care if Pluto is a planet or not,I just want a definition that makes sense)

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'")

He says he personally considers the debate closed, but since we don't seem to be able to move on, he proposes some rules for the discussion.

There's a lot of good stuff here, but this struck me as new information:

Misleading statements about the previous vote should also be disallowed. Yes, the whole IAU procedure was a bit mucked up, but the results would likely have been the same no matter who was in the room at the time. Surveys done after the IAU vote – yes there were some! – showed that astronomers by a large number thought that the 8 planets definition was a good one. So complaining about the IAU vote gets you the label of “misinformed about how most astronomers think."

I thought that was a particularly strong claim. I wonder who does those surveys? :-)

--Greg

[Alan Stern]

I'd sure like to know too. The only one I know of is the Sykes-Stern petition, which in 48 hours after being introduced gained 300+ signatories who were displeased with the IAU vote.

Brown's assertion that the vote "would" have been the same is unsupported.

Worse, voting in science is about the worst way one can go: can you imagine if there were voting on evolution, global change, etc.? Voting is antithetical to science, which works by archieving consensus based on which models best fit an ever expanding base of data.

Anyway, The GPD later this week in Maryland will feature debate and no votes. Come to the meeting or tune in if you can't and are interested.

-Alan

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'")

He says he personally considers the debate closed, but since we don't seem to be able to move on, he proposes some rules for the discussion.

There's a lot of good stuff here, but this struck me as new information:



I thought that was a particularly strong claim. I wonder who does those surveys? :-)

--Greg

[tedstryk]

It reminds me of how Stephen Colbert decides whether an idea is right or wrong based on how well it sells. For example, he changed positions on global warming because Al Gore's book sold more copies than those written to oppose his position (for those outside the U.S., the Colbert Report is a parody news program).

[Hungry4info]

Okay, I'll ask my question in a different way:

Do the people at this coming debate have the authority to change the status of Pluto?

i.e. if the people at this debate want to call Pluto a planet, will Pluto be called a planet? Regardless of what it is.

[Mongo]

Worse, voting in science is about the worst way one can go: can you imagine if there were voting on evolution, global change, etc.? Voting is antithetical to science, which works by archieving consensus based on which models best fit an ever expanding base of data.

I agree. However, in this case the debate is over terminology, not science. In my own opinion (for what it is worth), the term 'planet' is obsolete and should be retired. I would go with several sets of terms for each type of object: a set of terms for composition -- 'gas giant', 'ice giant', 'terrestrial' and 'ice dwarf'; a set of terms for orbital status -- orbiting the Sun, orbiting another body that in turn orbits the Sun, or in a mean-motion resonance with a more massive Sun-orbiting body; and a set of terms for gravitational self-rounding (including non-typical objects like 2003 EL61) -- fully gravitationally relaxed, partially relaxed, unrelaxed.

So Pluto would be a fully gravitationally relaxed ice dwarf in a mean-motion resonance with a more massive Sun-orbiting object.

Luna would be a fully gravitationally relaxed terrestrial orbiting a more massive Sun-orbiting object.

Vesta would be a partially gravitationally relaxed terrestrial orbiting the Sun.

And so on.

[Alan Stern]

I agree. However, in this case the debate is over terminology, not science. In my own opinion (for what it is worth), the term 'planet' is obsolete and should be retired. I would go with several sets of terms for each type of object: a set of terms for composition -- 'gas giant', 'ice giant', 'terrestrial' and 'ice dwarf'; a set of terms for orbital status -- orbiting the Sun, orbiting another body that in turn orbits the Sun, or in a mean-motion resonance with a more massive Sun-orbiting body; and a set of terms for gravitational self-rounding (including non-typical objects like 2003 EL61) -- fully gravitationally relaxed, partially relaxed, unrelaxed.

So Pluto would be a fully gravitationally relaxed ice dwarf in a mean-motion resonance with a more massive Sun-orbiting object.

Luna would be a fully gravitationally relaxed terrestrial orbiting a more massive Sun-orbiting object.

Vesta would be a partially gravitationally relaxed terrestrial orbiting the Sun.

And so on.

Mongo-

Since planetary science is a field and planetary scientists have a profession, I do not think we can or want to retire the term which planets. Instead, our field and our profession need to come to a consensus on what we, the practitioners, consider to be planets vs. smaller and vs. larger things. That astronomers hijacked this process is about equivalent to brain surgeons, rather than cardiologists, deciding where the dividing lines between veins, arteries, and capillaries are, and the public/press following along because "they are all doctors, after all."

As to Hungry4Info's question, no one really has the authority to change the status of Pluto or other bodies. Science doesn't work by such decrees-- it works by finding the best solution that fits the data, which is fundamentally about achieving consensus, not votes or decrees.

Hope this helps.

-Alan

[surreyguy]

To register for Great Planet Debate conference web participation, click: http://tinyurl.com/6xcqec
Watch the talks and debate on line!

-Alan

Are we able to participate in the conference as a whole, then? I have registered, but I thought all that gives me is the chance to hear Sykes and Tyson duke it out. I look forward to that, but my expectation is of more heat than light to be honest.

[Alan Stern]

Are we able to participate in the conference as a whole, then? I have registered, but I thought all that gives me is the chance to hear Sykes and Tyson duke it out. I look forward to that, but my expectation is of more heat than light to be honest.

I believe all the invited talks will be posted as videos and the slide presentations from most or all of the talks at the entire meeting will also be posted. That said, I am not a meeting organizer and cannot vouch this is absolutely correct. As to Sykes/Tyson, I am hoping for a more scientific debate, but knowing both and considering both fiends for 20+ years, I will say I do expect some entertaining barbs too!

-Alan

[Greg Hullender]

knowing both and considering both fiends for 20+ years, I will say I do expect some entertaining barbs too!

Gee . . . they seem so nice on TV!

--Greg :-)

[Greg Hullender]

Since planetary science is a field and planetary scientists have a profession, I do not think we can or want to retire the term which planets.

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

[surreyguy]

Ah, that'll be good, if so. Keep me out of (or in) mischief for the weekend.

[surreyguy]

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'...

[Greg Hullender]

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

[djellison]

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

[surreyguy]

OK, I get you. We seem to be straying off 'Dwarf Planet Eris' so I'd better stop.

[JRehling]

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.

[alan]

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

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.”

[Greg Hullender]

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 :-)

[Alan Stern]

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.

[Alan Stern]

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

[Juramike]

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?

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

[nprev]

Totally agree, Mike; said it before & I'll say it again, natural things exist along a continuum.

(I call this the "Platypus Argument").

[Greg Hullender]

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

[Alan Stern]

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

[Greg Hullender]

Totally agree, Mike; said it before & I'll say it again, natural things exist along a continuum.

(I call this the "Platypus Argument").

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

[Alan Stern]

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

No, everything is unified. Planets are a class of bodies bigger than boulders and rubble piles but smaller than stars. ...Unless I miss your point, this is unifying, and a fine train to ride.

[Juramike]

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

Well, you can bin things. But sometimes things can go in more than one bin.

[A slightly off-topic example: Stromatolites were originally assigned species. But as time goes on, it appears that stromatolites are fossilized microbial mats that may have resulted from several species. A newer classification system is based primarily on shape and structure of the stromatolite, totally ignoring the microbe that created it.]

[Another case: Early stage cancer is not a specific disease. It is a member of a matrix of disorders, with an initial gene defect causing loss of cellular control in one vector, and the tissue type in another. Once this is realized, the War on Cancer will not be fought on a single front, but as a multitude of small skirmishes. (Metastatic cancer is, unfortunately, most of the full matrix)]

[Another example: Biological science is famous for uncovering a new receptor or enzyme. Usually, further examination reveals a whole plethora of enzymes. Serotonin receptors are a great example. There are over 13 different serotonin receptors. There is even a naming committee for these receptors (with back-and-forth arguments as well.) One of my favorite quotes is "Note that there is no 5-HT1C receptor since, after the receptor was cloned and further characterized, it was found to have more in common with the 5-HT2 family of receptors and was redesignated as the 5-HT2C receptor." ]

The beauty of studying the patterns is that there are so many different ways to group things.

Remember the "One of these things is not like the others" song on Sesame Street? I was the kid always trying to find a relationship to group the "obvious exception" choice back in and exclude one of the other objects.

-Mike

[EDIT: found a Cookie Monster video clip]

[nprev]

No, everything is unified. Planets are a class of bodies bigger than boulders and rubble piles but smaller than stars. ...Unless I miss your point, this is unifying, and a fine train to ride.

I'm flattered!

One thing to keep in mind is that categories are a human invention, a very useful way for us to rationally perceive the Universe and discern relationships, as Mike pointed out. Nature does not sort itself; we do the sorting.

IMHO, the only things that sort themselves into completely discrete and unique (though identical within each category) entities are subatomic particles. It is a marvel to contemplate the fact that such simplicity at such a small level (possibly down to the mere six flavors of quarks) can be organized at macroscales into the diversity of things in the Universe.

[Greg Hullender]

No, everything is unified. Planets are a class of bodies bigger than boulders and rubble piles but smaller than stars. ...Unless I miss your point, this is unifying, and a fine train to ride.

Yeah, you miss my point. ;-)

I'm okay with the "Planetary Science" train. I'm not okay with the "Ignorance Eternal" train.

The former is the one that says "planets are what planetary science studies . . ." and all that follows from that.

The latter is the one that says "everything is a continuum; all entities are unique; we cannot ever know more or say more about anything." Did you see the "platypus" reference? This is the logic that argues "the term planet is meaningless -- and even the term MAMMAL is meaningless."

--Greg

[nprev]

Did you see the "platypus" reference? This is the logic that argues "the term planet is meaningless -- and even the term MAMMAL is meaningless."

Not meaningless; merely artificial, and (literally) an artifact of the way we perceive the Universe.

We need points of reference to make sense of things & determine relationships. "Mammal" is a pretty good distinction, but the platypus is a great example of a borderline case. Nature is not bound to what we say it should be or not is all I'm saying. There are literally no true dichotomies in the natural world.

Biology offers abundant examples: slime molds are a beaut. It gets even worse when considering microorganisms, in fact. Under some taxonomies, we're up to five, count 'em, five distinct kingdoms of life...a pronounced increase from the traditional two of plant & animal that we all know from school.

Only point I'm making is that whatever the outcome of the GPD might be, and even if a consensus emerges, it'll be pretty much subjective at the core. There aren't any absolute distinctions that can be made. Moreover, as Mike again pointed out, we'll find objects someday that will challenge any definition we might make. (My personal fav in the near-term is finding a Mars-sized or better KBO 1000AU or more out...)

In all likelihood, it will be an eternal debate, and certainly not restricted to astronomy. Imagine what might happen if someday we find a complex alien ecosystem... ...oy, vey!!!

[volcanopele]

Don't forget that planetary scientists also study moons, asteroids, comets, dwarf planets, Trans-Neptunian Objects, etc. We don't just study planets

[lyford]

Ok, so if a planetary scientist were less than 5 ft. in height... no I don't really want to go there.

[dvandorn]

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?

Ah, but that kind of thing goes on all the time. Music is redefined into different catagories as time passes and it is seen in context with its moment(s) in history. And, of course, *anything* that is categorized as "modern" is doomed to be renamed as it fades into the more and more distant past.

Much moreso, far more basic categorizations and names change constantly. Meet anyone from Stalingrad lately? Or someone who lives in Czechoslovakia? Or Persia? Just ask the Poles -- they've gone through periods in history when their entire country ceased to exist, for decades and more at a time. Or the Slavs in general, who were enslaved so many times by so many conquerors that the very name of their ethnicity entered many languages as the definition of the very concept of slave.

How different is it to go to sleep in the Soviet Union and wake up in the independent state of Kazakhstan than it is to go to sleep in a solar system with nine planets and wake up in one with eight? Or 30? Or 3,000?

Things change as time goes on, and as they change we have more and more information -- more and more history -- that puts bits and pieces of our Universe into a new context. From whether the world calls it Peking or Beijing to whether Pluto is called a planet, a dwarf planet, an icy dwarf, or a cartoon dog.

This way we have of changing/refining the categories as we learn more and put things into better and better context helps us understand and come to terms with our place in the Universe. And as the old saw goes, it's not an event, it's a process. What is debated today and decided tomorrow will inevitably be re-interpreted, re-debated and re-decided over and over as time goes on. The best thing we can do, exactly as Alan has said, is try to attain a consensus that satisfies the maximum number of people, that is driven by relatively rational principles, and that reflects our *best* understanding of the science involved.

-the other Doug

[JRehling]

I think we definitely need to restrict the debate to exclude people who can't tell the difference between planets and stars.

It can be pretty hard to tell the difference between Saturn and Regulus in a lot of circumstances.

Through a car window in the growing light of dawn, when you're uncertain which way is due north, etc.

And try spotting Uranus without mechanical assistance and see if you're immediately sure which magnitude 5.8 object it is.

It can be pretty hard to come away from the context of looking at books and articles, but there is a real world of lights and sounds, and it's in that context where the "pointlike source of light" definition of star is perfectly useful. So you don't have to say things like, "There, in Capricorn, between the two pointlike sources of light which could be either stars or perhaps one of them is Uranus or even Vesta or a dim comet..." A word of one syllable comes in pretty handy.

[dvandorn]

It can be pretty hard to come away from the context of looking at books and articles, but there is a real world of lights and sounds, and it's in that context where the "pointlike source of light" definition of star is perfectly useful. So you don't have to say things like, "There, in Capricorn, between the two pointlike sources of light which could be either stars or perhaps one of them is Uranus or even Vesta or a dim comet..." A word of one syllable comes in pretty handy.

Which takes us back to the very origin of the word planet. Back in the days when the only way we could chart the seasons and predict celestial events was to examine the sky and the stars. Some of the most revered astronomers of the early ages spent lifetimes plotting the movements of the stars in the heavens. And while most stars moved in easily predictable patterns, some of them -- and indeed, some of the brightest of them -- moved in odd and eldritch fashions, passing through the static and unchanging constellations in non-intuitive, hard-to-predict patterns that repeated (with major variations) over the course of months in some cases, or over the course of decades in others.

These were the planetes, the wanderers.

So, the original meaning of the term had absolutely nothing to do with the physical characteristics of the bodies. It only referenced the different way in which they traversed our skies from all of the other stars.

As I said, as time goes on, context changes...

-the other Doug

[JRehling]

Ah, but that kind of thing goes on all the time. Music is redefined into different catagories as time passes and it is seen in context with its moment(s) in history. And, of course, *anything* that is categorized as "modern" is doomed to be renamed as it fades into the more and more distant past.

Much moreso, far more basic categorizations and names change constantly.

Yes, but it's also resisted all the time and ignored all the time. And it's potentially a battle of wills between the would-be authorities and the public; sometimes the battle easily goes one way, and sometimes easily the other way. E.g. (thanks again, Wikipedia).

http://en.wikipedia.org/wiki/Name_of_Pittsburgh

"On December 23, 1891, a recommendation by the United States Board on Geographic Names to standardize place names was signed into law. The law officially changed the spelling of the city name to Pittsburg, and publications would use this spelling for the next 20 years. However, the change was very unpopular in the city, and several businesses and organizations refused to make the change. Responding to mounting pressure, the United States Geographic Board (a successor to the original United States Board on Geographic Names) reversed the decision on July 19, 1911, and the Pittsburgh spelling was restored."

The majority has the capacity to make authorities' rulings irrelevant if they feel strongly enough about it. The IAU certainly has no more force to it than the law changing the name of Pittsburgh. It's not only possible to force the decision to be overturned; it's possible to make it irrelevant whether it's overturned or not.

The Pluto/planet situation is a little more nuanced, because every act of writing "Pittsburgh" tacitly chooses one spelling or another. The real point with Pluto is that there is no scientific reason whatsoever to so label it or not. A scientific paper on Ganymede doesn't need a footnote saying "Ganymede is a satellite of Jupiter." Anyone reading the paper would presumably know that. Likewise with Pluto. If there were a sentence added to a serious research paper asserting which class of object it is, whichever class it mentioned, that sentence would be pure noise to the signal of the rest of the paper.

[Stephen]

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.

Hmm. But since dwarf planets and plutoids are NOT planets does this mean "Planetary Scientists" will NOT be studying the geology of Pluto?

Presumably that means "dwarf planets" be studied by "dwarf planetary scientists" instead. (Visions of little green geologists peering through telescopes and launching space probes!)

======
Stephen

[Alan Stern]

Hmm. But since dwarf planets and plutoids are NOT planets does this mean "Planetary Scientists" will NOT be studying the geology of Pluto?

Presumably that means "dwarf planets" be studied by "dwarf planetary scientists" instead. (Visions of little green geologists peering through telescopes and launching space probes!)

======
Stephen

A portion of my point yesterday seems to have been misunderstood, or at least not very well put on my part, so despite being a slow and error prone typist, I'll elaborate a little and hopefully clarify the intended point:

Given there is a field called planetary science and a profession called planetary scientist, I think it is a reasonable (and in fact good thing) for those of us in the field and profession to come to our own consensus on what we mean when we refer to the central objects after which the field and profession are named.

I further think that is up to the practitioners, and rather than practitioners of related fields (read: astronomy, dynamics) to make this determination for ourselves. That a group that was >80% (some would say >90%) non-planetary scientists made a determination in Prague about what they consider to be a good definition of planet is a historical fact. I submit that the numerous technical problems generated by the astronomer's definition of '06 is in fact related to their tangential relationship to planetary science.

I don't wonder that a similarly problematic (disastrous?) and contentious result might obtain if the DPS met to reclassify objects in astronomy like stellar types, galaxies, or GRBs, and then put out declarations to the the press about it.

Now, onward from what I said yesterday, what is truly regrettable, and what I do believe will now change, is that the press and public believe that experts in the relevant subject matter domain made the planet definition determination. They did not. This is in significant measure why so many planetary scientists jumped on the Sykes-Stern petition the week after the 2006 IAU meeting.

-Alan

[Phil Stooke]

Absolutely right, Alan. The IAU has not really recognized the change in planetary science which occurred in about 1960 with the work of Hackman, Mason and (of course) Gene Shoemaker - the moon and planets became essentially geological objects, and the practitioners in their study mostly geologists, geophysicists, meteorologists and so on. It's like the last gasp of the Urey-Shoemaker dispute, so well told in Don Wilhelms' book 'To a Rocky Moon'.

Of course, this is complicated a bit by an object like Eris, which - at the moment - can only be studied by astronomical means. We have to recognize the broad mix of disciplines involved, and astronomy is part of that. But as you suggest, people who study these objects, from whatever background, should be the ones making the decisions.

Phil

[Phil Stooke]

JRehling: "And, of course, *anything* that is categorized as "modern" is doomed to be renamed as it fades into the more and more distant past."

Yes indeedy. 'Post-Modern' has now been dropped in favor of 'Pre-Next'.

Phil

[Ken McLean]

Should we be waiting on further evidence to support planetary accretion such as the Modern Laplacian Theory before deciding what constitutes a planet, ie. born out of solar/stellar system formation? And if so, does that mean we need to class satellites like Titan - which has been postured by some to have formed independently of Saturn's orbit - as a planet? If the orbit of a planet changes does it cease to be a planet, despite being compositionally very similar?

[Greg Hullender]

Don't forget that planetary scientists also study moons, asteroids, comets, dwarf planets, Trans-Neptunian Objects, etc. We don't just study planets

You're undermining Alan's argument, you realize. I don't think we can allow you to study comets, unless they're REALLY big comets. :-)

--Greg

[Juramike]

Objects smaller than the Sun occupy a multidimensional continuum of values. Level of differentiation, atmosphere, size, distance from parent star, crustal materials, past/current geologic processes, etc. Choose the right dimensions, and there will be a unique place for everything: Io, Pluto, Eris - everything could get a coordinate.

All of the objects could be plotted in multidimensional space and subjected to cladistic analysis to draw up clusters of objects. But when you define up the clusters, you may end up drawing up borders that may not make much sense in the big scheme of things. And some of these might end up being arbitrary.

For instance, my own personal level of "interesting objects" [crustally differentiated objects with a solid surface]: Mercury, Venus, Earth, Moon, Mars, Ceres, Io, Europa, Ganymede, Titan, Triton, Pluto.

My list of "preferred interesting objects" [crustally differentiated objects which may have had "recent" geological activity] includes: Venus, Earth, Mars, Io, Europa, Ganymede, Triton, Pluto

And my arbitrary list of "most preferred interesting objects" [crustally differentiated objects which may have had recent geological activity and have an atmosphere and that we've taken pictures of the surface]: Venus, Earth, Mars, Titan

All this demonstrates that the groupings and definitions we give objects are arbitrary in the eye of the definer. (The data itself is not, but how the data is grouped is.)



Pluto will still be Pluto whether we call it a "planet" or not.

Whether Pluto is a "planet" or not, for me, is an uninteresting discussion.

A much more intereseting discussion would try to answer:
How is Pluto similar/different from Earth?
How is Pluto similar/different from Titan?

Those are the questions I get excited about.

-Mike

[djellison]

FYI - the actual pluto debate itself has been had at UMSF before. It ended with raised tempers, arguments, attacks, people running to teacher to claim they were getting bullied. See the several threads in this sub-forum for further examples.

We're not going down that road again.

Whos job it is to decide, however, is a pertinent and interesting debate. Keep it nice.

[Alan Stern]

Objects smaller than the Sun occupy a multidimensional continuum of values. Level of differentiation, atmosphere, size, distance from parent star, crustal materials, past/current geologic processes, etc. Choose the right dimensions, and there will be a unique place for everything: Io, Pluto, Eris - everything could get a coordinate.

All of the objects could be plotted in multidimensional space and subjected to cladistic analysis to draw up clusters of objects. But when you define up the clusters, you may end up drawing up borders that may not make much sense in the big scheme of things. And some of these might end up being arbitrary.

For instance, my own personal level of "interesting objects" [crustally differentiated objects with a solid surface]: Mercury, Venus, Earth, Moon, Mars, Ceres, Io, Europa, Ganymede, Titan, Triton, Pluto.

My list of "preferred interesting objects" [crustally differentiated objects which may have had "recent" geological activity] includes: Venus, Earth, Mars, Io, Europa, Ganymede, Triton, Pluto

And my arbitrary list of "most preferred interesting objects" [crustally differentiated objects which may have had recent geological activity and have an atmosphere and that we've taken pictures of the surface]: Venus, Earth, Mars, Titan

All this demonstrates that the groupings and definitions we give objects are arbitrary in the eye of the definer. (The data itself is not, but how the data is grouped is.)



Pluto will still be Pluto whether we call it a "planet" or not.

Whether Pluto is a "planet" or not, for me, is an uninteresting discussion.

A much more intereseting discussion would try to answer:
How is Pluto similar/different from Earth?
How is Pluto similar/different from Titan?

Those are the questions I get excited about.

-Mike

Mike-

I agree with the high "interest factor" in your two questions just above, start a thread! But regarding planet definition, I hope the the topic (for everyone, not just this forum) needs to move from a "contest" over Pluto (let it fall where it may) to a rational one about planet categorization in general. Putting Pluto in the middle of it clouds the arguments, with people claiming there are issues of sentimentality, American pride, etc.; it distracts attention from the important issue of getting a workable definition and categorization of planets. Sykes and others (not sure about Tyson) have accepted this point and will be echoing it at GPD later this week.

Are you going to be at GDP?

-Alan

[JRehling]

A title I always find funny is "Lunar and Planetary Science", as though the Moon is the sole non-planet to be discussed in this context. Either it should be called "Lunar and Ganymedian and Mirandan and ... [...] ... and Cometary and Planetary Science" or the lunacy of listing just ONE exception should be discarded immediately. Why would the term be broad enough to include Saturn's rings, but not the Moon?

I think the simple category error here is the presumption that the question "Who decides" is going to end up having an answer. Who decided how Pittsburgh would be spelled? Who decided that the English definite article was "the"? Who decided that when a group is asked to identify itself, the answer that sounds best is "It's us" rather than "It's we"?

The IAU *happened* to come up with a torturous and counterintuitive definition and they *happened* to make a decision that impacts the textbooks and they *happened*, as Alan notes, to consist more of people who study stars rather than solar system objects. However, the idea went sour at the point that the implication was made that a smoke-filled room owned the term "planet", which provides no service to science for objects in our solar system.

[pumpkinpie]

I've registered to watch the debate but I never got any email confirmation. Am I all set? What do I have to do to watch it?

[Juramike]

I think the Great Planetary Debate will work itself out over the next several years to decades. And it won't be from a small group in a smoke-filled room, it will be from scientists looking at a much larger dataset (of as-yet undetected and unanalyzed objects) and grouping things according to trends.

A likely example is the historical development of the Periodic Table. From the initial five elements: earth, wind, fire, water, and lifeforce (see avatar), we now have a clear grouping into 118 (and counting) atomic elements. What is very interesting is that early attempts tried to pigeonhole the elements strictly according to atomic mass (law of octaves). It wasn't until Mendeleev ordered elements according to chemical reactivity with guidance from atomic mass that a clear pattern emerged that allowed elements to be systematically grouped.

[Now, what would've happened if the "inert gas" compound XeF2 [CAS# 13709-36-9] had been known back then? Again, there are always exceptions to definitions.]

Years from now, we'll all look back on this and laugh....then get back to work colonizing Titan.

-Mike

[Alan Stern]

I've registered to watch the debate but I never got any email confirmation. Am I all set? What do I have to do to watch it?

Pumpkinpie- I just inquired on your behalf with meeting organizer Hal Weaver. He says you and about 500 of your closest friends who have also registered for the web participation will be getting email info later today answering your particular questions and more.

-Alan

[laurele]

We may need to come to the realization that no one permanently "decides" such things. Students actually learn more from finding out there are multiple schools of thought driven by different interpretations of the same facts. Maybe some discussions need to be left open for now with caveats that things may change as we learn more. No one is teaching there are X number of exoplanets because it is obvious that we are discovering new ones all the time and that the number and types of exoplanets discovered will inevitably keep changing. It's just a suggestion, but maybe the best way for textbooks and educators to approach the planet question is to point to the Dawn and New Horizons missions, which in only seven years will provide us with a whole new set of data on which to base these decisions. Every time we send a mission to another planet, whether a flyby, orbiter, rover, or lander, we discover new things that no one could have anticipated, such as the water vapor in Mercury's very thin atmosphere.

It's just my opinion, but a reversal of the IAU statement that dwarf planets are not planets at all would go a long way in resolving this issue regarding Ceres, Pluto, Eris, MakeMake, and other round KBOs.

I'm going to be attending the GPD in person, and I look forward to a wonderful, tremendous learning opportunity.

[tedstryk]

I think a lot of this trouble stems from the questionable process by which the IAU adopted the resolution. Waiting until after most of the delegates had left to bring it up created a lot of bad feelings. Not to mention that the definition passed doesn't really make sense. My fear is that this mess might weaken the IAU's role, something that would create chaos.

[Greg Hullender]

But regarding planet definition, I hope the the topic (for everyone, not just this forum) needs to move from a "contest" over Pluto (let it fall where it may) to a rational one about planet categorization in general. Putting Pluto in the middle of it . . . distracts attention from the important issue of getting a workable definition and categorization of planets.

It does seem to me that Planetary Scientists are the only ones in a position to do such a thing. If there were a consensus around a really solid definition, I'd expect the other IAU members would defer to it.

Maybe it would help to give a special name to the Magic Eight; call them "Classical Planets" for example. Round, isolated, in circular orbits in the ecliptic -- they certainly SEEM special enough to merit special attention.

Things like the moon or Ganymede could be "Secondary Planets". Again, from a Planetary Science point of view, I don't see how any rational definition can leave them out.

Planets that are part of a belt (like Ceres or Pluto) could stay "Dwarf Planets" but those would now be "planets," not minor planets.

Stuff above the meteorite level could be "subplanets" and we'd just retire the term "minor planet".

Probable planets (e.g. fairly bright KBOs) could be called "planetoids" until we had enough data to class them as dwarf planets or subplanets.

I'm still not ready to consider comets to be any kind of subcategory of planet, but I suppose you could "define" comet as an icy subplanet in a highly elliptical orbit etc.

Kids in school would learn the classical planets. Enterprising ones would learn the secondary and dwarf planets on their own.

--Greg

[surreyguy]

Maybe I'm just belabouring the obvious here, but while some categorisations (e.g., all bodies whose name begins with 'E') are arbitrary, the good categorisatons are those which reflect theory in some way. That's what distinguishes categories such as '>2000km diameter' from 'roundness'. The thing which I guess I find odd is when people find it hard to switch viewpoint, and thus what categorisation is relevant for the discussion at hand. If you want to discuss tectonic features then the roundness criterion is relevant; if you are talking about the way the architecture of the Solar System has been sculpted over time, then orbital dominance is what you want.

Of course, some definitions may be more useful than others for the purpose of knowing which committee gets to name a body, but you'd think that issue could be settled without people crying 'but what about the children'...

I guess I'm saying that I don't think that there's any such thing as an inherent quality of 'planetness' which we can know - that seems a no brainer, put like that, but a lot of the arguments one sees seem to be predicated on something like it. For example, the use of 'what if we discovered...' scenarios.

[Alan Stern]

Pumpkinpie- I just inquired on your behalf with meeting organizer Hal Weaver. He says you and about 500 of your closest friends who have also registered for the web participation will be getting email info later today answering your particular questions and more.

-Alan

Now I am told they are getting flooded with extra log in requests for web participation and won't cut off the list until morning. Only then will they send out the instructions, answers to questions, etc.

-Alan

[Juramike]

Are you going to be at GDP?

I guess I was more interested than I thought. I signed up to get the webcast.
(Hopefully it'll get through my work's firewall.)

[laurele]

Kids in school would learn the classical planets. Enterprising ones would learn the secondary and dwarf planets on their own.

--Greg

I like your ideas, but I think kids should be taught the dwarf planets and secondary planets too, not necessarily to memorize, but at least to illustrate that they are an important part of the solar system. Even back in the 70s when I was in elementary school, we learned about the larger moons of the planets. Leaving out Titan, the Galilean moons and the dwarf planets seems to me to be doing a disservice to the kids.

[tedstryk]

I thing the moon versus planet definition works. Even planet-sized moons have histories so intertwined with their parent planet that it separates them from objects in solar orbit (even Triton was melted down in the process of being captured).

I don't know if this would be a good one for the Planetary Society to get caught up in. The debate is to emotional. The Planetary Society is a non-partisan group (and I am referring to sides in scientific debates, not party politics, although that would also be true I guess), and to risk a result that makes it look petty or turns some of the community against it would be dangerous. Also, it is primarily a group that works to advocate the funding needs of Planetary Science in Congress and to educate the public about planetary science and planetary missions. That even includes educating people about what is being debated. But to step into a debate that some might see as an attempt to supplant the IAU and to risk having a position adopted that alienates some of its constituencies doesn't seem worth it.

[mcaplinger]

...while some categorisations are arbitrary, the good categorisatons are those which reflect theory in some way.

I'm not sure I would use "arbitrary" and "good" as opposites like this. Many (most?) uses of terminology are "arbitrary" but have managed to avoid the emotionalism and controversy that this one has caused.

If it were up to me, I would have just said that everything Pluto-sized and bigger was a planet and everything smaller wasn't, but somehow this has been dismissed as being too "unscientific".

The whole thing reminds me of the vociferous debate I was involved in about whether longitudes should be positive to the east or west (also horribly confused by the IAU.)

[JRehling]

Maybe it would help to give a special name to the Magic Eight; call them "Classical Planets" for example. Round, isolated, in circular orbits in the ecliptic -- they certainly SEEM special enough to merit special attention.
[...]
Kids in school would learn the classical planets. Enterprising ones would learn the secondary and dwarf planets on their own.

I don't understand what the motive is to create a term (even a reasonable one) for the purpose of singling out a group. If the purpose is to create a cutoff for educators, perhaps. But scientifically, Mars is still more similar to Pluto than it is to Saturn. Your comments above, especially the ones I've quoted, imply that this isn't about science but about providing direction to educators.

I'll point out that elementary school math teachers neither seek nor find direction in cutting-edge research mathematics, showing just how different those two sides of the topic are. Serious academics in mathematics interact with "quotients" all the time, but they aren't any better than your typical fourth-grade math teacher (who likely has forgotten any calculus they ever knew) to determine the nomenclature in an elementary school text. In fact, the math wonks are possibly especially poorly-suited to do that.

But this puts a pinpoint on the divide between the science issue and the educational issue. And I think the shame of it is that while educators should look to researchers for the basic facts (eg, does Venus have volcanoes?), which is an objective matter, this labeling and nomenclature is not an objective matter, and handing the reins to the researchers to help decide what the kiddies will be taught is just going to make people jaded about what scientists do.

As an aside, I have bought a number of books about the planets for my son, and the subtle misinformation that's rampant in most of them tells me that any possible lesson in classifying bodies correctly (if there were a "correctly") is way below the signal-noise ratio as it is.

(Sample misinformation: Venus's thick clouds MAKE its atmosphere dense.)

[pumpkinpie]

I like your ideas, but I think kids should be taught the dwarf planets and secondary planets too, not necessarily to memorize, but at least to illustrate that they are an important part of the solar system. Even back in the 70s when I was in elementary school, we learned about the larger moons of the planets. Leaving out Titan, the Galilean moons and the dwarf planets seems to me to be doing a disservice to the kids.

I taught over 16,000 students in a portable planetarium this year. Part of the show was letting the kids choose where in the solar system to visit. Most classes chose to go to Pluto. When I asked what it "is," close to 100% had at least one person who knew it was a dwarf planet. In most classes I heard a chorus of the correct answer.

Knowing its label, of course, isn't enough. That's just a form of memorization, and has no meaning without explanation. I would talk about why its category changed, and that there are bound to be more additions/subtractions/reclassifications as our knowledge of the solar system changes.

[Greg Hullender]

Your comments above, especially the ones I've quoted, imply that this isn't about science but about providing direction to educators.

Educators are an interested party, since kids can understand this stuff. Contrast math, where higher math is utterly unintelligible to even a talented undergraduate student -- much less an elementary school kid.

It's not completely frivolous to consider educators. Fascination with the planets is a first step into science for many people.

To recap:

Planetary Scientists (not the Planetary Society!) ought to have first call; this is their field of study, so they have the biggest stake.

The IAU itself needs a criterion for assigning names, and that does need to be based on what can be observed -- not what properties might be observed if only we could send a probe.

But educators inspire the next generation -- both the young scientists and the interested non-scientists who are happy to see their tax dollars spent exploring space. Their needs cannot drive the definition, but any definition certainly needs to take them into account.

--Greg

[Greg Hullender]

I taught over 16,000 students in a portable planetarium this year. Part of the show was letting the kids choose where in the solar system to visit. Most classes chose to go to Pluto.

Yep, kids like superlatives. I felt that way as a kid too. It's hard to beat "furthest away," although I wonder if Jupiter came in second? (Actually I'd guess Saturn, since the rings are unique.) If they knew about Sedna, they might have picked that.

Pleasing the kids isn't the same as educating them, though. All kids know this already. :-)

--Greg

[nprev]

It's not completely frivolous to consider educators. Fascination with the planets is a first step into science for many people.

That's an excellent point on several levels; certainly I was first interested in science by the very concept of planets.

I hope that some educators will participate in the GPD. They may bring some perspective to the whole issue by defining concepts that really communicate with people (and, hopefully, not trying to sell a particular viewpoint.) SInce IMHO the whole thing is quite subjective, it might be much more important to make the final result intelligible & teachable.

[JRehling]

I taught over 16,000 students in a portable planetarium this year. Part of the show was letting the kids choose where in the solar system to visit. Most classes chose to go to Pluto. When I asked what it "is," close to 100% had at least one person who knew it was a dwarf planet. In most classes I heard a chorus of the correct answer.

Knowing its label, of course, isn't enough. That's just a form of memorization, and has no meaning without explanation. I would talk about why its category changed, and that there are bound to be more additions/subtractions/reclassifications as our knowledge of the solar system changes.

I would dispute that it is the "correct" answer any more than the law made "Pittsburg" the correct spelling of that city's name.

Age and background are important variables, but I think this Planet Debate -- not just the particular IAU decision, but the debate itself, as it's been transmitted -- is an absolute disaster for primary education. Speaking as a parent who's bought a few books for his son, some of which were updated with impressive speed. For very young kids, the meta-arguments about classification systems are completely incomprehensible. And I have books where the page devoted to Pluto is now half about this issue. This is a shame first because it displaces whatever else could have been said in that half-page. Second, because kids below a certain threshold of grasping abstractions totally miss whatever point could be made beautifully to a student of the philosophy of science. It's like taking an elementary school text about a tropical island with imagery and comments about the weather and diet and replacing them with information about how the local legislature works. For kids who are sufficiently below the level of understanding for that, it doesn't even provide the building blocks of understanding -- it's just 50 seconds of noise, the way a literature lecture in Hungarian would fail to educate a mature English speaker of one iota of the subject matter or Hungarian.

This subject matter near and dear to our hearts gets a limited amount of discussion in the classroom, and this issue only serves to crowd out some of the real content to replace it with opinion presented as fact. With a tinge of pedantry to boot. That's no wins and three losses.

[JRehling]

Educators are an interested party, since kids can understand this stuff. Contrast math, where higher math is utterly unintelligible to even a talented undergraduate student -- much less an elementary school kid.

It's not completely frivolous to consider educators. Fascination with the planets is a first step into science for many people.

To recap:

Planetary Scientists (not the Planetary Society!) ought to have first call; this is their field of study, so they have the biggest stake.

The IAU itself needs a criterion for assigning names, and that does need to be based on what can be observed -- not what properties might be observed if only we could send a probe.

But educators inspire the next generation -- both the young scientists and the interested non-scientists who are happy to see their tax dollars spent exploring space. Their needs cannot drive the definition, but any definition certainly needs to take them into account.

But kids cannot understand the comparative pros and cons of alternative classification systems. Not before about ninth or tenth grade, on average. Younger than that, and a discussion like that will just be noise. And if instead you just give them the IAU definition as fiat, you're passing opinion off as science.

No, it certainly is not frivolous to consider educators. I'd go much further -- this issue is primarily of interest to educators, and has done them the disservice of asking them to accept an arbitrary and divisive definition with the misinformation that it is a scientific truth newly had.

"This" is not Planetary Scientists field of study. As I mentioned before, the class of body that Pluto might be does not inform scientific papers on Pluto, just as papers about Mars do not hinge on Mars being a planet. Research scientists have no stake in this, but have chosen to browbeat educators into accepting a fiat which is not science, shaky classification, and poor education. And this would be equally true if they had (or "will", as they likely will, in time) handed down a definition ruling Pluto to be a planet.

Just to take an arbitrary example of the non-usefulness of this term for scientists, here's a poster/paper about the spectra of Pluto and Charon: http://www.lpi.usra.edu/meetings/acm2008/pdf/8150.pdf

The paper doesn't anywhere use the terms "planet" or "dwarf planet", or any terms for Charon, for that matter. Can we conceive of any way in which such terms could better inform the science, if they were included in this paper? For any proposed definition of "planet"? I sure can't think of one.

In essence, the term has no use for scientists. It has a folk use, like "hill" and "river", and is therefore useful in folk senses, in the classroom. For scientists to call this their field and therefore their term is like the legislature saying that city names are their field and therefore theirs to decide. So it began in Pittsburg and so it ended in Pittsburgh.

[Greg Hullender]

In essence, the term has no use for scientists. It has a folk use, like "hill" and "river", and is therefore useful in folk senses, in the classroom. For scientists to call this their field and therefore their term is like the legislature saying that city names are their field and therefore theirs to decide. So it began in Pittsburg and so it ended in Pittsburgh.

It is this argument that I have been most bothered by -- it seems incredibly anti-science to me. But only a planetary scientist can answer it with any authority.

Your Pittsburgh example is poor by the way, since (the way I heard the story) it's the only US city that resisted standardization.

--Greg

[JRehling]

It is this argument that I have been most bothered by -- it seems incredibly anti-science to me. But only a planetary scientist can answer it with any authority.

That statement baffles me. Axiomatic trust in authority? Scientists have the answers because they are scientists?

In a software company, it's frequently evident that the engineers are not the best people to name things. Just because astronomy is not-for-profit doesn't change that. The engineers know the software best, spending their days hands-deep in it. That does not make them the best ones to lay down the nomenclature, either for internal or external purposes. It's quite a separate thing from the subject matter expertise.

While I would expect to trust scientists first in a scientific matter, this is a nonscientific matter which happens to be attached to objects that science studies. And while one might expect them to have uses for terms they use in their work, I cited the brief paper/abstract on Pluto to show that the term is not essential to science, and I would certainly welcome an example where the term "planet" was helpful to any scientific paper on any solar system object. If it's about Mars, it's about Mars.

And Pittsburgh is not a poor example because it's the only example of a place that resisted the fiat. One, because it's only the largest of several places. (Pittsburgh, KS; Edinburgh, Indiana; Plattsburgh, NY; Newburgh, NY; Newburgh, IN). Two, because the point is that public usage is a force to be reckoned with. If there were no local affection for a particular spelling elsewhere, then it was a one-sided tug-of-war that the authorities won by default. In Pittsburgh, the two went head to head and the authorities lost.

[alan]

It's too bad the debate tends to fixate on Pluto and whether the dwarf planets should be considered planets. I think the techniques used to decide which of the TNO's are dwarf planets is more interesting. For example, determining how large an object needs to be before it is in hydrostatic equilibrium, and the methods used to estimate the diameters of the objects.

I've seen some claims that an icy body would be in hydrostatic equilibrium if it is over 450 km in diameter. But I've also seen a presentation (IIRC by Tancredi) that used the shape of light curves and some models to estimate the density and roughness of objects which found a couple of objects to be either to rough or not dense enough to be in hydrostatic equilibrium. Some of those objects have been estimated using infrared radiation detected by the Spitzer Space Telescope to be 600-700 km in diameter. It looks like these estimation methods will need to be verified by other methods such as determining the size and shape by observing stars being occulted by the objects.

[djellison]

Scientists have the answers because they are scientists?

Biologists classify animals (a cow is still a cow no matter what genus it's in).
Paeleontologicists classify fossils (T-Rex is T-Rex regardless of who you consider its cousins to be).
Librarians classify books (Roving Mars is still Roving Mars if you put it in the science section or the biography section).

Planetary Scientists should classify planets.

[surreyguy]

Planetary Scientists should classify planets.

You'd think that would be a no-brainer, wouldn't you?

The only caution I'd have is to avoid circularity (!): you define planetary scientists as people who study planets, and then this group defines planets. For example, I would think people would count the study of asteroids and comets under planetary science (though I'd be interested to hear if people think otherwise), and you don't want to end up with a situation where yet more people feel excluded by the outcome of a definitional debate.

That said, the representation at GPD seems encouragingly broad.

Conversely, educators should decide how they will convey the science to the public (and, yes, there will be educators at GPD too - go look at the abstracts), with input, not legislation, from the scientists. I'm surprised more hasn't been made of the idea of a technical definition - for example, a strawberry is not technically a berry, and a shark is not technically a fish, and scientists and the public both seem to live happily with that.

[djellison]

you define planetary scientists as people who study planets, and then this group defines planets.

At that point, we enter the realm of utterly pointless semantics. We all know what planetary scientists are. They study the 'things' out there. Earth, Mars, Titan, Pluto etc etc.... the bodies pertinent to the issue in hand. Thus they should be classifying them.

People who study quasars, nebulae, cataclismic variables and so on are not and were not the right body for that.

[Stephen]

Planetary Scientists should classify planets.

This is starting to sound like a potential turf war; and like all turf wars it generally all comes down to where you draw the line...and who is entitled to exercise the power to draw those lines.

So "Planetary Scientists should classify planets", eh?

OK, but who gets to decide what is a planet and what isn't (so as to allow planetary scientists to get on with their all-important classification work)? Planetary scientists themselves?

That is to say, do planetary scientists ALONE get to decide not just what a planet is but where the line is between (say) planets and stars. (Eg is a brown dwarf a star or is it a planet?)

On the other hand those who prefer to classify stars (let's call them "starry scientists", "star scientists" for short; after all if you can have "PLANETary scientists"... ) might like to have some kind of a say of their own in that sort of decision. That would, however, raise the question of just how much of say they would be entitled to. Are they only entitled to a say on drawing the line between stars and planets and would then be turfed out of the meeting room when the discussion turned to the line between (say) planets and comets? (Instead the "cometary scientists" would be allowed in and given a say. )

Of course the very line implied above between "planetary scientists", "star scientists", and "cometary scientists"--not to mention "moon scientists", "cometary scientists", and "plutoidary scientists" (let's try to be consistent here! )--raises the issue of just who exactly is a "planetary scientist" anyway?

Higher up this thread somebody (volcanopele) pointed out: "Don't forget that planetary scientists also study moons, asteroids, comets, dwarf planets, Trans-Neptunian Objects, etc. We don't just study planets." That statement could be construed to suggest that a geologist is basically nothing more than a "planetary scientist" who specialises in a single planet: Earth! (And something similar might be said of, "moon science", 'cometary science" etc. ) Or to phrase the matter another way, "planetary science" might be said to be not a branch of geology. Geology (aka "Earth science") is actually a branch of "planetary science"!

On the other hand, is "planetary science" the study of any planet EXCEPT Earth? If so, that would seem to exclude GEOlogists per se from having a say in deciding what exactly is a planet.

======
Stephen

[Juramike]

a strawberry is not technically a berry, and a shark is not technically a fish...

...and a cow with 50% mouse genome is technically no longer a cow(wt) [wt = wild type].



How about we let the term "planet" have the widest possible use? Let everything go in there.

(OK, make a cut somewhere: like "objects composed of normal-generacy atoms at a density > interstellar gas nebula that are not currently undergoing fusion")

That will allow "planetary" scientists to study gas giants, comets, ice giants, moons, rocks, KBO's, etc.
Each paper will need to define the set of comparitive objects de novo: "We compare Pluto with other KBO planets [Sedna, Eris, Makemake,...]"

And educators will have to introduce students to the full wonderful diversity of objects in and beyond our solar system.


Eventually, better definitions will arrive, most likely from the same set of comparitive objects being used in the scientific literature. (Just like the chemical reactivity patterns eventually helped define the Periodic Table).

-Mike

[djellison]

Quite.

[Ken McLean]

Why don't we just accept the geo- prefix as its proper meaning of ground/earth (as opposed to Earth) and call it all geoscience?

[JRehling]

Biologists classify animals (a cow is still a cow no matter what genus it's in).
Paeleontologicists classify fossils (T-Rex is T-Rex regardless of who you consider its cousins to be).
Librarians classify books (Roving Mars is still Roving Mars if you put it in the science section or the biography section).

Planetary Scientists should classify planets.

"Biologists classify animals" is a good one to look at. First of all, they do so with controversy and alternate approaches of many kinds.
I think George Lakoff laid out a pretty good look at this and how biologists really aren't very good at stepping back and considering the meta-issues of classification, peerless as though their knowledge may be of the DNA and the organs and so on. He has a very good analysis of some of the controversy which I think is very relevant to the planet debate, but is also way too long to copy-paste here.

But I think it's a useful case to look at because there are some similarities, and the biology controversy surrounding the kingdoms is several years further along. And also has relevance for kiddies' textbooks.

One there were two kingdoms in biology: plant and animal. Then three. Then two "empires". Then 4 kingdoms, followed by 5 and by 6. Then three domains. Some of these various systems were refinements of some other, compatible. Sometimes they were incompatible and led to division, name-calling, hair-pulling, etc. We can't rehash all of the drama.

But step back and consider the relationship of this to the children's schoolbooks. At which points in the debate do you shred the previous edition, buy a new one and teach the new classification system as fact? Keep in mind that we're talking about 12 years on average between a new system. And each new system is proposed but not accepted with unanimity. The idea that any of this strikes anyone as a matter of fact is as incomprehensible as someone saying that the child who said that Pluto was a dwarf planet is "correct".

This is all very good stuff for students of the history and philosophy of science -- wonderful tangles of complexity and controversy and elusive truth. But it's horrible subject matter for children 9 years old. They just don't get it. Can't. And lots of the PhDs don't get it either, as Lakoff describes. They get one system or another and live by it as a religion, but they can't see the interrelation of the alternate systems that their colleagues favor.

In some cases, though, there is an important basis in the biological classification of kingdoms. Some tiny critter's genetic tree might depend crucially on some phenotype or genotype. It's controversial, but worth pursuing. There is reason to believe in a light at the end of the tunnel.

For planetary science, the term "planet" isn't even useful -- or I'd like someone to point out how it is useful in discriminating the kinds of bodies we're talking about. A paper on Pluto's spectrum cannot possibly be informed by whether or not the thing cleared its orbit. The definition they've latched onto has nothing to do with what they study.

So the harm in all of this is to take a vote of disputed authority, and promptly rewrite the textbooks and tell the kiddies that we've learned something through science, when science had nothing to do with it. And keep an eye on your watch, because the Whittaker system of biological kingdoms had 8 years before the next one came along, which is even less time than Pittsburgh lost its "h".

[stevesliva]

Three (or more) issues here:

1. The IAU definition sucks.
2. The IAU lacked authority.
3. 'Planet' could end up being as imprecise a term as 'continent' or as precise a term as 'metal.'

You go in an infinite loop from #3 back to #1 because of the whole "cleared its neighborhood" crapola. So a planet is the biggest thing around? Right, like lakes are bigger than the biggest ponds around. Mountains are bigger than the biggest hills around.

A lot of people are either bothered or not bothered by number 3. With some terminology that predated science, like the word 'metal,' we have been blessed with some rather precise terms. This is generally because they had specific, quantized characteristics, and not relative characteristics. Metals were defined as ductile, shiny, malleable, whatever. They were not defined as less shiny than diamonds and more shiny than rocks. Turns out there is conductivity, electrons, etc, but what is a metal and what is not has been relatively constant.

On the other hand, 'Continent' has somehow not seen obsolescence due to science discovering plate tectonics, even though we now know there is a fault above India and not one between Europe and Asia. So Europe isn't really a continent, and India is??? Try to read wikipedia for a precise definition of 'continent.' It's all about "convention." Try telling every grade school teacher that we now have the continents of Eurasia and India. In my opinion, either way would be fine, but you are just redefining an admittedly imprecise term. The maps of the world on wikipedia's plate tectonics article and wikipedia's continent article do not match. Science doesn't match the pre-existing term, yet it will still adopt it when discussing "supercontinents" and the like. Schools still teach students the continents, even though it's not a precise term.

You can count me as not bothered by #3-- I'd take it either way-- precise, or defined "by convention." But I certainly understand the disgust with the IAU's botched attempt at "precise."

[surreyguy]

To me the significant point about the biological analogy is that there is not a unique classification system. Classifications as 'top predator', 'predator', etc., or aerial, marine, littoral, etc. are just as valid as the phylogenetic one depending on the kind of investigation one undertakes. But they can be completely cross-cutting. It's easy to kid oneself that the phylogenetic classification is somehow 'real' or at least trumps the others, and that there might be something similar for bodies 'out there'. I don't think it is, and I don't think there is.

[Floyd]

"Biologists classify animals" is a good one to look at. First of all, they do so with controversy and alternate approaches of many kinds.

A few comments from a microbiologist:
I think there is some confusion between scientific research and authority to define scientific terms.
Progress in science results from experiments where data is generated and analyzed. Hard science deals with measurements and validating hypotheses. However, every field need a vocabulary to communicate within the speciality and to the broader community. The assigning of objects (molecules, bacteria, planets) to groupings has more to do with esthetics than science (but should be scientifically informed). Determining the mass of a virus or planet is a scientific task which we can do with great precision. Coming up with definitions or names depends on building consensus (no standard error bars) among scientists in the field.
In biology, we can determine the evolutionary distance between living organisms by sequencing the DNA for the small ribosomal RNA and counting the mismatches in the aligned sequences. This measurable information is helping to define the grouping of all living organisms (Kingdom, Phylum, Order ...Genus, Species). In microbiology, an international committee validates all names, but microbiologists are free to ignore approved names for what they think is correct. Usage and consensus eventually rule. The scientists responsible for naming grouping and objects in biology do so only for their area of expertise. Zoologists name animals, Botanist name plants and microbiologist name bacteria and archaea. Seems logical to me for planetary scientist to come up with the definition of a planet. Its helpful if the scientific definition does not differ too much from common understanding or general usage (but often it does for good reason).
The IAU definition seem to flunk the esthetics test as well as the consensus of people in the field test.
-Floyd

[JRehling]

All of these examples are useful for setting up a classification of Classifications.

"Continent" has three useful candidate definitions.

1) The large, nearly-contiguous landmasses evident on globes. Ignoring the isthmi (there's a word you hadn't seen yet this decade) of Suez and Panama, you have North America, South America, Australia, Africa, Antarctica, and Eurasia. If you're a traveler -- an extreme mountaineer, perhaps -- it's quite useful. Or for setting up international fishing domains or somesuch.

2) The landmasses known to the ancients, augmented with the four discovered later. Same as above, but with Europe and Asia separated.

3) The landmasses whose tectonic plates whose areas are centrally or primarily land instead of sea. That puts India and Arabia on the list, with Eurasia grouping Europe and Asia.

One thing I find obnoxious about the whole planet thing is the presumption that because the people using #3 are scientists that their definition is "The" definition, leaving the PhDs to "tut tut" and stroke their beards kindly in derision, and leaving museum docents to tell the child who "knows" about #3 that he/she is correct and leaving the poor, misinformed kids brought up on literature and culture to sulk in their incorrectness. It's so wrong. It's not only factually wrong; it's immoral.

No one should begrudge geologists the use of #3. It's great for what they're doing. It's useful. It's a happy world where they use it for their purposes without feeling like silly Virgil and the whole Classics department are ignorant because they use #2 and brow-beating the elementary schools of the world into adopting #3 because it's a fact. Although it's great if geology teaches that #3 is useful -- for geology.

Now if scientists had stumbled upon a scientifically useful definition of planet and kept it to the scientific domain without sending out a memo that the silly people are incorrect and ignorant, that would have been fine. But what has happened has deviated from that in three unfortunate ways:

1) The memo has been sent out. Kids who use that definition are told they're correct. Kids who don't aren't.
2) The definition was almost painstakingly crafted to be useless to scientists! Far worse than if geologists had brow-beaten the geographers into submission, this is a case where the scientists have created a definition that ONLY has relevance on the other side of the boundary. The scientists themselves have no use for it.
3) Per my observation of the books I have (unfortunately) bought and taken into my own house, actual scientific content that was present in earlier editions has been eliminated and replaced with this fad. Whatever meager information was once there about Pluto, it's now been cut in half. Instead of telling them that we can use the light from Pluto to tell that it's made of ice, we're telling them something that isn't science.

[Greg Hullender]

That is to say, do planetary scientists ALONE get to decide not just what a planet is but where the line is between (say) planets and stars. (Eg is a brown dwarf a star or is it a planet?)

I think the point is that everyone already knows what it is that Planetary Scientists study. That's not at issue, even a little bit, and with that the rest of your argument collapses.

As for the arguments that others keep making that Planetary Scientists themselves have no use for the term, let me quote Alan Stern from earlier in the thread:

Since planetary science is a field and planetary scientists have a profession, I do not think we can or want to retire the term which planets. Instead, our field and our profession need to come to a consensus on what we, the practitioners, consider to be planets vs. smaller and vs. larger things.

Note that this is the quote that changed my mind.

I also thought of another group who might appreciate a good definition of planet as well as a selection of subcategories. Those would be the scientists who are doing simulations of solar system formation. It could be useful for them to have a better vocabulary to describe what sort of bodies their simulations are generating. I suspect those guys are already Planetary Scientists of some stripe or another, but I'm not sure. Theirs would certainly be a useful voice in the debate, I'd think.

--Greg

[JRehling]

Per the term "planetary", it's clear that the field is concerned with things that aren't planets. I believe we can rightly say that some biologists are concerned with things that aren't alive, but that relate to life. Both on macroscopic scales and microscopic. And Saturn's rings aren't even in the ballpark of being anything someone would call a planet. But I don't see why that calls for a definition of planet. A biologist doesn't need a formal definition of "life" before studying proteins. I don't even see why a definition of "life" would be useful before, during, or after someone starts a study of proteins.

The current IAU definition of "planet" does seem to be to have some possible use for dynamicists. As Greg posited, for discussion simulations of planetary system evolution and so on. Although exactly which terms they'd find useful (and why they would want to steal the term "planet" instead of something like "accretion nucleus"), we'd need a dynamicist to say. But I think it would be just as inappropriate to have someone like that create a definition that impinges on elementary school textbooks as it would someone who studies the surface and interior processes of such worlds.

[Greg Hullender]

One thing I find obnoxious about the whole planet thing is the presumption that because the people using #3 are scientists that their definition is "The" definition, leaving the PhDs to "tut tut" and stroke their beards kindly in derision, and leaving museum docents to tell the child who "knows" about #3 that he/she is correct and leaving the poor, misinformed kids brought up on literature and culture to sulk in their incorrectness. It's so wrong. It's not only factually wrong; it's immoral.

I don't see this, though. There are countless popular terms that don't match the scientific ones, and it doesn't bother anyone. An architect friend once told me that what I call "asphalt" he calls "asphaltic cement," and that for builders, asphalt is just one of the ingredients. Matters a lot if you're a builder, but the general public doesn't care. It's cute to know that a tomato is technically a fruit, not a vegetable, but only a botanist cares. Kids learn about it, but they don't go correcting their parents about it.

Or consider a rock that falls from space. In space, it's a "meteroid" (and presumably an object a Planetary Scientist might want to study), but once it hits the atmosphere, it becomes a "meteor" (perhaps of interest to Meterorologists) :-) and when it hits the ground, it's a meterorite (and belongs to Geology). Normal folks don't know these distinctions (if I've even got them right myself) and they don't care. They just call everything a meteor. A bright kid might correct his elders in a museum -- "That's not a meteor, dad; it's a meteorite!" -- but they just chuckle.

I can't for a minute see how any of this rises to the level of a moral issue. And kids "brought up on literature and culture" simply say "who cares?" They never give the wrong answer in the first place.

--Greg

[surreyguy]

Yay! Registration came through. And... you can submit questions... Bwahahaha!

[Greg Hullender]

In other news, I got my "Instructions for Viewing The Great Planet Debate Webcast" e-mail about an hour ago. So it's tomorrow, starting at 1:30 PM PDT (2030 UT).

--Greg

[JRehling]

I can't for a minute see how any of this rises to the level of a moral issue. And kids "brought up on literature and culture" simply say "who cares?" They never give the wrong answer in the first place.

If there is a room full of kids who are offering answers, and after one of them gives the "asphaltic cement" answer and the docent says "Yes -- correct!", the kids who gave other answers before that, without getting the positive feedback, certainly notice.

And my ideals for education are not a one-child = one-subject delineation where the literature/culture kids have to feel like they're on enemy turf in the science museum, where the science-kid gets his "Yes -- correct!"s for a day. If it's because the science kids actually DOES know a fact (like the Sun being bigger than the planets), then that's great. If it's because of a matter of interpretation that someone's going to pretend is a fact, eg, a geologist saying the geographical definition is wrong, then it's a problem.

If a kid who'd been told that Europe was a continent interacted with someone preaching that the tectonic plates determine the continents, telling the kid that he/she is not correct is not appropriate.

And portraying a vote that went one way as an advance in knowledge and a determination of what's correct is also not appropriate. If it were correct in the conventional sense, this debate wouldn't be taking place.

[djellison]

Yay! Registration came through. And... you can submit questions... Bwahahaha!

Not got mine yet.

[Floyd]

JRehling It is clear that you don't like the IAU telling everyone (public, educators) that their definition is a new "Scientific truth". I think most people on this forum would agree. Its just a definition which is neither true or false, but rather useful or not or esthetic or not—most would agree that IAU's definition is not great, or we would not be having this discussion. However, at times you seem to imply that arrogant scientists are to blame for confusing the public. I don't think this is the case. I think we should allow the possibility of a disconnect of the general definition of a word from the definition most useful to a scientific discipline. Do you agree that scientist should be free to give very specific definition of words for their specialty as long as they don't put out press releases stating that a simple definition is a "TRUTH". I sort of like the very old definition of a planet as anything that wonders relative the distant stars. Children and the public should be made aware of the fact that there are often multiple definitions--I agree that "right answeres" should generally have more qualifications.
Floyd

[JRehling]

I'd be happy if this were a situation where a term had a scientific use and a folk use, and never the two did meet. A wonderful example of that is "work", which has a definition in physics and a definition in ordinary life which is quite different. (Except when a laborer hauls things up a hill, and activity which meets both definitions.) Hopefully, no one was ever lectured that their job wasn't work because it failed to meet the physics definition.

However, this "planet" definition has no apparent scientific use, and is being used to *replace* the way the term was previously used. So it's a total strike-out. It doesn't help science, and it does impact the folk audience (kids, laypeople).

And while I agree that a very astute audience (graduate students in the history and philosophy of science) could really sink their teeth into these distinctions, the books I've bought for my son are aimed at an audience that is struggling to understand how a space rock could create a hole in the surface of a planet. Meta-classification is way too abstruse a subject for them. So the discussion doesn't enrich their education. It replaces a small part of it with static. The same way that replacing a small portion of a kid's book about a small country with a paragraph about their bicameral legislature would be static.

[Stephen]

3. 'Planet' could end up being as imprecise a term as 'continent' or as precise a term as 'metal.'

Actually, what constitutes a "metal" to a geologist (or an engineer) is quite different to what an astronomer means by that word!

Which, of course, raises the question of what would happen if the geologists' union decided that they had the right to determine the meaning of the word "metal"? Would astronomers thereafter follow the new "official" definition or would they blithely ignore the dictates of the geologists and continue to use their own idiosyncratic version of the word (namely, that every element but hydrogen and helium is a "metal")?

======
Stephen

[laurele]

I can't for a minute see how any of this rises to the level of a moral issue. And kids "brought up on literature and culture" simply say "who cares?" They never give the wrong answer in the first place.

--Greg

Some kids might get so confused by all of this that they just decide it's not worth learning and give up on the subject altogether. When thinking of education, we need to focus on how to excite kids about astronomy rather than turn them off to it.

Also, regarding the IAU requirement that an object clear its orbit: wouldn't that preclude any binary planetary systems since two planets orbiting one another would not be considered to have "cleared their orbits"?

[Greg Hullender]

However, this "planet" definition has no apparent scientific use, and is being used to *replace* the way the term was previously used. So it's a total strike-out. It doesn't help science, and it does impact the folk audience (kids, laypeople).

1) Actually, I think your argument is that any planet definition is useless, and we've already established that this claim is false. I don't know why you keep repeating it. At this point, you need to get a bona fide Planetary Scientist to make that claim, and I don't think you can find one. Failing that, you should drop it.

2) It does occur to me that a word like "planet" is very different from words like "fruit" or "work" in that the general public has no independent experience with planets, so the scientific definition has to be the only definition. Contrast fruit, where the common definition requires it to be sweet (thus excluding the tomato) or work, where the popular and scientific terms only vaguely match. No one is bothered by this conflict, and scientists are free to redefine either term without much notice from the public.

But for "planet" the only defiinition that matters is the scientific one. The public cannot create its own term, since it has no use for it. Some special term for the eight planets the public can actually see with (at most) binoculars probably makes sense, but even that's weak; almost no one is looking.

Planetary Scientists should define to term to suit themselves, and everyone else should accept their definition. They should give some guidance to educators, perhaps along the lines I've suggested, but that's it. It's just not anyone else's business. (Clearly I have drunk Alan's Kool-Aide to the lees.) :-)

3) It does seem clear that the IAU overstepped. Their real message seems to be that they don't want any more "planets," but their actions sinice suggest they're reserving the "cool" names for bodies large enough to be round. That being the case, since their whole role is assigning names, they're unaffected by any serious proposed definition anyway. I'd argue that removes them as a party with a legitimate interest.

--Greg

[Greg Hullender]

Some kids might get so confused by all of this that they just decide it's not worth learning and give up on the subject altogether. When thinking of education, we need to focus on how to excite kids about astronomy rather than turn them off to it.

Also, regarding the IAU requirement that an object clear its orbit: wouldn't that preclude any binary planetary systems since two planets orbiting one another would not be considered to have "cleared their orbits"?

Well, for it to rise to a "moral issue," I really think it needs to be so bad that it makes the kids kill their teachers (or vice versa), and I don't think we've seen that yet. :-)

As for the "cleared its orbit" definition, I think I see how that can be cleaned up, but I now think that's the wrong way to go.

--Greg

[dvandorn]

Do also remember that whatever definition of planet upon which we achieve consensus doesn't only need to account for solar system objects. Such a definition ought also to include bodies orbiting other stars.

I can conceive of a lot of solar systems in which major planets have not (yet) cleared their orbital neighborhoods. Young systems, for example, where accretion is *nearly* finished, or older systems where large planets are migrating closer to, or farther away from, their stars. Or systems in which a hot mega-Jupiter, orbiting its star in two or three days, finally spirals in and hits the Roche limit.

Are all of the bodies in such systems not planets because of these circumstances? Does "planet" only and forever describe only eight bodies in orbit around our Sun, disregarding bodies that are already described as "extrasolar planets"?

Or do we need to get better data on other systems to find out just how many adjustments we need to make to *any* definition of planet based only on our experience of our own solar system?

-the other Doug

[Stephen]

2) It does occur to me that a word like "planet" is very different from words like "fruit" or "work" in that the general public has no independent experience with planets, so the scientific definition has to be the only definition. ... [F]or "planet" the only defiinition that matters is the scientific one. The public cannot create its own term, since it has no use for it. Some special term for the eight planets the public can actually see with (at most) binoculars probably makes sense, but even that's weak; almost no one is looking.

FYI the word "planet" (which derives from the Ancient Greek for "wanderer"), and the concept behind it, is a very ancient one. It existed long before science was even thought of, and thus long before the true nature of planets was discovered.

In other words, it was the public not the scientists who first noticed the wandering stars in the heavens and who created both the word and the concept behind it for those "stars". Astronomers and other scientists are merely the johnny-come-latelies who are now making the most use of it!

Why then should it be the scientists alone who now decide what that word means? That would look an awful lot like expropriation, IMHO. That is to say, science would have presumptively taken custody of a public word and decided to dictate to that public what that word should mean.

======
Stephen