Tyson and Sykes Duke Out the Great Planet Debate; Flatow Almost Flattened

A debate today between astronomer Neil deGrasse Tyson and planetary scientist Mark Sykes, moderated by NPR’s Ira Flatow, addressed the issue of Pluto’s planetary status. There was lots of arm-waving and finger-pointing, endless interruptions, disagreements on details big and small, and battling one-liners. The two scientists sat at a table with the moderator between them and Flatow was often obscured by Tyson and Sykes getting in each other’s faces in eye-to-eye confrontation. At one point, Flatow was hit by Tyson’s ebullient arm motions. Yes, it was heated. But it was fun, too. It ended up being not so much a debate between the Pluto-huggers and the Pluto-haters as a disagreement over the lexicon of astronomy and planetary science and, primarily, the definition of a planet. Pluto’s planetary status was definitely not decided here, and the debate concluded with an amicable agree-to-disagree concurrence that the scientific process is an ongoing, evolving practice. But it wasn’t without fireworks.

At the start of the Great Planet Debate, Flatow laid down the ground rules, which included no throwing of perishable items, but that was about the only rule that didn’t get disregarded. Tyson, director of the Hayden Planetarium in New York and host of Nova ScienceNow, and who is in the camp that Pluto is not a planet, began his opening statements with “It’s simple. The word ‘planet’ has lost all scientific value.” He went on, saying “planet” doesn’t tell you much and you have to ask all sorts of questions such as is it big or small, rocky or gaseous, in the habitable zone or not, etc. “If you have to ask twenty questions after I say I’ve discovered a planet, the word has lost its utility.” Tyson said “planet” had utility far back in time when there wasn’t much else we knew about, but we know so much more now. “If we’re going rely on one word and put them all in one pot, what are we doing as scientists and educators? The time has come to discard the useless words and invent a whole new system to respect the level of science we have achieved…We’re in desperate need of a new lexicon to accommodate this knowledge,” he said.

Sykes, director of the Planetary Science Institute, and who believes Pluto should be reinstated as a planet, began, “How we categorize things is part of the science process. It is natural for humans to group things together with common characteristics as a tool to better understand and how they work. This applies to biology and astronomy as well.” He continued that we have discovered planets around other stars and continue to find Kuiper Belt objects that will need to be classified, so classifying objects is not a useless task. The IAU (International Astronomical Union) bit the bullet and decided on a classification, but unfortunately, Sykes said, what they came up with was not very useful.

That was the end of decorum, as Tyson interrupted with, “You wanted a definition. They gave you a definition and now you’re complaining about it!”

“Absolutely,” said Sykes, wanting to continue, but Tyson quickly chimed in, “And let me add…”, where Sykes butted in with “You have to let me start before you add!”

Flatow looked around and said, “I think I’m in a danger zone here.”

Thus began the debate.

Mark Sykes
Mark Sykes

Sykes said that any definition has to have a reason, or a purpose. According to the IAU’s definition, planets have to orbit the sun, they have to be round, and they have to have cleared their orbits, among other things. There was immediate confusion with this definition, which Sykes said was a little “goofy.” In order to be a planet, an object has be bigger the farther away it is from the sun, and it ignores the physical characteristics. He believes it’s useful to group things together that are similar and then have subcategories. So, you have planets, under which are terrestrial, gas giants, ice planets, etc.

Tyson said that even for him, the IAU’s definition falls short of taking the total amount of information to task. “If you only want to call round things planets, that puts Pluto in the same class as Jupiter. I happen to like round things. But what other lexicon might be available to group similar things together?”

“That’s why god made subcategories,” said Sykes. “It’s good to have a good general starting point for classifying things.”

Neil de Grasse Tyson
Neil de Grasse Tyson

Tyson humorously pointed out this debate is big only in the US, which he attributed to Disney’s creation of the lovable, dimwitted cartoon bloodhound named Pluto. School kids, grownups, op-ed writers all say Pluto is their favorite planet. “I am certain that the word ‘plutocracy’ is traceable to what Disney has done, so it’s hard to extricate the sentiment we have for the planet from the dog.”

Sykes said the IAU didn’t expand our perspective on planets, but narrow it. “The planet count went down, and what was the justification of that? The proponents have never given a good explanation of what was motivating that perspective.”

Tyson said numbers aren’t important, but words and definitions are, and we definitely need new ones.

Both scientists gave good arguments for their cause, and since I’m decidedly on the fence with this issue, I found myself leaning towards one option or the other, as each one spoke. Sykes, who wants to see Pluto reinstated as a planet, wants to take what we have and make it better, while Tyson, who thinks Pluto is a comet, wants to start over with new and better words and definitions.

It was an entertaining and educational debate with two well-spoken and intelligent scientists who sometimes weren’t very polite, however. (Sykes said, “When were’ not fighting we get along fine.”) The most important thing, they both agreed though, was that scientists are actually talking about this issue in the public eye and people are interested. But more importantly, the public is seeing the scientific process in action. They said this debate shouldn’t be about making things easy, or worrying about “not confusing the public.” Learning science shouldn’t be rote memorization of lists of objects, but a discussion of how objects are similar and different. “My recommendation to school teachers,” said Tyson “is to get the notion of counting things out of your system and comb the solar system for the richness of objects. Ask about different ways to combine the different objects in our solar system and have a discussion about their different properties.”

The debate will be available online, and we’ll post a link to it here when it is.

Sykes ended with his closing argument: “We both have issues with what happened with the IAU, its part of an ongoing presentation, but the important things is that the public gets to see the debate, and it’s not a battle over what list and what numbers you have, but the debate of the issues. That’s more important whether either of us have convinced you of one perspective. Science in this country is too much memorizing lists promulgated by those in authority. This is helping to expose the messy side of science. This debate is good and positive.”

Tyson ended by saying how charmed he is at the level of public interest in this subject. “How many sciences get to have their issues debated in the op-ed pages and comics?” He said he was happy with the word “planet” until all the data started pouring in from our explorations. “There should be a way to celebrate a new way to think about things. There ought to be a way to capture that” he said.

Obviously, this is not the last word on the subject from either scientist, or either side of the debate.

But that’s a good thing.

For more info on the Great Planet Debate.

24 Replies to “Tyson and Sykes Duke Out the Great Planet Debate; Flatow Almost Flattened”

  1. Pluto is not a comet. It is much bigger than any comet and far more rocky. It may have an eccentric orbit, but the fact thta it doesn’t approach the sun or come anywhere near the inner solar system is a crucial distinction. Any object brought close enough to its parent star will start out-gasing and develop a tail like a comet, so the argument that if you put Pluto in Mercury’s orbit it will grow a tail is nothing but a straw man.

  2. Sykes, director of the Planetary Science Institute, and who believes Pluto should be reinstated as a planet

    I may have the wrong end of the stick here, but I don’t think that’s quite fair to Sykes. He believes something that would indeed lead to the ‘reinstatement’ of Pluto, but that description makes it sound like it’s getting Pluto back that he cares about, rather than the wider definitional questions.

  3. I watched the debate live, and it was nothing but entertaining and enlightening! I tended to agree with Tyson the most, thinking that scientists need to go about thinking of the solar system (and other solar systems) in a whole new way. Thinking in terms you already understand is simply limiting, while leaving room for expansion is accommodating new reason and growth.

    Great debate though, can’t wait until it’s available to watch again!

  4. I guess all the debates on earth, no matter how expert they are, are going to solve this problem.
    When is a planet not a planet?
    When is a rock a stone?
    When is a tree a shrub?
    When is a horse a pony?
    Or is a horse a high pony? People on high horses should be able to answer that one.
    When is a mountain a hill?
    A rose by any other name, blah blah blah.

    But I can just imagine the jovian folk on Jupiter having to decide whether our four terrestrial rocks are planets or not. It could be pointed out that one of them is a greenish, brownish, bluish wet stone.

    Surprising really. Perspective must have something to do with it, and it’s not Pluto’s fault after all. Ever since it was discovered and called a planet, everybody has been happy about it, even Disney. Who suddenly decided that the rules had to be changed and the cat put among the pigeons?

    George Orwell was right; there’s no doubt about

    ‘In the land of mules there are no rules’, wrote Ogden Nash, and he seems to be right as well.
    (Hmmm, mule, a cross between a horse and a donkey. When is a??????/???/?…..I rest my case, no sorry, – bag…

    David ( description – human, male, grey hair, blue eyes, two arms, two legs, owns a vacuum cleaner but hasn’t cleaned the floors for a week. Reclassify to humanid or humanoid – forthwith).

  5. I teach high school physics, for years I’ve been giving my students the chance to categorize the celestial objects by their known characteristics. the students themselves have been claiming that pluto looks more like a comet (that just doesn’t approach the sun) than a planet. If only it didn’t have those 3 pesky moons, the biggest hang up for my students.

  6. This is all utterly ridiculous. Pick a definition via a recognised body, and stick to it.

    How about, at a time when we are having to battle pseudo-science, anti-science and magical thinking from as far up as the leadership itself, we stop undermining science with public displays of childish in-fighting?

  7. If Pluto hadn’t been found by an American, these arguments would never be happening. Move on guys, the IAC have spoken.

  8. I’m not surprised by the difficulties. Analogously in biology there are at least 26 species concept, and no one can cover all biological populations. AFAIU biologists doesn’t care about species definitions, they care about speciation.

    Species are recognized by the process (so as it’s evolution, by homologies and differences), not by physical characteristics nor by therefore useless species concepts.

    Hmm. The analogous process to speciation by “descent with modification” would be coalescence out of the planetary disk by “aggregation with collisions”, right? So you can recognize different populations of objects, and analogously astronomers are looking for how to define a “species” of planets, not a species concept. Oops, that analogy would make inner system asteroids, planets and most moons much the same “species”.

  9. At least there is common ground. The fact the definition of a planet needs to be re-written.
    I have this odd feeling the IAU is waiting for us to get more data on Pluto before they change any definitions. Which to me is a problem in itself; since you are then creating a definition to meet your findings; one way or the other.

    Realistically, I believe “Planet” is a pretty general term, and the IAU made it more specific than necessary. The term “dwarf planet” should be on equal footing with “gas giant”, “Ice giant” etc. Allow “planet” to be general, and then add your specifics and become more detailed. Right now, this distinction doesn’t officially exist.

    When you want to use Pluto’s somewhat excentric orbit as a failing requirement; remember some rather large planets outside the solar system have been found to have excentric orbits as well.

    I could go either way on whether or not Pluto is a “planet”. After all, we really don’t know a lot about this body. Nearly everything about it is assumed. However, there is no doubt this definition needs to be re-written. Not just as a definition, but a classification, where there are sub-classes as well. Which is a no brainer, since we don’t have any 2 planets which are remotely the same.

    Most of all, we need to remember there are planets in other systems, and defintion(s) will need to fit them as well. Finally, ensure they are clear and understandable. A body which must have its orbit cleared in order to be a planet is nonsense. In reality, none of them have accomplished this, and our system is constantly moving through the cosmos, where anything could show up out of nowhere.

  10. I like Tyson and the PR that he’s giving to astronomy. But I wish he would show up to other events and use his increasing celebrity status to promote space and science. It’s rather suspect that he shows up to something as headline-grabbing as the Pluto debate. I haven’t seen the same attention given to other events, like perchlorate, ISS, moon research, etc etc etc.

  11. The answer, i believe, is in widening the defenition of planet and then use sub-classes to further distinguish them.

    I realy don’t understand why there is an issue arround this at all…

    We all are confortable with a vague notion of planet as being a big round celestial object going arround a sun.

    There is nothing wrong with fine tuning this notion, like “a planet must have it’s round shape due to is’t own gravitational forces”, or some other features, but we shounldn’t go too far, for we may loose a “ground” or “base” definition class.

    Let’s look at an example from biology: The term “cell”, while not very specific, as a huge scientific value beacause when someone uses it, you will know what is being discussed. If taken in a context it doesn’t even need further specification. Think about this sentence uttered between to biologists: “The cell as grown 15%” – I would say that’s a very realistic piece of conversation… And that the term “cell” is meaningful and very useful.

    We should consider the term planet in a similar way, so that a realistic sentence between to astronomers could be something like “The planet is 2.5 AU distant from it’s sun.”…

    Another thing about the current definition of planet: As anybody checked if the planets that have been discovered around other stars have cleared their orbital paths? No? … So are they planets???


  12. I also don’t understand the aversion to sub-categories. I think the main problem is that we’ve had 9 planets now for 78 years, and everyone involved in this discussion does not remember a time when there were any more or any less planets in the solar system. What confuses me is why the IAU is so comfortable in letting the number go DOWN instead of UP.

    I think the logical thing to do is just says there are 11 planets for now and sub-categorize them (4 terrestrial, 2 giants, 2 ice giants, and 3 dwarfs). As for exoplanets, we have a pretty good idea of what separates stars and planets, and since we’re not even getting close to the mass of Pluto in those surveys, they should just be called planets of suspected type “blah.” I mean star classifications are so fluid that I just don’t see a problem with this.

  13. James, the number is 12, after Makemake. We have 4 dwarfs now.

    I’m starting to believe that only after New Horizons sends photos of Pluto and people realize it will look pretty much like a creamish version of Mars, and Dawn sends photos of Ceres and people realize it’s visually pretty similar to Mercury, will the scales go overwhemlimgly to the side of reason.

    One might imagine that simple facts like the exclusion of extrasolar planets from the definition (since we haven’t got the slightest clue if their neighborhoods are clean or not) would make people think that perhaps that’s not the right way to go if you don’t shortsight yourself to the solar system alone, but apparently not. They’ll have to see how planetary dwarf planets actually look.

    And… come on. Calling Pluto (or Eris, or Makemake, or whatever) a comet is just plain dumb. Any planetary or asteroidal body that gets close enough to its star starts to exhibit comet-like characteristics, as clearly demonstrated by “Osiris”, an extrasolar planet with two thirds the mass of Jupiter which is visibly evaporating. Will Tyson also try to make the case that Osiris is in fact a comet? Puh-lease.

    And may I repeat my mantra? “This ain’t about Pluto!”

  14. When is a planet not a planet? I feel that Bode’s Law should be considered a factor to resolving this problem.

    Seven out of eight planets comply with Bode’s Law, which is an exponential function of planetary sequence which only Neptune and Pluto do not quite fit into. However, both Neptune and Pluto are very great distances from the sun, which may account for their wayward behaviour. [theory] Neptune though, is undoubtedly a planet. Does anyone argue with that?

    If we give Neptune the benefit of that doubt, then it must surely be the size and elliptical orbit of Pluto that condemns it to an inferior classification. But why both Neptune and Pluto are as they are, must be relegated to theory, because we simply do not know, therefore demotion becomes a decision based on ignorance of essential facts. Agree?

    If we can agree that Neptune more or less occupies a Bode or similar predicted zone in the scheme of things, then what of Pluto?

    As it is ‘orbital period’ that establishes the zones in the first place, we could suggest that although Pluto’s orbit is not anywhere near concentric, it does exist in a zone of space mostly beyond Neptune’s. That some mishap has possibly occurred to throw it off balance with the magnetic plane common to the rest, should that go against its being a planet? I think not. And I’m quite sure that all would agree that if earth were suddenly orbitally tilted, and the others remain as they are, all hell would break loose if science suggested that our earthly classification would have to be demoted. Agree?

    If Pluto is the largest object within a zone beyond Neptune, it is the major collector of particles in that zone, and therefore will grow at the expense of any other smaller object, just as all the other planets have. Agree?

    So can we please stop this ridiculous debate? Most of us will call Pluto a planet regardless, and hopefully the rest can just drop it and do something more useful as changing the textbooks on unfounded theoretical whim, which almost equates with, ‘is it a stone or a rock?’ or ‘Is it a mountain or a hill?, has to be crazy. Agree?

  15. There are several other Kuiper Belt objects that share the eccentricity of Pluto’s resonance ratio with Neptune. If I recall correctly, the number exceeds 30. Pluto has failed to clean them out of its orbit. No matter.

    Nomenclature is something that has not been quite as defined as the biological sciences have. Astronomers assign the word “planetary nebula” to something that has no connection to planets at all. It is possible that the term “planet” will be redefined to where any body that circumvents the sun in a predicted amount of time is a planet. That would include all of the gases, dust, asteroids, moons and even all of the space junk we have left . So they need to draw the line somewhere or accept that there are billions of planets.

    Horizon should settle the issue and I see no reason why we cannot wait. What is the rush? Pluto doesn’t care so why should we care? Wasn’t the sun declassified as a planet after being one for so many years before Copernicus? After the fate that Bruno faced, would any here claim that Tyson will be burned at the stake by his opponents?

  16. Planet is a series of letters (or sounds) that only has meaning because we imbue it with meaning. In choosing what meaning this word should represent, it is not really important what the precise contours of that meaning are, only that they be well specified by some competent authority that we can defer to. IAU is such an authority, and they’ve provided a serviceable definition of planet that allows us to employ that word without ambiguity. It makes no sense to me why we shouldn’t merely accept them on their own authority. If they had defined it differently, that would have also been acceptable. Now that it is defined, anyone working against that definition is just diluting the meaning of the word. Perhaps it’s too “authoritarian” of me to say this, but I think the IAU definition is the true definition by virtue of the fact that they say so, and anyone who uses the word planet in a way inconsistent with that definition is wrong per se.

  17. Sorry, but I have to object in the strongest possible terms to this concept that “the IAU has spoken, and they are the authority.” Just accepting anything they say because they say it is not science; it’s religion. In the words of Dr. Mark Sykes, that’s elevating the IAU to “Holy Mother Church” with a priesthood that makes decisions and does so in a closed and very byzantine fashion. The IAU has not even provided a “serviceable” planet definition–they have provided vague linguistic nonsense by saying a dwarf planet is not a planet and by establishing the nebulous concept of requiring an object to “clear its neighborhood.” And they did this in a process that violated their own bylaws by introducing a new resolution on the last day against the recommendation of their own committee, and rushing that resolution through with only four percent of the IAU voting. No absentee or electronic voting was allowed.

    Accepting that a person or group is an “authority” because that person or group says so is a dangerous precedent. Science is supposed to be about critical thinking and seeking knowledge, not imposition by decree. The IAU does not have a blank check to do whatever it chooses, make a mess of an issue and then claim everyone has to follow its dictates because it is “the authority.” Through its actions, the IAU has shown itself inept in both the process and outcome of this debate and can therefore be said to have abdicated whatever claim to authority it has in this matter.

    Additionally, consider the fact that most planetary scientists are not members of the IAU. Planetary science is branching off into its own field. Shouldn’t the experts who actually study planets be the ones who define what they are?

  18. Good work Laurel Kornfeld.,

    I can imagine someone standing up in one of these priesthoods saying:- A planet has to be a body with beautiful deep blue oceans, green fields, lush forest, wonderful animals and birds and fish, an atmosphere with clean clear blue skies; Then someone interjects and says, ‘but there’s only one body meets that criteria’.

    The point is that there are no two planets alike, so, yes, Pluto is small, and so is Mercury. Jupiter is big – so what…..? Who made the rules in the first place anyway? As I’ve said before, ‘when is a rock a stone or when is a mountain a hill?’ I’m going to call Pluto a planet, one of the nine, and I’m sure a lot of other people will as well.


  19. Many of the 300 exoplanets we have discovered have very eccentric and inclined orbits. Should that disqualify them from being considered planets, and if so, why? The dwarf planet category could be useful IF we get rid of the linguistic nonsense that states dwarf planets are not planets at all. Then it would be very useful in accurately describing a subcategory of objects that may not dominate their orbits but still have the same geophysical processes as the larger planets.

  20. There are two problems regarding Pluto’s position as a planet. One;- its orbit is so eccentric that it spends several years inside the orbit of Neptune. Two;- its orbit is inclined to the plane of the ecliptic at an angle of 17 degrees compared with single figures for the rest of the solar system. The dwarf status allows educators to teach how our complex solar system works.

  21. Well, although it’s true that many of the exoplanets discovered so far have quite eccentric orbits (and it’s useful to stress out that they are *all* larger than the Earth), I don’t think we have any data regarding inclination. Remember that it’s not our ecliptic that matters there, but the local orbital plane. And, given what we know about the mechanism of planetary formation and the fact that the protoplanetary disks are *disks*, it’s not likely that the variety in inclination will be comparable to the variety in eccentricity we are already seing.

    Still, it’s perfectly possible that we’ll end up finding large planets in high-inclination orbits. Which in my vew means that is quite inadecuate as a limiting factor for what a planet is.

    It’s time people abandon once and for all the preconception that planets have to be in low-eccentricity orbits, all in the same plane, and spaced regularly. Bode’s law is dead, as dead as Kepler’s music of the spheres. The Universe is a messy place and does not obey our desire for order. Planets come in all sorts of configurations and sizes, and it’s about time we learn to deal with that fact.

  22. About this planets definition – thing … I very much appriciate so many comments on this matter. Not in, or with the purpose, of defining our ”planets solar system” – but in order to define ‘what is what’ – out there.

    I appriciate Sykes comment saying that ”any definition has to have a reason, or a purpose”.

    I wouldn’t mind if our solar system only contains 8 planets, allthough my emotions bases on my time of historical understanding react against this. I would submit to an eventually clear scientific explanation and purpose of another comprehension of – what and how our solar planet system is, and what belongs to this. But that’s onfurtunately not the case with the IAU’s definition.

    I believe there are three components in our discussion of the planet definition:

    1) The scientific … pure knowledge as we by now agree on, to be proved about matters and shapes.

    2) The psycological … We want to define things for our own sake – the univers really don’t care. The universe in itself doesn’t need to be defined – it is what it is – rather chaotic … doing and finding its own possible ways and systems without any purpose defined be humans. .

    3) The philosofical … Deals with not a single observation or some restrictive definitions of things, but comprehend a deeper understanding as to the why’s and how’s things relate and reacts to itself and the surroundings. Allthough philosofical viewpoints are depending on scientifis ‘faktums’ it goes byon the selective mediate faktums, and trying to define things in longer proposeable terms.

    The different viewpoints are more or less inclined to ‘either or’ to these components.

    Let me guess on what’s going on psycological in the IAU’s way of thinking.
    As I beleive, like the rest of us, they have feelt a certain amount of content in the ‘Nine planet solar system’. Now, with the latest discoveries – they feel rather unsetled about this ‘nine planet solar system’ … understandable – and what a disorder – our general understanding of our solar system rattles. Somehow Pluto have allways seems to be a bit different from the other planets, now believed to be a rocky icy planets – possibly a bit similar to asteroids. And now, so many more off these – what a mess – a disorder in our comprehention og what is our ‘solar planets system’?. They beleive to have only two choices. Maintaining our present view of the ‘nine planets solar system’ or an ever changing definition of that … or, withholding the present, due to facts contravicting this.
    Between these two unsettled evils – they seems to prefer to give rid of Pluto, in order to get a defininately and long lasting definition of what our solar planets system is. No more disorder.

    If this is the case? It’s understandable from a psycological point of view. But let us remember – the univers really don’t care, (and I don’t either). Why not settle on a more comprehensive and futuristic point of understanding? There are other solar systems, and much more to be defined – why not find a definition which is more basic and universal – including what other solar systems definitions of stars/solar planet systems are – and to be defined – and make our own solar systems definiton in accordance with this more universal way of thinking/understanding and definition of matters?

    As mentioned before, I beleive the IAU untill now underestimate an importent observation of matters … the ability of the cosmis matters to create spherical shapes – the very first indication of nature to create order in chaos – in a certain sense the essentials for the evolution of organic life.
    In astronomical terms physical astronomi explain the achiments of this sphrical shape as due to gravitational forces. I believe this is correct, but I also realise that untill now we don’t really know what gravity is. We know quite exactly how it behave, but actually don’t know what create gravitation.
    I have my own theories, which I can not yet prove. But no matter what is the explanation, I beleive we all should have a deep respect and gratitude that spherical shapes can envolve in this universe, and agree to call this phenomens for planets – then we on a simple term know – what we a talking about. Subsequently we can make all kinds of subclasifications, as to the different kinds of planets. Why not be a bit humble – as to all what we don’t know?

    Have a nice sol.


  23. When is a dwarf planet not a planet? Why, when it’s a DWARF planet, of course. When is a dwarf planet a planet? Why, when it’s a dwarf PLANET, of course. Go figure! In any case, good terminology should be a prerequisite for good definitions.

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