At present, the International Astronomical Union classifies five objects as dwarf planets: Ceres, Pluto, Eris, Haumea, and Makemake, though dozens of others are thought likely to be so classified in future. The qualifying feature of dwarf planets is that they must "have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical shape)."[1][2][3] Those dwarf planets lying beyond the orbit of Neptune are termed "plutoids" after Pluto. Except for Pluto and Ceres, observations are insufficient for direct classification. However, based on present knowledge of how icy bodies gravitationally relax into equilibrium shapes, there are a significant number of potential candidates amongst the population of trans-Neptunian objects (TNOs).[4] There were some 70 candidates as of 2008, but it is possible that this number will increase to as many as 2000.[4]
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Changes to IAU naming procedures
The IAU has modified its nomenclature procedures such that objects considered highly likely to be plutoids receive differing treatment when receiving names than other TNOs. Objects that have an absolute magnitude less than +1 (and hence a mathematically-delimited minimum diameter of 838 km[5]) will be overseen by two naming committees rather than one. Once so named, the objects are declared to be dwarf planets by the IAU. Makemake and Haumea are the only TNOs to have proceeded through the naming process as presumed plutoids.
Candidates
Mike Brown estimates that at a diameter somewhere between 200 and 400 km, an icy body relaxes into hydrostatic equilibrium. Thus, all TNOs listed are those known or suspected to be 400km or above in diameter.[4] However, diameter estimates vary widely, and they are therefore ordered here by their absolute magnitudes, H, rather than diameter. Theoretical minimum diameters correspond to a maximum albedo of 1. Although many TNOs are thought to be dark, and therefore substantially larger than this lower limit, Eris has a high albedo of 0.8–0.9, and the Haumea family are also thought to be bright.
At present, Ceres is the only identified dwarf planet within the asteroid belt. At the time it announced the term "plutoid", the IAU noted that "current scientific knowledge lends credence to the belief that Ceres is the only object of its kind. Therefore, a separate category of Ceres-like dwarf planets will not be proposed at this time."[3] The likeliest exception would be 4 Vesta, the asteroid belt's second-most massive body; Vesta appears to have a fully differentiated interior and was therefore at least in equilibrium at some point in its history.[6] The third-most massive object, 2 Pallas, has a somewhat irregular surface, and is thought to have only partially differentiated. Mike Brown estimates that, since rocky objects become rounded far less easily than icy objects, rocky objects below 900 km in diameter may not be in hydrostatic equilibrium.[4]
List by absolute magnitude (H)
Under 3
These TNOs are over a thousand km across in Brown's estimation, and have theoretical minimum diameters greater than 333 km.
| Name | H | Category | Diameter (km) | Min. diam.[7] |
Mass (1020 kg) |
Average distance from the Sun (AU)[4] |
||
|---|---|---|---|---|---|---|---|---|
| by [4] | by [8] | others | ||||||
| Sedna | 1.56 | detached object | 1800 | 1500 | < 1600[9] | 650 | 17–61 | 486.0 |
| 2007 OR10 | 1.9 | SDO | 900–1400 | 550 | 67 | |||
| Orcus | 2.3 | plutino | 1100 | 909 | 875–1020 [9] | 460 | 6.2–7.0 | 39.34 |
| Quaoar | 2.7 | cubewano | 1290 | 1260 | 655–1050 [9] | 400 | 10–26 | 43.58 |
Between 3 and 4
These minor planets have theoretical minimum diameters of 210–330 km.
| Name | H | Category | Diameter (km) | Mass (1020 kg) |
Average distance from the Sun (AU)[4] |
||
|---|---|---|---|---|---|---|---|
| by [4] | by [8] | others | |||||
| (55636) 2002 TX300 | 3.1 | haumeid | 800 | 709 | (min. 320) | 1.6 - 3.7 | 43.11 |
| Vesta | 3.2 | asteroid | 578×560×458 km[10] | 2.67 ± 0.02[11] | 2.361 | ||
| Ixion | 3.2 | plutino | 980 | 570 | 430–910 [9]; 900–1230 [12] | ~5.8 | 39.65 |
| (55565) 2002 AW197 | 3.27 | cubewano | 940 | 793 | 625–850[9]; 770–1010 [12] | ~5.2 | 47.30 |
| 2005 QU182 | 3.4 | SDO | 801 | 925[5][13] (550-1240)[14] | 113 | ||
| (202421) 2005 UQ513 | 3.4 | cubewano | 838 | 925[5][13] (550-1240)[14] | 43 | ||
| 2007 UK126 | 3.5 | SDO | 878 | 530-1190[14] | 73 | ||
| (55637) 2002 UX25 | 3.6 | cubewano | 810 | 649 | 570-795 [9] | ~7.9 | 42.53 |
| (174567) 2003 MW12 | 3.6 | cubewano | 740 | 838 | 45.94 | ||
| Varuna | 3.7 | cubewano | 780 | 874 | 755-1025 [15]; 480-800 [9] | ~5.9 | 42.90 |
| 2002 MS4 | 3.79 | cubewano | 740 | 726 | 600-850 [9] | 41.90 | |
| 2006 QH181 | 3.8 | semi-detached | 765 | 67.3 | |||
| (84522) 2002 TC302 | 3.8 | 5:2 SDO | 710 | 1200 | 920-1480[9] | ~.78 | 55.02 |
| (145452) 2005 RN43 | 3.9 | cubewano | 740 | 730 | 41.53 | ||
| (90568) 2004 GV9 | 3.9 | cubewano | 680 | 677 | 610-750 [9] | 42.23 | |
| (42301) 2001 UR163 | 3.97 | 9:4 SDO | 620 | 636 | 51.40 | ||
Between 4 and 5
| Name | H | Category | Diameter (km) | Mass (1020 kg) |
Average distance from the Sun (AU)[4] |
||
|---|---|---|---|---|---|---|---|
| by [4] | by [8] | others | |||||
| (145453) 2005 RR43 | 4.0 | haumeid | 697 | ||||
| (84922) 2003 VS2 | 4.0 | plutino | 610 | 725 | 540-925 [9] | 39.27 | |
| (208996) 2003 AZ84 | 4.0 | plutino | 710 | 686 | 590-785 km[9] | 39.45 | |
| 2004 XA192 | 4.0 | cubewano | 46.98 | ||||
| (120178) 2003 OP32 | 4.1 | haumeid | 650 | 666 | 43.24 | ||
| Pallas | 4.13 | asteroid | 582×556×500±9 km[6] | 2.11±0.26[16] | 2.772 | ||
| (120347) 2004 SB60 | 4.2 | cubewano | 560 | 580 | 41.97 | ||
| 2003 UZ413 | 4.3 | plutino | 607 | ||||
| (120348) 2004 TY364 | 4.3 | other TNO | 540 | 554 | 38.72 | ||
| (145451) 2005 RM43 | 4.4 | SDO | 560 | 580 | 89.73 | ||
| 2004 NT33 | 4.4 | cubewano | 554 | ||||
| 2004 XR190 (Buffy) | 4.47 | SDO | 540 | 554 | 57.36 | ||
| (119951) 2002 KX14 | 4.5 | cubewano? | 560 | 560 | 380-780 [9] | 39.01 | |
| (144897) 2004 UX10 | 4.5 | plutino | 529 | 39.1 | |||
| (19308) 1996 TO66 | 4.56 | haumeid | 540 | 900 | 43.19 | ||
| 2004 PR107 | 4.6 | lost | 520 | 529 | ~45 | ||
| 2001 QF298 | 4.7 | plutino | 490 | 505 | 39.30 | ||
| (26375) 1999 DE9 | 4.7 | 2:5 TNO | 490 | 505 | 55.72 | ||
| 38628 Huya | 4.7 | plutino | 480 | 480 | 39.76 | ||
| (145480) 2005 TB190 | 4.7 | detached | 505 | 76.38 | |||
| (175113) 2004 PF115 | 4.7 | plutino | 39.18 | ||||
| (47171) 1999 TC36 | 4.73 | plutino | 440 | 39.27 | |||
| 2007 JH43 | 4.7 | plutino | 500 | 39.56 | |||
| 2003 QX113 | 4.7 | detached | 450 | 461 | 49.9 | ||
| (24835) 1995 SM55 | 4.8 | haumeid | 470 | 702 | 41.64 | ||
| (120132) 2003 FY128 | 4.8 | detached | 430 | 49.77 | |||
| (82075) 2000 YW134 | 4.8 | 8:3 TNO | 430 | 57.77 | |||
| 19521 Chaos | 4.9 | cubewano | 450 | 745 km | 45.56 | ||
| 2002 XV93 | 4.9 | plutino | 430 | 39.22 | |||
| 2002 CY248 | 4.9 | cubewano | 410 | 46.18 | |||
| 2007 JJ43 | 4.9 | 48.32 | |||||
| 2008 OG19 | 4.9 | SDO | 67 | ||||
| 2000 CN105 | 5.0 | cubewano | 430 | 44.65 | |||
Above 5
| Name | H | Category | Diameter (km) | Average distance from the Sun (AU)[4] |
|---|---|---|---|---|
| (79360) 1997 CS29 | 5.1 | cubewano | 410 [4] | 43.87 |
| (119979) 2002 WC19 | 5.1 | twotino | 410 [4] | 47.67 |
| 1999 CD158 | 5.1 | SDO | 410 [4] | 43.69 |
| 2006 HH123 | 5.2 | lost | 400[8] | ~56 |
| (15874) 1996 TL66 | 5.4 | SDO | 632,[4] 460-690 [9] | 83 |
| 2003 QW90 | 5.4 | cubewano | 560,[4] 580[8] | 43.65 |
| Hygeia | 5.43 | asteroid | 500×385×350[17] | 3.139 |
| 2002 KW14 | 5.3 | SDO | 510,[4] 529[8] | 47.08 |
| (35671) 1998 SN165 | 5.8 | cubewano | 460 [9] | 37.93 |
References
- ^ "IAU 2006 General Assembly: Result of the IAU Resolution votes". International Astronomical Union. 2006. http://www.iau.org/iau0603.414.0.html. Retrieved 2008-01-26.
- ^ "Dwarf Planets". NASA. http://solarsystem.nasa.gov/planets/profile.cfm?Object=Dwarf&Display=OverviewLong. Retrieved 2008-01-22.
- ^ a b "Plutoid chosen as name for Solar System objects like Pluto". Press release. http://www.iau.org/public_press/news/release/iau0804/.
- ^ a b c d e f g h i j k l m n o p q Mike Brown. "The Dwarf Planets". http://web.gps.caltech.edu/~mbrown/dwarfplanets/. Retrieved 2008-01-20.
- ^ a b c Dan Bruton. "Conversion of Absolute Magnitude to Diameter for Minor Planets". Department of Physics & Astronomy (Stephen F. Austin State University). http://www.physics.sfasu.edu/astro/asteroids/sizemagnitude.html. Retrieved 2008-06-13.
- ^ a b Savage, Don; Jones, Tammy; and Villard, Ray (1995-04-19). "Asteroid or Mini-Planet? Hubble Maps the Ancient Surface of Vesta". Hubble Site News Release STScI-1995-20. http://hubblesite.org/newscenter/archive/releases/1995/20/image/c. Retrieved 2006-10-17.
- ^ Minimum diameter = 1329*10(−H/5)
- ^ a b c d e f Robert Johnston. "List of Known Trans-Neptunian Objects". http://www.johnstonsarchive.net/astro/tnoslist.html. Retrieved 2008-01-20.
- ^ a b c d e f g h i j k l m n o Barucci, M.A.; John Stansberry, Will Grundy, Mike Brown, Dale Cruikshank, John Spencer, David Trilling, Jean-Luc Margot (2007). "Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope". Kuiper Belt. http://arxiv.org/abs/astro-ph/0702538v1. Retrieved 2008-01-20.
- ^ Thomas, P. C.; et al. (1997). "Impact excavation on asteroid 4 Vesta: Hubble Space Telescope results". Science 277: 1492. doi:.
- ^ Baer, James; Chesley, Steven R. (2008). "Astrometric masses of 21 asteroids, and an integrated asteroid ephemeris" (PDF). Celestial Mechanics and Dynamical Astronomy (Springer Science+Business Media B.V. 2007) 100 (2008): 27–42. doi:. http://www.springerlink.com/content/h747307j43863228/fulltext.pdf. Retrieved 2008-11-11.
- ^ a b David C. Jewitt. "Kuiper Belt". http://www.ifa.hawaii.edu/faculty/jewitt/kb.html. Retrieved 2008-01-22.
- ^ a b Assuming an albedo of 0.09.
- ^ a b c "Absolute Magnitude (H)". NASA/JPL. http://neo.jpl.nasa.gov/glossary/h.html. Retrieved 2008-12-09.
- ^ Dave Jewitt: Size and Albedo of Kuiper Belt Object (20000) Varuna
- ^ Baer, James; Steven R. Chesley (2008). "Astrometric masses of 21 asteroids, and an integrated asteroid ephemeris" (PDF). Celestial Mechanics and Dynamical Astronomy (Springer Science+Business Media B.V. 2007) 100 (2008): 27–42. doi:. http://www.springerlink.com/content/h747307j43863228/fulltext.pdf. Retrieved 2008-11-11.
- ^ Baer, James; Steven R. Chesley (2008). "Astrometric masses of 21 asteroids, and an integrated asteroid ephemeris" (PDF). Celestial Mechanics and Dynamical Astronomy (Springer Science+Business Media B.V. 2007) 100 (2008): 27–42. doi:. http://www.springerlink.com/content/h747307j43863228/fulltext.pdf. Retrieved 2008-11-11.
External links
- Which are the Dwarfs in the Solar System? Tancredi,G; Favre,S. Icarus, Volume 195, Issue 2, p. 851-862.
See also
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