List of possible dwarf planets#Likeliest dwarf planets

Image:Ixion-Spitzer2007.gif depends on the albedo (the fraction of light that it reflects). Current estimates are that the albedo is 13–15%, a bit under the midpoint of the range shown here and corresponding to a diameter of 620 km.]]

Beside directly orbiting the Sun, the qualifying feature of a dwarf planet is that it have "sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape".{{cite web |website=International Astronomical Union |title=IAU 2006 General Assembly: Result of the IAU Resolution votes |url=http://www.iau.org/iau0603.414.0.html |date=24 August 2006 |access-date=2008-01-26 |url-status=dead |archive-url=https://web.archive.org/web/20070103145836/http://www.iau.org/iau0603.414.0.html |archive-date=2007-01-03 |df=dmy-all}}{{cite web|url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Dwarf&Display=OverviewLong |title=Dwarf Planets |website=NASA |access-date=2008-01-22 |archive-url=https://web.archive.org/web/20120723014035/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Dwarf&Display=OverviewLong |archive-date=2012-07-23 |url-status=dead |df=dmy-all}}{{cite press release |url=http://www.iau.org/public_press/news/release/iau0804 |title=Plutoid chosen as name for Solar System objects like Pluto |date=11 June 2008 |access-date=2008-06-15 |archive-url=https://web.archive.org/web/20110702012327/http://iau.org/public_press/news/detail/iau0804 |archive-date=2011-07-02 |url-status=dead |df=dmy-all}} Current observations are generally insufficient for a direct determination as to whether a body meets this definition. Often the only clues for trans-Neptunian objects (TNO) is a crude estimate of their diameters and albedos. Icy satellites as large as 1,500 km in diameter have proven to not be in equilibrium, whereas dark objects in the outer solar system often have low densities that imply they are not even solid bodies, much less gravitationally controlled dwarf planets.

{{dp|Ceres}}, which has a significant amount of ice in its composition, is the only accepted dwarf planet in the asteroid belt, though there are unexplained anomalies.{{cite journal |title=A basin-free spherical shape as an outcome of a giant impact on asteroid Hygiea |url=https://www.eso.org/public/archives/releases/sciencepapers/eso1918/eso1918a.pdf |display-authors=etal |last1=Vernazza |first1=P. |last2=Jorda |first2=L. |last3=Ševeček |first3=P. |last4=Brož |first4=M. |last5=Viikinkoski |first5=M. |last6=Hanuš |first6=J. |journal=Nature Astronomy |volume=273 |issue=2 |pages=136–141 |doi=10.1038/s41550-019-0915-8 |hdl=10045/103308 |access-date=2019-10-28|year=2020 |bibcode=2020NatAs...4..136V |s2cid=209938346 |hdl-access=free}} 4 Vesta, the second-most-massive asteroid and one that is basaltic in composition, appears to have a fully differentiated interior and was therefore in equilibrium at some point in its history, but no longer is today.{{cite press release

|author1=Savage, Don

|author2=Jones, Tammy

|author3= Villard, Ray

|date=1995-04-19 |title=Asteroid or mini-planet? Hubble maps the ancient surface of Vesta

|id= News Release STScI-1995-20

|website=HubbleSite

|url=http://hubblesite.org/newscenter/archive/releases/1995/20/image/c

|access-date=2006-10-17 |df=dmy-all}} The third-most massive object, 2 Pallas, has a somewhat irregular surface and is thought to have only a partially differentiated interior; it is also less icy than Ceres. Michael Brown has estimated that, because rocky objects such as Vesta are more rigid than icy objects, rocky objects below {{convert|900|km|mi}} in diameter may not be in hydrostatic equilibrium and thus not dwarf planets. The two largest icy outer-belt asteroids 10 Hygiea and 704 Interamnia are close to equilibrium, but in Hygiea's case this may be a result of its disruption and the re-aggregation of its fragments, while Interamnia is now somewhat away from equilibrium due to impacts.{{cite journal|arxiv=1911.13049|doi=10.1051/0004-6361/201936639|title=(704) Interamnia: A transitional object between a dwarf planet and a typical irregular-shaped minor body|year=2020|last1=Hanuš|first1=J.|last2=Vernazza|first2=P.|last3=Viikinkoski|first3=M.|last4=Ferrais|first4=M.|last5=Rambaux|first5=N.|last6=Podlewska-Gaca|first6=E.|last7=Drouard|first7=A.|last8=Jorda|first8=L.|last9=Jehin|first9=E.|last10=Carry|first10=B.|last11=Marsset|first11=M.|last12=Marchis|first12=F.|last13=Warner|first13=B.|last14=Behrend|first14=R.|last15=Asenjo|first15=V.|last16=Berger|first16=N.|last17=Bronikowska|first17=M.|last18=Brothers|first18=T.|last19=Charbonnel|first19=S.|last20=Colazo|first20=C.|last21=Coliac|first21=J.-F.|last22=Duffard|first22=R.|last23=Jones|first23=A.|last24=Leroy|first24=A.|last25=Marciniak|first25=A.|last26=Melia|first26=R.|last27=Molina|first27=D.|last28=Nadolny|first28=J.|last29=Person|first29=M.|last30=Pejcha|first30=O.|s2cid=208512707|journal=Astronomy & Astrophysics|volume=633|pages=A65|bibcode=2020A&A...633A..65H|display-authors=29}}

Based on a comparison with the icy moons that have been visited by spacecraft, such as Mimas (round at 400 km in diameter) and Proteus (irregular at 410–440 km in diameter), Brown estimated that an icy body relaxes into hydrostatic equilibrium at a diameter somewhere between 200 and 400 km. However, after Brown and Tancredi made their calculations, better determination of their shapes showed that Mimas and the other mid-sized ellipsoidal moons of Saturn up to at least Iapetus (which, at 1,471 km in diameter, is approximately the same size as Haumea and Makemake) are no longer in hydrostatic equilibrium; they are also icier than TNOs are likely to be. They have equilibrium shapes that froze in place some time ago, and do not match the shapes that equilibrium bodies would have at their current rotation rates.{{cite web |url=http://www.planetary.org/blogs/emily-lakdawalla/2012/3389.html |title=Iapetus' peerless equatorial ridge |website=www.planetary.org |access-date=2 April 2018}} Thus Rhea, at 1528 km in diameter, is the smallest body for which gravitational measurements are consistent with current hydrostatic equilibrium. Ceres, at 950 km in diameter, is close to equilibrium, but some deviations from equilibrium shape remain unexplained.{{cite book|chapter-url=https://meetingorganizer.copernicus.org/EPSC2018/EPSC2018-645-1.pdf|display-authors=4|author1=Raymond, C.|author2=Castillo-Rogez, J.C.|author3=Park, R.S.|author4=Ermakov, A.|author5=Bland, M.T.|author6=Marchi, S.|author7=Prettyman, T.|author8=Ammannito, E.|author9=De Sanctis, M.C.|author10=Russell, C.T.|date=September 2018|chapter=Dawn Data Reveal Ceres' Complex Crustal Evolution|title=European Planetary Science Congress|volume=12|access-date=19 July 2020|archive-date=30 January 2020|archive-url=https://web.archive.org/web/20200130111631/https://meetingorganizer.copernicus.org/EPSC2018/EPSC2018-645-1.pdf|url-status=live}} Much larger objects, such as Earth's moon and the planet Mercury, are not near hydrostatic equilibrium today,{{cite journal |author1=Garrick |author2=Bethell |display-authors=etal |year=2014 |title=The tidal-rotational shape of the Moon and evidence for polar wander |journal=Nature |volume=512 |issue=7513 |pages=181–184|doi=10.1038/nature13639 |pmid=25079322 |bibcode=2014Natur.512..181G |s2cid=4452886 |url=https://escholarship.org/uc/item/0012r6g6 }}{{cite book |via=Google Books |chapter-url=https://books.google.com/books?id=QzXZs_xSLk4C&q=Hydrostatic+equilibrium+mercury&pg=PA23 |title=Mercury |chapter=Hydrostatic equilibrium of Mercury|page=23|isbn = 9780387775395|last1 = Balogh|first1 = A.|last2 = Ksanfomality|first2 = Leonid|last3 = Steiger|first3 = Rudolf von|publisher = Springer Science & Business Media|date = 23 February 2008}}{{cite journal|title=The low-degree shape of Mercury|display-authors=etal|first1=Mark E.|last1=Perry|first2=Gregory A.|last2=Neumann|first3=Roger J.|last3=Phillips|first4=Olivier S.|last4=Barnouin|first5=Carolyn M.|last5=Ernst|first6=Daniel S.|last6=Kahan|journal=Geophysical Research Letters|volume=42|issue=17|pages=6951–6958|date=September 2015|doi-access=free|doi=10.1002/2015GL065101|bibcode=2015GeoRL..42.6951P|s2cid=103269458}} though the Moon is composed primarily of silicate rock and Mercury of metal (in contrast to most dwarf planet candidates, which are ice and rock). Saturn's moons may have been subject to a thermal history that would have produced equilibrium-like shapes in bodies too small for gravity alone to do so. Thus, at present it is unknown whether any trans-Neptunian objects smaller than Pluto and Eris are in hydrostatic equilibrium. Nonetheless, it does not matter in practice, because the precise statement of hydrostatic equilibrium in the definition is universally ignored in favour of roundness and solidity.

The majority of mid-sized TNOs up to about {{Val|900|-|1000|u=km}} in diameter have significantly lower densities (~ {{Val|1.0|-|1.2|u=g|up=ml}}) than larger bodies such as Pluto (1.86 g/cm³). Brown had speculated that this was due to their composition, that they were almost entirely icy. However, Grundy et al. point out that there is no known mechanism or evolutionary pathway for mid-sized bodies to be icy while both larger and smaller objects are partially rocky. They demonstrated that at the prevailing temperatures of the Kuiper Belt, water ice is strong enough to support open interior spaces (interstices) in objects of this size; they concluded that mid-size TNOs have low densities for the same reason that smaller objects do—because they have not compacted under self-gravity into fully solid objects, and thus the typical TNO smaller than {{Val|900|-|1000|u=km}} in diameter is (pending some other formative mechanism) unlikely to be a dwarf planet.

In 2010, Gonzalo Tancredi presented a report to the IAU evaluating a list of 46 trans-Neptunian candidates for dwarf planet status based on light-curve-amplitude analysis and a calculation that the object was more than {{convert|450|km|mi}} in diameter. Some diameters were measured, some were best-fit estimates, and others used an assumed albedo of 0.10 to calculate the diameter. Of these, he identified 15 as dwarf planets by his criteria (including the 4 accepted by the IAU), with another 9 being considered possible. To be cautious, he advised the IAU to "officially" accept as dwarf planets the top three: Sedna, Orcus, and Quaoar. Although the IAU had anticipated Tancredi's recommendations, by late 2023 only Quaoar had been accepted.

Mike Brown considers 130 trans-Neptunian bodies to be "probably" dwarf planets, ranked them by estimated size. He does not consider asteroids, stating "in the asteroid belt Ceres, with a diameter of 900 km, is the only object large enough to be round."

The terms for varying degrees of likelihood he split these into:

• Near certainty: diameter estimated/measured to be over {{convert|900|km|mi}}. Sufficient confidence to say these must be in hydrostatic equilibrium, even if predominantly rocky. 10 objects as of 2020.
• Highly likely: diameter estimated/measured to be over {{convert|600|km|mi}}. The size would have to be "grossly in error" or they would have to be primarily rocky to not be dwarf planets. 17 objects as of 2020.
• Likely: diameter estimated/measured to be over {{convert|500|km|mi}}. Uncertainties in measurement mean that some of these will be significantly smaller and thus doubtful. 41 objects as of 2020.
• Probably: diameter estimated/measured to be over {{convert|400|km|mi}}. Expected to be dwarf planets, if they are icy, and that figure is correct. 62 objects as of 2020.
• Possibly: diameter estimated/measured to be over {{convert|200|km|mi}}. Icy moons transition from a round to irregular shape in the 200–400 km range, suggesting that the same figure holds true for KBOs. Thus, some of these objects could be dwarf planets. 611 objects as of 2020.
• Probably not: diameter estimated/measured to be under 200 km. No icy moon under 200 km is round, and the same may be true of KBOs. The estimated size of these objects would have to be in error for them to be dwarf planets.

Beside the five older accepted by the IAU plus Quaoar, the 'nearly certain' category includes {{dp|Gonggong}}, {{dp|Sedna}}, {{dp|Orcus}}, {{mpl|2002 MS|4}}, and {{dp|Salacia}}. Note that although Brown's site claims to be updated daily, these largest objects haven't been updated since late 2013, and indeed the current best diameter estimates for Salacia and {{mp|2002 MS|4}} are less than 900 km. (Orcus is just above the threshold.)[https://web.archive.org/web/20131113235927/http://www.gps.caltech.edu/~mbrown/dps.html How many dwarf planets are there in the outer solar system? (updates daily)], updated 2013-11-01

File:TNO diameter-density plot - Rommel et al. 2025 Fig 1.jpg

Grundy et al. propose that dark, low-density TNOs in the size range of approximately {{Val|400|-|1000|u=km}} are transitional between smaller, porous (and thus low-density) bodies and larger, denser, brighter, and geologically differentiated planetary bodies (such as dwarf planets). Bodies in this size range should have begun to collapse the interstitial spaces left over from their formation, but not fully, leaving some residual porosity.

Many TNOs in the size range of about {{Val|400|-|1,000|u=km}} have oddly low densities, in the range of about {{Val|1.0|-|1.2|u=g/cm3}}, that are substantially less than those of dwarf planets such as Pluto, Eris and Ceres, which have densities closer to 2. Brown has suggested that large low-density bodies must be composed almost entirely of water ice since he presumed that bodies of this size would necessarily be solid. However, this leaves unexplained why TNOs both larger than 1,000 km and smaller than 400 km, and indeed comets, are composed of a substantial fraction of rock, leaving only this size range to be primarily icy. Experiments with water ice at the relevant pressures and temperatures suggest that substantial porosity could remain in this size range, and it is possible that adding rock to the mix would further increase resistance to collapsing into a solid body. Bodies with internal porosity remaining from their formation could be at best only partially differentiated, in their deep interiors (if a body had begun to collapse into a solid body, there should be evidence in the form of fault systems from when its surface contracted). The higher albedos of larger bodies are also evidence of full differentiation, as such bodies were presumably resurfaced with ice from their interiors. Grundy et al. propose therefore that mid-size (< 1,000 km), low-density (< 1.4 g/cm³) and low-albedo (< ~0.2) bodies such as Salacia, Varda, Gǃkúnǁʼhòmdímà, and {{mpl|55637|2002 UX|25}} are not differentiated planetary bodies like Orcus, Quaoar, and Charon. The boundary between the two populations would appear to be in the range of about {{Val|900|-|1000|u=km}}, although Grundy et al. also suggest that {{val|600|-|700|u=km}} might constitute an upper limit to retaining significant porosity.

If Grundy et al. are correct, then very few known bodies in the outer Solar System are likely to have compacted into fully solid bodies, and thus to possibly have become dwarf planets at some point in their past or to still be dwarf planets at present. Pluto–Charon, Eris, Haumea, Gonggong, Makemake, Quaoar, and Sedna are either known (Pluto) or strong candidates (the others). Orcus is again just above the threshold by size, though it is bright.

There are a number of smaller bodies, estimated to be between 700 and 900 km in diameter, for most of which not enough is known to apply these criteria. All of them are dark, mostly with albedos under 0.11, with brighter {{mpl|2013 FY|27}} (0.18) an exception; this suggests that they are not dwarf planets. However, Salacia and Varda may be dense enough to at least be solid. If Salacia were spherical and had the same albedo as its moon, it would have a density of between 1.4 and 1.6 g/cm³, calculated a few months after Grundy et al.'s initial assessment, though still an albedo of only 0.04.{{cite journal |last1=Grundy |first1=W.M. |last2=Noll |first2=K.S. |last3=Roe |first3=H.G. |last4=Buie |first4=M.W. |last5=Porter |first5=S.B. |last6=Parker |first6=A.H. |last7=Nesvorný |first7=D. |last8=Levison |first8=H.F. |last9=Benecchi |first9=S.D. |last10=Stephens |first10=D.C. |last11=Trujillo |first11=C.A. |display-authors=6 |title=Mutual orbit orientations of transneptunian binaries |journal=Icarus |date=December 2019 |volume=334 |pages=62–78 |doi=10.1016/j.icarus.2019.03.035 |bibcode=2019Icar..334...62G |s2cid=133585837 |url=http://www2.lowell.edu/~grundy/abstracts/preprints/2019.TNB_orbits.pdf |url-status=dead |archive-url=https://web.archive.org/web/20190407052940/http://www2.lowell.edu/~grundy/abstracts/preprints/2019.TNB_orbits.pdf |archive-date=2019-04-07 |df=dmy-all}} Varda might have a higher density of 1.78±0.06 g/cm³ (a lower density of 1.23±0.04 g/cm³ was considered possible though less probable), published the year after Grundy et al.'s initial assessment;{{cite journal

|display-authors = etal

|first1 = D. |last1 = Souami

|first2 = F. |last2 = Braga-Ribas

|first3 = B. |last3 = Sicardy

|first4 = B. |last4 = Morgado

|first5 = J. L. |last5 = Ortiz

|first6 = J. |last6 = Desmars

|date = August 2020

|title = A multi-chord stellar occultation by the large trans-Neptunian object (174567) Varda

|journal = Astronomy & Astrophysics |volume = 643 |pages = A125 |doi = 10.1051/0004-6361/202038526 |arxiv = 2008.04818

|bibcode = 2020A&A...643A.125S |s2cid = 221095753 }} its albedo of 0.10 is close to Quaoar's.

In 2023, Emery et al. wrote that near-infrared spectroscopy by the James Webb Space Telescope (JWST) in 2022 suggests that Sedna, Gonggong and Quaoar internally melted and differentiated and are chemically evolved, like the larger dwarf planets Pluto, Eris, Haumea, and Makemake, but unlike "all smaller KBOs". This is because light hydrocarbons are present on their surfaces (e.g. ethane, acetylene, and ethylene), which implies that methane is continuously being resupplied, and that methane would likely come from internal geochemistry. On the other hand, the surfaces of Sedna, Gonggong and Quaoar have low abundances of CO and CO₂, similar to Pluto, Eris and Makemake but in contrast to smaller bodies. This suggests that the threshold for dwarf planethood in the trans-Neptunian region is a diameter of ~1000 km (thus including only Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar and possibly Sedna).{{cite journal|last1=Emery|first1=J. P. |first2=I. |last2=Wong |first3=R. |last3=Brunetto |first4=J. C. |last4=Cook |first5=N. |last5=Pinilla-Alonso |first6=J. A. |last6=Stansberry |first7=B. J. |last7=Holler |first8=W. M. |last8=Grundy |first9=S. |last9=Protopapa |first10=A. C. |last10=Souza-Feliciano |first11=E. |last11=Fernández-Valenzuela |first12=J. I. |last12=Lunine |first13=D. C. |last13=Hines |author-link=|date=2024|title=A Tale of 3 Dwarf Planets: Ices and Organics on Sedna, Gonggong, and Quaoar from JWST Spectroscopy|journal=Icarus |volume=414 |doi=10.1016/j.icarus.2024.116017 |arxiv=2309.15230|bibcode=2024Icar..41416017E }}

The assessments of the IAU, Tancredi et al., Brown, and Grundy et al. for some of potential dwarf planets are as follows. For the IAU, the acceptance criteria were for naming purposes; Quaoar was called a dwarf planet in a 2022–2023 IAU annual report.{{cite web |url=https://www.iau.org/static/science/scientific_bodies/divisions/f/division-f-annual-report-2022-2023.pdf |title=Report of Division F "Planetary Systems and Astrobiology": Annual Report 2022-23 |last= |first= |date=2022–2023 |website= |publisher=International Astronomical Union |access-date=8 December 2023 |quote=}} An IAU question-and-answer press release from 2006 was more specific: it estimated that objects with mass above {{val|5|e=20|u=kg}} and diameter greater than 800 km (800 km across) would "normally" be in hydrostatic equilibrium ("the shape ... would normally be determined by self-gravity"), but that "all borderline cases would need to be determined by observation."{{cite web |title='Planet Definition' Questions & Answers Sheet |url=https://www.iau.org/static/archives/releases/doc/iau0601_q_answers.doc |publisher=International Astronomical Union |date=August 24, 2006 |access-date=October 16, 2021}} This is close to Grundy et al.'s suggestion for the approximate limit.

Several of these objects had not yet been discovered when Tancredi et al. did their analysis. Brown's sole criterion is diameter; he accepts significantly many more as "highly likely" to be dwarf planets, for which his threshold is 600 km (see below). Grundy et al. did not determine which bodies were dwarf planets, but rather which could not be. A red Image:X mark.svg marks objects that are not dense enough to be solid bodies; to this is added a question mark for the objects whose densities are not known (they are all dark, suggesting that they are not dwarf planets). Emery et al. suggest that Sedna, Quaoar, and Gonggong went through internal melting, differentiation, and chemical evolution like the larger dwarf planets, but that all smaller KBOs did not. The question of current equilibrium was not addressed; nonetheless, it is not generally taken seriously despite being in the definition. (Mercury is round but known to be out of equilibrium;Sean Solomon, Larry Nittler & Brian Anderson, eds. (2018) Mercury: The View after MESSENGER. Cambridge Planetary Science series no. 21, Cambridge University Press. Chapter 3. it is universally considered as a planet according to the intent of the IAU and geophysical definitions, rather than to the letter.){{Cite tweet |user=plutokiller |last=Brown |first=Mike |number=1624127764969459713 |title=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}} This would be relevant for Quaoar, as in 2024, Kiss et al. found that Quaoar has an ellipsoidal shape incompatible with hydrostatic equilibrium for its current spin. They hypothesised that Quaoar originally had a rapid rotation and was in hydrostatic equilibrium, but that its shape became "frozen in" and did not change as it spun down due to tidal forces from its moon Weywot.{{cite journal

|display-authors = etal

|first1 = C. |last1 = Kiss

|first2 = T. G. |last2 = Müller

|first3 = G. |last3 = Marton

|first4 = R. |last4 = Szakáts

|first5 = A. |last5 = Pál

|first6 = L. |last6 = Molnár

|title = The visible and thermal light curve of the large Kuiper belt object (50000) Quaoar

|journal = Astronomy & Astrophysics

|date = March 2024

|volume = 684

|issue =

|pages = A50 |doi = 10.1051/0004-6361/202348054

|arxiv = 2401.12679

|bibcode = 2024A&A...684A..50K}} If so, this would resemble the situation of Saturn's moon Iapetus, which is too oblate for its current spin.Cowen, R. (2007). Idiosyncratic Iapetus, Science News vol. 172, pp. 104–106. [http://www.sciencenews.org/articles/20070818/bob8ref.asp references] {{Webarchive|url=https://web.archive.org/web/20071013165655/http://www.sciencenews.org/articles/20070818/bob8ref.asp |date=2007-10-13 }}{{cite journal| doi = 10.1016/j.icarus.2010.01.025| last1 = Thomas| first1 = P. C.| date = July 2010| title = Sizes, shapes, and derived properties of the saturnian satellites after the Cassini nominal mission| journal = Icarus| volume = 208| issue = 1| pages = 395–401| url = http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf| bibcode = 2010Icar..208..395T| access-date = 2015-09-25| archive-date = 2018-12-23| archive-url = https://web.archive.org/web/20181223003125/http://www.ciclops.org/media/sp/2011/6794_16344_0.pdf| url-status = dead}} Iapetus is generally still considered a planetary-mass moon nonetheless,Emily Lakdawalla et al., [https://www.planetary.org/worlds/what-is-a-planet What Is A Planet?] {{Webarchive|url=https://web.archive.org/web/20220122142140/https://www.planetary.org/worlds/what-is-a-planet |date=2022-01-22 }} The Planetary Society, 21 April 2020 though not always.{{cite journal |last1=Chen |first1=Jingjing |last2=Kipping |first2=David |date=2016 |title=Probabilistic Forecasting of the Masses and Radii of Other Worlds |journal=The Astrophysical Journal |volume=834 |issue=1 |page=17 |doi= 10.3847/1538-4357/834/1/17|arxiv=1603.08614 |s2cid=119114880 |doi-access=free |bibcode=2017ApJ...834...17C }}

Two moons are included for comparison: Triton likely formed as a TNO before it was captured by Neptune, and Charon is larger than some dwarf planet candidates.

{{See also|Category:Possible dwarf planets}}

The following trans-Neptunian objects have measured diameters at least {{convert|600|km|mi|-1}} to within measurement uncertainties; this was the threshold to be considered a "highly likely" dwarf planet in Brown's early assessment. Grundy et al. speculated that 600 km to 700 km diameter could represent "the upper limit to retain substantial internal pore space", and that objects around 900 km could have collapsed interiors but fail to completely differentiate. The two satellites of TNOs that surpass this threshold have also been included: Pluto's moon Charon and Eris' moon Dysnomia. The next largest TNO moon is Orcus' moon Vanth at {{val|442.5|10.2|u=km}} and a poorly constrained {{val|87|8|e=18|u=kg}}, with an albedo of about 8%.

Ceres, generally accepted as a dwarf planet, is added for comparison. Also added for comparison is Triton, which is thought to have been a dwarf planet in the Kuiper belt before it was captured by Neptune.

Bodies with very poorly known sizes (e.g. {{mpl|2018 VG|18}} "Farout") have been excluded. Complicating the situation for poorly known bodies is that a body assumed to be a large single object might turn out to be a binary or ternary system of smaller objects, such as {{mpl-|532037|2013 FY|27}} or Lempo. A 2021 occultation of {{mpl-|612911|2004 XR|190}} ("Buffy") found a chord of 560 km: if the body is approximately spherical, it is likely that the diameter is greater than 560 km, but if it is elongated, the mean diameter may well be less. Explanations and sources for the measured masses and diameters can be found in the corresponding articles linked in column "Designation" of the table.

• The bodies with estimated diameter over 900 km are bolded; they have general consensus as being dwarfs, per the previous section. Charon is also bolded, as it has sometimes been considered a possible dwarf in its own right; Triton is bolded as a former KBO that is still rounded and geologically active. Orcus and Sedna are put in the next category due to uncertainties.
• Those with estimated diameter between 700 km and 900 km are in bold italic; most are borderline possibilities, but in most cases are too poorly known for much certainty. They tend to be dark, suggesting that they are not dwarf planets, but some might be dense enough to be fully solid bodies.
• The others, having estimated diameter below 700 km, are unlikely to be dwarf planets on the basis of current evaluation, but may be transitional (partially compressed) bodies.
• Light grey indicates objects whose densities may or may not be higher than 1.5 g/cm³.
• Dark grey indicates those whose densities are known to be lower, and hence if the data is correct cannot be dwarf planets.
• Satellites are highlighted in pink, as under the current definition a dwarf planet must directly orbit the Sun.

All of these categories are subject to change with further evidence.

{{notelist|group=table|refs=

The geometric albedo $A$ is calculated from the measured absolute magnitude $H$

and measured diameter $D$ via the formula: $A\; =\backslash left\; (\; \backslash frac\{1329\backslash times10^\{-H/5\}\}\{D\}\; \backslash right\; )\; ^2$. Ranges have been given for Triton, Pluto, and Charon, which have been observed up close and therefore have known local albedo variations.

This is the total system mass (including moons), except for Pluto, Haumea, and Orcus.

}}

For objects without a measured size or mass, sizes can only be estimated by assuming an albedo. Most sub-dwarf objects are thought to be dark, because they haven't been resurfaced; this means that they are also relatively large for their magnitudes. Below is a table for assumed albedos between 4% (the albedo of Salacia) and 20% (a value above which suggests resurfacing), and the sizes objects of those albedos would need to be (if round) to produce the observed absolute magnitude. Backgrounds are blue for >900 km and teal for >600 km.

{{notelist|group=table2|refs=

The diameter can be calculated from the measured absolute magnitude $H$, and for an assumed albedo $p$, via the formula: $D\; =\; \backslash frac\{1329\backslash times10^\{-H/5\}\}\{\backslash sqrt\{p\}\}$

}}

• Lists of astronomical objects
• List of trans-Neptunian objects
• List of gravitationally rounded objects of the Solar System
• List of former planets
• Planetary-mass moon

{{reflist|25em|refs=

{{cite web

|title = How many dwarf planets are there in the outer solar system?

|publisher = California Institute of Technology

|author = Michael E. Brown

|author-link= Michael E. Brown

|url = http://web.gps.caltech.edu/~mbrown/dps.html

|date = 13 September 2019

|access-date= 24 November 2019

|archive-url = https://web.archive.org/web/20191013130649/http://web.gps.caltech.edu/~mbrown/dps.html

|archive-date= 13 October 2019

|url-status=live}}

{{cite journal|date=2010|title=Physical and dynamical characteristics of icy "dwarf planets" (plutoids)|journal=Icy Bodies of the Solar System: Proceedings IAU Symposium No. 263, 2009|author=Tancredi, G.|volume=263|pages=173–185|doi=10.1017/S1743921310001717|bibcode=2010IAUS..263..173T|doi-access=free}}

{{cite web|title=List Of Trans-Neptunian Objects|url=http://www.minorplanetcenter.net/iau/lists/t_tnos.html|website=Minor Planet Center}} Retrieved 15 July 2023.

{{cite web|title=List Of Centaurs and Scattered-Disk Objects|url=http://www.minorplanetcenter.net/iau/lists/t_centaurs.html|website=Minor Planet Center}} Retrieved 15 July 2023.

{{cite web

|type = 2022-04-11 last obs.

|title = JPL Small-Body Database Browser: (2021 DR15)

|url = https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=54231255

|publisher = Jet Propulsion Laboratory

|accessdate = 25 October 2022}}

{{cite web

|type = 2022-03-09 last obs.

|title = JPL Small-Body Database Browser: (2018 VG18)

|url = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=3836918

|publisher = Jet Propulsion Laboratory

|access-date = 25 October 2022}}

{{cite web

|type = 2022-06-16 last obs.

|title = JPL Small-Body Database Browser: (2021 LL37)

|url = https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=54281066

|publisher = Jet Propulsion Laboratory

|accessdate = 25 October 2022}}

{{cite web

|type = 2020-06-25 last obs.

|title = JPL Small-Body Database Browser: (2020 MK53)

|url = https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=2020%20MK53

|publisher = Jet Propulsion Laboratory

|access-date = 15 July 2023}}

{{cite web

|type = 2021-08-24 last obs.

|title = JPL Small-Body Database Browser: (2018 AG37)

|url = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=54114199

|publisher = Jet Propulsion Laboratory

|access-date = 25 October 2022}}

{{cite web

|type = 2021-04-16 last obs.

|title = JPL Small-Body Database Browser: (2020 FY30)

|url = https://ssd.jpl.nasa.gov/sbdb.cgi?sstr=54117580

|publisher = Jet Propulsion Laboratory

|access-date = 25 October 2022}}

}}

• [http://ssd.jpl.nasa.gov/sbdb_query.cgi NASA JPL Small-Body Database Search Engine]
• [http://public-tnosarecool.lesia.obspm.fr/Published-results.html TNOs are cool public database], incl. diameters and albedos measured by Herschel and Spitzer to date, Herschel OT KP "TNOs are Cool: A Survey of the Transneptunian Region"
• [http://web.gps.caltech.edu/~mbrown/dps.html How many dwarf planets are there in the outer solar system? (updates daily)] (Mike Brown)
• [http://www.gps.caltech.edu/~mbrown/dps_notes.html Details on the dwarf planet size calculations] (Mike Brown)
• [http://adsabs.harvard.edu/abs/2008Icar..195..851T Which are the Dwarfs in the Solar System?] Tancredi, G.; Favre, S. Icarus, Volume 195, Issue 2, p. 851–862.

{{Dwarf planets}}

{{Trans-Neptunian objects}}

{{Solar System}}

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Possible dwarf planets

Category:Lists of trans-Neptunian objects

Category:Solar System