User:Kepler-1229b/sandbox/pdpold

In 2010, Gonzalo Tancredi presented a report to the IAU evaluating a list of 46 candidates for dwarf planet status based on light-curve-amplitude analysis and a calculation that the object was more than 450 kilometres (280 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 not yet accepted: Sedna, Orcus, and Quaoar.^[1] Although the IAU had anticipated Tancredi's recommendations, a decade later the IAU had never responded.

Mike Brown considers 130 trans-Neptunian bodies to be "probably" dwarf planets, ranked them by estimated size.^[2] 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."^[2]

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

• Near certainty: diameter estimated/measured to be over 900 kilometres (560 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 600 kilometres (370 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 500 kilometres (310 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 400 kilometres (250 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 200 kilometres (120 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 accepted by the IAU, the 'nearly certain' category includes Gonggong, Quaoar, Sedna, Orcus, 2002 MS4 and Salacia.

Grundy et al. propose that dark, low-density TNOs in the size range of approximately 400–1000 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.^[3]

Many TNOs in the size range of about 400–1000 km have oddly low densities, in the range of about 1.0–1.2 g/cm³, that are substantially less than 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 1000 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 is also evidence of full differentiation, as such bodies were presumably resurfaced with ice from their interiors. Grundy et al.^[3] propose therefore that mid-size (< 1000 km), low-density (< 1.4 g/ml) and low-albedo (< ~0.2) bodies such as Salacia, Varda, Gǃkúnǁʼhòmdímà and (55637) 2002 UX25 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 900–1000 km.^[3]

If Grundy et al.^[3] are correct, then among known bodies in the outer Solar System only Pluto–Charon, Eris, Haumea, Gonggong, Makemake, Quaoar, Orcus, Sedna and perhaps Salacia (which if it were spherical and had the same albedo as its moon 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)^[4] 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.

The assessments of the IAU, Tancredi et al., Brown and Grundy et al. for sixteen of the largest potential dwarf planets are as follows. For the IAU, the acceptance criteria were for naming purposes. Several of these objects had not yet been discovered when Tancredi et al. did their analysis. Brown's sole criterion is diameter; he accepts a great many more as highly likely to be dwarf planets (see below). Grundy et al. did not determine which bodies were dwarf planets, but rather which could not be. A red marks objects too dark or not dense enough to be solid bodies, a question mark the smaller bodies consistent with being differentiated (the question of current equilibrium was not addressed).

Mercury, Iapetus, Earth's moon and Phoebe are included for comparison, as none of these objects are in equilibrium today. The first three of these objects are round at present, but Phoebe is not. Triton (which formed as a TNO and is likely still in equilibrium) and Charon are included as well.

Designation	Measured mean diameter (km)	Density (g/cm3)	Albedo	Per Grundy et al.[3][4]	Per Brown[2]	Per Tancredi et al.[1]	Per IAU	Category
Mercury	4880	5.427	0.142	(no longer in equilibrium)[5]				(planet)
The Moon	3475	3.344	0.136	(no longer in equilibrium)[6][7]				(moon of Earth)
N I Triton	2707±2	2.06	0.76	(likely in equilibrium)[8]				(moon of Neptune)
134340 Pluto	2376±3	1.854±0.006	0.49 to 0.66					2:3 resonant
136199 Eris	2326±12	2.43±0.05	0.96					SDO
136108 Haumea	≈ 1560	≈ 2.018	0.51				(naming rules)	cubewano
S VIII Iapetus	1469±6	1.09±0.01	0.05 to 0.5	(no longer in equilibrium)[9]				(moon of Saturn)
136472 Makemake	1430+38 −22	1.9±0.2	0.81				(naming rules)	cubewano
225088 Gonggong	1230±50	1.74±0.16	0.14			NA		3:10 resonant
P I Charon	1212±1	1.70±0.02	0.2 to 0.5	(possibly in equilibrium)[10]				(moon of Pluto)
50000 Quaoar	1110±5	2.0±0.5	0.11					cubewano
90377 Sedna	995±80	?	0.32					detached
1 Ceres	946±2	2.16±0.01	0.09	(close to equilibrium)[11]				asteroid
90482 Orcus	910+50 −40	1.53±0.14	0.23					2:3 resonant
120347 Salacia	846±21	1.5±0.12	0.04					cubewano
(307261) 2002 MS4	778±11	?	0.10			NA		cubewano
(55565) 2002 AW197	768±39	?	0.11					cubewano
174567 Varda	749±18	1.27±0.06	0.10					4:7 resonant
(532037) 2013 FY27	742+78 −83	?	0.17			NA		SDO
28978 Ixion	710±0.2	?	0.10					2:3 resonant
(208996) 2003 AZ84	707±24	? 1.1±0.2	0.10					2:3 resonant
S IX Phoebe	213±2	1.64±0.03	0.06	(no longer in equilibrium)[12]				(moon of Saturn)

The following trans-Neptunian objects have estimated diameters at least 400 kilometres (250 mi) and so were considered "probable" dwarf planets in Brown's early assessment. Not all bodies estimated to be this size are included. The list is complicated by bodies such as 47171 Lempo that were at first assumed to be large single objects but later discovered to be binary or triple systems of smaller bodies.^[13] The dwarf planet Ceres is included, but not other asteroids. Explanations and sources for the measured masses and diameters can be found in the corresponding articles linked in column "Designation" of the table.

The Best diameter column uses a measured diameter if one exists, otherwise it uses Brown's assumed-albedo diameter. If Brown does not list the body, the size is calculated from an assumed-albedo of 9% per Johnston.^[14]

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