List of possible dwarf planets
The number of dwarf planets in the Solar System is unknown. Estimates have run as high as 200 in the Kuiper belt and over 10,000 in the region beyond. However, consideration of the surprisingly low densities of many dwarf-planet candidates suggests that the numbers may be much lower, possibly only nine among bodies known so far. The International Astronomical Union (IAU) required dwarf planets to be in hydrostatic equilibrium, and notes five in particular: in the inner Solar System and four in the trans-Neptunian region: , , , and . The last two were accepted as dwarf  planets for naming purposes and will keep their names if it turns out they are not dwarf planets. Only Pluto is actually confirmed to be in hydrostatic equilibrium, due to the results of the "New Horizons" mission. Other trans-Neptunian objects have been called dwarf planets if they appear to at least be solid bodies: planetologists generally include at least , , , and . Limiting values. 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 . 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. , which has a significant amount of ice in its composition, is the only accepted dwarf planet in the asteroid belt, though there are 	List of possible dwarf planets
14147935	unexplained anomalies. 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. 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 in diameter may not be in hydrostatic equilibrium and thus not dwarf 	List of possible dwarf planets
14147936	planets. The question remains open if the two largest icy outer-belt asteroids 10 Hygiea and 704 Interamnia are also dwarf planets. 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 	List of possible dwarf planets
14147937	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. 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. Much 	List of possible dwarf planets
14147938	larger objects, such as Earth's moon and the planet Mercury, are not near hydrostatic equilibrium today, 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. The majority of mid-sized TNOs up to about in 	List of possible dwarf planets
14147939	diameter have significantly lower densities (~ ) than larger bodies such as Pluto (1.86 g/ml). 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 in diameter is (pending some other formative mechanism) unlikely to be a dwarf planet. Tancredi's assessment. 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 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. Although the IAU had anticipated Tancredi's recommendations, a decade later the IAU had never responded. Brown's assessment. 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: Beside the five accepted by the IAU, the 'nearly certain' category includes , , , , , and . Grundy "et al".’s assessment. Grundy "et al". propose that dark, low-density TNOs in the size range of approximately 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 have oddly low densities, in the range of about , 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". propose therefore that mid-size (< 1,000 km), low-density (< 1.4 g/ml) and low-albedo (< ~0.2) bodies such as Salacia, Varda, Gǃkúnǁʼhòmdímà, and 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 , although Grundy et al. also speculated that 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, Orcus, and Sedna are either known (Pluto) or strong candidates (the others). There are a number of smaller bodies, probably between 700 and 900 km 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 (0.18) an exception; this suggests that they are not dwarf planets. However, Salacia and Varda may be  dense enough to 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/cm, calculated a few months after Grundy et al.'s initial assessment, though still an albedo of only 0.04. Varda might have a higher density of 1.78±0.06 g/cm (although a lower density of 1.23±0.04 g/cm was still considered possible though less probable), published the year after Grundy et al.'s initial assessment; its albedo of 0.10 is close to Quaoar's. Likeliest dwarf planets. The assessments of the IAU, Tancredi  et al., Brown, and Grundy et al. for sixteen of the largest potential dwarf planets (the ones whose estimated diameters are above 700 km) 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 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 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). The question of current equilibrium was not addressed. Some objects are included for comparison. Mercury, Iapetus, and Earth's moon are round but known to be out of equilibrium today. Callisto, Rhea, and Titan have shapes that are consistent with hydrostatic equilibrium, but it has been questioned if they are actually in it. Triton formed as a TNO, and Charon is larger than some  dwarf planet candidates. Phoebe is small and not round today, but may have been in equilibrium in the past. Largest measured candidates. The following trans-Neptunian objects have measured diameters at least 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 and a poorly constrained , 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. "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 or Lempo. A 2020 occultation of ("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. All of these categories are subject to change with further evidence. </ref> Brightest unmeasured candidates. 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 cyan for >600km. </ref>