List of possible dwarf planets

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Illustration of the relative sizes, albedos, and colours of the largest trans-Neptunian objects

It is estimated that there may be 200 dwarf planets in the Kuiper belt of the outer Solar System and up to 10,000 in the region beyond.[1][2] The International Astronomical Union (IAU) has accepted four of these: Pluto, Eris, Haumea, and Makemake, as well as Ceres in the inner Solar System. This article lists these and the more likely of the remaining known possibilities.

IAU naming procedures[edit]

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%[3]) 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 values[edit]

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

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".[4][5][6] Current observations are generally insufficient for a direct determination as to whether a body meets this definition. 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), Michael Brown estimated that an icy body relaxes into hydrostatic equilibrium at a diameter somewhere between 200 and 400 km.[1]

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.[7] The third-most massive object, 2 Pallas, has a somewhat irregular surface and is thought to have only a partially differentiated interior. Brown has estimated that, because rocky objects 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]

After Brown and Tancredi made their calculations, it was discovered that Iapetus (1,470 km in diameter) and smaller moons of Saturn with well-determined shapes are not in hydrostatic equilibrium as had been thought. They have a hydrostatic shape that froze in some time ago and that does not match the shape an equilibrium body would have at their current rotation rates.[8] Rhea (1,530 km) is the smallest body for which detailed measurements are consistent with hydrostatic equilibrium.[9] If trans-Neptunian objects behave similarly, the cut-off value for current equilibrium may be around 1,500 km, larger than Haumea, Makemake, and probably (2007) OR10—indeed, of all known bodies other than Pluto and Eris. The IAU has not addressed the issue since these findings.

Tancredi's assessment[edit]

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, with another nine being considered possible. To be cautious, he advised the IAU to "officially" accept as dwarf planets the top three: Sedna, Orcus, and Quaoar.[10] Although the IAU had anticipated Tancredi's recommendations, as of 2013, they had not responded.

Brown's assessment[edit]

Brown's categories Min. Number of objects
nearly certainly >900 km 10
highly likely 600–900 km 13
likely 500–600 km 25
probably 400–500 km 38
possibly 200–400 km 289
Source: Mike Brown,[11] as of August 2, 2015. (Summary figures differ on M. Brown's website using a cumulative count).

Mike Brown considers a large number of trans-Neptunian bodies, ranked by estimated size, to be "probably" dwarf planets.[11] 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".[11]

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.
  • Probable: diameter estimated/measured to be over 400 kilometres (250 mi). Expected to be dwarf planets, if they are icy, and that figure is correct.
  • Possible: 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.

Likeliest dwarf planets[edit]

The following trans-Neptunian objects have estimated diameters at least 300 kilometres (190 mi) and so may be dwarf planets. Not all bodies estimated to be this size are included. The list is complicated by bodies such as (47171) 1999 TC36 that were at first assumed to be large single objects but later discovered to be binary or triple systems of smaller bodies.[12] The asteroid Ceres is added for comparison.

The default sort is per Brown's size estimate. The IAU-recognised dwarf planets have bold names. Brown's diameter estimates are in red when they are based upon an assumed albedo. Explanations and sources for the measured masses and diameters can be found in the corresponding articles linked in column "Body" of the table.

Body Per Brown[11] Measured per
measured
Diameter
per assumed albedo
Result
per Tancredi[10]
Category Best[a]
Diameter
km
H
Diameter[b]
(km)
Geometric
albedo
(%)
Mass
(Zg)
H

[13][14]

Diameter
(km)
Geometric
albedo (%)[c]
Small
albedo=100%
(km)
Large
albedo=4%
(km)
Eris −1.1 2330 99 16700 −1.2 2326 99 2310 11548 accepted (measured) SDO 2326
Pluto −0.7 2329 64 13050 −0.8 2372 66 1921 9605 accepted (measured) 2:3 resonant 2372
Makemake 0.1 1426 81 −0.3 1478 107 1526 7629 accepted cubewano 1478
(225088) 2007 OR10 2 1290 19 2 1280 17 529 2645 SDO 1280
Haumea 0.4 1252 80 4000 0.1 1430 79 1269 6346 accepted cubewano 1430
Quaoar 2.7 1092 13 1400 2.4 1074 17 440 2200 accepted (and recommended) cubewano 1074
Sedna 1.8 1041 32 1.5 995 45 666 3330 accepted (and recommended) detached 995
Orcus 2.3 983 23 580 2.2 917 28 483 2413 accepted (and recommended) 2:3 resonant 917
(307261) 2002 MS4 4 960 5 3.7 934 7 242 1209 cubewano 934
Ceres 939 3.3 946 9 291 1454 main belt 946
Salacia 4.2 921 4 450 4 854 6 211 1053 possible cubewano 854
(208996) 2003 AZ84 3.7 747 11 3.8 727 10 231 1155 accepted 2:3 resonant 727
2013 FY27 3.4 741 14 3 334 1669 SDO 741
Varuna 4 732 9 3.6 668 14 253 1266 accepted cubewano 668
(55637) 2002 UX25 3.9 704 11 125 3.8 665 12 231 1155 cubewano 665
(90568) 2004 GV9 4.2 703 8 4 680 10 211 1053 accepted 3:5 resonant 680
(145452) 2005 RN43 3.9 697 11 3.9 679 11 221 1103 possible cubewano 679
(202421) 2005 UQ513 3.8 676 12 3.4 498 31 278 1388 cubewano 498
Varda 3.8 676 12 265 3.4 705 16 278 1388 possible cubewano 705
Ixion 3.8 674 12 3.8 617 14 253 1266 accepted 2:3 resonant 617
(55565) 2002 AW197 3.9 669 12 3.5 768 12 265 1326 accepted cubewano 768
Chaos 5 612 5 4.8 600 6 146 729 cubewano 600
(229762) 2007 UK126 3.7 612 17 3.5 599 20 265 1326 SDO 599
(278361) 2007 JJ43 4.3 602 10 3.9 221 1103 cubewano 602
(84522) 2002 TC302 4.2 591 12 3.8 584 16 231 1155 2:5 resonant 584
2012 VP113 4.4 588 10 4 211 1053 detached 588
2010 KZ39 4.4 588 10 4 211 1053 cubewano 588
(78799) 2002 XW93 5.4 584 4 5.5 106 528 SDO 584
(230965) 2004 XA192 4.5 575 9 4.1 339 35 201 1006 1:2 resonant 339
2010 RF43 4.5 575 9 4.1 201 1006 SDO 575
2013 FZ27 4.5 575 9 4.1 201 1006 cubewano 575
2002 XV93 5.4 564 4 5 549 6 133 665 2:3 resonant 549
2003 UZ413 4.6 562 9 4.2 192 960 2:3 resonant 562
2008 ST291 4.6 562 9 4.2 192 960 detached 562
2006 QH181 4.6 549 9 4.3 183 917 SDO 549
2014 UM33 4.6 549 9 4.3 183 917 cubewano 549
2010 RE64 4.6 549 9 4.3 183 917 SDO 549
2010 FX86 4.6 549 9 4.3 183 917 cubewano 549
2004 XR190 4.6 549 9 4.3 183 917 detached 549
(84922) 2003 VS2 4.1 537 15 4.2 523 13 192 960 2:3 resonant 523
2004 NT33 4.7 536 8 4.4 423 17 175 876 cubewano 423
(145451) 2005 RM43 4.7 536 8 4.4 175 876 possible SDO 536
(120348) 2004 TY364 4.8 524 8 4.5 512 11 167 837 2:3 resonant 512
(42301) 2001 UR163 4.8 524 8 4.5 167 837 possible SDO 524
2008 OG19 4.9 512 8 4.6 160 799 SDO 512
2010 VK201 4.9 512 8 4.6 160 799 cubewano 512
2014 FC69 4.9 512 8 4.6 160 799 detached 512
2007 JH43 5 500 7 4.7 153 763 2:3 resonant 500
2003 QX113 5 500 7 4.7 153 763 SDO 500
2015 FG345 4.9 139 696 3:5 resonant 492
2014 FT71 5.1 489 7 4.8 146 729 4:7 resonant 489
(175113) 2004 PF115 4.5 482 12 4.4 406 19 175 876 2:3 resonant 406
(307982) 2004 PG115 5.2 478 7 4.9 139 696 SDO 478
(119979) 2002 WC19 5.2 478 7 4.9 139 696 1:2 resonant 478
(82075) 2000 YW134 5.2 478 7 4.9 139 696 detached 478
2007 XV50 5.2 478 7 4.9 139 696 cubewano 478
2010 EK139 3.8 475 25 3.8 470 24 231 1155 SDO 470
(26375) 1999 DE9 5.2 474 7 5 461 8 133 665 possible SDO 461
(35671) 1998 SN165 5.7 473 4 5.6 393 7 101 504 cubewano 393
(145480) 2005 TB190 4.4 469 15 4.6 464 12 160 799 detached 464
(119951) 2002 KX14 4.9 468 10 4.9 455 10 160 799 cubewano 455
(120132) 2003 FY128 5.1 467 8 4.9 460 9 139 696 SDO 460
2010 TJ 5.3 467 7 5 133 665 SDO 467
2010 VZ98 5.3 467 7 5 133 665 SDO 467
2011 FW62 5.3 467 7 5 133 665 2:3 resonant 467
2010 RF64 5.3 467 7 5 133 665 cubewano 467
Huya 5 466 8 4.9 458 9 139 696 accepted 2:3 resonant 458
(126154) 2001 YH140 5.8 459 4 5.5 106 528 cubewano 459
(84719) 2002 VR128 5.6 459 5 5.4 449 6 111 553 2:3 resonant 449
1999 CD158 5.4 456 6 5.1 127 635 4:7 resonant 456
2010 EL139 5.4 456 6 5.1 127 635 2:3 resonant 456
2003 QX111 6.8 453 2 6.8 58 290 2:3 resonant 453
2006 HH123 5.4 452 6 5.2 121 606 2:5 resonant 452
2008 UA332 5.5 446 6 5.2 121 606 cubewano 446
2008 NW4 5.5 446 6 5.2 121 606 cubewano 446
2010 ET65 5.5 446 6 5.2 121 606 SDO 446
(315530) 2008 AP129 5.5 446 6 5.2 121 606 3:5 resonant 446
(305543) 2008 QY40 5.5 446 6 5.2 121 606 SDO 446
2010 HE79 5.5 446 6 5.2 121 606 2:3 resonant 446
2011 GM27 5.5 446 6 5.2 121 606 cubewano 446
2013 FC28 5.5 446 6 5.2 121 606 cubewano 446
2014 FY71 5.5 446 6 5.2 121 606 SDO 446
2013 JW63 5.5 446 6 5.2 121 606 1:2 resonant 446
2005 CA79 5.5 446 6 5.2 121 606 1:2 resonant 446
(26181) 1996 GQ21 5.5 446 6 5.2 121 606 SDO 446
2001 QF298 5.4 421 7 5.2 408 9 121 606 2:3 resonant 408
(303775) 2005 QU182 3.8 415 33 3.5 416 41 265 1326 SDO 416
(144897) 2004 UX10 4.8 409 14 4.5 361 21 167 837 possible 2:3 resonant 361
2003 UA414 5.6 370 8 5.3 116 579 cubewano 370
2002 PJ149 5.6 370 8 5.3 116 579 cubewano 370
2002 CY248 5.6 370 8 5.3 116 579 cubewano 370
1995 SN55 6.2 370 4 6 84 419 centaur 370
(308379) 2005 RS43 5.6 370 8 5.3 116 579 1:2 resonant 370
2010 JK124 5.6 370 8 5.3 116 579 2:3 resonant 370
2010 RO64 5.6 370 8 5.3 116 579 cubewano 370
2010 TR19 5.7 355 8 5.4 111 553 SDO 355
2010 TY53 5.7 355 8 5.4 111 553 2:3 resonant 355
2010 VR11 5.7 355 8 5.4 111 553 cubewano 355
2010 VW11 5.7 355 8 5.4 111 553 SDO 355
2011 JF31 5.7 355 8 5.4 111 553 cubewano 355
2007 JF43 5.7 355 8 5.4 111 553 2:3 resonant 355
2010 ER65 5.7 355 8 5.4 111 553 detached 355
(48639) 1995 TL8 5.7 355 8 5.4 111 553 detached 355
2001 QS297 5.7 355 8 5.4 111 553 cubewano 355
(307616) 2003 QW90 5.7 355 8 5.4 111 553 cubewano 355
(143707) 2003 UY117 6.3 354 4 6.1 80 400 2:5 resonant 354
2004 PD112 6.3 354 4 6.1 80 400 detached 354
2002 CV154 6.3 354 4 6.1 80 400 cubewano 354
2000 CQ105 6.3 354 4 6.1 80 400 SDO 354
2005 RP43 6.3 354 4 6.1 80 400 SDO 354
(15874) 1996 TL66 5.4 344 11 5.4 339 11 111 553 accepted SDO 339
2002 GH32 5.8 340 8 5.5 106 528 3:5 resonant 340
2002 XH91 5.8 340 8 5.5 106 528 cubewano 340
(312645) 2010 EP65 5.8 340 8 5.5 106 528 1:2 resonant 340
2007 PS45 5.8 340 8 5.5 106 528 cubewano 340
2008 CT190 5.8 340 8 5.5 106 528 SDO 340
2013 FB28 5.8 340 8 5.5 106 528 cubewano 340
(82158) 2001 FP185 6.4 336 5 6.2 76 382 SDO 336
2012 XR157 5.9 326 8 5.6 101 504 1:2 resonant 326
2011 HP83 5.9 326 8 5.6 101 504 SDO 326
2010 RN64 5.9 326 8 5.6 101 504 cubewano 326
2010 PK66 5.9 326 8 5.6 101 504 cubewano 326
2010 PU75 5.9 326 8 5.6 101 504 SDO 326
2010 AH2 5.9 326 8 5.6 101 504 1:2 resonant 326
(437360) 2013 TV158 6.5 325 4 6.3 73 365 SDO 325
(148209) 2000 CR105 6.5 325 4 6.3 73 365 detached 325
2004 TF282 6.5 325 4 6.3 73 365 SDO 325
(184314) 2005 EO302 6.5 325 4 6.3 73 365 cubewano 325
2001 KA77 5.6 324 10 5 133 665 cubewano 324
(307251) 2002 KW14 5.9 322 8 5 133 665 cubewano 322
2007 OC10 5.4 315 13 5.7 96 481 SDO 315
(308634) 2005 XU100 6.6 312 4 6.4 70 349 4:7 resonant 312
2010 FC49 6 312 8 5.7 96 481 2:3 resonant 312
2014 FV71 6 312 8 5.7 96 481 SDO 312
2014 WT69 6 312 8 5.7 96 481 detached 312
2010 VQ11 6 312 8 5.7 96 481 cubewano 312
2001 RU143 6 312 8 5.7 96 481 2:3 resonant 312
2001 XD255 6 312 8 5.7 96 481 2:3 resonant 312
(168703) 2000 GP183 6.6 312 4 6.4 70 349 2:3 resonant 312
(79978) 1999 CC158 6 312 8 5.7 96 481 SDO 312
2003 UB292 6 312 8 5.7 96 481 cubewano 312
  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. ^ The geometric albedo A is calculated from the measured absolute magnitude H and measured diameter D via the formula: A =\left ( \frac{1329\times10^{-H/5}}{D} \right ) ^2

See also[edit]

References[edit]

  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. ^ Dan Bruton. "Conversion of Absolute Magnitude to Diameter for Minor Planets". Department of Physics & Astronomy (Stephen F. Austin State University). Retrieved 2008-06-13. 
  4. ^ "IAU 2006 General Assembly: Result of the IAU Resolution votes". International Astronomical Union. 2006. Retrieved 2008-01-26. 
  5. ^ "Dwarf Planets". NASA. Retrieved 2008-01-22. 
  6. ^ "Plutoid chosen as name for Solar System objects like Pluto" (Press release). 
  7. ^ 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. 
  8. ^ [1]
  9. ^ [2]
  10. ^ a b Tancredi, G. (2010). "Physical and dynamical characteristics of icy "dwarf planets" (plutoids)". Icy Bodies of the Solar System: Proceedings IAU Symposium No. 263, 2009. 
  11. ^ a b c d Mike Brown, How many dwarf planets are there in the outer solar system?
  12. ^ "AstDys (47171) 1999TC36 Ephemerides". Department of Mathematics, University of Pisa, Italy. Retrieved 2009-12-07. 
  13. ^ "List Of Trans-Neptunian Objects". Minor Planet Center. 
  14. ^ "List Of Centaurs and Scattered-Disk Objects". Minor Planet Center. 

External links[edit]