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

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.

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.

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

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

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

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

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).

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.

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

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

Gee . . . they seem so nice on TV!

--Greg :-)

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

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

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'...

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

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

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

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.

I found this quote about Nature and Science from his latest post interesting

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 :-)

I really need to learn to type, it's going to limit my career if I don't.

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

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

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

(I call this the "Platypus Argument").

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

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.

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]

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.

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

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!!!

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

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

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

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.

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

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.

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

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

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

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?

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

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

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.

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