Well, the latest news on the International Astronomical Union's campaign to categorize solar-system bodies for the rest of us is that they have now voted to demote Pluto from planetary status, and leave the system with only 8 "planets". In addition to those, we now have (so far) 4 "dwarf planets": Pluto, its moon Charon, the asteroid Ceres, and the globe informally known as Xena. None of the moons of any of the planets are themselves considered planets, despite the fact that the largest of them (Saturn's Titan) is larger than the planet Mercury.

So the questions for debate:

1. Do you agree with these designations?

2. Given that (just to take one example) Mercury arguably has much more in common physically with our moon than it does with, say, Saturn, is there really any point to having a "scientific" definition of the word planet? Can such a completely arbitrary definition aid in scientific research in any meaningful way?

3. If the answer to #2 is No, then is this a sign that the scientific establishment is exercising, or attempting to exercise, too much power and influence over matters not properly within their purview?

1. Do you agree with these designations?

Sure, why not. Pluto is not like the rest of the planets. Its path around the Sun is significantly different than the other planets. It and its moon, Charon sort of orbit each other, rather than Charon orbiting Pluto. Pluto is more accurately described as a Kuiper belt object than a planet.

2. Given that (just to take one example) Mercury arguably has much more in common physically with our moon than it does with, say, Saturn, is there really any point to having a "scientific" definition of the word planet? Can such a completely arbitrary definition aid in scientific research in any meaningful way?

If we make the definition too specific, we'd have no definition at all. The inner planets are all significantly different than the outer gas giant planets. But they all orbit the Sun in more or less the same plane with regularity.

3. If the answer to #2 is No, then is this a sign that the scientific establishment is exercising, or attempting to exercise, too much power and influence over matters not properly within their purview?

Definitions are always arbitrary, based upon current understanding of the phenomenon. We should tread softly when changing definitions, as it only leads to confusion as some people use the new definition while others use the old one. The change is what should not be arbitrary. Was there a sound reason to reclassify Pluto? I think there was. Does the proposed changed make a minimal impact?

Well,

Now:

My Very Educated Mother Just Showed Me Neptune!!

MVEMJSMN

It is important to evaluate the definition they came up with if we want to talk about the science rather than a specific result of that definition. From the same article:


That seems reasonable to me, it doesn't have anything to do with politics and based on this definition Mercury is still a planet because it meets all of the criteria.

1. Do you agree with these designations?


No,


2. Given that (just to take one example) Mercury arguably has much more in common physically with our moon than it does with, say, Saturn, is there really any point to having a "scientific" definition of the word planet? Can such a completely arbitrary definition aid in scientific research in any meaningful way?

3. If the answer to #2 is No, then is this a sign that the scientific establishment is exercising, or attempting to exercise, too much power and influence over matters not properly within their purview?

Forgive me for taking childish wonder as a priority over science, but this isn't my kind of science, it's classification, and I'm operating under the premise that great science proceeds from childish wonder.

The designation for a planet is that a planet is something to explore. A planet has personality, you can draw a picture of it, put it in a textbook, differentiate it from an asteroid.

A planet may or may not have life on it, and a planet always has the possibility that somewhere beneath the crators -- or under the rusted dust, or inside of the volcanos, or frozen in the ice, or swimming around in endless swirls of gas -- there could be life.

If a planet were to be suddenly attacked -- I remember the asteroid that crashed into jupiter in '97-- people would rally around that planet with an inspiring fervor. People would talk about how beautiful that planet is, publish pictures of it on the internet, see only the good in that planet, treat it with great fraternity. Oprah might fly out to Saturn or wherever, and buy something for it.

If Dave Letterman can make a specified joke about a sun-orbiting object in space, then that object is a planet.

Finally, the true judge of what is or is not a planet are the children. If some kid with a lisp and box of crayons can lie stomach-down on plush carpeting and draw a picture of what he considers to be a planet -- be it gaseous, brackish, non-spherical, or cold -- then that is a planet, and it may have life on it, and at some point in the distopian twilight zone future, we may have to put that planet down.

1. Do you agree with these designations?

To me this is kind of the issue you can find in classifying an organism or specie if you will. To define what particular organism is what and so on basically anymore is derived in an developmental and ecological sense or so on etc...

So to take lets say the universe and put it in the idea of an ecology, you can find various differences or "organisms" in that "ecology". You can have asteroid belts, of course with difference in such, stars and the various forms of those, black holes, quasars, comets, meteors, asteroids, and of course the list can go on, will grow over time and most likely will be subject to change. So to take the term planet, and apply it to the universe as an ecology again, what organism would be a planet, any object in space of course will not qualify, so what should it be, earth is a planet, but what about its moon, well in that we see that such a phenomena seems to occur, that bodies in space say like earth can have other bodies in its orbit, just as the planets basically do the same to the sun as the moon or moons do to planets. So with the idea that such is general observable and is naturally occurring what’s the difference in Pluto as put forth by the scientists for changing the idea of Pluto being a planet, that it does not occur naturally the same way that most the rest of the planets do in our solar system. So basically in the ecology, such an organism could be maybe applied to in terms of definition in the same way speciation works, that how Pluto and the bodies around it act is not the same as the rest of the planets do in our solar system, or there is difference there you don’t have in others, such as one bird to another, or a bird to lizard, all living things, and of course an asteroid and a planet is just a body of mass in space, but for the reality of it how do you go about working on the differences they have or hold in reality.

So with that, you can see that such a definition or decision is being based on the reality of the natural world, and of course observations of such and where current perception of such currently stands at. The scientists basically found that to simply call Pluto a planet would not work simply because its state of affairs if you will is not the same as everything else we call a planet. In another 20 years the whole definition of course could change, but it all simply comes back to the idea of science trying to obtain a factual understanding of nature or the natural world, and for this coming from humans with a mind, it basically has to come in some tangible form, such as a definition.

2. Given that (just to take one example) Mercury arguably has much more in common physically with our moon than it does with, say, Saturn, is there really any point to having a "scientific" definition of the word planet? Can such a completely arbitrary definition aid in scientific research in any meaningful way?

See #1

3. If the answer to #2 is No, then is this a sign that the scientific establishment is exercising, or attempting to exercise, too much power and influence over matters not properly within their purview?

See #1

But that still doesn't answer the question of why scientists even need a definition for the word "planet". What is it that these 8 objects have in common, that other objects in the solar system (like Titan and our moon) don't, that's particularly relevant from a researchers perspective.

I think drewyorktimes and I are very much on the same page here. "Planet" doesn't need to be a scientific term at all. It's just a cultural term. And I think our society is becoming too conditioned to uncritically take everything scientists say as gospel, even when they're just giving their opinion.


Well, maybe she just showed "Us" Neptune...unless the IAU finally decided to do something about all the Uranus jokes.

HA! Maybe she wasn't so educated after all! My brothers were never scholars, so there was only ME and not US.

But we do have a definition of a planet, which I think was the generally accepted one before. As CJ said:



Actually, we should probably drop #2. Pluto is round and orbits the Sun. It hasn't cleared its orbit of other objects, however, but then neither has Neptune, since Pluto crossing its orbit.

I grew up with Pluto has the ninth planet too, but the description of it has really only taken shape over the last two decades. Pluto has a very eccentric orbit. Its orbit varies from 29 AU at its closest out to 29 AU at its furthest. Pluto was actually the eighth planet from 1979 to 1999. It is once again the ninth planet and will be for the next 200 years.

In addition, the plane at which Pluto orbits is 17 degrees off from the plane of the rest of the planets. Mercury's orbit is inclined at 7 degrees, but the other planets are ecliptic. This is important because other minor solar system objects also vary from the ecliptic plane.

Pluto is a dwarf planet, which the IAU has defined as:


It was the discovery of the Kuiper belt which showed scientists that Pluto was not unique. It was simply the nearest (not the largest) of the belt of small objects that orbit the Sun at vast distances from the Sun. UB313 is a Kuiper Belt Object (KBO) that is larger than Pluto.

The history of this debate is summarized nicely here.

The Kuiper Belt can be seen as a distant asteroid belt. In 1807, the first four asteroids that were discovered were listed as planets. By 1851, 15 asteroids had been found.

As the paper says:




I certainly hope you were being facetious with your reference to a child's imagination determining a planet. My kids might draw the moon, but it isn't a planet. Furthermore, I doubt any kids are dwelling on the cosmic significance of Pluto (the dwarf planet, not Mickey's dog).

I very much agree with the definition of a planet offered by the IAU. Pluto has always been an oddball object, as Amlord has excellently pointed out. Once it became clear that there were many small objects in the Kuiper Belt, the strangeness of Pluto made a lot more sense.

There is a precedent for changing the official scientific designation of Pluto. When Ceres was discovered on the very first day of the Nineteenth Century, it was reasonable to think of it as a planet. When similar objects were later discovered in the same region of the Solar System, it became clear that they were better thought of as a new kind of object -- asteroids.

I must strongly disagree that these designations are arbitrary or that "the scientific establishment" (whatever that might be) is somehow exercising too much power. Definition is one of the most important functions of science. Without it, scientific exploration would be seriously crippled.

Let's look at biology for some examples. It is not at all arbitrary to insist on as strict a definition of "life" as possible. Is a virus alive? Is a prion alive? The answers to these questions -- indeed, the search for answers to these questions -- are a vital part of biological science. Similarly, the search for a greater understanding of why Pluto is better thought of as a Kuiper Belt object than a planet will add greatly to astronomical science.

Wow, it varies THAT MUCH?!



I really don't see how. Pluto, by any other designation, can still be studied just as meticulously. Calling it a "planet" or a "dwarf planet" or a "KBO" doesn't make any harder or any easier to study its properties, its origin, or the information it contains about its surroundings. I agree that definitions are important, but scientific definitions should be based on some sort of scientific utility. The reason I called this one arbitrary is that there doesn't seem to be much rhyme or reason to it from that perspective. What scientific utility is there to a classification that separates two very similar objects such as Mercury and our moon, yet lumps together two very dissimilar objects such as Mercury and Neptune? To put the question another way, whose experience do you think would be more valuable if you were looking for a scientist to interpret data from a Mercury probe - a scientist who's extensively studied our moon, or a scientist who's extensively studied Neptune?

The point I'm making is that science doesn't necessarily have to use the terminology of popular culture, and conversely, scientists don't need to be dictating the meanings of terms used by popular culture.

Wow, this thread is my thread for typos and gaffes. Holy cow.

The real variance is from 29 AU to 49 AU. It is a hugely eccentric orbit compared to the rest of the planets. Neptune, for example, varies from 29.8 AU to 30.3 AU.

Focusing on Pluto as a KBO rather than a planet will cause increased interest in studying KBOs, how they were formed, etc. Lumping Pluto is as another planet doesn't seem to lend itself to opening this line of inquiry.

Now that is huge. I had no idea it was that much.

I'm actually not all that opposed to changing Pluto's designation. If there has to be an "official" determination of what is and is not a planet, the one the IAU came up with is about as good as can be expected (plenty better than including Ceres as a planet). But I'm still not convinced that the word planet is all that useful to science in the first place. What he have in the solar system are a bunch of celestial objects. They can be classed in various ways, but the "planet" classification seems to be about the most pointless from a scientific standpoint. Obviously, the 4 gasballs should belong to the same class, possibly broken down into two subclasses. Venus, Earth, and Mars are actually quite similar in a lot of ways, so could be classified together. I don't know enough about the composition of the moons of the gasballs to know to what extent they should be classed with other objects, but in general, the fact that one object circles the sun while another circles a smaller object shouldn't, in itself, put them into separate classes if the objects themselves are very similar to each other. Neptune's moon Triton should probably be classed with Pluto, Charon, and Xena.

Where I think the word planet is most useful is as a way of designating "landmarks" (loosely speaking) thoughout the solar system. But as long as they're universally recognized as such, there's no real need for the definition to have a lot of scientific logic to it.

Now that Pluto has been sent down to the minors, who will we be calling up?

Or will be stick with an 8 planet rotation?

Inquiring minds want to know.

Actually, the planet status is important from a scientific standpoint.

One thing is the theories surrounding the formation of the Solar System. We have had hypotheses since the 17th century on this, but really no consensus. The reason is that there are a variety of inconsistencies dealing with where the planets are, what their axis of rotation is with respect to the ecliptic plane, their actual position in the ecliptic plane, and so forth.

Pluto is odd because it is a terrestrial object waaaay out there, which doesn't fit into the planetary formation theories because of the insufficient mass so far out. Pluto is more likely an object thrown out there by the gravity interactions between Jupiter and the original Kueper belt. Pluto/Charon is theorized as a collision of two Kueper belt objects, ala the collision that created our Moon (and hence, our atmosphere).

There is real science at work here. Reclassification of planets have happened before. This designation will help to differentiate between planets formed at the solar system's creation and other objects (like Kueper belt and Oort belt objects) which were created via a different process.

From a scientific point of view, there will be eight planets. It is very unlikely that there will ever be any other objects discovered in the solar system which will be scientifically designated as planets.

This brings up the interesting distinction between scientific designation and popular terminology. An accusation has been made that the scientific community is trying to dictate the terms used by the general public. In the first place, I don't think the popular culture will change very much because of this. People will still talk about "the planet Pluto" all the time, just as many people will continue to refer to spiders, scorpions, and centipedes as "insects." In everyday conversation, that's fine. When appropriate, however, people can be educated about the proper scientific use of these words.

So now the definition of a planet has to do with how it was formed? Because that wasn't mentioned in the IAU's definition. If that's the new definition, I can see the validity to it, provided they're willing to change Pluto's designation if their theory of its formation turns out to be incorrect.

And they will be just as wrong. General ignorance of facts does not make the mistake right. And in a generation from now, I guarentee you schoolchildren will name the eight planets, and probably the smart ones will be able to name the dozen or so KBO's discovered to date. Just like the smart kids in 1931 started adding Pluto to the 8 planet system that existed prior to 1930.

I have to admit, I am somewhat baffled by the initial questions:

1. Do you agree with these designations?

What's to disagree with? Pluto has always been an odd-man out, it was designated a planet primarily because the initial estimates of its size in 1930 put it massively larger than it actually is, in fact it is somewhat smaller than earth's moon. We have no idea if it has an atmosphere or not, common guesses are that it does not, it is a rock, and it does not even have a 'moon' per say, as it and Charon have a binary orbit, meaning they essentially orbit each other rather than one the other. Given the recent discovery of all the Kuiper belt objects, it was necessary to come up with a strict definition of what a Planet actually is. I don't really see any room for disagreement with the experts in the field.

2. Given that (just to take one example) Mercury arguably has much more in common physically with our moon than it does with, say, Saturn, is there really any point to having a "scientific" definition of the word planet? Can such a completely arbitrary definition aid in scientific research in any meaningful way?

Firstly, Irrelevant, they are two different kinds of planets, one is a solid, the other is a gas giant. Mercury fits the criteria of a planet, so does Saturn, Pluto does not.

Secondly, the definition is not in any way arbitrary, it was decided following strict criteria by an international collection of the exprts in the field of Astronomy. How exactly is that 'arbitrary'?

Thirdly, of course there is a reason to have a scientific definition of a Planet. Without one, the word will rapidly become meaningless, as estimates are there may be THOUSANDS of near planetary size rocks out in the Kuiper belt. Do we want our grandchildren to have to memorise the 2,500 different planets in the solar system? If not, then we need to differentiate, and thus we need a definition.

3. If the answer to #2 is No, then is this a sign that the scientific establishment is exercising, or attempting to exercise, too much power and influence over matters not properly within their purview?

I'm sorry, can you explain to me exactly how astronomy is not the purview of astronomers? Who would you rather have making the decision? Kofi Annan? George Bush Jr? I can just see the 10th planet in the Solar system oficially named "the planet Therewerewmdiniraqhonest"

I mean where will it end? If we allow these pesky astronomers to make decisions regarding astronomy, we might end up with physicists making decisions regarding physics, or doctors making decisions regarding medicine. Where would we be then, I ask you?

Who else on planet earth (ironic) other than astronomers would be better qualified to make decisions regarding astronomy? The US senate? NATO? The Christian Right? OPEC? Last time I checked, the purview of scientists is science (regardless of the attempts of the Christian right to disagree).

Pluto is no longer a planet. What's the problem, exactly?

You're just begging the question. The criteria are arbitrary, and I explained why.


And how does that answer the question I asked, which is how this definition would provide meaningful aid to scientific research? If it does not, then why do scientists concern themselves with it?

Vermillion:

(1) Pluto has an atmosphere, at least according to most:

http://www.nineplanets.org/pluto.html


(2) Yes, Pluto is a rock, as are Mercury, Venus, Earth and Mars. We call them, or at least we used to, terrestrial planets, as opposed to gas giant Jovian planets [Jupiter, Saturn, Uranus and Neptune].


(3) item 3 of the stated definition, or rather, its application to Pluto is absurd. Banner headline in the National Enquirer: US Scientists Support Greatest Hoax Ever!!!!!!

How so? Pluto will never collide with Neptune, as related in the linked-to article, and so if Pluto's orbit intersecting Neptune's orbit was the basis, and it was, for Pluto failing to meet item 3, well, then that was no objection or failing at all. And the hoax is, well, has the earth cleared a path? If so, then why the billions of US dollars being spent to look for so-called near earth objects? So the earth hasn't anymore cleared a path than has Pluto or any other planet. And so call the application of item 3 to Pluto the mother of all Orwellian thought processes.


(4) And 300 out of more than 2,000 does not a consensus make. And before you toss out "expert" just who are those 300 that don't make a consensus? The rebellion has otherwise already begun:

http://news.bbc.co.uk/2/hi/science/nature/5283956.stm

And please also note the description of the one re the others. So scientists are just as petty and pathetic as the rest of us [though you've done your best to deny that proposition here on any number of occasions].

(5) the definition isn't scientific at all, but wholly arbitrary. What do Mercury and Jupiter have in common? They are accretions that orbit the sun. That is all. One is a barren lifeless rock while the other is a giant ball of gas. And, again, in defense of Pluto, at least it has a tenuous atmosphere and some satellites, unlike Mercury.


Now let me leave you with something that I wrote, well, sorry, two pieces that I posted on a sports blog, after the subject came up there, with two non-substantive corrections, starting with:

"Pluto got a raw deal and demands to be traded, to a solar system with inhabitants that treat planets with respect. I mean, it wasn't too long ago that management [the IAU] said:

"No proposal to change the status of Pluto as the ninth planet in the solar system has been made by any Division, Commission or Working Group of the IAU responsible for solar system science. Lately, a substantial number of smaller objects have been discovered in the outer solar system, beyond Neptune, with orbits and possibly other properties similar to those of Pluto. It has been proposed to assign Pluto a number in a technical catalogue or list of such Trans-Neptunian Objects (TNOs) so that observations and computations concerning these objects can be conveniently collated. This process was explicitly designed to not change Pluto's status as a planet."

Pluto otherwise wishes to make clear the fact that it is a planet, since it has satellites and is otherwise massive enough to retain an atmosphere [tenuous, but still an atmosphere]. And management brings up this lame concept of orbit. Orbit, shmorbit, who really cares? And Pluto's satellites are Charon, Nix, and Hydra. In their devious and despicable efforts to defame Pluto, management had previously reported that Pluto and Charon might be a "binary planet" system, but Pluto wishes to make clear, as management must now admit, that Charon does not have an atmosphere. Charon is otherwise Pluto's child, created long ago when some massive object collided with the then proto-Pluto. Pluto wishes to also make clear that in its continuing efforts to defame him, management has rather convenienty ignored that the mechanism of Charon's creation was precisely that same mechansim that gave rise to the earth's moon, but yet we don't hear management reporting that it wishes to downgrade the earth's status. Lastly, this entity called the Baltimore Sun, and Pluto will forgive the name, but the Baltimore Sun at least sees the lame and pathetic attempt to unjustly accuse and malign Pluto for what it is:

http://tinyurl.com/zzm4d

And, yes, Pluto is indeed here, a sphere, and so management need get used to it...

And now:

"Post-script:

Pluto also wishes to direct the attention of humanity to Dr. Bojan Pecnik, who correctly reports that the planet-defining criteria ought to simply be whether or not the object in question has the ability to retain an atmosphere and otherwise orbits the sun [and not some other planet, like that pretender named Triton]. The gravitational dominance of one's orbital zone, which is the misguided mantra of those so set on falsely denigrating Pluto, otherwise speaks only to the dynamics of Pluto's surrounding environment and says nothing at all about Pluto's intrinsic physical property. Pluto would simply ask the arrogant defamers whether they have any idea, even an inkling, of how it hard it is for tiny Pluto to retain an atmosphere as against the vacuum that is interplanetary space?

Pluto otherwise wishes to express its solidarity with Mercury, which does not have an atmosphere, but has the ability to retain one, and so Mercury stands as an appreciated and welcome member of the planetary club. Pluto otherwise has no objection to Ceres and Xena being added to that club. Pluto also appreciates and is otherwise humbled by the efforts of those who conducted the "Save Pluto" campaign. Lastly, Pluto takes immeasurable pride in the fact that it will soon be assuming its rightful role as the resting place of the ashes of Clyde Tombaugh, the "discoverer" of Pluto. Power to the people!"

What about atoms then, in relation to cultural usage. An atom is not just that, you can have oxygen atoms, carbon atoms, atoms of every element on the periodic table of elements, should they all just be called atoms period? I think the same could be said of planets, its not really a reference to a body in space as much as its a reference to more properties then that, such as its orbit. Back to my example there is three known types of oxygen isotopes or atoms, they are all called oxygen of course but as far as naming goes there is parts there to that function of the name or definition to allow the reader to understand and see the difference such as oxygen 16.

Jupiter has many moons, atmospheres can be found on some, I am not sure if all, or if we have even found all of them. Should those be planets? How about a star? You know the earth is not perfectly round really, it has mountains and depressed areas liquids come to fill, certainly not a perfect sphere, maybe that has to do with the physics of light and our atmosphere, maybe even the biology of our eyes.

So if Pluto does not behave as we see in the other eight planets, how should the definition come to reflect this, should it simply be called Pluto -d, or something like that, would still in form denote Pluto from just being a regular planet, because Jupiter would not have that unless it had something like Jupiter +d. Point being the definition again is something that is being used to describe the natural world, if Pluto behaved exactly the same as say the other eight, this would not be a debate issue, but of course the scientists concerned notice the difference as so then it lead to this, can it change, of course it can, and probably will, who knows how science will look at space in a hundred years.

As for how the culture uses the word, well that’s an issue of personal freedom, whenever I have a discussion about such things with people, I never really start to talk in hard scientific terms, but should science then simply base its understanding around cultural perception? I would think that would require the culture to become very scientific or else the domain of science would simply become null in purpose and value in relation to its goals.

If you want to call Pluto a planet, go ahead, I don’t think scientists will have you labeled a traitor or toss some with us or against stance at you On that note though, if a person wants to come to understand science in a current sense and work with issues, such as if you wanted to become an astronomer and try to get Pluto back into being nothing more then a planet, you would have to come to understand a great many things first, or the stuff scientists argue over with each other or use to further our understanding of the natural world in the first place.

Just so I don't impart false information, I was hoping that someone would correct my intentional error, but since that didn't happen, Mercury does have an atmosphere [as tenous as Pluto's].