Trans-Neptunian Objects

by Wm. Robert Johnston
last updated 15 October 2017

Contents:

Link to List of known trans-Neptunian objects and Centaurs


Dynamical classes:

Classes of outer solar system objects, with numbers of known objects (2,797, as of 8 October 2017) in parenthesis (see note below):

Note that these counts are approximate, since these classifications are in some cases not universally defined and since orbits are not well determined for some objects. In the case of resonance objects, accurate classification requires extended observations and dynamical studies. These counts include delineations based on preliminary orbital elements (listed as possible members), and classifications for objects in such cases are subject to revision.

The graph below plots eccentricity versus semimajor axis for outer solar system objects by class (click here for a larger version). Black asterisks indicate values for Jupiter, Saturn, Uranus, Neptune, and Pluto (from left to right). The light blue curves indicate values corresponding to perihelion distances of 40 AU, 45 AU, and 50 AU (from left to right on the graph).


Distribution by distance:

Below is a histogram of outer solar system objects by distance (click here for a larger version)

Including Sedna, 12 trans-Neptunian objects have aphelion distances beyond 800 AU. (Another 4 unusual asteroids have aphelia over 800 AU; these may be inactive comets.) A total of 64 TNOs (plus 9 more unusual objects) have aphelion distances exceeding 200 AU. Relatively few (12) have been discovered with perihelion distances greater than 47 AU, and only 6 with perihelion distances greater than 50 AU. Data thus far suggests than there is indeed a cutoff to the classical TNO population around 47 AU, although the discoveries of Sedna and 2012 VP113 suggest an unrecognized population of much more distant objects (see below).

Of the 2,797 outer solar system objects counted above, 84 (3.0%) have inclinations from 40° to 90°, and 86 (3.1%) have retrograde orbits. Most if not all of the latter objects may actually be comets no longer showing cometary activity.

The graph below (click here for larger version) shows estimated TNO size versus perihelion distance. A line indicates the nature of the cutoff that would result from detectability limits; in other words, objects lying along this line would have the same apparent brightness from Earth (assuming the same albedo). Note the lack of detected objects with perihelions beyond 47 AU.

The graph below (click here for larger version and discussion) shows eccentricity versus semimajor axis for outer solar system objects. Green lines indicate the location of orbital resonances with Neptune where objects have been found. The second resonance from the left is the 2:3 resonance, location of a cluster of objects (the Plutinos).


Largest objects:

The 29 largest known TNOs (plus one satellite) are, with estimated diameters:

Diameters with question marks are estimated (see discussion here). For comparison, the largest asteroid, (1) Ceres, is 920 km in diameter. A total of 73 TNOs appear to be at least 500 km in diameter and 315 at least 300 km. The total volume of known TNOs (including Pluto) is estimated at 203% of that of the Moon (36% in the Pluto system, 30% in the Eris system, and 10% in the Haumea system). (A note: these size-associated figures are very dependent on the assumed albedo value for these objects. The above figures assume an albedo of 9% for objects with unmeasured diameters/albedos.) For more discussion of large TNOs see:

The graph below (click here for larger version and discussion) plots albedo vs. diameter for TNOs and centaurs with measured diameters.

The chart below (click here for larger version) shows the orbits of some of the largest known TNOs with the outer planets.


Binary objects:

Below is a plot of TNO and asteroid size ratios vs. separation:

In 2001 the TNO 1998 WW31 was found to be double, and companions to other TNOs have since been found. The possibility of companions for six more TNOs has been suggested (for (20000) Varuna, (32929) 1995 QY9, (33128) 1998 BU48, (47932) 2000 GN171, 2003 SQ317, and 2010 WG9). In 2005 two companions to (136108) Haumea were discovered, shortly before two additional satellites of Pluto were reported (with additional discoveries later bringing Pluto's total to five satellites). In 2013 (10199) Chariklo was found to have a ring, followed by Haumea in 2017. Data for the 82 TNOs known to have satellites or rings are given below:

TNOcompanion(s)component diameters (km)separation (km)orbital period (d)year
reported
(134340) PlutoCharon 23701210 19,573 6.3871978
Styx 6 42,490 20.1622012
Nix 43 48,840 24.8552005
Kerberos 9 57,730 32.1682011
Hydra 38 64,740 38.2022005
(10199) Chariklo rings 250 -- 405 0.78 2014
(26308) 1998 SM165 S/2001 (26308) 1 270 80 11,380 130.20 2002
(38628) Huya   410210 1,700? 3.2? 2012
(42355) Typhon Echidna 160 90 1,580 18.9822006
(47171) LempoHiisi 290260 870 1.9072007
Paha 140 7,410 50.3 2002
(48939) 1995 TL8   180 80 420? 1.4? 2005
(50000) Quaoar Weywot 1070 80 13,800 12.3 2007
(55637) 2002 UX25   660210 4,770 8.3092007
(58534) Logos Zoe 80 60 8,220 309.9 2002
(60458) 2000 CM114   170130 2,200? 15? 2006
(60621) 2000 FE8   150110 1,200? 8? 2007
(65489) Ceto Phorcys 220170 1,840 9.5542006
(66652) Borasisi Pabu 130100 4,530 46.2892003
(79360) Sila-Nunam Nunam 250240 2,780 12.51 2005
(80806) 2000 CM105   160120 2,700? 23? 2005
(82075) 2000 YW134   220 80 1,900? 10? 2005
(82157) 2001 FM185   140120 3,100? 33? 2011
(88611) TeharonhiawakoSawiskera 180130 27,700 828.8 2001
(90482) Orcus Vanth 920280 9,010 9.5392007
(119067) 2001 KP76   150150 8,900? 130? 2008
(119979) 2002 WC19   520130 4,100 8.4032007
(120347) Salacia Actaea 850290 5,600 5.4942006
(123509) 2000 WK183   110100 2,370 30.92 2007
(134860) 2000 OJ67   140110 2,270 22.06 2005
(136108) Haumearings 1600-- 2,290 0.4852017
Namaka 160 25,660 18.2782005
Hi'iaka 320 49,900 49.46 2005
(136199) Eris Dysnomia 2330510 37,600 15.7902005
(136472) Makemake S/2015 (136472) 1 1430180 21,000? 12.4 2016
(139775) 2001 QG298   140120 170 0.5742004
(148780) Altjira   250220 9,900 139.6 2007
(160091) 2000 OL67   150120 7,800? 120? 2008
(160256) 2002 PD149   190160 24,000? 470? 2007
(174567) Varda Ilmare 720330 4,810 5.7512011
(182933) 2002 GZ31   200120 2,100? 12? 2007
(208996) 2003 AZ84   720 70 7,200? 12? 2007
(225088) 2007 OR10   1510300 15,000? 68? 2016
(229762) 2007 UK126   610110 3,600? 6? 2011
(275809) 2001 QY297   170150 9,960 138.11 2007
(303712) 2005 PR21   230140 3,600? 22? 2008
(341520) Mors-Somnus Somnus 100100 21,000 971.7 2008
(364171) 2006 JZ81   120 80 33,000 1,500 2011
(385446) Manwe Thorondor 140 80 6,670 110.18 2006
(469420) 2001 XP254   110 80 1,200? 12? 2011
(469505) 2003 FE128   190140 2,100? 13? 2012
(469514) 2003 QA91   190180 1,900? 9? 2007
(469705) 2005 EF298   140110 7,700 128.11 2011
1998 WV24   110100 1,400? 14? 2008
1998 WW31 S/2000 (1998 WW31) 1 150120 22,600 587.3 2001
1999 OJ4   80 70 3,270 84.12 2005
1999 RT214   100 70 3,300? 64? 2006
1999 RY214   120 80 1,500? 15? 2009
1999 XY143   210180 2,700? 14? 2009
2000 CF105   60 50 33,000 3,990 2002
2000 CQ114   80 80 6,900 220.7 2004
2000 QL251   150140 5,000 56.45 2006
2000 WT169   200170 2,600? 14? 2009
2001 FL185   140 90 1,900? 17? 2007
2001 QC298   240190 3,810 19.23 2002
2001 QQ322   170160 3,900? 32? 2008
2001 QW322   130130102,000 6,280 2001
2001 RZ143   110 90 1,600? 17? 2007
2001 XR254   170140 9,300 125.6 2007
2002 VF130   120110 22,000? 760? 2009
2002 VT130   250200 2,500? 10? 2009
2002 XH91   300180 20,000? 190? 2009
2003 HG57   160160 13,000? 210? 2012
2003 QR91   210190 1,800? 8? 2007
2003 QY90   80 80 8,500 309.7 2003
2003 TJ58   60 50 3,800 137.68 2007
2003 UN284   120 80 54,000 3,180 2003
2003 WU188   180130 1,300? 6? 2007
2003 YS179   140130 7,800? 120? 2011
2003 YU179   170 90 2,000? 15? 2009
2004 KH19   180130 13,000? 210? 2011
2004 PB108   240130 10,400 97.02 2007
2005 EO304   150 80 70,000 3,580 2005
2005 GD187   120100 7,600? 150? 2011
2005 VZ122   120 50 2,300? 30? 2011
2006 BR284   90 70 25,300 1,500 2011
2006 CH69   100 80 27,000 1,420 2010
2006 SF369   140140 3,100? 28? 2008
[hst5]   140140 16,000?1,000? 2011

Values of binary TNO separations or orbital periods if marked by "?" are approximate, assuming that observed (projected) separations are comparable to the semimajor axes and that both components have densities of order 1,000 kg/m3. For additional data see the following listings:

With 81 binary/multiple TNOs (or SDOs/centaurs) (through October 2017) in a population of 2,198 objects, it appears that binary TNOs are quite common. Binary TNOs identified in 2005 include several close binaries, suggesting more binaries that cannot yet be resolved.

For more information on binary TNOs, see the Asteroids with Satellites section at this web site.


General links:


© 2001-2015, 2017 by Wm. Robert Johnston.
Last modified 15 October 2017.
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