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The number of dwarf planets in the Solar System is unknown. Estimates run as high as 200 in the Kuiper belt[1] and over 10,000 in the region beyond.[2] However, consideration of the surprisingly low densities of many dwarf-planet candidates suggests that the numbers may be much lower (e.g. at most 9 among bodies known so far).[3] The International Astronomical Union (IAU) has accepted five: Ceres in the inner Solar System and four in the trans-Neptunian region: Pluto, Eris, Haumea, and Makemake, the last two accepted for naming purposes.

Contents

IAU naming proceduresEdit

In 2008, the IAU modified its naming procedures such that objects considered most likely to be dwarf planets receive differing treatment than others. Objects that have an absolute magnitude (H) less than +1, and hence a minimum diameter of 838 kilometres (521 mi) if the albedo is below 100%,[4] are overseen by two naming committees, one for minor planets and one for planets. Once named, the objects are declared to be dwarf planets. Makemake and Haumea are the only objects to have proceeded through the naming process as presumed dwarf planets; currently there are no other bodies that meet this criterion. All other bodies are named by the minor-planet naming committee alone, and the IAU has not stated how or if they will be accepted as dwarf planets.

Limiting valuesEdit

 
Calculation of the diameter of Ixion depends on the albedo (the fraction of light that it reflects), which is currently unknown.

Beside directly orbiting the Sun, the qualifying feature of a dwarf planet is that it "has sufficient mass for its self-gravity to overcome rigid-body forces so that it assumes a hydrostatic equilibrium (nearly round) shape".[5][6][7] 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 is a crude estimate of their diameters and albedos. Icy objects as large as 1500 km in diameter have proven to not be in equilibrium, whereas dark objects are unlikely to have been resurfaced and thus not have the active geology expected of a dwarf planet.

Ceres is thought to be the only dwarf planet in the asteroid belt. 4 Vesta, the second-most-massive asteroid, appears to have a fully differentiated interior and was therefore in equilibrium at some point in its history, but it is not today.[8] The third-most massive object, 2 Pallas, has a somewhat irregular surface and is thought to have only a partially differentiated interior. Michael Brown has estimated that, because rocky objects such as Vesta and Pallas are more rigid than icy objects, rocky objects below 900 kilometres (560 mi) in diameter may not be in hydrostatic equilibrium and thus not dwarf planets.[1]

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.[1] However, after Brown and Tancredi made their calculations, better determination of their shapes showed that Mimas and the other mid-sized moons of Saturn up to Iapetus are no longer in hydrostatic equilibrium. They have an equilibrium shape that froze in some time ago, and do not match the shape equilibrium bodies would have at their current rotation rates.[9] Thus Ceres, at 950 km in diameter, is the smallest body for which detailed measurements are consistent with hydrostatic equilibrium,[10] and Iapetus, at 1,470 km, is the largest body known to not be in equilibrium. It is not clear whether trans-Neptunian objects would behave more like Ceres or Iapetus; thus, some or all trans-Neptunian dwarf planets smaller than Pluto and Eris might not actually be in equilibrium.[citation needed] The IAU has not addressed the issue since these findings.

Furthermore, mid-sized TNOs up to about 900 or 1000 km in diameter have lower densities than larger bodies. 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 temperatures of the Kuiper Belt, water ice is strong enough to support open interior spaces (interstices) in objects of this size, and conclude that they 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 object smaller than 900 or 1000 km in diameter is (pending some other formative mechanism) unlikely to be a dwarf planet.

Tancredi's assessmentEdit

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 the assumption that the object was more than 450 kilometres (280 mi) in diameter. Some diameters are measured, some are best-fit estimates, and others use an assumed albedo of 0.10. Of these, he identified 15 as dwarf planets by his criteria (including the four accepted by the IAU), with another nine 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.[11] Although the IAU had anticipated Tancredi's recommendations, as of 2013, they have not responded.

Brown's assessmentEdit

Brown's categories Min. Number of objects
nearly certainly >900 km 10
highly likely 600–900 km 16
likely 500–600 km 38
probably 400–500 km 63
possibly 200–400 km 534
Source: Mike Brown,[12] as of Jun 21, 2018. (Summary figures differ on M. Brown's website using a cumulative count).
EarthMoonCharonCharonNixNixKerberosStyxHydraHydraPlutoPlutoDysnomiaDysnomiaErisErisNamakaNamakaHi'iakaHi'iakaHaumeaHaumeaMakemakeMakemakeMK2MK22007 OR102007 OR10S/2010 (225088) 1S/2010 (225088) 1WeywotWeywotQuaoarQuaoarSednaSedna2002 MS42002 MS4VanthVanthOrcusOrcusActaeaActaeaSalaciaSalaciaFile:EightTNOs.png 
Artistic comparison of Pluto, Eris, Haumea, Makemake, 2007 OR10, Quaoar, Sedna, 2002 MS4, Orcus, Salacia, and Earth along with the Moon.

Mike Brown considers a large number of trans-Neptunian bodies, ranked by estimated size, to be "probably" dwarf planets.[12] He did not consider asteroids, stating "In the asteroid belt Ceres, with a diameter of 900 km, is the only object large enough to be round".[12]

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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Probably not: diameter estimated/measured to be under 200 km. No icy moon under 200 km is round, suggesting that the same is true for 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 2007 OR10, Quaoar, 90377 Sedna, Orcus, 2002 MS4 and Salacia.

Grundy et al's assessmentEdit

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 400–1000 km have oddly low densities, in the range of 1.0–1.2 g/cm3, that are substantially less than dwarf planets such as Pluto, 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 possibly 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, low-density 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 900–1000 km.[3]

If correct, then among known bodies in the outer Solar System this would leave only Pluto–Charon, Eris, Haumea, 2007 OR10, Makemake, Quaoar, Orcus and high-albedo Sedna (but probably not low-albedo 2002 MS4) as being likely to have achieved hydrostatic equilibrium at some point in their histories, and thus to possibly be dwarf planets at present.

Likeliest dwarf planetsEdit

The assessments of the IAU, Tancredi et al., Brown and Grundy et al. for the dozen 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).

Iapetus, the largest body known to not be in hydrostatic equilibrium, is included for comparison.

Designation Measured mean
diameter (km)
Per IAU Per Tancredi
et al.[11]
Per Brown[12] Per Grundy
et al.[3]
Category
  134340 Pluto 2377±3   (measured, in equilibrium) 2:3 resonant
136199 Eris 2326±12       SDO
136108 Haumea 1596 to 1632  
(naming rules)
    cubewano
  S VIII Iapetus 1469±6 (measured, not in equilibrium) (moon of Saturn)
136472 Makemake 1430+38
−22
 
(naming rules)
    cubewano
(225088) 2007 OR10 1230±50 NA     SDO
50000 Quaoar 1110±5       cubewano
90377 Sedna 900 to 1200       detached
90482 Orcus 910+50
−40
      2:3 resonant
(307261) 2002 MS4 934±47 NA     3:5 resonant
  1 Ceres 946±2   (measured, in equilibrium) asteroid
120347 Salacia 854±45       3:5 resonant
(532037) 2013 FY27 740+90
−85
NA  ?   SDO
(208996) 2003 AZ84 727+62
−67
   ?   2:3 resonant

By Brown's criteriaEdit

The following trans-Neptunian objects have estimated diameters at least 400 kilometres (250 mi) and so are considered "possible" dwarf planets by Brown's criteria. 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 added for comparison.

The default sort is per Brown's size estimate. The IAU-recognised dwarf planets have bold names. Explanations and sources for the measured masses and diameters can be found in the corresponding articles linked in column "Designation" of the table.

Designation Per Brown[12] Measured per
measured
Diameter
per assumed albedo
Result
per Tancredi[11]
Category Best[a]
diameter
km
H
Diameter[b]
(km)
Geometric
albedo

(%)
Mass[c]
(1018 kg)
H

[14][15]

Diameter
(km)
Geometric
albedo[d]
(%)
Small
albedo=100%
(km)
Large
albedo=4%
(km)
136199 Eris −1.1 2330 99 16600 −1.1 2326±12 90 2206 11028 accepted (measured) SDO 2326
134340 Pluto −0.7 2329 64 13030 −0.76 2376±3.2 63 1886 9430 accepted (measured) 2:3 resonant 2376
136472 Makemake 0.1 1426 81 −0.2 1430±14 104 1457 7286 accepted cubewano 1430
(225088) 2007 OR10 2 1290 19 1750 1.8 1230±50 22 580 2901 SDO 1230
136108 Haumea 0.4 1252 80 4006 0.2 1632±51 55 1212 6060 accepted cubewano 1632
50000 Quaoar 2.7 1092 13 1400 2.82 1110±5 11 363 1813 accepted (and recommended) cubewano 1110
90377 Sedna 1.8 1041 32 1.83 995±80 33 572 2861 accepted (and recommended) detached 995
90482 Orcus 2.3 983 23 641 2.31 910+50
−40
25 459 2293 accepted (and recommended) 2:3 resonant 910
(307261) 2002 MS4 4 960 5 3.6 934±47 7 253 1266 3:5 resonant 934
1 Ceres 939 3.36 946±2 9 283 1414 asteroid belt 946
120347 Salacia 4.2 921 4 438 4.25 854±45 5 188 939 possible 3:5 resonant 854
2018 VG18 3.6 253 1266 SDO 895[citation needed]
(208996) 2003 AZ84 3.7 747 11 3.74 727+62
−67
11 237 1187 accepted 2:3 resonant 727
(532037) 2013 FY27 3.5 721 14 3.15 740+90
−85
18 312 1558 SDO 740
(55637) 2002 UX25 3.9 704 11 125 3.87 665±29 11 224 1118 3:5 resonant 665
(90568) 2004 GV9 4.2 703 8 4.25 680±34 8 188 939 accepted 3:5 resonant 680
20000 Varuna 4.1 698 9 3.76 668+154
−86
12 235 1176 accepted cubewano 668
(145452) 2005 RN43 3.9 697 11 3.89 679+55
−73
11 222 1108 possible cubewano 679
(55565) 2002 AW197 3.8 693 12 3.3 768+39
−38
14 291 1454 accepted cubewano 768
174567 Varda 3.7 689 13 266 3.61 717±5 12 252 1260 possible cubewano 717
28978 Ixion 3.8 674 12 3.83 617+19
−20
14 228 1139 accepted 2:3 resonant 617
(202421) 2005 UQ513 4 643 11 3.5 498+63
−75
28 265 1326 cubewano 498
2014 UZ224 4 643 11 3.4 635+65
−72
19 278 1388 SDO 635
(523794) 2015 RR245 4.2 615 10 3.8 231 1155 SDO 615
(523692) 2014 EZ51 4.2 615 10 3.8 231 1155 detached 615
2010 RF43 4.2 615 10 3.9 221 1103 SDO 615
229762 Gǃkúnǁʼhòmdímà 3.7 612 17 136 3.7 632+34
−34
15 242 1209 SDO 632
19521 Chaos 5 612 5 4.8 600+140
−130
6 146 729 cubewano 600
(84522) 2002 TC302 4.2 591 12 3.9 584+106
−88
14 221 1103 2:5 resonant 584
2015 KH162 4.4 587 10 4.1 201 1006 detached 587
(78799) 2002 XW93 5.4 584 4 5.5 106 528 SDO 584
2010 JO179 4.5 574 9 4 211 1053 SDO 574
2010 KZ39 4.5 574 9 4 211 1053 detached 574
(523759) 2014 WK509 4.5 574 9 4.4 175 876 detached 574
2012 VP113 4.5 574 9 4 211 1053 detached 574
2017 OF69 4.6 160 799 2:3 resonant 565
2002 XV93 5.4 564 4 5.42 549+22
−23
4 110 548 2:3 resonant 549
(42301) 2001 UR163 4.6 561 9 4.1 201 1006 possible SDO 561
(523639) 2010 RE64 4.6 561 9 4.4 175 876 SDO 561
2004 XR190 4.6 561 9 4.3 183 917 detached 561
(523671) 2013 FZ27 4.6 561 9 4.4 175 876 1:2 resonant 561
2014 AN55 4.6 561 9 4.1 201 1006 SDO 561
2008 ST291 4.6 549 9 4.4 175 876 detached 549
2010 FX86 4.6 549 9 4.7 153 763 cubewano 549
(230965) 2004 XA192 4.6 549 9 4.2 339+120
−95
32 192 960 1:2 resonant 339
(84922) 2003 VS2 4.1 537 15 4.1 523+35
−34
15 201 1006 not accepted 2:3 resonant 523
(455502) 2003 UZ413 4.7 536 8 4.3 183 917 2:3 resonant 536
(120348) 2004 TY364 4.7 536 8 4.52 512+37
−40
10 166 829 not accepted 2:3 resonant 512
2006 QH181 4.7 536 8 4.3 183 917 SDO 536
2014 YA50 4.7 536 8 4.6 160 799 cubewano 536
2015 BP519 4.8 524 8 4.5 167 837 SDO 524
(482824) 2013 XC26 4.8 524 8 4.4 175 876 3:5 resonant 524
(145451) 2005 RM43 4.8 524 8 4.4 175 876 possible SDO 524
(470443) 2007 XV50 4.8 524 8 4.4 175 876 cubewano 524
(470308) 2007 JH43 4.9 513 8 4.5 167 837 2:3 resonant 513
(278361) 2007 JJ43 4.9 513 8 4.5 167 837 cubewano 513
(82075) 2000 YW134 4.9 513 8 4.5 167 837 detached 513
(523681) 2014 BV64 4.9 513 8 4.7 153 763 cubewano 513
2014 FC72 4.9 513 8 4.7 153 763 detached 513
2014 HA200 4.9 513 8 4.7 153 763 SDO 513
2015 BZ518 4.9 513 8 4.7 153 763 cubewano 513
2014 WP509 4.9 513 8 4.5 167 837 cubewano 513
(523742) 2014 TZ85 5 501 7 4.8 146 729 4:7 resonant 501
2014 FC69 5 501 7 4.6 160 799 detached 501
2013 AT183 5 501 7 4.6 160 799 SDO 501
(499514) 2010 OO127 5 501 7 4.6 160 799 3:5 resonant 501
(523645) 2010 VK201 5 501 7 5 133 665 cubewano 501
(315530) 2008 AP129 5.1 490 7 4.7 153 763 cubewano 490
(470599) 2008 OG19 5.1 490 7 4.7 153 763 SDO 490
(523635) 2010 DN93 5.1 490 7 4.8 146 729 detached 490
(444030) 2004 NT33 5.1 490 7 4.8 423+87
−80
12 146 729 4:7 resonant 423
2003 QX113 5.1 490 7 5.1 127 635 SDO 490
2003 UA414 5.1 490 7 5 133 665 SDO 490
(119979) 2002 WC19 5.1 490 7 4.7 153 763 1:2 resonant 490
(523693) 2014 FT71 5.1 490 7 5 133 665 4:7 resonant 490
(472271) 2014 UM33 5.1 490 7 4.7 153 763 cubewano 490
(175113) 2004 PF115 4.5 482 12 4.54 406+98
−75
16 164 821 2:3 resonant 406
(307982) 2004 PG115 5.2 479 7 4.8 146 729 SDO 479
(48639) 1995 TL8 5.2 479 7 4.8 146 729 TNO 479
(523752) 2014 VU37 5.2 479 7 5.1 127 635 cubewano 479
(495603) 2015 AM281 5.2 479 7 4.8 146 729 detached 479
2014 BZ57 5.2 479 7 5 133 665 cubewano 479
2014 HZ199 5.2 479 7 5 133 665 cubewano 479
471143 Dziewanna 3.8 475 25 3.8 470+35
−10
24 231 1155 SDO 470
(26375) 1999 DE9 5.2 474 7 4.9 461±45 9 139 696 possible 2:5 resonant 461
(35671) 1998 SN165 5.7 473 4 5.5 393+39
−38
7 106 528 cubewano 393
(145480) 2005 TB190 4.4 469 15 4.4 464±62 14 175 876 detached 464
2010 RF188 5.3 468 7 5.2 121 606 SDO 468
(26181) 1996 GQ21 5.3 468 7 4.9 139 696 SDO 468
(119951) 2002 KX14 4.9 468 10 4.86 445±27 10 142 709 cubewano 445
2014 JP80 5.3 468 7 5.1 127 635 2:3 resonant 468
2014 JR80 5.3 468 7 5.1 127 635 2:3 resonant 468
2011 WJ157 5.3 468 7 5 133 665 SDO 468
2013 FS28 5.3 468 7 4.9 139 696 SDO 468
2015 AJ281 5.3 468 7 5 133 665 cubewano 468
(523750) 2014 US224 5.3 468 7 5 133 665 cubewano 468
(523757) 2014 WH509 5.3 468 7 5.2 121 606 4:7 resonant 468
(120132) 2003 FY128 5.1 467 8 4.6 460±21 12 160 799 SDO 460
38628 Huya 5 466 8 5.04 406±16 10 130 652 accepted 2:3 resonant 406
(84719) 2002 VR128 5.6 459 5 5.58 449+42
−43
5 102 509 2:3 resonant 449
(307616) 2003 QW90 5.4 457 6 5 133 665 cubewano 457
(469306) 1999 CD158 5.4 457 6 5 133 665 4:7 resonant 457
2010 RF64 5.4 457 6 5.7 96 481 cubewano 457
(523640) 2010 RO64 5.4 457 6 5.2 121 606 cubewano 457
2010 TJ 5.4 457 6 5.7 96 481 SDO 457
(445473) 2010 VZ98 5.4 457 6 4.8 146 729 SDO 457
(523653) 2011 OA60 5.4 457 6 5.1 127 635 cubewano 457
(308379) 2005 RS43 5.4 457 6 5 133 665 1:2 resonant 457
2010 ER65 5.4 457 6 5.2 121 606 detached 457
2014 OJ394 5.4 457 6 5.1 127 635 detached 457
2014 QW441 5.4 457 6 5.2 121 606 cubewano 457
(523772) 2014 XR40 5.4 457 6 5.2 121 606 cubewano 457
2014 AM55 5.4 457 6 5.2 121 606 cubewano 457
2003 QX111 6.8 453 2 7.1 51 253 2:3 resonant 453
(471137) 2010 ET65 5.5 447 6 5.1 127 635 SDO 447
2010 EL139 5.5 447 6 5.6 101 504 2:3 resonant 447
(471288) 2011 GM27 5.5 447 6 5.1 127 635 cubewano 447
(471165) 2010 HE79 5.5 447 6 5.1 127 635 2:3 resonant 447
2014 FY71 5.5 447 6 5.4 111 553 4:7 resonant 447
2014 CO23 5.5 447 6 5.3 116 579 4:7 resonant 447
(523690) 2014 DN143 5.5 447 6 5.3 116 579 cubewano 447
(532093) 2013 HV156 5.5 447 6 5.2 121 606 1:2 resonant 447
(523773) 2014 XS40 5.5 447 6 5.4 111 553 3:5 resonant 447
2014 XY40 5.5 447 6 5.1 127 635 cubewano 447
2015 AH281 5.5 447 6 5.1 127 635 cubewano 447
(523738) 2014 SH349 5.5 447 6 5.4 111 553 cubewano 447
2012 VB116 5.2 121 606 cubewano 429
(469372) 2001 QF298 5.4 421 7 5.43 408+40
−45
7 109 545 2:3 resonant 408
(303775) 2005 QU182 3.8 415 33 3.8 416±73 31 231 1155 SDO 416
(144897) 2004 UX10 4.8 409 14 4.75 361+124
−94
17 149 746 possible 2:3 resonant 361
  1. ^ The measured diameter, else Brown's estimated diameter, else the diameter calculated from H using an assumed albedo of 8%.
  2. ^ Diameters with the text in red indicate that Brown's bot derived them from heuristically expected albedo.
  3. ^ This is the total system mass (including moons), except for Pluto and Ceres.
  4. ^ The geometric albedo   is calculated from the measured absolute magnitude   and measured diameter   via the formula:  

See alsoEdit

ReferencesEdit

  1. ^ a b c Mike Brown. "The Dwarf Planets". Retrieved 2008-01-20.
  2. ^ "Today we know of more than a dozen dwarf planets in the solar system [and] it is estimated that the ultimate number of dwarf planets we will discover in the Kuiper Belt and beyond may well exceed 10,000".The PI's Perspective
  3. ^ a b c d W.M. Grundy, K.S. Noll, M.W. Buie, S.D. Benecchi, D. Ragozzine & H.G. Roe, 'The Mutual Orbit, Mass, and Density of Transneptunian Binary Gǃkúnǁʼhòmdímà ((229762) 2007 UK126)', Icarus (forthcoming, available online 30 March 2019) DOI: 10.1016/j.icarus.2018.12.037,
  4. ^ Dan Bruton. "Conversion of Absolute Magnitude to Diameter for Minor Planets". Department of Physics & Astronomy (Stephen F. Austin State University). Archived from the original on 2010-03-23. Retrieved 2008-06-13.
  5. ^ "IAU 2006 General Assembly: Result of the IAU Resolution votes". International Astronomical Union. 2006. Archived from the original on 2007-01-03. Retrieved 2008-01-26.
  6. ^ "Dwarf Planets". NASA. Retrieved 2008-01-22.
  7. ^ "Plutoid chosen as name for Solar System objects like Pluto" (Press release).
  8. ^ Savage, Don; Jones, Tammy; Villard, Ray (1995-04-19). "Asteroid or Mini-Planet? Hubble Maps the Ancient Surface of Vesta". Hubble Site News Release STScI-1995-20. Retrieved 2006-10-17.
  9. ^ "Iapetus' peerless equatorial ridge". www.planetary.org. Retrieved 2 April 2018.
  10. ^ "DPS 2015: First reconnaissance of Ceres by Dawn". www.planetary.org. Retrieved 2 April 2018.
  11. ^ a b c Tancredi, G. (2010). "Physical and dynamical characteristics of icy "dwarf planets" (plutoids)". Icy Bodies of the Solar System: Proceedings IAU Symposium No. 263, 2009.
  12. ^ a b c d e Michael E. Brown. "How many dwarf planets are there in the outer solar system? (updates daily)". California Institute of Technology. Retrieved 2 June 2017.
  13. ^ "AstDys (47171) 1999TC36 Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved 2009-12-07.
  14. ^ "List Of Trans-Neptunian Objects". Minor Planet Center.
  15. ^ "List Of Centaurs and Scattered-Disk Objects". Minor Planet Center.

External linksEdit