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You might love Pluto, but since 1930 it has been a glaring (if hard to see) error in astronomical decision-making.
The vote today to boot Pluto off the list of planets gives the word “planet” some scientific meaning.
Astronomers stared down public opinion and made the right decision. Now they have a big job: to stay the course in the face of immediate and future outcry from the public or from any astronomers would would revise the main points of the decision.
August 24th, 2006 at 8:24 am
There’s a pretty simple answer the astronomers can make to any complaints: a lot of people think spiders are insects, but they’re not. A lot of people think chimpanzees are monkeys, but they’re not. A lot of people think Pluto is a planet, but it’s not.
Anyone who thinks the definition of a planet should never be changed, I wonder what they would say to Copernicus, who changed the definition of a planet to include Earth?
August 24th, 2006 at 8:27 am
Sorry, but you are wrong. Pluto was a planet for over 70 years, and I do not accept the retrofitting of the meaning of a word. If there had been a sceintific definition when Pluto was discovered, that would have been different. But there was not, and thus the word was defined by Pluto as much as by any other planet.
Beyond which, I dislike the idea that a planet has to be the dominant force in its orbital scope. It’s too limiting. And why should we say that Pluto is dominated by Neptune? Why not the other way around. This decision lacks proper rigor. It should be revisited in the future, and you should be among those who revisit it.
August 24th, 2006 at 8:48 am
‘The vote today to boot Pluto off the list of planets gives the word “planet” some scientific meaning.’ It’s obvious you are in favor of the demotion and personally I don’t really care one way or another. But isn’t it obvious that not only did they not give the term planet some scientific meaning, but the actually stripped most of that meaning away? The ruling was only for this solar system. A good scientific term categorizes what you know and allow you to categorize what you don’t. As of now we can not surely call anything outside of solar system a planet without worrying about what criteria they’ll place on them. Sure we assume that big gas giant out by another star has “cleared its orbit” but we’re guessing aren’t we.
And great, if we find a very dark 10,000-year-orbit gas giant in our solar system larger than Jupiter way out in the outer Oort clout it will be, by our new “scientific” definition a Dwarf Planet. Congratulations, history will be so impressed by the forethought we gave our scientific definitions.
August 24th, 2006 at 8:58 am
sdelmonte
“Sorry, but you are wrong. Pluto was a planet for over 70 years, and I do not accept the retrofitting of the meaning of a word.”
So you don’t think Earth is a planet either, since it was not a planet for several thousand years prior to 1543. Interesting argument.
Since in your view Earth is not a planet, what is it?
August 24th, 2006 at 9:02 am
What if we originated on Jupiter? Wouldn’t Earth be a “dwarf planet”?
I do not consider a strict definition required: We give names to any space object of even minimal interest (even if they do look like a number.)
Why not just use “Planet” as the highest classification for objects circling stars to differentiate from other objects and either
never use it for trivial objects or
only use it for the technical name (ala the Latin names for plants) or
add suffixes to differentiate size: -oid for tiny, -ic for gigantic, -ike for earth-like size.
August 24th, 2006 at 9:04 am
Good decision by the IAU! We finally have a scientifically sound definition of planet, and we have a category for all those dwarf planets in the Kuiper belt. Now, let’s move on to real science: how about those methane lakes on Titan?
August 24th, 2006 at 9:12 am
Actually, it is already obvious this definition is not going to last either. Not only did we lose Pluto at a planet, but over 200 extrasolar planets as well. It’s a shortsighted decision that will just bring up a new debate soon enough when we try to figure out just what those big things around other stars are. Since as of today they are no longer planets.
And I am quite sure we will eventually find objects far more unusual than Pluto and Ceres around these other stars.
That’s why, personally, I thought the original proposal was the best because it was the most open to the unusual circumstances we will find. Just looking at our own solar system, and building a definition that fits just these 8 and not that other rabble will surely fail when we look elsewhere.
This just postpones the debate and really answers nothing. For that reason, I am deeply disappointed in this decision.
August 24th, 2006 at 9:26 am
Personally, I liked the idea of keeping Pluto’s status as a Planet for historical reasons. The new definition would’ve been applied for new discoveries.
But, a decission is made, which means we all have to stick on that for “standard reasons”, but that doesn’t mean we can not still call Pluto a planet on a familiar way. For me, Pluto is a Historical Planet.
Copernicus changed the term in order of the comtemporary visible universe.
Pluto was found under that same concept, and that triggered the search for the Planet X. And astronomers worldwide accepted the idea of terming Pluto as a Planet for more thatn 70 years.
Now visible universe is expanding before our eyes and new worlds had been and will be discovered. Such worlds will carry a scientific designation
and it’s ok. That’s the proper way for such worlds. But Pluto… the historical
Pluto we all accepted when we learned about the Solar System and none
of us complained about that, is now pulled away from the oficial list.
Science Method should keep things simple. I’m not saying the work made
by the IAU is wrong. It shed a new light for discoveries to come. But trashed away a historical member of our Family.
Regards
August 24th, 2006 at 9:46 am
Why is it necessary to continually re-write history? What’s so reprehensible about Pluto being called a planet? Hmmmmm? Forget the scientific re-definition — even this new one is pretty dodgy. The fact is, astronomers still have no complete understanding of planetary system formation and this whole brouhaha over Pluto shows it. They can point out all sorts of reasons why Pluto shouldn’t be a planet, but can’t apply any good reasons why the other 8 should! Let’s take Mercury — Mercury is slightly smaller in diameter than the moons Ganymede and Titan but more than twice as massive. So what makes Mercury a planet and Ganymede and Titan not? What about Jupiter? Shouldn’t it be a small brown dwarf? But then the definition of “brown dwarf” isn’t too well put together either.
Clyde Tombaugh pulled Pluto out of a mass of photographic plates, at a time before CCDs and computer enhancements. I think it is wrong to denigrate his work by claiming that Pluto doesn’t meet some arbitrary and contrived definition of the word “planet.”
August 24th, 2006 at 9:46 am
I don’t yet know exactly where I fall on this debate, but the following thought occurred to me almost immediately when I heard about this new definition:
Since Pluto crosses Neptune’s orbit, can it be said that Neptune has “cleared it’s neighborhood?” Does Neptune therefore fail the new definition as well?
August 24th, 2006 at 9:55 am
The thrust of the decision to demote Pluto is scientifically sensible. But as you can see in the update to my story, there are serious problems with the wording.
It is going to be incredibly interesting to see where this goes.
The IAU is recognized as the governing body for nomenclature of space things. But clearly many astronomers are now disillusioned with the process. New Horizons mission leader Alan Stern told me that an email is circulating among astronomers that calls the IAU the “Irrelevant Astronomical Union.”
Will the IAU resolution stand? Will disaffected astronomers abandon the organization or work within the system to push for another vote at the next meeting?
August 24th, 2006 at 10:03 am
Well, really, has anyone looked at it from Pluto’s point of view? Demoted from planethood to being a dwarf? It’s a sad day.
“Pluto’s Lament”
http://daypoems.net/poems/2801.html
More seriously, I have in my library an 1855 book on astronomy that lists the planets of that time, 26 in number, 18 of them them asteroids. And I think that’s the conceptual bullet that the IAU dodged with today’s vote.
I think the strict constructionist interpretation of planethood will stand.
Tim Bovee
Washington, D.C.
August 24th, 2006 at 10:20 am
VERY, VERY BAD DECISION - Astronomers are supposed to be intelligent they can use context, the general public can’t so easily. Ask a school kid - now before they get indoctrinated, kids love smartasses - I have a long list of objections and points but the main one is that including Pluto, Xena and Ceres in the list of planets was correct. The kindergarten objection to the first proposal - “what will we call the moon when it becomes a planet” was ludicrous - we’d call it ‘the Moon’ - if we are still here of course. I personally would include all moons that are round as planets - a different debate - however as a simple physicist I can very easily find a way to exclude them (and Charon) using exactly the same measurements as you’d need to determine the barycentre, maybe it wasn’t convenient to consider that! In my opinion, and it is just that, a planet is a big round cold thing in space - very easy, needs a bit of expansion to define round and cold but thats all thats needed - that would even include objects which have formed in outer space like little stars that haven’t switched on. They are not the same as solar system planets - so what?
OK clearing the orbit is a good point, so we have another type of planet, thats all. We already have several, maybe even eight based on the eight planets we are allowed now, but certainly inner and outer, or small and large or gas or rocky or …. Context stupid!
Last point here - if there has to be a smartass name for the eight planets we are allowed to have, “classical planet” just isn’t it - that term means and always will mean the Sun, the Moon, Mercury, Venus, Mars, Jupiter and Saturn. Find another less confusing term - or is history to be subject to the will of the Astronomers too! Thats god-like power, very appropriate for this sort of decision.
August 24th, 2006 at 10:43 am
I agree with eek10bears comment, specially for his last point.
Uranus, Neptune and little Pluto were not considered “classical” by the simple fact that they were not visible to the naked eye.
Pluto IS a historical planet, and we all agree on that since we learned that on school, even the members of IAU.
That new definition would be applied to newfound bodies, but not for Pluto.
Now, as Mr. Britt just wrote: clearly many astronomers are now disillusioned with the process.
I’m one
Regards
August 24th, 2006 at 10:51 am
Neptune’s Demotion is Long Overdue
(1) (c) has cleared the neighbourhood around its orbit.
Neptune’s and Pluto’s orbits swap every few years.
Base on this new definition Neptune most be demoted immediately since Pluto and Charon has been demoted.
Saturn’s and Uranus’s Demotion is Long Overdue
(1) (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape
At same time we need to demote Uranus and Saturn since these planets does not match up with Earth standard model. They have rings that help them to be self-gravity.
Venus’s and Uranus’s Demotion is Long Overdue
While we are at it lets add more definitions
(1)(d) has an rotation on a vertical axis
(1) (e) has a rotation that is counter-clockwise from the relative north pole.
Venus rotates clockwise, and Uranus rotates on a horizontal axis rather than a vertical one.
August 24th, 2006 at 11:07 am
The obvious problem with this definition is the wording “has cleared the neighborhood around its orbit”. What exactly does that mean? Obviously more work is needed.
I think the real problem is that neither side of the debate is approaching the issue from a purely rational standpoint. Yes, those who preferred to consider Pluto a planet (and I’ll admit to being one of them) felt that way in part for sentimental reasons. But at least in public, few of those who opposed Pluto’s planetary status gave any solid scientific rationale. Usually the argument came down to “it’s too small”. Well, ok, but then exactly how big should a planet be? It just happens that in our solar system, as far as we know at this point, there is a big gap in size between Mercury and the next smaller objects orbiting the Sun, namely UB313 and Pluto. But what if there was an object with, say, one third or half the mass of Mercury? Would that object be a planet? In fact it’s conceivable that such an object might possibly exist in the outer reaches of the solar system (and if it had even one-third Mercury’s mass, it would probably have a diameter that was pretty close to Mercury’s). By the new IAU definition, of course, it would probably still not qualify as a planet — even if it was as big as Mercury. But if such an object were to be discovered in the future, either in our own solar system or in some other planetary system, then we might have another odd situation where we have a “dwarf planet” that is bigger than the smallest “planet”. So while this defintion may seem to solve things in terms of what we know now, it isn’t a truly satisfactory solution.
Though it wasn’t perfect either, the original draft provided a better defintion. Sure it would have added a lot of planets, but what’s wrong with that? Mike Brown and others who disliked it argued that “planets should be special”, but isn’t that also an emotional response? It will be interesting to see how this discussion plays out, though it’s a little depressing to be reminded that scientists are not the rational, dispassionate beings we often imagine them to be.
August 24th, 2006 at 11:20 am
Pluto will ALWAYS be a planet, and I will not rest until this gross, massive injustice is rectified. Anyone who thinks Pluto shouldn’t be a planet is an astro-elitist and quite frankly can burn in Hell.
August 24th, 2006 at 11:37 am
HORRIBLE, HORRIBLE DECISION. PLUTO WILL ALWAYS BE A PLANET AND ANYONE WHO THINKS OTHERWISE WILL BURN IN HELL.
August 24th, 2006 at 11:39 am
First I want to thank Robert Roy Britt for the information on this topic. Most people don’t realize that it is difficult to arrive at a unified definition that people with diverse opinions can agree with (the comments here illustrate that). Second, people should not be upset with the changing definitions of a planet. The scientific and common names of animals are changed all the time (often despite history). Biologists have learned to live with the uncertaintly that comes with new knowledge. Certaintly, astronomers are capable of that versatility as well. I look forward to the next discovery that will test the limits of the current definitions.
August 24th, 2006 at 11:53 am
Demote Pluto
The debate over Pluto rages: What is a planet? It is a question that calls us to take sides: the rationalists who insist that it can no longer be considered a planet, and the sentimentalists who will hear none of…
August 24th, 2006 at 11:54 am
You may find this hard to believe, but the legal field has grappled with issues like this for centuries, i.e., new situations requiring a finer line to be drawn in what time and progress eventually shows to be overly generalized characterizations. Given that long human experience with creating definitions, it has been shown that public policy considerations rarely mentioned in this debate exist and should be employed and legal tools for dealing with these considerations can also be useful. For example, one public policy generally states that the advancement of science is public good. Space science is often advanced with publicly funded space probes. Given that Congress controls the purse strings, and the public more or less control Congress, is it so hard to image that a “planet” is likelier to receive a space probe than a less well recognized body? Witness the Pluto Express probe. Had Pluto been labeled something less than a planet, say 2003 UB313, there is a real possibility that Congress would not have ponied up the dough to launch a probe at this time, clearly a minus for science and public policy. So when the IAU fiddles with the definition of “planet” it should be cognizant that it may affect funding for probes to these bodies. Another related public policy is promotion of science to the public. Demoting Pluto achieves the exact opposite. It makes no difference that Pluto is a cold, dark and essentially airless world that would kill you in seconds if you were directly exposed to it, Pluto is a favorite planet to children. Children who not only can grow up to be scientists, but children whose parents influence Congress to send probes to far-flung worlds. Therefore, demoting Pluto is against public policy and may hurt science.
Admittedly there is some tension between what the astronomers want to call a planet and what the public thinks is a planet. Thus, a legal tool should be employed, the grandfather clause. In short, Pluto should be “grandfathered in” to league of planets. The law is chock full of exceptions and there is no intellectual inconsistency for a legalistic definition like “planet” to have exception too, especially if it advances legitimate public policy.
August 24th, 2006 at 11:55 am
The decision by the IAU is fundamentally sound. Scientifically, it allows us to classify the planets in the two major groups (terrestrial and jovian) while allowing for a wide variety of types of minor bodies. Pluto never should have been classified as a planet in the first place and while I have always admired the story of Clyde Tombaugh and know that there are many who revered him, that is not the basis for scientific classification. Most of the concerns I have seen posted are about terminology such as “classical planet” and “dwarf planet” and I think that there will probably be room for revision there in the future. But the basis of the decision is the right one and science moves forward. Pluto is still there awaiting the New Horizons spacecraft and I am sure that will be an interesting mission to a very strange little double world. It is kind of funny to see how passionate people get about this. It is afterall, a matter of semantics rather than reality. But as a friend at the IAU meeting told me, “You’ve never seen astronomers so fired up about anything!”
August 24th, 2006 at 11:57 am
Personally I feel the proper definition of a planet should be classified as the following:
The full definition of a “planetoid” should be the first classification. A planetoid is any body with sufficient mass to attract debris or gas to increase it’s mass. An “asteroid” is any planetary debris found floating freely either in orbit around a star or in deep space that cannot directly attract material on a regular basis. Those planets that are too small to form into a true spheroid object by it’s own gravity should be considered a dwarf planetoid or asteroid depending on it’s nature as previously described.
Any planetoid body large enough to form into a spheroid shaped object and orbiting in the same direction along the same planetary plane as other planets in conjunction or otherwise similar orbital paths, even if some are eliptical in nature. The body must be within the solar system’s Oort boundry. The spheroid plantetary object may have moons, asteroids or other objects within it’s orbital path, but is should still be considered a planet if it’s on the plane of the eliptic with it’s star.
Any planet found in posession of life, should be considered a terestrial planet. Earth is a terestrial planet, but also is defined as a planet. If a moon is found to be in possession of life, it should similarly be classified as a terestrial moon.
Any planetoid body that is large enough for solar combustion, but have not started the process (larger than Jupiter by 50% or more), should be considered brown dwarfs even if there is no solar output.
Any planetoid object outside the planetary plane having essentric or reversed orbits to the rest of the planetary plane should be considered rogue planets.
Spheriod objects that orbit another larger body, but are smaller than it’s companion, are to be considered a moon, unless the object is 75% the size of it’s companion, in which case it would be considered a binary planet. If more than one that are 75% or more of the companion but less than 99%, continue with trinary, etc.. The object that is the largest of the system is the planet. If a planetary system is found that has 2 identical sized planets, or more, they should be considered for a special designation to be determined later, but can be considered binary/trinary/etc.
Any object that was once a spheroid but was damaged by collision and is now a non-spheriod shape, could be considered either a rogue or dwarf depending on it’s origional status but the word “former” should be in place before the naming designation. If it was origionally a planet, it should remain as designated a “former planet”. The asteroid belt if it is later proven to have truely been a planet should be re-classified to be the “former planet” and it’s name.
Of course, yes, all this would still mean declassifying Pluto as a planet, but as we go beyond the local solar system into other star’s planetary objects we need to properly define what a “Planet” really is, and what is categorized as a rogue or dwarf planet.
Any planetoid spherical or otherwise found outside a solar system’s Oort bondry should be considered a quasi-rogue planet or some form of the meaning “wanderer” or “castaway” attached to the name. Every effort should be made to determine the planetoid’s original solar system and any orbital path. If a planet is a deep space, but orbiting a star, it should be considered rogue even if it’s orbiting along the same planetary plane.
August 24th, 2006 at 12:26 pm
I’m sure Gustav Holst would be very pleased with this recent decision.
August 24th, 2006 at 12:30 pm
I think the definition is correct, but I’m appalled to see that only 420 or so astronomers voted on the definition. This all but guarantees there will be continuning conflict over the definition. We haven’t heard the last of this debate.
August 24th, 2006 at 12:36 pm
Forgive me, but it seems rather childish to insist that Pluto continue to be considered a planet just because that’s what you learned in school. Science progresses. When I was in school, the Periodic Table ended at 106 or 107. Should I insist that 108 thru 112, discovered since my school days, aren’t elements, just because they weren’t discovered when I was in school?
Whether this group’s definition should or will stand, or if they should be the recognized authority on the topic, may be a subject for debate. But, as I understand it, this is the first actual, “official” scientific definition of the word. For the sake of clarity, I at least applaud a step in the right direction.
August 24th, 2006 at 12:39 pm
If you mean that Holst’s choice of movements was intended as a definition of the word “planet,” then you’d have to say he agreed with sdelmonte, that Earth is not a planet.
August 24th, 2006 at 12:50 pm
The new definition may or may not be an ideal one, but a definition must be found that eliminates Pluto. I was a proponent of keeping Pluto as a planet until the number of trans-Neptunian objects and other spherical bodies uncreased as it has. There is such a huge difference between the terrestrial and Jovian planets and the scads of little icy spheres we now know about, that they must be discriminated from the big guys.
There is one important piece of history that everyone on this site has missed so far — that there is a striking parallel for Ceres. Ceres was discovered and included as a planet in the early 1800s. I suppose school children learned its name as well. But when it was found to be one of thousands of similar objects, it became ridiculous to classify them along with the classical planets. So should it be with Pluto. My father learned the names of the 8 planets; so should my grandchildren.
By the way, the application to other solar systems is no problem. If a big satellite of a star is found, it may be named a planet if it is big enough to have theoretically cleared its orbit. And it probably would have. If extrasolar objects are eventually found that make us wish we had a different definition, let us worry about that then.
Last comment: for the PI of Pluto Express to be grousing about changing the classification of his target object is so self-serving that it’s embarassing to the community.
August 24th, 2006 at 12:51 pm
One of the worst ideas to come out of this decision is that of the term ‘dwarf planet’. Now we have objects which are ‘dwarf planets’, but are not planets. Dumb.
What I have been teaching in my introductory college astronomy classes (for over 10 years) is that the classification of objects in the solar system are: terrestrial planets, gas giants, ice dwarfs, asteroids, and comets. As arbitrary as any other definition (an ice dwarf could become a comet), but at least there is no need to play with or explain how a ‘planet’ is not a planet.
I will admit, however, that part of me was hoping for an expanded planet list - and then watching how astrologers would invent new BS to take into account the expanded solar system.
August 24th, 2006 at 1:04 pm
revisionism is the realm of people that
1. have nothing better to do
and/or
2. think they are smarter that everyone else
August 24th, 2006 at 1:08 pm
Okay, what i don’t understand was why they didn’t go the route of classifications?
Habitable planets like Earth could be a Class M planet
gaseous planets like Jupiter could be a class G planet
small cold planets like Pluto, Sedna, etc. could be Class I planet
or whatever makes more sense.
Anything that can’t form a somewhat spherical surface because it’s surface gravity, and thus it’s mass is to low, would be an asteroid or Comet or meteor or… you get my drift
August 24th, 2006 at 1:16 pm
Somebody please clear up an obvious misunderstanding I have about this new definition:
Since Pluto’s orbit crosses within that of Neptune, it is, under the new definition, not considered a planet.
However, since Pluto’s orbit crosses within that of Neptune, and Neptune has not cleared it away from it’s neighborhood, how is Neptune still considered a planet within the new definition?
It seems that there are a lot of astronomers that need to go back to school. There are some basic logical problems with this “definition”.
August 24th, 2006 at 1:17 pm
Odd the post I jsut made didn’t show up…
August 24th, 2006 at 1:40 pm
IAU definition makes good sense, and is a great compromise. However, there is a thing in law called “grandfathering.” Pluto should be a “grandfathered” planet.
Perhaps the definition should be as stated by IAU, but with the addition, “Any body recognized as “planet” before August 24, 2006, shall remain defined as “planet.”
John
August 24th, 2006 at 1:58 pm
Personally, I’m am very confused about the new definition. It doesn’t make sense to me, and I don’t have a major in astronomy or anything. I’m an amature. It would make better sense if they put it in words the whole public could understand, becase from what I am reading, the definition seems to be causing some conflict. Anyway. I am curious why they are suddenly demoting Pluto now? It’s been a planet for over 70 years, and to suddenly change it, it’s insane. Only 424 astronomers were allowed to vote for the demotion of Pluto. That’s less than 5%! I consider that insane. But anyway, Pluto will always remain a planet in my book.
August 24th, 2006 at 1:58 pm
Was the committte the same guys that came up with VHS and Beta or HD and Blu-Ray ??? This whole controvery was inane. Charon a moon of Pluto becoming a planet ???? Earth’s Moon becoming a planet because in the distant future it will drift away from the Earth ??? Why not Titan….it has an atmosphere. All they did was confuse everyone and then made themselves look like the genuises they aren’t by coming up with a decision. With all the press they got you think they had solved world peace. This whole mess could have been solved so simply…. Planet - any body of mass with gravity than is roughly spherical and revolves in an ecliptical plane around a stellar body. Anything else is a moon or minor planetary body. Bottom end of scale…..Mercury…anything smaller is a minor planetary body, moon or asteroidal body. Pluto is now out. Ceres is now out. Earth’s moon is still a moon. Charon is a moon around a minor planetary body. Xenia is a minor planetary body (or whatevery you want to call it). Comets are still comets. Problem is now solved. That didnt take much time at all. Now maybe we need to get the President to pardon Pluto or the Pope to give special dispensation so that Pluto can be reunited with the solar system.
August 24th, 2006 at 2:00 pm
I am thrilled that the IAU had the courage to demote Pluto.
I much prefer having a solar system with eight major planets then having a solar system with 200 planets where 192 of them are all smaller than our own moon!
And this business about grandfathering Pluto is silly. I just can’t imagine reading a science book 400 years from now that says, “Only eight of the nine planets meet the IAU definition of a planet. But the ninth one is still called a planet because people in 2006 were outraged”
August 24th, 2006 at 2:27 pm
My problem with this “definition” is that it seems specifically constructed so as to exclude Pluto. In that sense, it is a great disservice to Science.
A good scientific definition is one that is useful to science. If we end up with 8 planets, 12 planets, or 500 planets, then so be it. Who ever said that a solar system could only have a few planets? Why can’t a solar system have 50?
August 24th, 2006 at 3:00 pm
Now we’re left to wonder what Pluto’s bretheren out there will be named. Probably not Greek names. One cool (and perhaps controversial) idea: sell the names to corporations or individuals.
Meanwhile, NASA now has a mission en route to an object that used to be a planet.
More in my latest (and probably last) story on this today, here.
August 24th, 2006 at 3:04 pm
If the 12 planet scenario is accepted after all, I guess we could have:
My Very Educated Mother Curiously Just Served Us Nine Cheese Pizzas, X-tra Large. *
*Note: this puts Charon in front of Pluto and we’d need a body for “Large”, but I hear there may be hundreds more planets added in a few years, which would make our little mnemonic into a paragraph requiring its own mnemonic.
August 24th, 2006 at 3:21 pm
I don’t know what all the fuss is about. The fact that headlines keep reading that Pluto was ‘demoted’ is ridiculous! Is being called a Planet any more of an honor than being called a Dwarf Planet, or even a Comet or KBO? How exactly is it a demotion to simply reclassifly something that has absolutely no attribute of rank whatsoever? I certainly don’t think Pluto objects to whatever we call it. The need for a clear classification of objects in our Solar System is paramount to Astronomy, and should supercede any irrational attachments humans make to these distant, (seemingly) lifeless objects. It’s only fair to say that Mike Brown’s discovery (Xena) should be called a Planet, had Pluto continued to be; and if that were the case, then there’s no guessing just how many other such objects remain to be found which would keep contributing to the number of our ‘Planets’, not to mention to our confusion. The decision of the IAU was sound and based on the need for scientific clarity without regard to nostalgia, and rightly so. If anything, this is a great opportunity to demonstrate to children the process of advancing science in a way they can understand. Every kid knows the Planets, and we can now teach them that when new discoveries force us to re-examine long held perceptions, we move forward dispassionately and rationally, allowing new ideas to re-shape our knowledge. If scientists were always to acquiesce to the pressures of culture, nostalgia, tradition, or popular opinion, where would be today? I say Bravo, IAU!! and rock on, little Pluto!!
August 24th, 2006 at 3:26 pm
Did the public react this badly when mushrooms were demoted from the Plant Kingdom to the Fungi Kingdom?
When Ceres and her sisters were removed from the list of Planets, did people defiantly proclaim that “Ceres will always be a planet!”?
Oh, yeah, did you hear the latest? The Sun doesn’t orbit the Earth.
Science has to adapt to new discoveries or it dies.
Scientists learned decades ago that Pluto was a lot smaller than they had expected, and I knew right away it was destined to be removed from the list of planets. This was the right decision, even if the wording needs to be refined.
As for claims that Neptune and Earth have not cleared their orbits, here’s a possible refinement: Planets are objects that have cleared their orbits of other bodies with stable orbits. Earth has many asteroids that pass nearby, and when they do they get flung into different orbits. But there are no other objects in a similar stable orbit. (A similar orbit is one with nearly the same orbital period.) There are also no objects with orbital periods near that of Neptune.
Pluto’s orbital period is 3/2 times Neptune’s period, so it’s not a similar orbit at all, even if its orbit crosses Neptunes. Orbital resonance with Neptune keeps Pluto’s orbit stable, as it does with all the rest of the Plutinos. But since most Plutinos also have orbital periods of 3/2 times Neptune’s, you really can’t say that Pluto has cleared its orbit. You can’t say that of any small body like Pluto or Ceres, but you can with larger ones like the Earth and Neptune.
My only question is this: Now that Xena it not a planet, will we get to keep the name Xena?
August 24th, 2006 at 4:14 pm
Robert, on April 11 you posted a column requesting, “If you can find a single professional astronomer who thinks this decision should not be made by the IAU, get them to comment here.” - http://www.livescience.com/blogs/2006/04/11/demote-pluto-and-kill-xena/
I stand by the point I made at the time that having the IAU wade into a question of semantics rather than science has succeeded in generating far more heat than light on the matter. This is one of the biggest astronomy stories to hit the mainstream media for some time, and as far as the average person on the street is concerned, hardly makes astronomy seem more relevant to their everyday lives. The point is, there is no single “right” way of defining what constitutes a planet, as the ongoing debate, which is just going round and round in circles, proves. Some folks will always be unhappy that their favorite definition was not the one that was picked. And as I said in April, the IAU don’t have the “right” answer either, when you consider that even if we attempt to define planet in a manner that depends entirely on physics rather than historical precedent, there are still several ways of looking at the problem. All the public sees is a bunch of crazy scientists who have nothing better to do than hurl invective at each other because someone else doesn’t agree with their pet name for something.
As for the question of naming new objects, it’s clear that there are many, many more objects out there to be discovered. Kind of like the situation in the early days of stellar astronomy; we all know of Sirius, Arcturus, Barnard’s Star, etc. But the suggestion that the IAU should regulate the naming of the miriad of Kuiper Belt objects, etc., is as absurd as suggesting that names ought to be required for all the stars in the Hubble Guide Star Catalog. Obviously commercial companies have jumped into a niche here (viz. International Star Registry, et al.) and I can see there is perhaps some merit in suggesting that the IAU ought to get in on this business and make a bit of money for science education on the side.
In the end, though, I’m perfectly happy with 2003 UB313 keeping its catalog identification. That’s more than sufficient as far as I am concerned. The naming scheme is already in place. If folks also want to call it a planet, a dwarf planet, Xena, or name it after some god or godess, that’s fine by me. In the meantime, I’d prefer my colleagues put a little more effort into disseminating the (often fascinating) subjects of their research to a wider public, and less into semantic irrelevancies.
August 24th, 2006 at 4:35 pm
What? Grandfathering pluto as a planet is “silly?”
1. How about respect for the discoverer of Pluto. Respect for his belief that the name “Planet” and the school girl who named it “Pluto” was going to be for “forever.”
2. How about “Tradition?” We should perhaps reclassify every mountain smaller than Everest as a molehill, since there are so many more “mountains” much larger in the Solar System currently discovered and yet undiscovered.” We will have so many mountains to name, that we whould just take away the term from all the “minor ones.” Using previous commentary logic about grandfathering being “silly,” perhaps our “mountains” on earth are surely not worthy of being in the same class as “mountains” on Mars, for example. After all, science moves on and we need to be ready to re-classify……….
3. Perhaps using the same logic of the person talking about “silly” to grandfather, we may find that an “atom” is no longer an “atom.” Would it be silly to continue to call the object just that, when perhaps a different scientific definition may one day be discovered?
August 24th, 2006 at 4:41 pm
Actually, this controvery seems to be a good teaching opportunity. The public is asking all sorts of questions like “Why do we see Neptune as having cleared its orbit?” This whole issue raises awareness of many recent discoveries about the nature of our solar system. I call that a good development.
August 24th, 2006 at 5:16 pm
Not to ridicule the members of the IAU, but this has got to be the most moronic idea ever conceived. I have no problem with demoting Pluto, but what is your reasoning: size, orbit, inclination, or what?
The entire purpose of this vote was to define what constitutes a planet. Give us a definitive reason behind this demotion, not some vague concept of “an object that has cleared its orbit of debris.” By that definition, Earth isn’t a planet - ever heard of an NEO.
Wouldn’t it be more intelligent to apply the same logic to planetary objects that we utilize for categorizing life? Just like Kingdom, Phylum… a planetary version… Planet, Scale, Composition…
While the initial IAU definition had flaws, I believe it was on the right track.
Oh, and “Dwarf Planet” still has the word “Planet” in it. So, it’s still a planet, only causing further confusion on the definition of “Planet”. So to all of the IAU members who voted for this, I have one word of advise… “Go back to high school and take a refresher course in English!”
August 24th, 2006 at 5:20 pm
jalpha1, nice post!
when we teach to others the ways of science, we always try harder to make science get to the people the fastest, easiest and fully comprehensible way…
decissions like this one taken today… make our work as teachers harder and more difficult.
Science is for everyone, and not for some “enlightened” people.
August 24th, 2006 at 5:32 pm
Not that anyone should care what I think, but I like the ruling. However, a poor, unenlightened man asked me who these people think they are, and how many of my tax dollars are they spending for this nonsense? I looked at the IAU website and didn’t get an answer.
Does anyone know if there are grants or tax dollars at work here? Since it is an international institution, I don’t see how it can be directly funded by the US, but I suppose there could be money getting to them from our treasury. My answer to him was that he surely didn’t pay for it since he doesn’t believe the earth orbits the sun (inside joke). Thanks for any insight!
August 24th, 2006 at 6:16 pm
I remember reading, In one of my many science books, that for a body In space to become a planet requires a certain “Critical Mass” to be reached. When a body contains enough mass, It becomes round in shape, due to the pressure of It’s own gravity. Hence, asteroids are generally”Potato” shaped whilst planets are spherical. Although Pluto Is indeed small, It Is most definately round! Therefore, it has the required mass, Ergo it must be a Planet!
August 24th, 2006 at 6:20 pm
I can’t believe in this nation we would allow such a blatant example of profiling to occur. This just shows these astronomers for what they are, obvious anti plutites. It is disgraceful in a country that prides itself on tolerance to be so intolerant. I could go on, but suffice it to say, I will be contacting the ACLU, this may rise to the level of a hate crime
August 24th, 2006 at 6:50 pm
I agree with the IAU’s decision. Adding the dwarf planet catagory (or a middle catagory) makes sense. Essentially a swarm of similar sized objects constitues a belt not a plethora of planets, we do the same thing with the rings of Saturn. The IAU’s definition aren’t really science (they tried to base it on science so good for them) but astronomy (which means star-naming) vs. what should be called astrology (but is called astro-physics). The IAU might determine that we should name all the features on Callisto after Norse mythology or that one object in orbit around the sun is to be called a planet, these are arbitrary conventions not specifically scientific though scientists will abide by them during communications to keep things neat.
One note of regret among those above who disagree with me, alas, spacecraft probably won’t be commissioned to visit dwarf planets. Fortunately New Horizons is already on its way and Ceres will get a visitor the same year (DAWN launched next year) Pluto is incredibly interesting, the origin of its moon may well be similar to our own.
August 24th, 2006 at 9:09 pm
To anyone who doesn’t think it is obvious that the eight main planets, and only the eight main planets, have “cleared their orbital zones”, please read Steven Soter’s convincing argument in “What is a Planet?” at arxiv.org/abs/astro-ph/0608359 . When you calculate the amount of orbital clearing, you will find a gap of five orders of magnitude (!) between the eight main planets and all the smaller objects, like Pluto and Xena.
August 25th, 2006 at 12:21 am
If one wants Pluto and other spherical bodies to not be considered to be planets, one does not just place them in a subcategory of “planet” by preceeding it with the adjective “dwarf”. When the “gas giants” are called “gas giant planets” no one considers them not to be planets. Or when the other planets are called “minor planets, no one considers them not to be planets. So Pluto remains a type of planet. It would have been better to coin a new term for such bodies, such as, the mentioned “plutons” or maybe “megaastrons” for very large spherical bodies in belts other than the asteroid belt.
August 25th, 2006 at 12:33 am
Interesting comments. I find it strange that a body like the IAU could suddenly demote Pluto from a Planet to a “Dwarf.”
Makes no sense at all. After all, it does rotate around the Sun, has a moon, and it’s orbit maybe weird, passing inside
Neptune, so what?
The orbital mechanics that Clyde Tombaugh used to find this tiny planet were pure. It’s size are not magnificent, but still large enough, and spherical enough to remain classified as a planet in my opinion.
I dislike it very much when zealots fool around with these type of things. Rather than simply deciding among themselves about this issue, more astronomers need to be consulted.
I feel those who made this decision had an agenda. Why, I do not know. It was a bad one.
August 25th, 2006 at 6:41 am
The decision is narrow minded and mean. Pluto orbits the Sun and so what if its orbit is somewhat eliptical. The other now so call real planets do not have perfectly round orbits either. It also has a moon. Mercury and Venus have no moons, therefore they are not real planets either. No matter how you look it, Pluto is a planet that happens to be in the Kuiper Belt. So what?. If there are others there too, they are planets too. What is the fear of having 10 or 12 or more planets?. Anyway the discusion is moot. With the problems we have in this planet and the unavoidable WWIII coming from the Middle East, what the Solar System is consisted of makes little importance to the average human being. For me Pluto continues to be a planet and maybe Xena is also too. Charon is Pluto’s moon and there its stays.
August 25th, 2006 at 7:37 am
With Pluto no longer being classified as a planet, school children can no longer use the popular mnemonic, “My Very Educated Mother Just Sent Us Nine Pizzas” to remember the order of the planets in our solar system. I suppose the replacement should be, “My Very Educated Mother Just Sent Us… Nothing.”
I also suspect that scientists’ exclusion of Pluto from the planets was influenced by composer Gustav Holst’s exclusion of Pluto from “The Planets.” While the piece was written 15 years before Pluto’s discovery, the missing song may have led to some scientists subconsciously questioning the validity of Pluto’s planetary status.
- K Lawry
Sarasota, FL
August 25th, 2006 at 7:55 am
Actually by the definition of planet as “having cleared it’s orbit” we automatically have to demote the object we live on as well. After all, there is an object about one fourth its diameter in a similar orbit. Not to mention all the NEOs that have been discovered.
If you would plot Moon’s orbit on the eliptic you will find that its shaped like a rounded dodecagon. The Earth’s orbit around the sun is also a rounded dodecagon although it is closer to an elipse than the Moon’s.
My last complaint about the definition of planet is the small detail that all the other objects smaller than brown dwarfs that are not orbiting the Sun are no longer planets.
August 25th, 2006 at 8:54 am
I’ve created an online petition to the IAU to reinstate Pluto’s status as a planet. Personally, I think the disservice done to Mr. Tombaugh’s memory should be the prime consideration, rather than the nomenclature involved. If further Kuiper Belt objects of Pluto’s size are discovered, I’m fine with them not being classified as planets. As far as Pluto is concerned, however, tradition ought to be what we stick with. After all, nobody in the scientific community is going to have problems understanding the questions posed by objects in the Kuiper belt even if Pluto were to retain its “status”.
If you happen to agree, please visit http://www.petitiononline.com/mod_perl/signed.cgi?iaupluto&1 and sign my petition. Please spread the word!
–Geoff
August 25th, 2006 at 9:31 am
You are right. I have always had a problem with Pluto being called a planet. I considered it a Kuiper Belt object. In any event, I do not think that the issue is settled. Only a fifth of the registered attendees at the General Assembly bothered to stay and vote on this important definition. I think that the new definition, which still has some problems, will come up in the next General Assembly meeting.
Dennis
August 25th, 2006 at 9:45 am
The new definitions are troubling to me, it clearly does not define Earth, Mars or Jupiter as “planets, why? because these planets have not “cleared” thier area of large bodies. I simply state that all three of these planets have asteriods in thier celestial plane. As I sit here I wonder why this simple Idea was not put forth:
Any celestial body must meet the following critiria to be difined as a Planet:
Must meet the gravitational requirements of the original proposal of the IUA commitee.
Must have a stable and predictable orbit around the sun.
Must not have an orbit that centers around another celestial body.
Must have an atomosphere(the make-up of these atmospheres are not important, so long as they are sustained)
I know this is very simplistic however, all eight “traditional planet meet these conditions (even Mercury) as well as Pluto. It also excludes any moon with an atmosphere such as Europa, Io, etc. Many Kuiper Belt objects would not meet these requirements and any new objects would be classified as “dwarf planets” until all requirements are proven.
August 25th, 2006 at 11:17 am
When was the mnemonic changed from pie to pizza, as I have read lately? More than 40 years ago I learned it as “Served Us Nine Pies.”
To those whom are so aghast that Pluto is no longer a planet, and that it should so remain, I suggest they stop messing with tradition, and not use “Pizza” with the mnemonic. Of course, we need a new mnemonic now.
I believe science has to be based on fact, not emotion or tradition. It necessarily has to incorporate new findings, even if it changes long held “facts”.
Once there was a planet named Ceres between Mars and Jupiter. It is still there, but we know it as an asteroid. Ceres’ classification was changed when it was learned that there were other objects in it’s orbit.
I also believe that Tombaugh’s extraordinary discovery is not diminished by the change in classification. Rather than discover the last planet, he discovered the first Kuiper Belt object, or, dwarf planet.
Finally, Pluto does not share Neptune’s orbit, Pluto crosses Neptune’s orbit, as Near Earth obects cross the Earth’s orbit. Planets can only clear objects that share the same orbit. Crossing is not the same as sharing.
August 25th, 2006 at 2:04 pm
“Finally, Pluto does not share Neptune’s orbit, Pluto crosses Neptune’s orbit, as Near Earth obects cross the Earth’s orbit. Planets can only clear objects that share the same orbit. Crossing is not the same as sharing.”
Oh ok, so because Neptune is bigger it’s “Neptune’s” Orbit. Imagine if we all lived on Jupiter? There’d only be 1 planet and 8 Dwarf Planets.
Neptune crosses Pluto’s orbit ergo Neptune isn’t a planet. Sorry guys, you can’t have it both ways.
August 25th, 2006 at 3:55 pm
Turns out several leading astronomers, including Carolyn Shoemaker and David Levy, have circulated a petition to the professional astronomical community (not intended for distribution to the public, I’m afraid, I guess because they figure it will have more impact if it comes from a representative sample of the IAU members who weren’t able to make it to Prague) protesting the decision. They are concerned that the new definition “uses dynamics (location) rather than intrinsic properties to decide if an object is or is not a planet” and that under the new definition “the presence of an Earth orbiting its star between a Jupiter and a Saturn would mean the Earth could not be considered a planet since it could not clear its ‘neighborhood’”, so they agree with many of the points raised here.
It seems we have not heard the last of this. I wonder how long it will be before the mainstream media (who featured this story on many front pages this morning) and the public at large grow tired of this whole debate. As far as I am concerned, far from being a “good teaching opportunity” this ongoing saga will persuade the public at large that astronomy has become increasingly irrelevant. That can only be bad for astronomy as a whole, and consequently for astronomy funding.
When a proposal can be described in a blog such as this as “the most moronic idea ever conceived”, and simultaneously others are “thrilled that the IAU had the courage to demote Pluto” it’s clear this issue is far from settled.
August 25th, 2006 at 4:59 pm
To those who think the conference astronomers were being mean, or were biased against Pluto, or had other hidden motives, please allow me a chance to clarify our modern view of the solar system.
Pluto was once believed to be larger than Mercury, so we called it a planet, despite its unusual orbit. Then we discovered that it was tiny — It had roughly one tenth of Mercury’s mass. But it was still ten times more massive than anything else, so we kept calling it a planet.
But now that picture has changed. We have now discovered hundreds of objects that resemble Pluto in many ways. Pluto became the largest member of an entirely new class of similar objects, with similar orbits. In a nutshell, we’ve discovered a new asteroid belt, with a new kind of asteroid, of which Pluto is the second largest known member. So it has become important to create a new category, which we call Kupier Belt Objects, or KBOs.
Redefining Pluto does nothing to detract from Clyde Tombough’s discovery. If anything, his achievement grows in stature with each new KBO we find. But now, Pluto no longer resembles the other eight planets very well at all. It resembles the KBOs, and it belongs in that category.
As for tradition, Astronomers did exactly the same thing with the discovery of Ceres in 1801. The called it a planet until it became clear that hundreds or thousands of others like it would be discovered, so they created a whole new category. Pluto now follows in that proud tradition.
August 25th, 2006 at 5:45 pm
If Pluto isn’t a planet because it doesn’t clear a path for itself, then Neptune isn’t a planet because Pluto crosses its path. I guess that would make a really, really, big dwarf planet.
These new definitions of planets and dwarf planet is stupid and silly. I liked adding more planets to the family. As far as I am concerned, if it is round and orbits the sun, it is a planet.
August 25th, 2006 at 5:55 pm
Let me clarify that troublesome phrase about planets “clearing their orbits.” What this means is that they have cleared their orbits of anything that rivals them in size. Since the Earth is more than 100,000 times as massive as anything that crosses its path, it has definitely “cleared its orbit. So has Neptune. (That “100,000 times” criterion applies to all eight planets, but not to Pluto. Pluto shares its orbital characteristics with lots of other Plutinos, which together are more massive than Pluto.
This turns out to be a very useful distinction. I think the IAU did the right thing.
August 25th, 2006 at 6:51 pm
Your opinion is obvious. So is that of the IAU. This might as well be the U.N. The first planet that happened to be discovered by someone in the “New World” can be dumped with no problem! Now let’s see how consistant the logic really is-
I believe that the requirement of the definition is that all of the conditions must be met. On that basis, Pluto, Charon, and Xena are all far more round than Saturn. Saturn is substantially out of round. Using the new definition, Saturn should get the boot. If the IAU moves to remove Saturn from the list also, I’ll believe that they’re being consistent. If not, then we can dump something discovered by a common man from Kansas but not something discovered by one of the “ancient classical” civilations!!
August 25th, 2006 at 11:19 pm
To mfinenj: You might want to be a bit more informed before posting your comments. The proposal that defined planets on the basis of “gravitational equilibrium” (essentially meaning round) was rejected. Even with that definition, Saturn would have qualified.
September 13th, 2006 at 8:09 am
@everyone who says neptune doesn’t clear it’s neighborhood because pluto crosses its path:
pluto and neptune DO NOT cross orbits. pluto orbits on a highly inclined plane. granted- there are periods of time when pluto is closer to the sun than neptune - but this doesn’t not maintain that their orbits intersect. in fact, pluto and neptune never even get NEAR to each other.
from: http://en.wikipedia.org/wiki/Pluto
Pluto’s orbit is often described as ‘crossing’ that of Neptune. In fact, Pluto’s nodes (the points at which the orbit crosses the ecliptic) are both situated outside Neptune’s orbit and are separated by a distance of 6.4 AU (that is, over six times the distance of the Earth from the Sun). Furthermore, due to the orbital resonance between them, Pluto executes 2 full cycles while Neptune makes 3; this means that when Neptune reaches the ‘closest’ point on the orbit, Pluto remains far behind and when Pluto in turn reaches that point, Neptune is far (over 50°) ahead. During the following orbit of Pluto, Neptune is half an orbit away. Consequently, Pluto never gets closer than 30 AU to Neptune at this point in its orbit.
The actual closest approach between Neptune and Pluto occurs at the opposite part of the orbit, some 30 years after Pluto’s aphelion (its last aphelion was in 1866) when Neptune catches up with Pluto (i.e. Neptune and Pluto have similar longitudes). The minimum distance was 18.9 AU in June 1896. In other words, Pluto never approaches Neptune much closer than it approaches Saturn.