(1)

"We've already established that this claim is false?" Where? I've asked for an example of a scientific use, and none has been supplied. The burden of proof on something that hasn't been demonstrated is not to suppose its existence and ask someone else to prove its nonexistence.


(2)

Tempting, but false observation, that observing the planets is inherently science. Observing the planets is not inherently science any more than looking at Niagara Falls, a snowfall, a map of Belgium, or Playboy magazine is inherently science (geology, meteorology, cartography, and anatomy, respectively). Observing the planets is, by default, the enjoyment of pleasant scenery.

It's certainly true that for Pluto, only someone with a very serious telescope at their disposal can initiate their own observations, but anyone with an Internet connection can go to

http://nssdc.gsfc.nasa.gov/photo_gallery/p...lery-pluto.html

and gaze to their heart's content and see the very same best pictures of Pluto that any expert can. And it's not science to do so.

So I don't think that scientists "own" Pluto any more than they own Mount Fuji.

AOL released the logs of 35 million web searches their users had performed. 1085 of them contain the substring "pluto" but aren't "plutonium" or "plutocracy". Perhaps half of them either explicitly contain "planet" as well or are obviously about the icy body out there. If that same rate applies to other web searches, then there are about 5000 web queries about Pluto every day (in English). I'm betting not very many of those people are scientists. They're treating Pluto, with the tools they have at hand, the same way visitors to the Grand Canyon treat it. There's affection to it, and it's not science.

Good point. Honestly, and I almost gag to say it, but isn't this more of a PR issue than a scientific one?

We have a general category for sure: "things that orbit stars." Other stars doing so are easy to exclude, obviously. Thinking at this general scale, other things...not so much. Debris & leftovers from the key stellar formation event, really.

I'm not gonna state a position, just trying to provide another perspective. Maybe a planet is just what we think it is, if you can dig it.

EDIT: Dammit, after some more thought, I do want to state a position. I finally caught the logic behind IAU's current schema. "Minor planets" has long been the categorical definition for asteroids, which was no problem until KBOs came to light. Made sense; they were clearly not comparable to the classical planets.

Pluto was long thought to be possibly Earth-sized throughout much of the 20th Century, but always an anomaly. After 1978, we knew it was only half the diameter of the Moon, but nobody complained; after all, it had a moon of its own. Merely 20 years or so later, it became obvious that there were a host of objects not too different from Pluto in many ways. Then came Quaorar. And Sedna. And, finally, Eris.

Okay. This might work. I propose a new class of objects: "Plutoids" (not to be confused with "Plutinos", which share orbital similarities with Pluto but not other significant properties). Plutoids are objects of Pluto's diameter or better (but not exceeding the diameter of Mercury) that reside in the outer Solar System. They are a class unto themselves, modeled after the minor planet precedent. Anything smaller than the prototypical Plutoid is by definition a lowly KBO; anything larger than Mercury is by definition a planet.

Since I am utterly certain that everyone will accept this construct with tears of joy & starry-eyed admiration for me, my only request is that the Nobel Prize (along with the check) is mailed to me promptly. (Very promptly, if you please, because the rent is due & I don't want to hock more of my shiny metal...) Thank you, and good night!

Yet again, a thread on this topic is getting heated again, despite warnings about it.

After todays debate, the entire issue, and any associate debate, is going, formally, on the banned subject list.

I now have my registration details, so I'm in - and have a question submitted

Yup. Me too. It was pretty tough trying to boil it all down to one concise question.

Anyone else submit one?

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

I submitted two

1)

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

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

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



and

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

Good overarching questions.

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

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

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

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

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

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

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

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

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

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

--Greg

It's started

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

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

"Let the Games begin!!!"

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

Whoo-hoo! I'm in!

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

false alarm, they were only practicing the introductions

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

Never got confirmation email

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


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

which one is the 13th?

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

N deG T is wrong in thinking that Europe doesn't care. I don't think I've been to an astronomy society that hasn't had that debate.

Doug

I didn't get to see the end of it because in the 6-hour window in which my plumber could have showed up, he showed up during the debate, of course.

Any commentary on the value of this exercise? I'd like to hear more Europeans and Australians and etc. chime in on Neil's claim that only Americans care about this.

--Emily

Interesting debate. I think the best point made, and Tyson made it, was that educators need to move away (as quickly as possible) from teaching the solar system by counting planets, by memorizing their names. That is not science. Perhaps if people were educated more on the richness of the solar system, knew more about the moons of the outer solar system, and about the properties of each of the types of objects, I don't think the planet debate would be as highly charged.

And maybe the reason others may not be as interested is because planetary science is taught differently (perhaps better) in other countries. Here planets are taught as the be all and end all of planetary science, you might even learn a bit about their properties, but hardly anything is discussed about other objects, like moons. That's why something being called a planet seems so important here.

All..

I am not going to get into a discussion of details (still in shock after walking away unscathed from a car crash yesterday that totaled my just paid off car).

But I think the debate was lively and just wish more people could see science panel discussions like this to see how science works. Loved watching it no matter what the position of the Dr. Sykes and Dr. Tyson.

I agree the simplest definition of as planet is that the object is massive enough to undergo hydrostatic equilbrium.

I agree that under that simple definition can be many sub categories.... to reflect the richness of these bodies in the
universe we share.

Really loved the discussion.

Craig

Well, my views on this are well known and I'm not going to repeat them here. But I will comment on what's been said.

I respect NDgT a lot, as an Educator, broadcaster, writer and scientist, but IMO that was a rather silly and slightly arrogant thing to say and was very disappointing to hear. At the time of the IAU Conference it was BIG news, all over the TV and radio; my local BBC radio station and ITV TV station interviewed me on air about it. I was asked by countless people about what was going on. It was crazy. Now that has died down, but this is a subject that still generates a lot of interest, debate and passion over on this side of the pond. We have two astronomy monthly magazines here in the UK, and both have ran features on the debate and have featured letters and emails from readers. As Doug said, every astronomy society over here will have discussed the subject, and views are entrenched on both sides.

So, to suggest that this is only of interest to Americans is ridiculous, and disappointingly elitist.

Stunning news, I know, but over here we have electricity and running water now. Oh, and a space agency, too. We have thousands of astronomical societies, and bookstores full of books on astronomy and space. UMSF has many European members, as does TPS, I'm sure. To suggest that none of them care about this is just wrong.

One take home message I got (and I think Tyson made this point) was that it was OK to ignore the IAU ruling.

I'm cool with this, we usually ignore most of the IUPAC [International Union of Pure and Applied Chemistry] nomenclature rules during our everyday work. As long as we all know what we're talking about, it's cool.
["A picture is worth a thousand words, ten thousand if it's IUPAC"].

For the future, I'll just make a point of clearly defining the individual items if I ever use a blanket term that could be ambiguous.

-Mike

My sense is that in Britain that people who only have a passing interest in astronomy would be amused or bemused, but we don't have the kind of reaction from the public that Tyson described about his planetarium.

I found the debate more enlightening than I expected so a definite plus there. The contrasting aesthetics came across very well, I thought: Tyson's description of how his planetarium is organised, and Sykes's vision of Ceres.

When Mark Sykes pointed out that most Planetary Scientists aren't in the IAU, it convinced me they should just formalize their own definition and use it in their publications. From what Sykes said (and what we've heard from Alan Stern here), Planetary Scientists seem to be pretty close to a consensus on what sort of definition would meet their needs. Perhaps Allan Stern and Mark Sykes might write up something.

--Greg

I said a rude word when he said that. Quite loudly. Complete and utter...bu.....umm....nonsense. Every astronomy society I've been to up and down the country has had this discussion. London to Liverpool, I've had it with friends, family. Not as passionately as N de GT (who is?) - but still, it happens.

As a parent who has recently stocked up on a very large number of planet-related books for my son, I have a large number of gripes about their contents. A lot of these take the form of "fallout" from something innocuous higher up the research food chain. For example, my son wants to know why pictures of Venus's hillsides have big black stripes across them. It's where Magellan lacked data. There's nothing inherently wrong with data releases that handle the blanks that way, but when they appear unexplained in a kids' book, they distract quite a bit from the topic. False color images are another issue. When a kid's seen green stripes on Saturn in one picture, it's hard to explain infra-red radiation. It really puts the cart before the horse -- it's an explanation that's perfectly fine for some future day, but it is hell to make, unwittingly, the intro.

The almost total deemphasis of non-planets is another. I couldn't find a kid's book on Io, Europa, or Titan; definitely not in the Spanish language, which I'm using to read to my son. The books imply that it's more important to know how many satellites Uranus has (quick quiz -- anyone on here know without looking?) than what any of them are like. Or, lord forbid, that any of them might actually be as interesting as the planet itself.

This goes to the broader issue of how outreach could be improved. In my opinion, quite a bit. I think the screensaver images I created of the major solar system bodies (many thanks to people in this forum) are so dramatically superior, as a set, to any I've seen illustrate any book. I wonder how many kids have looked at ancient photos of Mercury and asked their parents why it has a checkerboard pattern and gotten a blank or spurious reply. In place of actual learning that could be happening.

I reckon Pluto is beheld by kids more than by scientists, and while it would make no sense to foist a kiddie definition upon the scientists, neither is it good education to foist a tortured dynamical definition on them. Shoot, we're talking about kids who won't learn what an ellipse is for another six years.

Just to chime in...

We here in Australia have the same reaction to that comment about 'only Americans care about this'.
The discussions I have seen here in magazines, in astronomy clubs and from the ten thousand plus students that I talk with every year, there is considerable interest in the outcome of the ongoing debate about Pluto (and other worlds) status.

I find kids feeling 'sad' for Pluto, teachers confused 'is it a planet, dwarf, plutoid and next week what?', and the public wondering if Pluto just disappeared (or on several occasions, 'blown up!').

On the weekend, we are holding our Open House at the Canberra DSN and one of the talks I will give is on this very subject.
It will be a packed room and I'll guarantee that every person WILL 'care about this'!

Welcome to my world! You have no idea how many discussions/heated discussions/arguments I've had with various publishers and editors over the content of my books. It's a constant battle to persuade them to use images that are realistic and "true" over ones that "look nice" or "dramatic" but give a very false impression of what's Out There. I actually had a fight over that Magellen image you mention; after getting the editor to understand that no, there weren't ACTUALLY black stripes on Venus, I then had to try and persuade him that unless we could explain the true "false colour/radar image" nature of the pic then the readers would be given a very false impression. I won that one. But I have lost many arguments, including ones re the use of those garish classic "false colour" Voyager images of Saturn and Uranus, and hideously over-coloured images of Mars....



Thankfully the editor I'm working with now is very open to input and wants to make the book as up to date as possible, so agreed to postpone work on the Saturn spread until after the Enceladus encounter, and we're leaving a blank box ready to update the Pluto page at the last possible moment.

If anybody wants to continue discussing this topic after it has been banned here, I suggest the Yahoo Group Major or Minor : What Makes It a Planet?

It has been two years since it was last active, but it's still available.

Bill

After they added Makemake the IAU site said there were 4 dwarf planets.

I thought maybe a new one had been added and hadn't been officially announced yet, perhaps the debaters were including Charon in their own list even though at least one of them mentioned that the IAU doesn't recognize it.

JRehling makes an excellent point. While memorizing the nine planets has been a cornerstone in schools, the dirty little secret is that teaching about the planets this way has been unsuccessful - most people forget it after the quiz is over, and it does nothing to inspire interest. The emphasis on the number of moons probably dates back to pre-space age time when we didn't know much more about these moons than how many there were and their very approximate sizes. But it definitely is less than inspiring.

A vivid memory of mine on the "planet bias" is the National Geographic poster of the Moon that came out in the Apollo era. I had it hanging on my wall in the early 70s, and again in the late 90s. It had a series of circles showing all of the solar system's largest satellites to scale. Each and every one of them was a silvery disc, identical except in size. The culture shock ("science shock"?) of seeing the cover of Science with the montage of the Galileans was world-shaking. Jupiter looked about the same way it did in the Pioneer images, which were decent, but the Galileans -- all four of them -- were stunningly complex. Seeing any one of them like that would have been jawdropping, but to see four, and no two of them alike, was incredible. I don't think another moment could be as surprising. Even Huygens, because we hoped to see what it found. Nobody even hoped to see the Galileans like that.

There is a law of small numbers that applies. Kids don't learn the entire periodic table (in my experience, anyway). Too many items. Kids in the US may learn 50 state capitals.

I made my son a screensaver of the planets and the most interesting satellites plus Ceres and Vesta, set them to scale but using a fourth-power of radius, so that places like Miranda and Vesta have visible detail while preserving the relation of which worlds are larger and which are smaller. And he learned all the names. I refer to the whole set as "planetas", but I add in that some of them are "lunas" of the others. I was pretty arbitrary in choosing the set, mainly going with the ones that had decent imagery available -- no Eris. And when the time comes to fill in more details on what the various places are like, we can fill those in. The total set numbers about 21, and I just don't describe the set as being of some magical size, the way English-speakers learn there are 26 letters and most of us learned there are 9 planets. To me, it's a lot less important for there to be a set of comfortingly fixed size or that the boundary be objective (I included Titan, Iapetus, and Enceladus, but not yet Dione or Rhea or any other Saturnian satellite). All I cared for was that he learned a bunch of them, that they were pretty, that he learned a tidbit or two about some of them -- hottest, biggest, smallest. Having known them all when he turned 2, I think he's gotten a pretty good introduction (he could see it from the chair where he eats). And I can't imagine anything that would have gunked it up more than having to explain categorization schemes.

It'll stick, JR. Check this:

"Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Pluto, Mercury, the Moon."

Memorized from the poster my Dad gave me when I was 2 or 3, in order of size as thought at the time. It sticks; and how I wish I still had that marvelous, magical poster! (Word of advice: Be sure to preserve these things for him, if you can; they are literally talismanic in later years.)

Gosh during that time, the "Moon" poster hanging on my bedroom wall was the one that came with the Pink Floyd Dark Side of the Moon LP. I still dream about green pyramids to this day.

Of course, Pluto was off by a bit

Nowadays it should be:

"Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Ganymede, Titan, Mercury, Callisto, Io, the Moon, Europa, Triton, Eris, Pluto."

When Pluto was discovered, we expected it (along with Triton) had a very low albedo (it turns out it has a very high albedo). Additionally, we thought the light from Pluto and Charon came from one object. I once saw an estimate suggesting its diameter was 6000 km!

I had a book with an illustration showing Pluto as a mirrorlike body of which we could only see the "reflected highlight" -- a circle of opposition surge -- while the majority of its apparent area was dark and unseeable.

The same book had an illustration of a volcano on Mercury in the "twilight zone" (permanent dusk, since the planet was thought to have tidally locked on the Sun) belching gas into a thin atmosphere, and snow clinging to rocky spires on Titan, with a ringed Saturn hanging in a blue sky. Beautiful fictions all around.

The admirable thing is how memorable images like that are. The real solar system has stuff that cool -- just not those particular things.

That book even managed to break the planet-only bias by including an illustration of Titan.

Per Jason's and Stu's complaint, it may be possible that book publishers know (the same way that advertisers who sell Cola know their line of work) that a book that *doesn't* feature the planets will lose out in sales to a book that gave Io, Europa, and Titan more attention than Mercury and Uranus. It's possible that a very important part of the lenses through which the population ends up viewing the solar system is a sales-time reaction to hunt for the "planets" (choir of heavenly angels sings) in all of their primacy and countability.

That wasn't actually my complaint; my complaint was over inappropriate, misleading and inaccurate images Full Stop, usually "false colour" images being used over beautiful real colour images. Case in point: whilst writing my latest book I had to fight for 3 days to get them to use a real colour photo of Victoria Crater instead of a false colour one. It didn't matter that the spread was called "Mars: the Red Planet", they wanted to use a false colour image showing VC in vivid blues and greens because it "looked more dramatic". I won, but only when I offered to let them use one of my colourisations of the same scene - with appropriate credit to NASA, etc, of course.

Remember to stick those guys in here (http://www.exoplanet.eu/catalog-all.php).

-Mike

I tend to think of them by mass, though:

Jupiter, Saturn, Neptune, Uranus, Earth, Venus, Mars, Mercury, Ganymede, Titan, Callisto, Io, The Moon, Europa, Triton, Eris, Pluto, ...

http://en.wikipedia.org/wiki/List_of_Solar...objects_by_mass

--Greg

Cool article! I'm going to be thinking of planets as objects in the yottagram range from now on!

An upgrade possible for Charon..?

And the Earth hasn't got rid of the Moon. Does that mean we are now a dwarf planet?

I still don't know what "clearing the neighbourhood" means, but I should have thought it included ending up in an orbital relationship.



There is something rather arbitrary about this criterion; for one thing, it depends upon the diameter of the body, which in turn is going to depend upon materials and density -- and the relationship might not even be constant. What would be argued of a system where the common center of gravity floats above a solid or liquid surface, but well inside an atmosphere? What about a center of gravity which is sometimes above, sometimes below the surface? That might already be the case for some of those binary asteroids or irregularly-shaped KBOs with moons.

Name a criterion to separate 'planet' and 'moon' that isn't.

The "binary" definition is definitely a separate matter, but similarly interesting.

I really find it odd that it could actually depend upon the time in the cycle. Suppose the barycenter passed through the tallest mountain on a world, but nowhere else.

Moreover, the barycenter of Sun-Jupiter is outside the Sun. I think that's a nail in the coffin right there.

Masswise, too, things tend to be more profoundly disparate than the barycenter measurement indications. Sun and Jupiter. Earth and Moon. Those primaries are obviously much more massive than the secondaries. Charon is only 14% the mass of Pluto. Maybe mass fraction is a better statistic to use, with some arbitrary threshold. At least it wouldn't depend upon the time of day.