Talk:List of possible dwarf planets/Archive 2

Lower limit?
Is there any point in having 300km as the lower limit? I think it would more meaningful if the limit were set at 400. Nergaal (talk) 21:52, 27 August 2015 (UTC)


 * Just a matter of how much we want to maintain. — kwami (talk) 23:14, 27 August 2015 (UTC)


 * See the discussion above for why that cutoff. It's somewhat arbitrary, but it's the nearest 100 below the published theoretical minimums. The database the list is generated from grabs everything in MPC and Brown, so it's easy to make it as big or small as we like. The only real maintenance fields are the measured sizes (primary size on the object's main page) and category. Category has a quick-and-dirty algorithmic default. So what cut-off do people want? Tbayboy (talk) 00:03, 28 August 2015 (UTC)


 * The 400km means "probably", while below is only "possibly". Wouldn't 400 make the most sense? There would be about 86 entries, likely a few more in the next years. Nergaal (talk) 16:29, 28 August 2015 (UTC)


 * Not going to search for "the discussion above", but I suspect the reason is that an object estimated at 350km could easily be > 400km. A cut-off of 300km should cover most objects > 400km. But we could make the cut-off 400 instead. I don't know what benefit those extra bodies are; I doubt that many people look at that part of the table. — kwami (talk) 22:43, 28 August 2015 (UTC)


 * Playing Devil's Advocate, this is a list of "possible" DPs. And, what's the down-side to a longer list, given that the maintenance difference is negligible? Personally, I'm okay with a cutoff anywhere below 600. I was planning an update next weekend (I usually do it first weekend of the month), so I'll make it 400 then unless somebody objects. That gives people a week to jump in here and object. Or, you could just remove the rows now and we'll see if anybody complains. Tbayboy (talk) 16:11, 29 August 2015 (UTC)
 * But why increase the cut-off if there is no actual downside of having a longer list? --JorisvS (talk) 16:17, 29 August 2015 (UTC)
 * Yes. I can just as easily generate it down to the dimmest TNO/centaur in MPC's tables. We've now got 2 calls for 400. Where would you it? Tbayboy (talk) 18:07, 29 August 2015 (UTC)
 * I always appreciated the detailed (longer) nature of the list. Currently, among the 50+ entries between 300 and 400 km there are about ten for which an article already exists. --  R fassbind  – talk   18:51, 29 August 2015 (UTC)
 * At d=213 km, Phoebe used to be round. Therefore, any pristine TNO the size of Phoebe could be round. The smaller the TNO, the less likely it is to be a DP. Anything below ~200 km is likely not to be round, but we don't exactly and their sizes are typically poorly known. It's for this reason that Brown includes everything down to d=100 km (at which point any object would need an unphysically low albedo to be big enough to be round). I don't object to doing the same, but I can understand if there are objections to that. But given Phoebe, it seems rather reasonable to include everything down to d=200 km. --JorisvS (talk) 20:49, 29 August 2015 (UTC)
 * SO you actually think there will be a recognized <400km dwarf planet in your lifetime? Nergaal (talk) 21:01, 30 August 2015 (UTC)
 * A body currently listed as 300km might turn out to actually be 500km. Many of these bodies don't currently have any size measurement, just an inferred size from an assumed albedo. Tbayboy (talk) 21:50, 30 August 2015 (UTC)
 * I am not disputing tht, but do you thin that during your lifetime any of those have a reasonable chance of being listed as dp? Nergaal (talk) 04:23, 31 August 2015 (UTC)
 * I suspect anything with an "abs magnitude estimate" less than 400km will be laughed at as a dp. Now if 38628 Huya turns out to be a spherical 390km in diameter we might accept a few known to be just below the 400km threshold. -- Kheider (talk) 07:56, 31 August 2015 (UTC)
 * Whether or not we'll know within our lifetime is irrelevant to the question. Only whether there is, with current knowledge, the possibility that they could turn out to be round. --JorisvS (talk) 09:35, 31 August 2015 (UTC)
 * What do you mean 'laughed at'. They may be petite, but if round DPs nonetheless. We don't know where the cut-off lies (and given Phoebe it may well lie closer to 200 km than to 400 km for at least some TNOs) and often have only very broad estimates of their size. --JorisvS (talk) 09:35, 31 August 2015 (UTC)
 * Anything below ~400km will be treated as "laughably" insignificant and not important on any dp list for the next 20+ years. But a next generation telescope might be able to pin down some of these diameters with reasonable accuracy. -- Kheider (talk) 16:05, 31 August 2015 (UTC)
 * Sound likely, but 'considered laughably insignificant' is not a valid criterion for inclusion. --JorisvS (talk) 16:18, 31 August 2015 (UTC)
 * "Within our lifetime", why not? All it takes is a lucky occultation to get a good size estimate. Several TNOs have albedos under 4%. Most won't be (and I think the real size limit will be more than 400), but this is a list of "possible", not "likeliest". While I think that anything under 500 (or even 600) is unlikely to be a DP, there's just not enough known about bodies in that size/temperature/composition space to say with any certainty. Tbayboy (talk) 12:13, 31 August 2015 (UTC)
 * Considering that the current accepted minimum is at 946 I highly doubt IAU will accept anything below 1/2 of that WITHOUT a good measurement (i.e. flyby?). Even with occultations I don't think IAU will hurry into naming something at 400km as dp. IAU has said nothing about new dp in SEVEN years, so it doesn't look like the number will grow that much anytime soon. Also, as a personal opinion, any list of more than 100 entries is unnecessary even on wikipedia. Nergaal (talk) 15:04, 31 August 2015 (UTC)
 * 100? And what of List of elements with its 118?
 * Those are officially recognized. This is an ORish list that could potentially be recognized at some point in the pretty far future. Nergaal (talk) 21:26, 2 September 2015 (UTC)
 * Wrong. 'Official recognition' has no relevance whatsoever on whether something is a DP. We can say with certainty that many objects in this list are DPs, and some aren't, we just basically don't have a clue which ones and what the probability is that an object will turn out to be DPs. This is science, not politics. --JorisvS (talk) 23:19, 2 September 2015 (UTC)
 * Not all the elements are recognized by IUPAC yet – 113, 115, 117, and 118 have been reported but are not yet officially recognized. Still, that doesn't seem to stop us from including them. Double sharp (talk) 03:19, 3 September 2015 (UTC)
 * Sure, the IAU will not hurry into it. However, the DP-ness of these candidates is not actually dependent on the IAU. Double sharp (talk) 15:12, 31 August 2015 (UTC)
 * It think it's likely the IAU won't make a formal statement even when, say, Sedna is visited by a spacecraft and it looks neatly round. --JorisvS (talk) 16:01, 31 August 2015 (UTC)
 * Why do you think under 500–600 km they are unlikely to be DPs? --JorisvS (talk) 16:01, 31 August 2015 (UTC)
 * A) Brown says 2002 UX25 is porous, which would make it not-DP, at ~700. B) Ceres is a noticeably lumpy in full-disc images. C) Proteus is a potato (in a temperature regime more like TNOs). D) Enceladus is (probably) not HE. Tbayboy (talk) 23:46, 31 August 2015 (UTC)
 * Combine that with what we know of Phoebe and we can emphatically say that we just don't know which ones are DPs, but that's also why this list exists. Proteus is indeed a potato, but it probably formed much later than the normal TNO, only after Triton wreaked havoc on the original system of moons of Neptune (which likely only happened when Neptune plunged into the proto-Kuiper belt, several hundred of millions of years after the formation of the Solar System), which means a lot less radioactive material was available to heat it. As for Enceladus, so is Iapetus, and if that's not in HE, Makemake and Haumea may well not be either. And of course, Ceres, may well not be either, something we should know rather soon. But if those universally accepted DPs are out of the window, then the whole DP category breaks down. That's why we should simply focus on what could be round (and that's basically what we have sources for anyway), and here Phoebe clearly indicates that those estimated 200–400 km are possibly round. --JorisvS (talk) 10:07, 1 September 2015 (UTC)
 * (following up my comment one indent up) From Brown's list: 2003 QX111 has a radiometrically determined size of 453km, with H=6.8. Deucalion (and a bunch of others) also has H=6.8, but, based on albedo assumption, he has it listed at 134km. (Yup, I'm ambivalent :-) ) Tbayboy (talk) 23:57, 31 August 2015 (UTC)
 * I think having a list of ~100 entries is enough. If that is ~350km so be it. But I would really stay away from objects that even at an albedo of 0 are not above 400km. Nergaal (talk) 21:26, 2 September 2015 (UTC)

I left it at 300km for this update until a consensus is reached. Tbayboy (talk) 15:21, 7 September 2015 (UTC)
 * It's a well crafted table I visit on a weekly basis. Thank you for that list; and for updating it regularly, Tbayboy. -- Cheers,  R fassbind  – talk   22:58, 7 September 2015 (UTC)

Given recent edits on Wikipedia, I do not want to see this list expanded to include objects estimated to be less than 300km in diameter. We will wind-up with too many article giving undue weight to them possibly being dps. -- Kheider (talk) 20:10, 3 October 2015 (UTC)

...

Let's put the point in a simple way here:

1. The minimum criteria for a SSSB being certified as a Dwarf Planet is that it should be wholly or mostly in hydrostatic equilibrium, IE have achieved a (near-)spheroid shape due to gravitational rounding entirely under its own weight.

2. The smallest body known for certain to exhibit this in the solar system is Saturn's moon Mimas, at 396km diameter. IE less than 400km.

3. It would be a very foolish thing to assume that the smallest self-rounded object in the solar system is a satellite which was first discovered centuries ago, whilst we continue to discover thousands of new objects on an annual basis, a fair proportion of them being around that size or at least, say, 96km smaller, and full details aren't yet known for a great swathe of those we have so far detected.

4. Fairly good candidates for being self-rounded are the centaurs Charilko and Chiron, even though they're actually more around 220-250km, so 300km may be too *high* a figure. We'll just have to see what the eventual spread is like if/when we get sufficient data to build a knowledge base.

5. Initial estimates for the lower bound of DP-qualifying-body sizes were "between 200 and 400km diameter". This just splits the difference.

6. As per the usual wiki policy links, there is no bandwidth cap, nor is there a finite amount of space or limits on page and word count; if it ends up spreading to thousands or hundreds of thousands of entries, then it can be split off into multiple numeric-index sub pages the same way as the master list of prefix-numbered SSSBs is... That's up to almost 450 individual pages of 1000 items each, at last count... sprawl can be fought with good organisation, and particularly each of the categories can be given its own page, then further broken up as desired.

That's the beauty of being on the interweb; more text data than any one person could comfortably read in a lifetime can be transferred over a typical broadband connection in an hour or two, and it takes up storage space that costs less than calories you burn waiting for the download to complete... 209.93.141.17 (talk) 06:23, 25 September 2017 (UTC)


 * Mimas is NOT known to be in hydrostatic equilibrium, and is doubtful to be in HE, and the much larger Iapetus (at around 1400 km) is known to not have a shape consistent with being in HE (see Thomas, Icarus 208 (2010) 395–401, analysing the shapes of Saturn's moons using Cassini images). The smallest object known to have a shape consistent with HE is Ceres at over 900 km. Theoretical anaylsis (Cole, and independently Lineweaver) puts the lower limit at over 300 km. Tbayboy (talk) 15:52, 25 September 2017 (UTC)