...is anyone else as tired of this debate as I am?

Not to denigrate the fine discussion & many valid points made, but boy would I love to see some closure. More & more I favor the "classical planets" concept: we got 9, that's all there is, unless we find something truly huge way out there someday.

Simplistic, yes...but since this whole thing is by now glaringly subjective, why not keep it simple? "Planet" is an honorary term in some ways, really; it's ancient as well. Maybe the line should be drawn temporally. Pluto was discovered in 1930, and was the last undisputed discovery of a planet; maybe it should be the last such, period. Anything else found has to be Mercury-sized or better to qualify.

Arbitrary? You bet. Unscientific? Yes, of course, because this is really not about science at all, it's about categorization & public perceptions. Still, this seems to make as much sense as other proposals with the added advantage of keeping the criteria understandable & easily applicable to new discoveries (and there's gonna be a LOT of them; just wait. We ain't seen nothin' yet.)

Like you wouldn't believe.

...My incredible psychic powers did not fail me!

Why is everyone so down on this debate and this process? People with a professional scientific interest are having their say... experienced amateur astronomers are having their say... enthusiastic skywatchers with no scientific background but a fascination with Out There are having their say... kids learn about the variety of objects in the solar syatem through it... the public were able to watch a quite historic debate on the internet, live... science is working before our eyes...

Much better to have this discussion, I think, than to just say "Whatever" with no opinion at all when a decree like this is handed down from above. Shows we're not sheep happy to trot in whichever direction the sheepdog wants.

"They can't even decide what a planet it - what's with that?"

Science does not come out of this well. Teachers are confused, students are getting mixed messages, text books are right today and wrong tomorrow. It's a bit of a farce - I wish it would just go away because ultimately it just doesn't matter. At the very best, this situation will end with headlines such as "After 5 years debate, Pluto IS a planet" or "6 Years on, Planet debate rages on" or "7 year itch, science squabble over Pluto continues" or "Planetary U-Turn, Pluto back in the pack".

Ever tried to explain why PLuto isn't a planet anymore? I'm embarrassed for science trying to explain it.

One word to sum up the entire thing

Crap

Doug

All true, pretty much, but I still say it's better to get this sorted out now than just bury our heads in the sand and pretend the problem's not there. It is there, it's not going anywhere. I was really fed up with this too, a while ago, thought it was a huge mistake, and I still think the Pluto decision was wrong and the IAU were ******** idiots for shrinking Sol system's planetary population instead of increasing it, but hey, water, bridge...

I've decided I should use this as an opportunity to get people talking about and interested in planets, of our own Sun and of others out there, and just get people interested in astronomy in general. There's a lunar eclipse tonight, but the weather is so rubbish here in Kendal right now that it's unlikely we'll see it. But people will still go up to the castle anyway, on the off chance, and they'll hang around a while in the hope of the cloud clearing I'm sure. As they wait we'll talk to them, about Phoenix, the Hubble repair mission, ths ISS, and also, yes, Pluto and the "Great Debate".

I think it's been fairly well demonstrated that 'science' is unable to sort this for itself. Two years on and we still have a nonsensical definition, a shed load of confusion, and frankly, a rather embarrassing 'debate' webcast that achieved 9/10ths of 4/5ths of exactly nothing. Some scientists made this mess, and science in general is incapable of resolving it.

This isn't a good thing.

I am a bit tired of of the debate but at the same time it is refreshing to see the public's attention perk up.

The silver lining in all this is that due to the incredible advance in our observing technologies we are finding all these new objects out in the Kuiper Belt and around other suns. The entire reason the question even came up is because of all these new discoveries....

The solar systems we are finding out there are very different in architecture to our own serene system.
http://astronomynow.com/080807Computersimu...initsplace.html

Delight in the fact that we are learning new things and discovering new worlds and worldlets at an increasing pace.

Great time to be alive....

Craig

Ever tried to explain why PLuto isn't a planet anymore?

The number of Outreach talks I give? Hmmm, yes, just a few times...

It usually goes something along the lines of "A tiny number of a small bunch of unelected people decided to turn history on its head and mess up something that wasn't messed up in the first place. But that's not the end of the story yet, so watch this space. In the meantime, if you want to think of Pluto as a planet - like me - fine; if you don't, that's fine too. Eventually heads will be banged against brick walls and sense will prevail. Until then, look at this picture of xxxx That's actually a..."

...good summary!

I honestly think that the "classical planet" concept will prevail. It makes the Solar System something relatively simple to visualize, yet allows room for all the other exotic critters.

And ya know...

Life is messy and so is the universe. I found the debate lively, and unstodgy. Scientists ARE human afterall. Falleable and as full of emotion as any one else.

It really does not matter how this falls out..... Pluto is still Pluto, Enceladus will still be geysering, the hydrocabon dunes of Titan will stll advance under the nitorgen/methane winds, and we will continue to be amazed and humbled at the wonders all around us.

Have to go watch my grandsons now.... I wonder what wonders they will know when they reach my age?

Craig

Stu...

and I apologize in advance because I am not currently a speaker to the public.... so I am not trying to presume anything here
and you may have already mentioned this, but one way to introduce to children the reason this debate is happening is BECAUSE we are learning SO many new things about these worlds and the universe that we are not so sure about our old definitions. And, my goodness, what wonderful things might THEY discover in the future that will turn definitions on their heads?

This is how science works.

Craig

Don't all the objects in a system orbit the barycenter? It the barycenter is outside the surface of Pluto what about Nix and Hydra?

Yep, that's one of my (**Outreachbabble Alert**) "Core Messages" and one of the reasons why this whole debate can be useful. Kind of a "lemons into lemonade" thing

Heck, throw the question back at them:
"What do you think it should be?" "Here are some objects in our solar system and some we've found elsewhere, where do you think it fits in?"


If you don't like the IAU decision, don't follow it. From here on in, I'm making up my own list.
I call my current set "round and possibly-differentiated bodies that orbit stuff"; everything else is a "rock" or an "ice chunk".

Discoveries will and should be always able to change the status quo. The definitions need to be flexible and adaptable or they quickly become irrelevant.

[EDIT: And no, I don't view the New Horizons mission as a checkbox visit to the "last planet"; I view it as the first mission to a completely new and important kind of planetary object: I expect huge surprises and discoveries at Pluto and major implications for other stuff "out there".]

[/flame off]

-Mike

The current decision never seemed as terrible to me as many make it seem... honestly, the only part I think doesn't make sense is the part where dwarf planets aren't planets. Hydrostatic equilibrium seems to be a point that a lot of people agree on. Why not leave it at that and talk about different kinds of planets? Eight major planets, four of them terrestrial, four of them gas giants, plus at least four dwarf planets, and a bunch of planet-moons... none of this seems to have much conflict with our current understanding of the solar system.

In any case, I think this isn't a huge problem... just a quibbling sort of thing that keeps going on. And I've explained the reasons the IAU had to demote Pluto to several people, without many problems.

It's not unlikely (indeed many suggest it is quite probable ) that a KBO the size of Mercury, Mars, or ever larger, will be found in the not too distant future. Would you call that a dwarf planet?

Doug

If and when a Mercury or larger sized object is found in the Kuiper Belt, the planet debate will be reinvigorated and be more widespread.

The current debate and the discussions on this thread have been useful to me in changing my view of the definition of a planet.

I think there ought to be some robustness built in to ANY kind of thoughts we have on this. It's nice to contemplate what it would mean to discover an Earth-sized KBO, but it's silly to craft a definition that has trouble grappling with such a discovery.

It would be like if the law against murder listed the weapons that counted, and then when someone was killed with a spoon, saying "WHOOPS! Didn't think of that one!" The law on murder thereby shouldn't restrict it based on the weapon, and on the long list of things that don't make sense would be to craft a definition that would be in trouble if an Earth-sized KBO were found and then sit on pins and needles waiting to see if we find one.

No definition should be so brittle in the face of easily-imaginable discoveries. We all knew that Eris could happen before they found it. It wasn't like they found a large body composed of neutrinos or a cloud of 9 quadrillion fist-sized chunks of ice circling each other. Something that weird, fine -- let that challenge your definition. And from time to time, mind-blowing discoveries do happen. But a slightly larger Pluto is not a metaphysical mind-bender. Any thoughts on this ought to be open to a Neptune-sized body 0.5 light years out, whether or not one exists.

With all due respect, no. Not only am I not tired of the debate; I welcome it. Why do we need an artificial sense of closure when the issue is obviously so open ended, when there is still so much more we are learning that could change or at least amend the planet definition issue many times.

At today's session on educating the public, we discussed what an amazing "teachable moment" this can be if teachers and those who do public outreach actually teach the controversy. Educators can present the perspectives of both sides and then ask students to come to their own conclusions. Some model lesson plans by NASA were handed out at the session. There was a general consensus that teaching that there is an ongoing debate as opposed to coming down firmly on one side or another is a wonderful opportunity to develop critical thinking skills.

Another issue that came up is, what exactly constitues the Kuiper Belt? One of the speakers--I think it was Dr. Mark Sykes--discussed how the term "Kuiper Belt" is used to describe a very large region that is really separated into multiple sub-regions. Pluto and the Plutinos in 3:2 resonance with Neptune are not actually in the Kuiper Belt proper area, which is slightly further out. That is where most KBOs are concentrated, as was displayed on a graph. Then there are the Scattered Disk Objects, which are at an even further distance and are literally scattered all over the place rather than located in the main clump of the Kuiper Belt. This data is very new and suggests Pluto may not be a Kuiper Belt Object after all.

With so much new data constantly coming in, with New Horizons on its way to Pluto and the Kuiper Belt, we know we're going to learn more about this region in the next few years than we have ever known to date. We know the study of extrasolar systems will bring us new data as well, data equally likely to surprise us. In light of this, why artificially cut off debate on what constitutes a planet? The reality is, this discussion has been ongoing and evolving for centuries and likely will continue to do so. Imagine if people had sought closure after the discovery of Uranus or Neptune, or even further back, after the heliocentric model of the solar system was first accepted in the 17th century. Would all the later data have been ignored because "we already had a consensus" and people didn't want to reopen the issue?

The prevalence and persistence of this debate means the public, at some level, is expressing interest in astronomy. It may not be from as broad a perspective as some people would like, but it's a start. Interest in this issue just might bring more people to a planetarium, observatory, or astronomy club and excite a new interest in the field. How can that not be better than having the public pay no attention and instead spend their time reading about Paris Hilton or Lindsay Lohan?

Mmm...very tempted to agree with you. However, I don't do outreach myself, so would be interested in Stu's and Doug's opinions. I get the feeling from them that the GPD isn't making their lives any easier; the trade-off would be if it's making their audiences larger.

Do have to agree that anything pushing people off of celebrinoise is inherently positive, though. I just wonder what the magnitude of any such effect might be. Inclined to think that people who attend outreach briefings, pay attention to astronomical news, etc., already are too hip to devote much attention to tabloid-style nonsense.

What makes the debate tiresome for me is two things: one, nothing new is said; people just keep repeating the same arguments over and over. Two, I seem to be unable to refrain from participating. :-)

--Greg

I feel your pain, Greg... ...just when I think I'm out, it drags me back in!!!

In reading through these responses I've realized something that I'd missed before about the debate.

I've never had much of a passion about the conclusion of the debate; I always had issues with the kinds of definitions that were floated, but I never had much invested in whether we had 10 planets or 8 or for that matter 25 (with all respect to the 'Classical Planets' option, I don't think that sticking with 9 planets is any longer a possible option).

But I realize there's another issue here; and it doesn't have to do with the facts of the case, or even with the technical side of astronomical taxonomies. It's about the progress of knowledge, and how it is presented.

To put it briefly: it's easy to explain "We used to have 9 planets, but now we have 10." "Why?" "Because we discovered a new planet we didn't know existed before." "Oh. Okay."

It's much, much harder to explain: "We used to have 9 planets, but now we have 8." "Why? Did the 9th one blow up?" "No, we changed our definition of what a planet was." "Why? What was wrong with the old one?" [...pause...] [...silence...]

It's easy for people to understand that discoveries are made, and new knowledge comes to the fore, and that they need to remember more things than their fathers before them. Classical civilizations knew three continents: Europe, Asia, and Africa. Columbus discovered South America (not in 1492 -- in 1498) and North America was discovered a short time later. Then people had to cope with five continents. Australia came along in the early 17th century and Antarctica in 1820. At no point has there been a serious attempt to reduce the number of continents (though it's long been apparent that the Europe/Asia distinction is artificial and arbitrary).

But to explain that, as it would seem, the process of discovery is going backwards -- that we are forgetting facts we used to know -- that we seemingly have less information than we had before -- this is very difficult to explain.

Of course, it's true that we really are learning more than we knew before, that our knowledge of the Solar System is much richer than before. But the logical corollary of that should be -- would be expected to be -- that we should ask non-astronomers to know more -- not to dumb down the Solar System into something that can be printed on the back of a mini-juice box. And I think it's the impression that we're taking a retrograde step, and raising a generation that not only won't know what the Kuiper Belt is, but won't even have ever heard of Pluto, that bothers folks.

Exactly! This is why I don't understand why we can't use a definition that keeps Pluto and doesn't make previously-known non-planets like Ceres planets. Calling anything Pluto-sized or bigger a planet would have that attribute, however "unscientific". I'd be happy to call Eris a planet.

But I also agree that we are saying the same thing over and over again in this thread, and I could imagine closing it for our own good.

That is great for students at a certain level. I'm not sure that that level is prior to graduate-level, however, and if it is, it's definitely not elementary or middle school material.

I could see an adult with interest in science finding the issue interesting and therefore concluding that it would be "amazing" to teach to young kids, but that alone wouldn't stop the effort from misfiring.

In an elite private high school, I first encountered the idea of contending systems of classification in tenth grade, and it was with things much more concrete than this.

For younger kids, this sounds like a lesson designed to be one of those where the educator speaks, heads nod, and the hour passes.

If they're a rubbish educator, yes. I have a hard time understanding how any teacher can make astronomy (there are planets with rings! a comet helped kill the dinosaurs! stars are enormous flaming balls of gas! when some stars die they turn into black holes that EAT other stars! Mars has a volcano 2x higher than Mt Everest!!) boring, but I've heard a few, or rather gone into a class after a teacher has "introduced" a class to astronomy and liquified their brains with a boredom ray, then I have had to try and stuff the gunk back into their skulls and get it to set again in an hour...

To be fair, most teachers simply don't have the time, resources or knowledge to cover the subject well - they have so many subjects to teach, it's hardly surprising - which is why they're (usually) very grateful to have someone come into a class and cover it for them, leaving them more time to deal with the Egyptians, the Victorians or whatever. Some teachers sit in on the talk and are as enthralled as the kids, as it's all "new stuff" to them too; others don't give a stuff and sit at the back, marking papers, preparing the next lesson, or flicking through the latest copy of "Celebrity Hello Ok Weddings", which is sad, and frustrating, and I want to grab them by the neck, Darth Vader style, lift them off the floor and tell them how they should be soaking up the info to pass on next time, but I don't. Besides, that kind of behaviour makes a repeat visit to a school rather less likely...

I've been on quite a - god, I hate this word, but I figure most people will relate to it so I'll use it - journey as an Outreacher with this whole Pluto thing. Before the IAU meeting I was pretty sure they'd leave Pluto alone and increase the number of planets in Sol system, not decrease it, and I even said as much in an interview feature thingy with my local TV station ("I think Pluto's safe," I said confidently into the camera, posing beside my telescope in the middle of the day. Shows what I knew, eh?). When the decision came down I was, frankly, furious. I saw it as a step backwards, and thought the IAU had bottled it, thrown away a chance to enhance the wonderous nature of the solar system, and tossed away an opportunity to show that astronomers and scientists can be bold and embrace new things and be, well, exciting! I thought the decision was cowardly and weak, and thought they had been pathetically meek about the whole thing.

( Of course, those opinions were based more on me being a die-hard (and often derided, lets face it) romantic and sentimentalist who has what many - here and elsewhere - believe to be an unrealistically melodramatic view of the universe and our place in it. I make NO apology for that, and never will; I'm not an engineer or a physicist, I'm just a guy who finds joy standing in a field at midnight watching shooting stars skate across the sky, who has actually cried when probes have landed safely on Mars, and gets all emotional thinking about the day Oppy or Spirit dies. Some people (not here, I hasten to add, although I can sense some people shaking their heads when they read my posts ) find that ridiculous, I know, but I don't lose any sleep over that; I'm confident and content that I see and feel the universe more personally and more intimately than they ever will )

I wasn't angry because of any scientific arguments, which many others here are more qualified to make, I was angry because through my eternally rose-tinted telescope eyepiece it was just wrong, a step backwards. I loved the idea of the planetary population growing; it just seemed so exciting! I'd have loved telling kids that there were new planets in our solar system! I'd actually been looking forward to it! Now... now I had to tell them that one of the planets they already knew wasn't a planet anymore. How the hell was I going to explain that, 1) when it was scientifically complicated, and 2) when I didn't agree with a damned word of it?

Well, it's my job to do that, as someone who is allowed to go into schools and given the privilege, honour and enormous responsibility of standing in front of a group of kids and putting new information into their brains, info which is going to stick there, so you'd better get it right... So what I've been doing is putting both sides of the debate, whilst acknowledging that it's something I feel personally quite strongly about but asking the kids to just think about it, watch what happens, and consider the Pluto thing as part of the Big Picture. It hasn't been easy; I started off post-IAU decision very angry and quite flustered about it, and I'm sure I left a couple of classes more confused about the issue than they were before I started, but hey, I'm only human.

But now, having been educated about the science behind this debate - to a large part here on UMSF by people who I respect enormously - I see this as a great opportunity to educate kids about how science works and to get them interested in and talking about planets. And this most definitely is a subject and issue that young kids (and I'm talking 7-12 yr olds here) can be taught about, if you have the patience, enthusiasm and, yes, skill to put it across. Now I am able to tell kids about Pluto That Was, Pluto That Is, and speculate about Pluto That Will be When New Horizons Flies Past. I get to talk about the same planet in three different ways! Win, Win, Win! Sure, it's been an absolute disaster, the way it's been handled, and Doug's right when he says that it's been bad for science and has been a destructive thing; I personally think it has made the IAU and astronomers look like befuddled old boffins with wild white hair and stained lab coats who shuffle about their dusty observatories in a fluster, unable to make up their minds about something incredibly important. But we are where we are, and we can either gnash our teeth or smile and get on with it. A while ago I would have done the former, but now I try and do the latter, and I think that when I talk to a class about this I give them an idea of how important it is that science keeps moving on, taking note of changes and new discoveries, and coming out the other side better.

In an ideal world I'd be able to tell them that sometimes science CAN be sentimental and romantic, and do the Right Thing rather than the Accurate thing, i.e. leave Pluto as an "honourary planet" simply because of its wonderful history and place in people's hearts and damn the science, but I guess, sadly, that will never happen.

I saw Pluto once, through a big telescope. Looked like a star. Strangest thing tho... looking at it I felt quite moved. Not like I was looking at a star at all...

Well said (like it could be anything else??? )

I dunno, man, I just dunno in so many ways. Trying to understand why rocking the fabled 'planet boat' is really in anyone's interest. Does it serve science? Hell, no. Any philosopical/naturist benefit evident? No. Does it screw up public perceptions? (Gee, really don't have to type it...)

Not to bitch without offering at least one solution. Just return to the status quo ante, and just leave it. There's no harm, no foul. The debate was healthy, but what it ultimately reveals is that we are creatures of perception, and the Universe is not structured in absolutes. We learned thereby, and really that's the important thing, is it not? Certainly it's the only thing even remotely connected to science (another construct of ours, but proven most valuable over time).

Before the IAU stirred up the hornets nest by 'settling the debate' we had the planets and the minor planets with the minor planets divided into subcategories such as asteroids, kuiper belt objects, centaurs, damocloids etc. I'm among those that thought Pluto was in the wrong after they started finding larger KBO. Saying that I see no reason not to have dwarf planets count as planets although I think they should be distinguished from the eight that dominate their neighborhood which Stern and Levison referred to as Uberplantets ( http://www.boulder.swri.edu/~hal/PDF/planet_def.pdf ) The storm over the planet definition could have been avoided if instead of claiming the word planet for themselves those promoting the dynamic definition came up with a name for their favorite subcategory.

The one thing I never understood why so many plutophiles feel a compelling need to keep other objects out of their club. Whats wrong with having 12, 20 or even 50 planets? If we end up with 50 planets no one going to force you or any of the school children to memorize all of them. What will likely happen is children will learn the 8 largest and some selection of the more interesting dwarf planets, probably the largest one (currently Eris), Pluto (because its special), Ceres (because it was the first one found and is one of the few that kids can see for themselves using binoculars), Sedna (because its may be a member of the inner oort cloud). In doing so they will learn something about the structure of the solar system. If we were to go back to 9 or 10 we are more likely to preserve the system where most kids just memorized the list and learned little beyond it.

I think you're giving the power of abstraction on the part of the educator way too much credit there. I have no doubt that an animated speaker can keep an audience's eyes on them while they read the phone book (I've seen it done, by Robin Williams, I think), but there's chain of ideas here that build on each other, and you can't, no matter how skilled or informed, convey Idea #1 in 3 minutes, have everyone with you, then convey Idea #2 which depended upon grasping Idea #1 in three minutes, have everyone with you, etc. and get to Idea #6 successfully. At each point in the chain, some fraction of the audience zones out, and a few links in, you're lucky if you have the One Bright Kid engaging you while the rest beg for him or her to be stricken down so this agony can end.

If that did work, then a skilled educator could have 8 year olds doing calculus after a series of 180 brilliant lectures. It only works if Gauss is the 8 year old. A lecturer is fully capable of giving those lectures and perhaps enjoying himself or herself quite a bit, but having the audience along for the ride requires a different audience.

I'm teaching the planets, too -- and I think it's easy to underestimate what a wildly abstract idea "clearing its orbit" is. First you have to have the idea that the orbit is a sort of permanent racetrack in the sky. But, scratch that idea of "permanent", because if they were all permanent than nothing would ever clear its orbit. You have to have the idea of larger bodies deflecting smaller bodies, and now you're trying to get the audience to accept the powerfully counterintuitive idea that gravity, which only pulls things towards each other, can sometimes end up pushing things farther away. If that were Idea #4 in the chain, you'd be providing the kids who only tuned in for that with a heck of a confusion. They get to tenth grade and tell the physics teacher that gravity can sometimes push things apart. The physics teacher tells him, no, you misunderstand, I don't know what some guy in the planetarium said, but please listen more closely next time, Johnny -- gravity pulls things together.

I'm not saying I go into a class and give the 8yr old kids enough info to let them sit an astronomy exam just that I leave them knowing a little - hopefully a lot - more about the universe and excited by it, and wanting to learn more, for themselves, after I've gone.

Slight break from the ordinary...substitute "I Got 9" for "I Got 6" in this classic Schoolhouse Rock video. We could all use some humor & a bit of funk at this point.

My spoon clearly was missing in this soup, so... I shall reveal my un-objective, un-sincere and un-scientific vision here too. (just couldn't stay quiet any longer, just as many of you have felt here)

Well, I am amazed how narrow-minded and concentrating on categories rather than real issues this has been for some parts of it. I mean, like some of you have said earlier, is it really THE thing if one is called planet and the other is something else? The real issue in my mind is the Solar System as a whole, as a complex system (maybe not in Newton's mind), and that in there we have an important place for every rock/comet/planet/kbo/plutino/uranino/mercurino... If the only argue here is "but what about the teachers who now have to figure out a new poem or song or wordplay to teach THE SOLAR SYSTEM" I start to cry. Planets ARE NOT the entire thing. Solar System has dynamics and mystery which goes well beyond just the biggest rocky/gaseous balls. And knowing the NAME of a planet does not tell ANYTHING about the planet itself.

You can teach the name of the planets with a catchy poem and imagine how Disney has its own planet out there. Woo-haa.
You can teach that the first president of USA (after Constitution) was Washington and World War II was fought in 1939-1945.

OR

You can teach WHAT the Solar System is, and HOW and WHERE. That it has a central star (and what a star actually is), bigger planets (both gas and rock) with moons, asteroid belt, smaller planets and comets further away from the star and Kuiper Belt etc etc. And that some moons have geysirs, atmospheres, underground oceans and how this all has been formed and what is our place in the universe. Suddenly it does not seem too important anymore to argue what is the cherry and what is the cream of the cake.

You can also teach what things lead into the World War II or to the independence of United States and all the other things around them, the mistakes, the choices, the politics, the personalities. Does it sound too important anymore to just memorize some years and numbers and leader names anymore? Would that teach us actually anything?

(I do not judge or criticize any particular school system because I really dont know any outside our own here behind the back of the creator, but at least I have been taught in the school the latter way. Which I am very grateful of.)

Science is a thing which develops. 1801 we had Mercury-Venus-Earth-Mars-Jupiter-Saturn-Uranus. Then BOOM we have Ceres. If the situation would be today the same, of course Ceres would be a planet... BUT. After a few decades we had found more and more of these "cereses" and found out that heyy, there's actually a wholelottathem so maybe Ceres is NOT a planet but more like these "other things" out there. So, Ceres no more planet. Afterwards we find out it was a right call. Then came Neptune, that was easy to put among its kind, so a planet. Then time passes. Happens Ceres round 2. We find Pluto. Hmm... it is 6 000km's in size (early estimates...) so it must be a planet right? Ok, good. We find Charon and get more detailed estimates of size... hmmm... this Pluto might not be a planet after all, but whatttaheck, let's keep it there still just to be sure. Then comes new KBO findings and finally Eris & pals. So, we are exactly in the same situation as after few decades when they had found Ceres. And again, we see that Pluto is part of its gang out there, KBO's etc. NOT among "normal planets". So, we should recognize that and accept that Solar System has different gangs. Gang of big gaseous ones, gang of big rocky ones, gang of asteroids, gang of KBO's, gang of comets... If you wanna and must have dwarf planet category, fine, have it and start to fill the list, but do these dwarf planets actually have anything in common? Can e.g. Ceres and Eris go under same title? I clearly see similarities between Mercury-->Mars and also Jupiter-->Neptune (compositions, location...) and then there are comets, asteroids, KBO's but please define me dwarf planet...

Wouldn't it be better just say that beside 8 planets there is asteroid belt, with biggest member of them being Ceres? That there is Kuiper Belt, with biggest members being Eris and Pluto/Charon? That there might be Oort Cloud, and biggest member so far being Sedna? Would it be too hard (read:scientific & accurate) and too unsexy to teach that at schools or read that from publications?

This sort of teaching and relaxed (still scientifically valid) categorization would not even pose a problem when we start to map these exo-systems with again totally new sort of planets and solar system objects. We could just say that ok, in this particular solar system thing are like this, and in that system things are like that. We would not have to lose the credibility of science by resetting all the books and terms every few years when we find something new. At the moment it feels like astronomy has some sort of "Windows update" -curse going on.

I know that for some people categories mean more than substance but please, putting emotions before practicality and science is not really helping anyone in the long run. Keeping Pluto as a planet would end up being just an exception nobody could actually never justify or explain to their children. "Yes it is wrong but let's keep it wrong because that has been the tradition." Sounding Soviet, anyone...? At the 19th century people propably had more balls when they made the call to demote Ceres. I raise my hat for those brave pioneers.

PS. I still believe that if Mickey Mouse had a dog named Rex, we wouldn't even have this emotionally flaming debate going on...

...I raise my hat to you, K-P! Brilliant post.

All I can add are four words: Subjective. Subjective. Subjective. Emotional.

Think that's just about the correct ratio for this debate. I've tried to call in Mr. Spock for mediation from a purely logical viewpoint, but can't get a good number. (I think he's ducking me, frankly.)

A couple of people have complained that this thread has been repeating arguments. I definitely have read some new and useful points in the past couple of days, but there is a lot of repeated ground here. I don't know if a FAQ (without facts?) or a Wiki handles it better than a list. At least to put things to the point of "Here is observation X, which has attracted support Y and rebuttal Z."

For example, the idea of an exception being problematic is often rebutted with the observation that Europe's status as a continent is a broadly-accepted analogue. Then if there's a rebuttal to that, let it so be noted. And if we get to an observation without a rebuttal, then everyone has to end up unanimously convinced -- right?

...and personally I have always felt that Europe as a "continent" is not a proper expression. Eurasia is. And without that artificial Suez-canal I would prefer even more Afro-Eurasia. Culturally Europe is an area. Yes. Nationally. Yes (European Union). Geographically there is a european peninsula (some sort of), but a true continent it is not, so let it be removed from that list of continents. Please.

Garg. I'm officially done with this entire debate now, and really don't care what a planet is. All I know is that I live on one, would like to visit others, but won't live long enough to be able to do so, unfortunately. Thank you, and goodnight!

So the question arises; is Australia a continent? While it has obviously achieved geometric equilibrium, it certainly hasn't cleared it's "neighborhood." Or do New Guinea and New Zealand count as continental satellites? All those other smaller islands are troubling, though. Maybe "dwarf continent" would be more appropriate.

Don't change your dreams, change the terms. Maybe if Texas would be called a planet, you would also live long enough then...?



(duck... and cover...)

...I've been to Texas many times. And, yeah, it's sorta like visiting another planet in some ways. Texas is really just a state of mind.

(Let me just hang that thought up here, pregnant with possibilities...)

I hereby claim the continent analogy for the state of despair. Or the state of arguing in circles, which I think was my original point.

And Stu, I thought rubbish was a noun? You've adjectived it.

Personally, with any argument that the definition needs to be simple, or the list short, I think there is way too much worry over people that just won't care one way or the other. Might trigger a few fleeting short-term synapses, but you're not making an impression. And if you do make an impression, they'll quickly gather that reality is a lot more interesting than a bulleted list.

It is, and I did. It's a Brit thing.

I second everything that Stu said. We underestimate children's capabilities when we assume they are incapable of understanding that there is a controversy between scientists holding two different perspectives or that sometimes we just need to wait for more data to come to a definitive conclusion. At the Great Planet Debate, NASA lessons on teaching this at the level of grades 2-5 and 9-12 were distributed along with exercises for the students to do to help them understand the controversy. For example, at the high school level, a hypothetical case of a new planet is presented, and students are asked to consider the facts, come to their own conclusions and then hold a debate. In evaluating the debate, the teacher looks for clear articulation of ideas, sound reasoning, rebuttal skills, etc.

As a "Plutophile," I--and I am guessing most others--are not wedded to teaching nine planets. Most of us have no problem with the solar system having 50, 100, 200 or more planets. What we object to is the limiting of the term planet to only those objects that dominate their orbits. Instead, we seek to use the quality of hydrostatic equilibrium as a broad measure to determine planethood since that is where differentiation and geophysical processes start to take place. This doesn't mean that we cannot distinguish planets based on dynamical characteristics through the use of subcategories. What this means is that the demotion of Ceres--and of Pluto and Eris--was in fact not a right call. Nineteenth century astronomers did not know that because they were incapable of imaging Ceres. During the 1990s, Hubble images showed that Ceres is round and definitely in a state of hydrostatic equilibrium. So if we use the hydrostatic equilibrium criterion, which many believe is the best because it is something everything ranging from giant to dwarf planets have in common--putting Pluto in the planet category does not make it an exception, just one of many in the dwarf planet subcategory.

This is not based on emotion, sentiment, or on Mickey Mouse's dog but on a genuine conviction by many planetary scientists and lay people as to what is the best classification method for objects in this and other solar systems. Yes, to a certain extent, every human being is subjective and emotional when it comes to issues about which they care a great deal. No one on either side of this debate can claim to be completely free of emotion about it; even Spock, being half human, couldn't do that. In fact, the sense of romance and excitement Stu experiences in observing the night sky is something that is contagious; kids pick up on it; they get excited about viewing objects like Jupiter and Saturn, and for some of them, it may be a first step towards a career in astronomy.

In summary, the existence of emotions on both sides does not change the fact that there are legitimate scientific arguments in favor of keeping the term planet broad while recognizing the differences among the many subclasses of planets through establishing multiple subcategories.

Interestingly, I did a quick web-search for this topic, to find some content to point to as a shell of the "FAQ" and found a nice expression of the pro-Europe sentiment... by Mike Brown, on a heavily-edited webpage (where he left some of the original copy mixed in with the edits) at:

http://www.gps.caltech.edu/~mbrown/planetlila/

But I cite this just to suggest that rather than repeat 9 steps in the argument ago and then wait foot-tapping for someone else to repeat 8 steps ago, and make this truly pointless, that we at least have a "reading list" of positions and then keep things on the topic of moving ahead instead of in circles.

It certainly doesn't sound nice to be underestimating children or calling them incapable, but it is true that certain lessons will shoot over certain kids' heads. Or get the "Mensa" kids engaged while losing the rest. And I think eye contact is often mistaken for engagement. I'd at least ask myself if all the students in the room understand why some parts of the Moon are full of craters, while other parts have fewer, and the Earth has fewer still, before this issue bubbled to the top of the list.

Maybe other people can think of better examples, but I have always been fond of Nick Hoffman's arguments for a White Mars (with CO2 playing the role that others suspect water to be playing). THAT is an example of a scientific debate. That is science at work, right or wrong. And it's impossible to follow it without learning some interesting things about Mars.

This planet issue isn't a scientific debate. It's scientists engaged in a non-scientific debate. It's like using a Jerry Springer episode to teach people American history instead of talking about Jefferson or Lincoln. The "White Mars" debate teaches the useful lesson that scientists don't always know the answer. The planet-definition debate teaches the lesson that scientists don't always know when they're outside their depth.

My problem with this whole debate is that it attempts to mix topics and goals. 'Planet' is an ancient term that has cultural meaning (and hence the fierceness of this debate). However, it is not a useful scientific classification. For example, Io seems to fit all the criteria for a terrestrial world except that it found itself orbiting a planet instead of the sun. However, the primary justifications I've read for a mission dedicated to Io is what it can tell us about the processes likely present early in the history of the other terrestrial planets.

Sometimes, a single world can fit multiple classes. Titan shares active weather systems in a dense atmosphere and a solid surface in common with Venus, Earth, and Mars. (Triton and Pluto's atmosphere's seem a bit thin for this class.) At the same time, Titan is a member of the class of icy bodies with internal oceans in common with Europa, Ganymede and possibly Triton and Pluto.

I think the scientists should accept that planet is a cultural term. They can and should come up with distinctive terms that classify bodies by their characteristics and not their place of orbit.

This debate isn't getting anywhere. We're getting longer and longer essays that actually don't say anything. And we have ALL done it, despite it being explicitly banned in the rules. I let it go for a few days - but realistically, it's not going to go anywhere - so I'm closing it.