Talk:List of possible dwarf planets


 * Archived discussion of the table: Talk:List of possible dwarf planets/Template talk

This is listed in the table; should it be removed, given that it does not actually exist? Double sharp (talk) 14:39, 2 July 2017 (UTC)
 * Gone. Thank you. Tbayboy (talk) 22:03, 2 July 2017 (UTC)

trimmed table
I cut out anything <400km diam, as even Brown says those are improbable and this is supposedly a list of the "likeliest" DPs. Also took out the comment that estimates based on albedo are in red, as that's no longer the case. Tagged VG18 as cn. Given that so little is known about it, shouldn't any claims here be reflected in its article? — kwami (talk) 20:48, 12 June 2019 (UTC)


 * Re 400 km, makes better sense now, post-Grundy, than when it was discussed previously. Note, however, that Tancredi "accepts" 1996 TL66 at 340 km.
 * Re red albedo-based diameter estimates: Not sure what you mean, they're still there in red. It's means Brown set the size based on his albedo estimate, not from any measured (mostly radiogenic) source. It's still mentioned in the column header note, so maybe it doesn't need to be in the lead-in text.
 * Re VG18 diameter, see the column header note: it's based on a generic assumed albedo of 8%. Per discussion here long ago, when the auto-grid was first created, an 8% albedo is assumed if there is not a measured value and if Brown doesn't list it (it was commonly used by the researchers at the time). The problem is that the press release numbers (when there's no actual measurement) are based on different albedo choices, and so don't compare well. There was even a case or two where the same body had different estimates based on which discoverer was interviewed. I've been thinking about bumping it up to 9%, since that's what Johnston uses in the absence of a measured value. With the 400 km cut-off, there are only 3 such bodies (plus 2017 OF69 and 2012 VB116). In effect, using Johnston as a backup to Brown.
 * Re G!kunll'homdima, the problem is that the non-accented spelling is what the source MPC page actually uses, and it just gets automatically picked up from there. I'll try to fix that, or at least manually restore it when I update. (By the way, this table is not based on the one in my sandbox, so changing it there does nothing here.)
 * I've been think of making some changes to the (now "Brown") table, but I'll mention it in a separate section when I've got a good window to discuss and work on it, probably in a month or so. Tbayboy (talk) 02:55, 13 June 2019 (UTC)
 * Grundy is one single source, i haven't seen anything from Brown or Tancredi responding to Grundy's paper. As such its merely one source among many, and it shouldn't yet be given as much weight as you're giving it.XavierGreen (talk) 17:04, 25 June 2019 (UTC)
 * One peer-reviewed source that is cognizant of the various findings of the last decade plus. Brown's informal (web-page) argument is premised upon Mimas being in hydrostatic equilibrium, and it has since been found to not be so (and Enceladus and Iapetus, and Proteus from even before Brown's page). That said, I'm okay with the table here ending anywhere in the 300-600 range (the theoretical minimum is about 350). I just think we should lose the heavy emphasis on Brown's back-of-envelope musing. Tbayboy (talk) 19:51, 25 June 2019 (UTC)

Is the Moon in hydrostatic equilibrium?
The article on hydrostatic equilibrium claims that the Moon (diameter 3474 km) is the largest body known to not be in hydrostatic equilibrium. This list gives Iapetus (diameter 1469 km) as the largest. At least one of them is wrong. Renerpho (talk) 13:23, 7 November 2019 (UTC)
 * I attempted to clarify it somewhat by adding the Moon to the table. I think the article on hydrostatic equilibrium, as well as this one, need some fairly extensive overhaul. Both currently are a mess! Renerpho (talk) 01:24, 25 November 2019 (UTC)
 * and to make things so confusing 10 Hygiea and 704 Interamnia appeare to be in hydrostatic equilibrium... and mercury, mars and venus are no longer in hydrostatic equilibrium , very confusing , and to make it more confusing the its from the ice/water vs rock/iron part well Io is in hydrostatic equilibrium. Joshoctober16 (talk) 17:03, 21 December 2019 (UTC)
 * Agreed. I gave several references that found that Mercury is not technically in hydrostatic equilibrium for its current rotation...obviously it's still round, still has cleared its orbit, and is thus still a planet regardless (if being a planet/dwarf planet required being in hydrostatic equilibrium, all the terrestrial planets and almost all known/likely dwarf planets would be excluded), I just think this obsession with hydrostatic equilibrium needs to be toned down a bit...I do wish the IAU would modify the dwarf planet criteria to reflect this (perhaps classify an object as a dwarf planet if it was in equilibrium at some point, even if it isn't now?) - Anonymous, 12/25/2019 — Preceding unsigned comment added by 2601:196:180:59F0:4492:BD9:D5EA:8274 (talk) 13:29, 25 December 2019 (UTC)
 * But how are we going to figure that out? By definition, we cannot measure its past state, only its present state. We can certainly guess if it was likely to be in HE at some point, but then what do we do with Vesta? And Phoebe, ignoring that it's a satellite? BTW, though Hygiea and Interamnia are bad enough as DP candidates, note that Methone may well be in HE at 1.45±0.03 km in radius, though that is easier for a satellite (like Methone is)! Double sharp (talk) 14:11, 25 December 2019 (UTC)
 * Methone is only in HE in its particulate layer, not in the solid part, and the IAU def is that gravity be sufficient to overcome rigid-body sources. Thus Methone is out, and we also cannot determine IAU-defined HE for bodies such as Europa that have liquid layers, and maybe those with significant tidal heating. As for Mercury, if it's not in HE then it is not a planet (per the IAU), as clearing the neighborhood is only half the definition. But IMO we will need some discussion to verify that the studies claiming Mercury is not in HE truly establish that as RS's. — kwami (talk) 08:41, 30 December 2019 (UTC)
 * If Europa is problematic, doesn't that imply (if I understand you correctly) that it's not even certain that the giant planets are planets? Double sharp (talk) 11:31, 30 December 2019 (UTC)
 * Europa's almost as rocky (or at least as dense) as Luna but only 2/3 the mass, so it seems possible to me that if it weren't being tidally heated it would have frozen out of HE. Though the IAU def doesn't mention anything about whether 'being massive enough' can or cannot be in conjunction with heating (assuming Europa's mantle under its ocean is in HE). And I haven't heard of anyone doubting that the gas giants are massive enough. If mean, if we're going to be legalistic, the IAU def doesn't say that planets actually are in solid-body HE, only that they're massive enough to be, so by that interpretation Jupiter would be a planet even if it doesn't have a solid core. One problem with attempting to be precise is trying to read in literal implications that were never intended, from wording that may have meant different things to different voters at the IAU. I suspect the current definition was a fudge to include Pluto as a DP but exclude it as a planet, and the wording of the resolution was just a best-guess effort so it would look superficially scientific. The IAU has also declared the big 8 to be planets, and Pluto to be a DP, so if the definition in the resolution doesn't work, I suspect the IAU will ignore the problem and astronomers will disregard the IAU definition until it dies of neglect. Maybe eventually the IAU will come up with a different fudge to get the results they want, but without the drama of a shift in paradigm in the popular press stirring things up, they probably won't bother, and the conception of planet and of DP/planetoid will continue to vary from astronomer to astronomer, and people won't worry about it.
 * Anyway, that's just a long-winded way of saying that if any of the big 8 don't meet the IAU def of 'planet', then I expect people will decide that the IAU definition is wrong rather than reclassify the planets based on an obviously unintended consequence of the definition. — kwami (talk) 16:50, 30 December 2019 (UTC)

Mercury
(Added a section header to make it easier to refer to this bit.) Double sharp (talk) 12:50, 2 September 2021 (UTC)

It seems that the situation you speak of may already be real (even if I can't remember seeing anyone actually point it out, other than the anon above from Christmas 2019). From Chapter 3 of the Cambridge Planetary Science book Mercury: The View after MESSENGER:

"For Earth, departure from the hydrostatic state is so small that a second-order theory is necessary to describe the observed flattening accurately ... But Mars, the Moon, and Mercury are far from hydrostatic equilibrium, so the source of these departures may be readily modeled. (We do not discuss Venus because its moment of inertia is not known.) ... The geoid of Mars is, to a good approximation, the sum of a hydrostatic Mars plus the Tharsis rise and the interior response to this massive load. ... The lunar spectrum also has a degree-2 excess, and this result has been used to argue that the Moon retains a fossil shape from an earlier and shorter Earth–Moon distance (Williams et al., 2001). ... To sum up, Mercury is out of hydrostatic equilibrium to a much greater degree than the Moon, but fossil rotational and tidal bulges cannot provide a causative explanation for Mercury (Matsuyama and Nimmo, 2009), whereas they can for the Moon (Keane and Matsuyama, 2014; Garrick-Bethell et al., 2014)."

Given that this is literally a study of Mercury, I think we would be on fairly solid ground to say that Mercury is not in hydrostatic equilibrium. So, if we interpret things literally, the IAU definition of planet says that Mercury is not a planet. (BTW, doesn't the Luna situation sound like the one Iapetus is in: freezing out when it rotated faster?)

However: I cannot believe that the IAU was actually thinking of HE, at least in this sense, even though they said HE. Because, per the actual resolution, Mercury is explicitly a planet. It doesn't fulfil the letter of the definition, but presumably it would not be there if it did not at least fulfil its spirit. Instead, it seems to me that the real idea is "a planet is something in orbit around the Sun that's round and gravitationally dominant". I find this not at all hard to believe, because "clearing the neighbourhood" was also loosely worded.

Of course, transition objects like Proteus, Vesta, and Pallas, not to mention TNOs like Varda that might not be solid (despite being larger than geologically active Enceladus, and planetary geology being kind of the point of demanding roundness), show that roundness is really quite difficult to formalise in our Solar System. At least there is a big difference between the dominant 8 and everybody else.

This does make me wonder if making statements about whether or not things are in equilibrium might often be too much, and if we might not be better off sticking to roundness. Double sharp (talk) 11:13, 18 August 2021 (UTC)


 * Thanks for that.
 * "I cannot believe that the IAU was actually thinking of HE, at least in this sense, even though they said HE." -- Maybe. But the definition was before the MESSENGER mission. I do suspect, however, that the definition is a figleaf to get the results people wanted, and they weren't too concerned with whether it was accurate. They needed something that sounded scientific to justify the decision they were making, regardless of which side of the Pluto debate they were on.
 * The Mercury problem could be fixed by dropping criterion #2. But as some have noted, criterion #3 would run into trouble if we find Planet 9, something Earth-size or larger that hasn't had time to clear its neighborhood.
 * In the end, I suspect this is going to be remembered as a bureaucratic fudge that has no real meaning, and that we're going to need a practical rather than a formal definition. If you're a planetary geologist, the question is whether a body acts like a planet geologically (or, as a first approximation, Stern's "if it looks like a world" rule of thumb). If you're a planetary-system dynamicist, the question is whether a body acts like a planet dynamically. "Cleared the neighborhood" is the rule of thumb for that in our system so far, but it won't work everywhere.
 * I like Brown's approach of dropping the term "dwarf planet" in favor of "planetoid" -- something that looks like a planet, as Stern said.
 * — kwami (talk) 19:09, 18 August 2021 (UTC)
 * I agree with you. That said, it seems that there was some indication of this before. That article's from 1984 and points out that Mercury is too oblate for its current spin (its flattening would be explained by 4.7-day rotation period, not the current 59-day one). That's pre-MESSENGER, but post-Mariner 10. In fact, it says the same thing about Venus (which is stuck between the Sun trying to lock it and the atmosphere trying to spin it up). Although that Cambridge Planetary Science book on Mercury notes that "[Venus'] moment of inertia is not known", and also that fossil bulges are not enough to explain Mercury. So, maybe take this as just some indications from then.
 * What does make me wonder, though, is why I've never found anyone other than the above IP who raised this problem with the IAU definition as stated, now that the shape of Mercury is better-known. I'd have thought that the IAU definition would've put HE's connection with planethood in the minds of people. The people who would notice this presumably study Mercury, so I might jokingly suggest that perhaps they just don't want to put the planethood of their chosen object of study in peril. XD Double sharp (talk) 04:38, 19 August 2021 (UTC)
 * What does make me wonder, though, is why I've never found anyone other than the above IP who raised this problem with the IAU definition as stated - You are pointing to a dilemma here: While the fact that Mercury is not in HE has been discussed in scientific articles for quite a while, the connection to the IAU definition may originate in this comment section, for all we know. This makes it original research, and thus not suitable for Wikipedia. One could argue for removing any mention of the problem from this article, as well as from IAU definition of planet (and any other place that has been edited in response to this thread). I am reminded of a discussion about a certain distant TNO... Renerpho (talk) 05:35, 19 August 2021 (UTC)
 * I definitely see your point. But if we say that Mercury is not in HE (which we have sources for, so we can), and that Mercury is a planet (which everyone agrees with), and that the IAU definition says planets should be in HE (which we also have sources for, so we can), then it seems to me that this looks so contradictory at first glance that the reader is going to wonder. Especially if we say nothing about it.
 * Perhaps we could say that HE in the IAU definition is meant loosely, on the grounds that the IAU definition clarifies HE as meaning "nearly round": (1) A "planet" [1] is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. Then this seeming contradiction would disappear. But I guess even this is a slight stretch when it is not said explicitly.
 * Since you made the additions. :) Double sharp (talk) 08:08, 19 August 2021 (UTC)
 * This is a question for linguists, and not an easy one! "Assuming a hydrostatic equilibrium (nearly round) shape" (your wording), "assume hydrostatic equilibrium (a nearly round shape)" (the wording in the IAU definition of planet article), and "being in hydrostatic equilibrium" (the vernacular understanding) are three different things. The wording is important here. We have to be careful which one we use, down to the letter, and be consistent about it. Mercury meets the first of those three versions of the criterion ("if it looks like a duck..."), it probably doesn't meet the second (that'd have to be addressed, using reliable sources), and it definitely doesn't meet the third (that's why we are here). We must be careful about how the IAU itself, and the scientific community as a whole, has been interpreting the definition. The problem is, I am not aware of any studies that address this (if you are, please point to them!). Doing so ourselves is so advanced that it borders on original research again. If we are careful then we might be able to make it work. Being consistent between articles looks like the necessary first step to me. If this topic is not discussed outside of Wikipedia then our articles shouldn't discuss it either, and the confusing statements should be erased from the Wiki. Renerpho (talk) 14:27, 19 August 2021 (UTC)
 * I've been taking the parenthetical to be a layman's translation for those who don't know what HE is. None of the astro lit that I'm aware of discusses roundness in absolute terms, but rather what the shape tells us about HE, mass distribution, frozen tidal bulges and the like. They seem to ignore the parenthetical altogether. A flying mountain battered into a round shape doesn't count, nor does something like Methone. — kwami (talk) 19:08, 19 August 2021 (UTC)
 * They seem to ignore the parenthetical altogether - But then we have a problem, don't we? Because most seem to use the layman's translation, not the actual definition. What they do is ignore everything but the parenthetical, and look at the shape of the surface (and whether there is an ellipsoid that fits the data). But surface shape is (at best) a proxy for HE. A flying mountain battered into a round shape doesn't count - Sure, but in the case of Mercury and the Moon, the shape of the surface isn't the issue, it's the gravitational field of the interior, the structure of the object's inner layers (like an offset core, or a core that's not itself in HE). If we care about nothing but the surface then Methone meets the criterion again. The IAU isn't clear about what it means: the shape of the surface, or the shape of the gravitational field as a whole? There are problems like this with the other criteria as well, like the lack of a clear definition for "clearing its orbit". The assumption seems to be that you know a planet when you see it, and that Mercury obviously is a planet, and so would be the Moon and Haumea (if it met the other two criteria). We now know that neither is in HE, but that doesn't matter! They got rid of the problem of how to check for HE in TNOs by replacing the criteria with a simple limit on absolute magnitude, which Haumea meets. And Mercury is a planet, too, because it is listed as an example of a planet in the definition. Neither of those objects has to be in HE to be a (dwarf) planet, if you take the IAU by the letter. Renerpho (talk) 19:51, 19 August 2021 (UTC)
 * An example for how this is handled in other Wikipedia articles: In the lead of List of gravitationally rounded objects of the Solar System, we define "gravitationally rounded" as objects that have a rounded, ellipsoidal shape due to their own gravity (hydrostatic equilibrium). Is that parenthesis a layman's translation, a clarification, or an additional criterion? There are objects listed in that article that are known to not be in HE (like Iapetus), without further mention of that fact. Mimas is listed, but Methone is not. Renerpho (talk) 20:11, 19 August 2021 (UTC)
 * Actually, that list does mention that Iapetus is not in equilibrium under "Satellites". And also that we don't know enough to be able to decide equilibrium for Charon, Dysnomia, and the Uranian moons. Perhaps, since that article title just says "gravitationally rounded", that parenthetical saying HE should be removed? Double sharp (talk) 03:49, 20 August 2021 (UTC)
 * I see, Iapetus is mentioned indirectly, as "all of the moons listed for Saturn apart from Titan and Rhea". Are we sure that Rhea is in HE? (Okay, that's a matter for the discussion at that article, or in the Saturn's moons and HE section below...) Rhea is a prime example of what I mean when I say that shape is only a proxy for HE. Perhaps, since that article title just says "gravitationally rounded", that parenthetical saying HE should be removed - Yes, if you can define what "gravitationally rounded" means, without referring to HE, go ahead! Renerpho (talk) 04:54, 20 August 2021 (UTC) Striking the last sentence. I didn't notice this was a featured list; a major change like this should first be discussed on the list's talk page. Renerpho (talk) 23:02, 20 August 2021 (UTC)
 * Last I had read, we did not know if Rhea was in HE, only that its shape was consistent with HE and there was no convincing evidence that it was not in HE. Though, that implies that it is almost completely undifferentiated. Which rings within me somewhat the alarm bells of Callisto.
 * I don't really know how best to define the notion (after all, the IAU just informally said HE instead of try to do so). I guess we could informally say that gravitational rounding means that the current shape is well-approximated by an ellipsoid and the body is large enough that self-gravitation becomes significant for internal geology and shaping. It's kind of hand-wavy, I guess, but not too different from Runyon, Stern et al.'s geophysical definition (but clearer, and not promptly self-contradicted by including Proteus as they did). The first clause would exclude Vesta, the second would exclude Methone and coincidentally-round Phobos. Double sharp (talk) 06:39, 20 August 2021 (UTC)
 * When I suggested to go ahead with removing the parenthesis, I didn't notice that the article we are talking about had featured status. A change like this should probably be discussed on its talk page, not here. My suggestion: Let's see what we do about the List of possible dwarf planets article here before messing up others (especially those at risk of losing featured or good article status). Renerpho (talk) 23:02, 20 August 2021 (UTC)
 * Makes sense to me. So, I guess the question here is: how do we plan on resolving the difference between stricto sensu HE and being round, across English WP? Currently it seems that HE is being treated as stricto sensu, and has been for a while: I'm pretty sure that the statement about Iapetus and Enceladus being out of HE has been on WP for years. The problem is that doing it consistently leads to questioning Luna and Mercury, and the latter, being a planet according to everybody, makes the IAU definition look confusing. Contrariwise, if we treated it as not stricto sensu, then it seems to fulfill the spirit better of what the IAU definition said (as well as what geophysical-definition proponents would tell you; I doubt any of them would countenance a definition that excluded geologically active Enceladus), but methinks it involves some mind-reading. Or at the very least nontrivial interpretation of the IAU parenthesis as the defining thing when actually it is not the same thing as what it seems to be defining.
 * Regardless of what we do, though, I think comparing Saturnian moons to TNOs may be giving the wrong idea in the first place. Ice is more plastic out at Mimas than out at Varda, so even though the latter is larger, Mimas managed to fully collapse and Varda probably did not. (Throw in tidal heating for Enceladus, of course.) Of course, comparing TNOs with Mercury gives even more of the wrong idea (it cannot reach true HE, probably partly because of the 3:2 resonance with Sol causing varying thermoelastic stresses, and anyway I doubt any TNOs are 70% metal XD). Double sharp (talk) 15:46, 24 August 2021 (UTC)
 * There are tides on Earth, which means it's not hydrostatic either, but that's clearly not what the IAU meant. If the deviations of Mercury are due to periodic stresses, which act faster than the hydrodynamic reaction can respond, then that would be a similar situation. Maybe "hydrodynamic equilibrium" would be a better term. But if Mercury has fossilized deviations from an equilibrium shape, then we have the situation of Luna or the moons of Saturn. A hydrodynamic definition would be OR, of course, and if Mercury does have fossilized deviations in its overall shape, then the IAU definition wouldn't work regardless. After all, the critical part of the definition is clearing the neighborhood, which can't be precisely defined but in our planetary system allows for an obvious dividing line; all the fine-sounding words are an attempt to put a fixed decision on a rigorous footing. — kwami (talk) 01:11, 25 August 2021 (UTC)

G!kun
Isn't G!kun only 600 km in radius? Please clarify this.PNSMurthy (talk) 04:33, 21 July 2020 (UTC)
 * That's its diameter. — kwami (talk) 09:25, 2 November 2020 (UTC)

bias in asteroid belt
There are likely several asteroids that were once in HE, such as Vesta, Psyche, Eunomia, Iris. Cherry-picking the icy ones like Interamnia (if indeed it ever was in HE) and then commenting that they're "all" icy bodies strongly implies that the ex-DPs are icy bodies. That's a bizarre bias to introduce into the article when there is no reason for it, so I don't understand why people are edit-warring over it. Also, emphasizing the possibility that Hygiea may be an (ex)-DP, when it's round because it's disrupted, is weird. Sure, it might be, but since another explanation for its roundness is given, it's hardly such a great candidate that it needs to be singled out. — kwami (talk) 09:21, 2 November 2020 (UTC)

Saturn's moons and HE
After re-reading the paper that suggested the Saturnian moons are not in HE, I've realized that the paper's results have been misinterpreted in this article. I'm not good at rewriting things, and I would still like the discuss this - from my interpretation of the paper (http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf), I see that
 * Rhea - in HE.
 * Mimas - deviates by only small margins, but very clearly not in HE
 * Iapetus - very clearly not in HE.
 * Dione - not in HE, but this may not mean anything as they have internal oceans that can overcome HE forces
 * Enceladus - same as Dione.
 * Tethys - Close to/not inconsistent with an HE shape.

Given my re-reading of the article it seems as if Tethys may be the second smallest object in HE (behind Ceres) - certainly should be worth rewriting some things. Ardenau4 (talk) 06:55, 4 November 2020 (UTC)


 * Rhea is not "in" HE, but has a shape consistent with HE. That could mean that, being closer to Saturn than Iapetus, where tidal forces are stronger, it despun earlier, before it froze out. Iapetus freezing out so early suggests that Rhea is probably not in HE (though the paper does not discuss this).
 * If Dione has an internal ocean, then can we say anything about HE? Which "rigid-body forces" are overcome? (Or does compressing to liquid count?) And wouldn't the shape suggest it does not have an internal ocean? That the Enceladean ocean is not global?
 * — kwami (talk) 18:23, 4 November 2020 (UTC)


 * Right, but in this case did Rhea ever freeze out? Clearly the actual situation is not as clear as the article makes it out to be - it's worth a re-write, but unfortunately I'm bad at rewriting things. Again - is there even a distinction between being "in" HE (Ceres), and having an equilibrium shape (Rhea, Tethys)? Ardenau4 (talk) 02:41, 5 November 2020 (UTC)


 * There's not enough evidence to know if Rhea froze out or not, though it would be extraordinary if Iapetus froze out and Rhea did not. (Not that there aren't plenty of extraordinary things in the SS.)
 * As for "is in" being present tense, the IAU apparently means that, as apparently does Stern. Vesta was clearly once in HE, but is no longer, and since Dawn, AFAICT no-one's proposed that it's a DP. Similarly, we know that Phoebe was once in HE, but Stern doesn't count it among the satellite planets. So when the definition of a planemo says it "is" in HE, we have to conclude that we're to take that literally.
 * As you note, the real definition, on the geophysical side, seems to be that a DP/planet is round. That's how Stern uses it in practice, since he counts Iapetus and Mimas as satellite planets, along w a bunch of TNOs, most of which aren't even solid bodies. But no-one's admitted that in years. (Since not long after 2006, when Stern said "if it looks like a planet, it's a planet"?) So we're stuck playing stupid with fake definitions on that side.
 * Things aren't so bad on the IAU side, since they only said that Haumea and Makemake had to be DPs based on their understanding at the time, and so would be named by the joint committee that was set up to name DPs, and that if it turned out they were not DPs after all, they'd keep their names. So those two were announced as DPs, but it's up to practicing astronomers to determine whether they actually are, or whether any body is in HE or not. Since that's almost never a possibility, the definition is pretty much ignored except when someone wants to make headlines. — kwami (talk) 06:38, 8 November 2020 (UTC)
 * Stern might not count Phoebe, but in the publication with Runyon et al. Vesta is counted as a planet. And so is Proteus. And so are non-solid TNOs like Varda. Which seems to make their real definition into simply a size-threshold at about Mimas... Double sharp (talk) 03:58, 20 August 2021 (UTC)


 * Runyon is so busy trying to prove he's right that he forgets that he needs to make sense. So Ceres is a rocky and metalic body that formed in the inner SS. 'Icy planets, most of which are probably dwarf planets' -- are the rest Classical planets? I agree that people should be able to use technical terms in a way that makes sense for their field (and of course they will, regardless of what the IAU says), but sounding like he can't count his toes does not make him very convincing. At least with this poster, the definition is coherent even if he ignores it -- in one of his other diatribes, even Jupiter did not qualify as a planet. — kwami (talk) 09:33, 22 August 2021 (UTC)
 * Even Jupiter did not qualify as a planet - That would definitely solve most of our problems. #AfD Renerpho (talk) 11:14, 22 August 2021 (UTC)
 * I see I accidentally linked the wrong thing by Runyon: in that poster Varda is a planet, but Vesta and Proteus are not. I meant to link to this one which includes Vesta and Proteus, sorry. Double sharp (talk) 12:08, 22 August 2021 (UTC)
 * Ah, yes, it's fun to try to parse that definition. If you're going to give a precise definition of a technical term, I would think that it would at least be coherent. But what would be the fun in that?
 * Okay, it's obvious what he means, but that's not even up to our non-GA standards. Taking "tri-axial ellipsoid" (since all ellipsoids are, by definition, tri-axial) to mean a scalene ellipsoid, like Mimas, as the phrase is typically used even in mathematical literature, a spheroid is not tri-axial. So, how exactly can a body assume a non-tri-axial shape that is "adequately" described as tri-axial? If it matches the first criterion, it fails the second, and if it matches the second, it fails the first. Ergo, planets do not exist.
 * His criticism of the IAU definition (apart from point 3) is just as bad. I wonder if he believes it himself.
 * And yeah, this was in 2017, after we'd seen Vesta up close, and AFAICT no-one counted it as a DP back then. And Proteus-Mimas were the original illustration of the likely sizes identifying HE vs non-HE bodies. So to put those in the list ... (just because they're larger than Mimas?)
 * I suspect the only purpose of these definitions, since Runyon et al. obviously don't pay any attention to them anyway, is to sound sufficiently sciency to impress a lay audience. In other words, they're devolving into pseudoscience. But, given that my insurance will cover ancient chiropcatic secrets that a "doctor" learned in a seance with the dead, perhaps the pseudoscience will impress the bureaucrats who decide their funding. — kwami (talk) 12:52, 22 August 2021 (UTC)
 * I wonder, at what mass would the shape of a blob of water in free-fall be controlled by self-gravitation? Put a film around it to keep it from boiling away, place it close enough to the Sun to keep it liquid, and we've engineered an entire planet! — kwami (talk) 13:19, 22 August 2021 (UTC)
 * I wonder, at what mass would the shape of a blob of water in free-fall be controlled by self-gravitation? Put a film around it to keep it from boiling away, place it close enough to the Sun to keep it liquid, and we've engineered an entire planet! — kwami (talk) 13:19, 22 August 2021 (UTC)

Is there some reason why we still keep Brown's values?
He doesn't update it daily anymore (last update date was 23 Feb 2021, so eight months ago), and the values are even older than that. Eris is still 1 km larger than Pluto there, Gonggong still hasn't got its name, and 2002 MS4 is still 960 km. Also Varuna is far too large. Most of all, it's entirely based on the argument that the icy satellites of the giant planets are a good proxy for TNOs, when we now know that they are not. Because of his "200km-400km" limit, he must be considering the moons of Saturn and Uranus; but TNOs are rockier, colder, and don't get to experience tidal heating the way something like Enceladus does and probably Miranda once did. Double sharp (talk) 20:38, 24 October 2021 (UTC)


 * He hasn't updated it regularly for years. IMO it's now obsolete, and all it ever was, really, was a list of objects by size. I don't think the leads of any of our TNO articles should say any longer that the object might be a DP based on Brown's list, and if there weren't so many of those claims I'd remove them -- even though many of them are my work, from back when Brown's assessment was the best we had.
 * But Brown is one of the biggest names in the field, and it was his imagination that lead to the greatest of these discoveries. So I don't think we should completely remove him from this article. IMO we should keep him in the first table, where we have "Per IAU, Per Tancredi, Per Brown, Per Grundy" though IMO it would be a good idea to rearrange the columns so that the most recent assessment comes first. [I just did that, and also changed Grundy et al. to green checks down to Orcus, as they call them DPs even if all they really show is that they seem to be solid bodies.]
 * The 2nd table, though, under 'Largest candidates': I don't see why Brown's non-peer-reviewed list should be the only named authority we use there. Not any more. Once upon a time he was all we really had; now we have better sources. Not as extensive, but that's because they don't judge as many objects to be likely to be DPs. I've gone ahead and removed Brown's columns. (Should we also truncate at a larger size, or is 400km good?) Also Tancredi, because we list him in the previous table, and he's not particularly notable today either. Also the column 'Notes on shape': who were we citing for that? It's not like we actually know the shapes of many of these bodies.
 * But isn't someone actively maintaining that table, updating it from their own spreadsheet as Brown updates his list? If so, we should coordinate with them. — kwami (talk) 01:02, 25 October 2021 (UTC)
 * Per kwami above. Double sharp (talk) 15:18, 25 October 2021 (UTC)

I've started removing our old, default citations of Brown's site -- worked up from the bottom of the list to D = 650km -- but there are still old assumptions of albedos with guesstimated diameters -- like an albedo of 0.07 for a suspected Haumeid. — kwami (talk) 06:41, 25 October 2021 (UTC)

2021 presentation for MS4 with lots! of occultation cords results in 800±24km. Error bars attributed to surface features > 20km. As you noted, it could be small but dense. But its albedo is presumably too low.

2018 VG18 might be worth proofing. — kwami (talk) 08:12, 25 October 2021 (UTC)


 * Yes, of course Brown is important for having co-discovered so many of the large TNOs. You have to go down to Varda, 2013 FY27, and Ixion before you get discoveries he wasn't involved in. I agree that his view should be in the first table, even though it has been obsoleted by later research.
 * In their first paper, Grundy et al. use 400 km as the start of their "transition region" that they study. However, that might just be because it was a prominently used value in the past. They later write We speculate that 600 to 700 km diameter objects like Gǃkúnǁ'hòmdímà and 55637 could represent the upper limit to retain substantial internal pore space and that by the time an object reaches 900 km, most of its internal pore space has been lost. Brown in fact did use 600 km as one of the dividing lines for his categories, and even then gave an out that a primarily rocky object at 600 km would not necessarily round. (Well, we now know that it probably doesn't even need to be that rocky.) Since we now know that objects less than 600 km are highly unlikely to be solid bodies (and that that limit is probably too generous), and this figure has a bit of pre-Grundy history as well, I've changed the cut-off to 600 km. Otherwise, the list is dominated by objects in the 400–600 km range that are no longer serious candidates. (As for why 600 and not 700, when that lets in both the bodies they mention: I feel it's good to show their sizes, and anyway uncertainties mean some objects we list in the 600–700 km range might really be larger.)
 * What's the bar being used for those in bold italics in the 2nd table? The ones that are still pretty uncertain according to Grundy et al.'s criteria? If so, then I feel they should be consistent with the 1st table. Double sharp (talk) 16:49, 25 October 2021 (UTC)
 * Forgot to ping you, sorry. Double sharp (talk) 18:38, 25 October 2021 (UTC)
 * I thought of it as a transitional category, to focus the reader on intermediate or indeterminate cases. I put Salacia in bold italics because I suspect it's still debatable. As you noted, Grundy et al. recently revised its density upward and called it "DP-sized" (it's dark, but some larger bodies are also dark, so we don't know that's critical), and it would be good to pay attention to what other sources might have to say. MS4, AW197 and FY27 could still be the size range of Salacia, and as you say are potentially more massive and more compressed and so better candidates. Not sure there's a great chance of that, but still an open question. (BTW, I think we should add a density column, even if it will be mostly empty near the bottom.) FY27 has a moon, so there's a good chance we'll know before long, but it may be that MS4 and AW197 are going to be undecidable for a long time. Though if we're lucky, we might get some solid conclusions on MS4 based on the shape determined by that incredible occultation event. Varda, Ixion and smaller bodies seem rather unlikely at this point, though of course that could always change.
 * I have no problem keeping this consistent with the first table, though we have less info on these. I should've at least explained what the bold and italics meant, but wasn't so sure myself. [Just added a blurb.]
 * Agreed, 600-km seems like a reasonable cut-off. It leaves us with a manageable list. Even if we knew they weren't DPs, I think it might be nice to keep them as the population of bodies that are likely to be partially compressed. I suspect such bodies will be more-or-less round, and still look like worlds, if not active ones apart from faults. But again, who knows!
 * I added 'see also Category:Possible dwarf planets' to keep the longer list handy for those who want more, but I'd imagine that will be a relatively small number of readers. — kwami (talk) 18:45, 25 October 2021 (UTC)
 * Yup, agreed that there should be a density column. I added some text noting that the bold and italics are just for the uncertain large ones that are probably over the 700 km threshold. (I'd say Ixion and AZ84 are too close to it; though error bounds for FY27 are huge, the estimate is at least pretty far over it.) I do agree with your suspicion that such bodies will probably look like worlds, and also that we really don't know at this point. And also that most readers will not be too interested in going below 600 km all the way down to bodies like Dziewanna and Huya. :)
 * For those where we have a satellite and hence know the density, though, like Gǃkúnǁʼhòmdíma, shouldn't we note that current scientific consensus is that these actually cannot be DPs if our data is right? Maybe Varuna also given that old estimation. Double sharp (talk) 20:01, 25 October 2021 (UTC)
 * (Keyword "if our data is right". Apparently Varda might well be denser at 1.78±0.06 g/cm3, though other solutions are presented.) Double sharp (talk) 20:14, 25 October 2021 (UTC)
 * Yeah, we should be clear on that. I was being weasely because we could use a more direct source. I think it's a matter of being so obvious that ppl don't bother to state it clearly. — kwami (talk) 20:29, 25 October 2021 (UTC)
 * I greyed out those rows. Also made Varda a borderline candidate again, on the grounds of that 2020 paper (although the smaller density may yet be right, still). Double sharp (talk) 20:42, 25 October 2021 (UTC)

IMO we might should restore bodies where 1-sigma crosses 600km. Several are now thought to be smaller than the high 500s we had in the table. But 2005 RM43 has occultation results of ≈644 km from 2020, and 2002 XW93 is still 565±72. 2014 AN55 and 2015 KH162 have a non-Brown guesstimate of 671, but I don't know if it's reliable enough for us to include. (Maybe no worse than several we have now, though both of them having the same estimated size is suspicious.) 2006 QH181 is 366–819 -- is that worth bothering with? Same 2010 RE64 at 350–780 -- 780km for 5% albedo, which isn't unreasonable for these bodies. 2008 ST291 and 2013 FZ27 as well, maybe. 2004 XR190 is >560 per 2020 occultation. 2007 JJ43 at 610+170−140. We have to cut off somewhere, but some of these may be notable. — kwami (talk) 21:12, 25 October 2021 (UTC)
 * Makes sense, so I restored those where we have an actual value, not just a guesstimate. So not XR190 with just ">560", but indeed JJ43 has been put back. Double sharp (talk) 21:36, 25 October 2021 (UTC)

I think I might add a separate table for what the diameters would be (for different albedos) for the unmeasured bodies. Not listing each separately, though: lumping together all bodies at each 0.1 difference in magnitude. That should cover the bodies that might belong in the table without watering it down with a bunch that probably don't. — kwami (talk) 22:52, 25 October 2021 (UTC)
 * Thanks for that! Double sharp (talk) 08:32, 15 December 2021 (UTC)

Table, "identified by IAU"
What does "identified by IAU" mean? The table and preceding section cites the 2022–2023 annual report as evidence that IAU identifies Quaoar as a dwarf planet. The report does mention Quaoar, and calls it a dwarf planet, but that's mainly because the paper it quotes does so in its title. Should this be seen as endorsement, or is it mainly a report of what the literature is doing? Is IAU expected to not report literature that disagrees with its definition, to avoid confusion? I'd much prefer a secondary source here, rather than the interpretation of Wikipedia editors! For 2015 RR245, we seem to care just as much about what others (in this case, the AGU) are claiming about IAU, rather than what IAU itself is saying about the matter. That's not "identification by IAU", in my opinion.

I only find the column "identified by IAU" useful as a reference for the "official" dwarf planet status. Right now, it's not that. Renerpho (talk) 13:36, 11 February 2024 (UTC)