Talk:IAU definition of planet

Requested move

 * The following discussion is archived. Please do not modify it. Subsequent comments should be made in a new section.

2006 definition of planet to 2006 and current definition of planet. The present title seems to suggest that there's a different definition of "planet" for each year. YouthoNation (talk) 22:04, 29 September 2008 (UTC)


 * Oppose. No need to complicate the title in this way. And actually, that's what it seemed like at the time... the definition in practice changed every year, much to the discomfort of primary school teachers. A better lead would be good, to make it clear that this is the current IAU party line and give a short (one-sentence?) summary of the background. Whether there's still enough opposition (anyone seen Save the Planet Pluto badge recently?) to warrant a mention in the lead I'm not sure, inclined to think there may be. Andrewa (talk) 00:07, 30 September 2008 (UTC)


 * Oppose, current definition of planet can redirect here, but this article only defines planet within the confines of the Solar System, there are other definitions in use for things that lie outside the Solar System. Besides, when a flag is changed, people refer to it by the first year in use. 70.55.203.112 (talk) 04:36, 30 September 2008 (UTC)
 * Oppose. If the article is to be moved, it should be moved to IAU definition of planet, which could then incorporate the IAU's 2003 definition and any potential 2009 definition.  Serendi pod ous  07:22, 30 September 2008 (UTC)
 * Oppose. It is better to move it to IAU definition of planet. Ruslik (talk) 10:04, 30 September 2008 (UTC)
 * Oppose. The proposed title is clumsy and seems to indicate that there are two different things. IAU definition of planet would be better as it indicates that this is the IAU's definition not some kind of agreement by people who write dictionaries. Icalanise (talk) 11:00, 30 September 2008 (UTC)
 * Oppose this move, but support a move to IAU definition of planet. Miami33139 (talk) 20:28, 30 September 2008 (UTC)
 * Oppose move to "2006 and current..." but support move to IAU definition of planet. —Josiah Rowe (talk • contribs) 00:51, 1 October 2008 (UTC)
 * Oppose move to "2006 and current..." but support move to IAU definition of planet (possibly IAU definition of planet in the Solar System, since it does not include extrasolar planets). --Cyclopia (talk) 09:31, 1 October 2008 (UTC)
 * We could incorporate the IAU's 2003 definition for extrasolar planets, which would expand the definition beyond the Solar System.  Serendi pod ous  10:51, 2 October 2008 (UTC)
 * The above discussion is preserved as an archive. Please do not modify it. Subsequent comments should be made in a new section.

A slight criticism of "Criticism"
The first paragraph of section Criticism subsection Substance doesn't end well:
 * ...(snip Stern's criticism)... His own earlier work on neighbourhood clearing, however, supported the distinction between the largest eight planets and the rest of the solar system. There is a substantial difference in the extent to which the neighbourhood has been cleared between Pluto and the eight planets. Also, Pluto's position is due to the gravitational effects of Neptune as they are in orbital resonance.

The citation num cites Stern's own work, but not any conclusion that his own work supports the "clearing the neighborhood" notion. An external citation/conclusion that his own work supports the idea of "clearing the neighborhood" is to be preferred, otherwise Wikipedia has an independent opinion, which is disallowed. The rebuttals are OK, but the text is written like WP have an opinion, so the text needs to be formulated: "Dr. Smith of University of Disponsin says to this that" ... Said: Rursus (☻) 08:32, 25 November 2008 (UTC)
 * Well, I agree. I will probably change this in the next several days. Ruslik (talk) 09:01, 25 November 2008 (UTC)
 * No one has, yet.96.225.212.89 (talk) 06:45, 28 January 2009 (UTC)
 * And ... not yet (09:05, 12 March 2009 (UTC)). I'll take a look too see if the fact details are elsewere on WP. ... said: Rursus (bork²) 09:05, 12 March 2009 (UTC)
 * I (consciously) added a weasel wording in order to clarify that the sentences in question is an uncited rebuttal. Otherwise the occurrence of the two last sentences in the para occurs inexplicably, unexpectedly and illogically to confuse. The solution is bad but provisional in order to find a direct rebuttal to Stern's arguments. If we cannot find citations, the two last sentences are WP:original research and therefore Evil, detestable and generally inferior. On timeout, say 1 month (?), they should be removed. ... said: Rursus (bork²) 09:21, 12 March 2009 (UTC)
 * Dude, take a zanax. I swapped over some sourced info from Definition of planet, OK? Seriously. People are taking this whole thing way too personally.  Serendi pod ous  09:29, 12 March 2009 (UTC)
 * Or ideologically. Now I'm trying to apply the WP ideology, make a defence for the Pro-IAU position (not mine actually!) by finding some reasonable source for the rebuttal against Sterns (and so mine) position. My real stand-point is for increasing the quality of Wikipedia, so in this I have temporarily changed my position. ... said: Rursus (bork²) 15:29, 12 March 2009 (UTC)


 * Hupp! You removed it? But I found this source that possibly can constitute a rebuttal. ... said: Rursus (bork²) 15:36, 12 March 2009 (UTC)


 * Doesn't matter, Browns rebuttal might suffice. Everything's fine and well! ... said: Rursus (bork²) 16:12, 12 March 2009 (UTC)

Hello, wouldn't the moon be considered a planet in this definition of what a planet is? It is a celestial body that orbits the sun, it has enough gravity to keep a round shape, and no other celestial bodies are in it's orbit. — Preceding unsigned comment added by 50.4.93.149 (talk) 03:15, 3 May 2014 (UTC)

If Wikipedia is all NPOV supposedly...
If there's reasonable dissention as to the appropriateness of this or whether this decision should be honoured, why is it considered vandalism to, for instance, state (in some more eloquent way but something like) on the Pluto page, "Pluto is the first trans-Neptunian object classified as a dwarf planet, or the ninth planet in the solar system, depending on who you ask"

It would seem that if Wikipedia is supposedly intended to be NPOV, then with numerous astronomers in contention on this subject, Wikipedia should not automatically support this decision and mark pluto as a dwarf planet by default and then mention the controversy buried away lower. Weaselly tactics like this support one side of a controversy that has strong proponents on both sides, and Wikipedia is clearly lending support to the IAU decision... and that's an opinion. That's a point of view that is anything but neutral.

If Wikipedia is going to support one side or another of this, it needs to start admitting it straight up, There should be clear statements that Wikipedia supports the IAU's decision and does not support the opinions of dissenting astronomers, and that at least in this instance, the NPOV policy has been suspended.

Otherwise, it needs to stop acting like that's the way things are. 96.225.212.89 (talk) 06:45, 28 January 2009 (UTC)


 * While I have no particular opinion about the proper way to do this, a neutral presentation of a subject will appropriately weight the alternative viewpoints. Relegation to a "lower" section may very well be appropriate if the most reliable and verifiable sources agree on a set of facts and follow similar interpretations of said facts to similar conclusions. The very fact that the IAU ruled in favor of this definition by a majority vote means that there will have to be some marginalization of the alternatives, and this article is itself devoted to explaining that majority opinion. Equal time to the minority is not required by NPOV. In fact, it's explicitly argued against at WP:WEIGHT.


 * WP might very well partake in a bad and philosophically destructive development in the outside thinking by following the current. The "neutrality" and "NPOV" is maintained technically, not by a political deliberation, so in effect this "neutral" position might in real reality be a not-so neutral position. Now, we're following citable criteria for classifying "planet", "dwarf planet" and "SSSB", if for example there occurs pretty established alternative classification schemes, say supported by 10% of professional astronomers, this would be added as an alternative classification in the infoboxes of the relevant space thingies. We're kind of limited by the mechanics of the WP process, specifically citeability and due weight acc2 academical criteria, so such a citeable alternative classification scheme is on my personal wish list. Maybe we should ask S. Alan Stern to present a such? ... said: Rursus (bork²) 09:40, 12 March 2009 (UTC)
 * Alan Stern would happily offer one, but it would just be his idea, not one backed by any established authority.  Serendi pod ous  13:17, 12 March 2009 (UTC)


 * Of course, but he certainly has enought authority to be able to present a definition that in time gets some more vindicators. Just a thought... ... said: Rursus (bork²) 15:22, 12 March 2009 (UTC)

Revision history as sections
While keeping an article that updates as the IAU revises the definition is sound in principle, many articles will link to the 2006 revision. A section that discusses the 2006 revision and which will not change names seems like a good idea. Numerous articles link to 2006 definition of a planet. While some articles are discussing the definition, many are discussing the revision. It might be good to have a more specific target for the redirect. As Wikipedians, we can recognized the value of revision histories. It might be good to keep a History of the definitions section and subsections for each formal revision. At the worst, it is a curiosity – a record of the process of a scientific body. Novangelis (talk) 16:19, 12 January 2009 (UTC)


 * Agreed. The article reads like a history of the debate.  The section on the current definitions could easily stand on its own as a much shorter, much clearer article.  Papercrab (talk) 05:22, 4 February 2009 (UTC)

Herschel and asteroids
The statement "Before the discoveries of the early 21st century, astronomers had no real need for a formal definition for planets" is not quite true. As noted in Definition of planet, Ceres and others were originally called planets before being reclassified as asteroids as suggested by Herschel. Some rewording needed here? JQ (talk) 07:04, 4 March 2009 (UTC)
 * Should we just say "Before the discoveries of the early 21st century, astronomers did not have a formal definition for the term planet" instead? --Ckatz chat spy  07:21, 4 March 2009 (UTC)

Philosophical/lingustic criticism
Seems like the philosophical/lingustic criticism against the definition ― defining "dwarf"-X as being not an X and "dwarf" irrespective of size ― actually exists independently of Wikipedia:Here! in the middle of the public's questions. But not easily sourceable. The awareness of confusions between descriptor "dwarf+planet" and definition "dwarfplanet" seems to be easily swept away, while one of the combatants require "a whole new language"! Odd! ... said: Rursus (bork²) 15:12, 12 March 2009 (UTC)


 * Not unusual:


 * a Bombay duck isn't a duck
 * white ants aren't ants
 * &, as Voltaire famously remarked, the Holy Roman Empire was neither holy, nor Roman, nor an Empire


 * Language is like that. Peter jackson (talk) 17:40, 7 May 2009 (UTC)


 * No, language is not just like that, see linguistics. This is about terms and defining them logically. I won't be surprised the day when astronomers find an extrasolar substar huh larger than Earth that hasn't "cleared" its neighborhood because of too young. Defining terms is more like not taxing the brains of the speakers with unnecessary garbage, see IUPAC. ... said: Rursus ( m bork³ ) 17:11, 8 December 2009 (UTC)


 * No, language is like that. Defining things logically makes a lot of sense, sure, but as it happens logic very often is overlooked. J IM ptalk·cont 22:36, 10 December 2009 (UTC)


 * How can logic be overlooked, when logic is the founding of thought? Hommedeterre1 (talk) 13:35, 27 June 2011 (UTC)

Earth not a planet?
The IAU specifying in 2006 that a spacial body must declutter its orbit to be classed as a planet raises issues in my opinion about whether or not Earth, which is surrounded by artificial space junk, can be called a planet when it is surrounded by manmade debris. Hommedeterre1 (talk) 13:31, 27 June 2011 (UTC)
 * Wikipedia talk pages are not places to express opinions about issues raised by articles, only issues with the articles themselves.  Serendi pod ous  18:07, 27 June 2011 (UTC)

Well then what is that place? Anon — Preceding unsigned comment added by 74.4.202.103 (talk) 01:33, 25 July 2011 (UTC)

This issue is still extant (with the IAU, not the Wikipedia itself). For clarity, there really does need to be an addition to the IAU planet definion to allow for moons. Otherwise, according to the IAU's own definition, the sun only has two known planets (Mercury and Venus; and I would even question Mercury, but that's another story), since all the other planet-sized objects ALL have natural objects following them around IN THEIR ORBITAL SPACE. It should also be modified to include an upper size limit (this will have to wait until they decide what constitutes a brown dwarf, of course), and be generalized to include planets orbiting other stars. The IAU definition, as it stands, was decided in a hugely emotional atmosphere, and holding to it unmodified does not serve knowledge, but exhibits unbridled hubris and nothing more than that. It was poorly decided, and it desperately needs to be amended. — Preceding unsigned comment added by 68.165.69.198 (talk) 18:47, 6 May 2013 (UTC)
 * You misunderstand the 'clearing the neighborhood' criterion. It doesn't require that a planet have nothing else anywhere near it, it requires that a large majority of the mass near it is dominated by the planet's gravity. Examples of an object being dominated by a planet's gravity include being trapped in orbit around the planet, or being forced into a resonant orbit like many Kuiper belt objects with Neptune, or being confined to small stable areas like the Trojan asteroids at Jupiter's Lagrangian points. After you set aside all cases such as those, then you consider all the uncontrolled objects crossing through a planet's orbital space and add up their mass. All the near-Earth asteroids added up are much less massive than the Earth itself. --Patteroast (talk) 04:01, 7 May 2013 (UTC)

Definition of moon?
Is there a comparable definition of what a "moon" is? Given the large and growing population of "moons" in the Solar System, I think it might be useful. I was thinking of something like in the following table:

The Stern-Levison parameter for a moon would be calculated assuming the moon orbited the star in the orbit of its primary. The definition of "quasiplanet" might be useful for exoplanets, since a habitable object could be a planet orbiting the star or a quasiplanet orbiting a gas giant orbiting the star.

Any idea whether anybody in the astronomical community proposed something like this? — Preceding unsigned comment added by Ambi Valent (talk • contribs) 22:18, 3 October 2012 (UTC)

Pluto is a planet, says the IAU
I found the IAU question and answers form very confusing. Seen here: http://www.iau.org/public_press/news/release/iau0601/q_answers/ There is a questions: Is Pluto a planet? They answer clearly 'Yes'. They then said they are merely sub classifying pluto, as in this instance a 'dwarf planet'. With this in mind, nothing has really changed. So when you talk about the planets in the solar system. Pluto is a planet and if you're an enthusiast you might say it's not a classical planet. [The last sentences of this discussion are wrong: there was a specific vote at the 2006 IAU General Assembly whether to define "classical planet" so as to have terms in parallel with "dwarf planet" but the proposal was voted down. So "dwarf planets" are not planets, according to the IAU. Exoplanets haven't been dealt with yet; they are also not technically "planets" by the IAU definition of "planet."] Clever wording by the IAU, but cultural definitions, history and context should have more impact on what people perceive and call things. A great example is how everyone calls Big Ben, in London, 'Big Ben'. Yet if you're an enthusiastic historian or local enthusiast you would inform others that it's the bell that's called Big Ben, not the Elizabeth Tower. However, if an International Clocktower Union of 8000 members announced from this day hence forth it will now be known as Elizabeth Tower on all postcards, well you get the drift, it wouldn't happen. I think it's another typical case of wikipedia allowing the enthusiasts dictatorial rights over the content that has cultural significance. You can't change history, Pluto is a planet and the IAU agree, where is the debate? — Preceding unsigned comment added by 31.55.94.12 (talk) 23:46, 5 June 2013 (UTC)
 * The IAU did say that people did not have to adhere to their view on a Planet.Magnum Serpentine (talk) 03:54, 4 July 2013 (UTC)
 * The Q&A that you link to is _not_ associated with the IAU resolution that created the "Dwarf Planets". Instead, it is associated with an earlier draft proposal, in which Pluto, Charon and Eris were all classified as Planets.  (See the section "Draft proposal" in this wikipedia article.)  Bluap (talk) 10:16, 4 July 2013 (UTC)

Incorrect numbers in Criticism/Process
The Criticism/process section states that only 424 members voted on the planet definition, which is resolution 5. But the IAU vote results show that the 424 was for resolution 6; the total vote for resolution 5 was not counted. The earlier "Plenary session debate" section indicates that over a thousand were in attendance for the votes. Why are we propagating a journalist's mistake? Tbayboy (talk) 21:19, 4 January 2014 (UTC)
 * That IAU source actually gives 411 voters for resolution 6A (adding up "237 votes in favour, 157 against and 17 abstentions"), and less than 400 for resolution 6B. Since it doesn't give the total votes for resolutions 1-5, the 424 claim is not contradicted by it: 424-91=333 votes against would be "many more" than 91 votes in favour; and there may well have been 13 people who left between 5 and 6A. The "over a thousand who attended the session" claim in the article is unreferenced and not supported by your IAU source, AFAICS. (And even if it was, it doesn't contradict the BBC's claim either, since there's no knowing whether the remaining ~600 people left before or after resolution 5.) Admittedly it is strange that the BBC gives an exact number for the vote while the IAU claims it wasn't counted.  --Roentgenium111 (talk) 18:24, 27 June 2014 (UTC)
 * I don't know where the "thousand" claim comes from, so I agree with the CN. The vote wasn't counted, so "424 votes cast" is wrong -- the number is not known. I haven't been able to find any original source for it, just apparent repeaters (i.e., none of the sources that state it indicate where the number comes from, who did the counting or what they counted). Note that the section "Plenary Session Debate" claims 30 abstainers (and 424 total) for 6A, not the IAU-ref'd number, so more cleaning is needed there.
 * Speaking extra-wikily, the IAU is correct about it not being counted: there was a video of the vote, which I saw, and they said there was no need to count. I doubt if it's still around, but you can look. There might also be a transcript lying around if you want to search. But I think the IAU ref is pretty solid. I'll do a quick check of Brown's Pluto book, since he describes the event there, as he watched it live. Tbayboy (talk) 19:30, 27 June 2014 (UTC)
 * While the vote wasn't counted officially by the IAU, it's certainly possible that one of the participants (or any present observer, e.g. a BBC journalist, if there was one) did an "unofficial" count, since it was presumably an open vote. (Or one could easily count the votes from the video you mention, in case it showed the whole plenum during the vote.) The 30 abstainers for 6A are indeed also contradicted by the IAU source - if there's no other source for it, maybe someone "calculated" it from the "misplaced" 424 figure and the other values?
 * FWIW, Margot's essay, also quoted elsewhere in the article, mentions "over 400 present" for the vote. --Roentgenium111 (talk) 20:04, 27 June 2014 (UTC)
 * Brown, in "How I Killed Pluto" book (pg 224), says the "yes" vote was so obvious that no count was made, and that was before any opportunity to vote "no" or "abstain". Also note that the BBC article doesn't say how many voted, only that 424 astronomers were there. There was no vote count, but somebody might well have kept track of the number of voting paddles distributed for the session, or something like that. Furthermore, from the book, before the 5B vote, Jocelyn Bell gave a clarification and referred to the non-astronomers present, so the >1000 might be including them. Good faith and all that.
 * As an aside, 424 is consistent with the 411 from the IAU 6A count, since abstentions were explicitly voted (according to an earlier edit). It seems reasonable that some people wouldn't bother to explicitly abstain, in addition to your comment that maybe some left, and we can throw in a few for simple miscounting.
 * Looking through the article history, the paragraph first said "under 500", unreferenced from an IP. That got changed to 424, unreferenced, by another IP. The "over a thousand" and "30 abstentions" was added by user Pasachoff, who's earliest edits include several of the page for one Jay Pasachoff, an American astronomer. You can construct your own hypothesis about that. :-)
 * I think those numbers should be removed from the "Plenary" section, just keeping the actual vote counts. They're not relevant there, anyway. In the "Process" section, the 424 can be kept (it is the number used in the complaints), but rephrased to drop the "cast a vote", and drop the subsequent sentence on the 6A number. There's a 2700 number there (from BBC, quoting Gingerich) which is at odds with the 2411 number from the IAU newletter quoted in "Plenary"; I think the latter should just be removed, since it's irrelevant in context (and probably wrong -- Gingerich also says only 10% of those 2700 voted). Tbayboy (talk) 01:39, 28 June 2014 (UTC)
 * Thanks for the research. The 2411 number isn't actually backed up by its claimed reference (the linked page seems to have changed); the IAU press release discussed above mentions "over 2500". I'd agree removing it from the plenary section, as well as the unreferenced "over thousand". But I would either keep the 424 number (replacing the wrong "chose to vote or indicate their abstention on Resolution 6A (below)" by "took part", as supported by BBC), or instead use the less specific "over 400" for Res. 5 given by Margot's source (which is very plausible from the IAU 6A count as well) so that we have at least a ballpark number for the number of voters.
 * Since Gingerich's 2700 number does not coincide with the IAU's number (and contradicts his own 10% claim), I think we shouldn't use it either outside "Process". We should also remove your January addition "However, that number was for Resolution 6A..." to "Process" since no source claims 424 participants for 6A, only for 5. --Roentgenium111 (talk) 15:36, 2 July 2014 (UTC)
 * I found a copy of the conference newsletters here. The figures given in the newsletter for the Res.6A vote was 237+157+30 = 424, so that's probably where that number came from. The other newletters can be accessed by changing nsiii_10 in the URL to nsiii_01, etc. I'm going to skim through them before making any changes, just in case something relevant pops up. Tbayboy (talk) 03:48, 3 July 2014 (UTC)
 * I didn't find much in a quick skim. In Newsletter 5 there's a comment that a quarter of the world's 10000 astronomers attended the conference. There's also a reply to a comment that makes clear that the H-E criterion does not include small rubble piles, pointing out the "overcome rigid body forces" wording. Tbayboy (talk) 00:59, 4 July 2014 (UTC)
 * You'd think the IAU would at least be competent enough to keep track of the numbers for such an important vote. Ikmxx (talk) 06:50, 17 May 2018 (UTC)

hi — Preceding unsigned comment added by 2605:6000:3345:EF00:9C0C:EA83:1A8F:466B (talk) 18:07, 21 October 2015 (UTC)

a couple of questions of wording

 * Astronomers also knew that more objects as large as Pluto would be discovered, and the number of planets would start growing quickly. ...

How could they know that? Perhaps knew should be thought it likely?


 * In 2006, the matter came to a head with the first measurement of the size of . That measurement had showed Eris (as it was believed to be until the 'New Horizons' mission to Pluto) to appear to be slightly larger than Pluto ...

This seems to say that New Horizons found that Eris was living under a pseudonym. What did it really intend to say? —Tamfang (talk) 19:03, 15 November 2015 (UTC)
 * I fixed the first; seems the second had already been fixed. Double sharp (talk) 08:58, 23 August 2021 (UTC)

IAU Euler Diagram
Per wikipedia article IAU Definition of a Planet https://en.wikipedia.org/wiki/File:Euler_diagram_of_solar_system_bodies.svg

According to the IAU Euler Diagram, the Trans-Neptunian Objects category does NOT overlap the Planets category. Therefore, if Planet Nine is indeed Earth-sized or much larger, there would be a true Planet in the Trans-Neptunian objects category, requiring the Euler diagram to change, expanding Trans-Neptunian objects category to overlap into Planets. — Preceding unsigned comment added by Contributions/ (talk) 21:25, 21 January 2016 (UTC)
 * Indeed. But not a problem as long as Planet Nine is not known to exist. Double sharp (talk) 08:09, 24 August 2021 (UTC)

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potential crisis of TNO planets
This got reverted, but is important:
 * It has also been argued that the definition would be in crisis if a body larger than Earth were to be found in the outer reaches of the Solar System, which did not meet criterion #3 due to the slow evolution of the orbital dynamics of that region.

Easy to source. Unfortunately, the only thing I have at hand is a badly written rant by Runyon et al. But the argument is made more cogently elsewhere. — kwami (talk) 04:28, 23 August 2021 (UTC)


 * Perhaps this might be suitable (an interview with Stern):

And the IAU definition is even worse, because it produces different categorizations for identical objects, depending on where they are. Get this — Earth at the same distance from the sun [as Pluto] would not be a planet by the IAU’s measure, because Earth can’t clear that zone either. I would say any definition that produces a result where Earth is not a planet under any circumstance is immediately indicted as ridiculous, because one thing we all agree is a planet is planet Earth!
 * Except for the little problem that that precise statement is not true: Earth would clear its orbit that far out. (He would have been right if he had said that Mercury could not clear that zone.) Double sharp (talk) 08:51, 23 August 2021 (UTC)

Ah, I see Brown has been more balanced. In he first argues that the common understanding of what a planet is involves where it orbits:

If Mercury were orbiting Jupiter rather than the Sun, it would clearly never have been considered a planet (as is the case for Ganymede), while if our Moon were in Mercury’s place, it would be (barely) observable with the naked eye and would have been considered a planet even before the Copernican Revolution. Clearly, the common use of “planet” includes orbital circumstances.

But he also concedes that the lack of a size requirement of the neighbourhood-clearing definition would go somewhat against that common understanding as well:

An interesting situation would arise if, for example, a Mars-sized object were found in the inner Oort cloud. By the dynamical definition this object would not be considered a planet, yet most people would instinctively feel that a body that size should indeed be called a planet.

So I've cited both of them and rephrased it to use Brown's Mars example. Double sharp (talk) 09:01, 23 August 2021 (UTC)


 * Thanks! That's exactly what we needed. — kwami (talk) 21:39, 31 August 2021 (UTC)

it is now known that Mercury does not meet criterion 2???
What the heck is with this, by User:Kwamikagami on August 18, 2021‎ ? Such horrible language to casually make! WHO KNOWS THIS?! I don't know this. I've never heard that argued once. WHERE in Mercury_(planet) does it say anything about this "now known" thing?! 
 * However, it is now known that Mercury does not meet criterion #2, but is nonetheless universally considered to be a planet.

— Preceding unsigned comment added by Tomruen (talk • contribs) 08:26, 31 August 2021 (UTC)

If we've misinterpreted that source, please clarify. I'm happy to be proven wrong. — kwami (talk) 21:42, 31 August 2021 (UTC)
 * (the OP): You might like to take a look at the discussion at Talk:List of possible dwarf planets. The relevant quote from the source is given there. Double sharp (talk) 12:50, 2 September 2021 (UTC)


 * It looks to me to be "original research". Unless an expert publicly connects this research to the IAU definition, describing if or how the definition would need adjusting to be consistent with these details, it just adds unnecessary confusion to this article. It should be REMOVED from this article, unless as a note and crosslinked to a statement in the Mercury article. Tom Ruen (talk) 18:15, 2 September 2021 (UTC)
 * I tend to agree with you, after thinking about it for a few weeks. Even a note kind of has trouble, though, because I have (still) not found any source explaining this difference between HE in the IAU definition (which actual astronomers voted for) and HE in the really strict sense that excludes Iapetus for having the wrong spin (despite being obviously round). So I don't see how to write such a note without OR. Double sharp (talk) 03:24, 3 September 2021 (UTC)

Mercury
I removed the line about Mercury supposedly not meeting the definition of a planet per the above discussion and elsewhere on Wikipedia. Everywhere this has been discussed there is seemingly complete agreement to remove the line, so I'm not sure why no one ever did it. But it is unsupported by the linked source, in my opinion, and I've even seen it cause confusion off site as well. If there's a good reason to re-add it then I'm all ears but I think we'll need a long stronger evidence than just a single source. Lazer-kitty (talk) 21:29, 16 January 2023 (UTC)
 * Mike Brown has actually commented on this early this year (so after those discussions): The real answer here is to not get too hung up on definitions, which I admit is hard when the IAU tries to make them sound official and clear, but, really, we all understand the intent of the hydrostatic equilibrium point, and the intent is clearly to include Merucry & the moon.
 * So, yeah, Mercury is not actually in HE and you can find that actually stated in RS, but everyone knows that "HE" in the IAU definition is just an official-sounding way to try to say "nearly round", and nobody actually takes it literally. We should probably cite him on this point.
 * This might interest you. Double sharp (talk) 09:37, 7 October 2023 (UTC)
 * We should then say under definition of a planet that the IAU definition is not to be taken seriously, that not even the IAU takes it literally, since they count Mercury as one of the 8 planets. — kwami (talk) 02:49, 8 October 2023 (UTC)
 * I've added some comments about how the HE clause is always treated to this and other relevant articles; please feel free to improve my wording. Double sharp (talk) 09:25, 8 October 2023 (UTC)