Trans-Neptunian Objects

by Wm. Robert Johnston
last updated 5 April 2014

Contents:

List of known trans-Neptunian objects and Centaurs


Dynamical classes:

Classes of outer solar system objects, with numbers of known objects (1,805, as of 22 March 2014) 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)

Eight trans-Neptunian objects--(87269) 2000 OO67, (90377) Sedna, (308933) 2006 SQ372, 2007 TG422, 2010 BK118, 2012 DR30, 2013 AZ60, and 2013 BL76--have aphelion distances beyond 800 AU. (Three unusual asteroids have aphelia over 800 AU: 2002 RN109, 2005 VX3, and 2007 DA61; these may be inactive comets.) A total of 84 TNOs (plus 19 more unusual objects) have aphelion distances exceeding 100 AU. Relatively few (22) have been discovered with perihelion distances greater than 46 AU, and only four with perihelion distances greater than 47 AU: Sedna at 76.1 AU, 2004 XR190 at 51.5 AU, 2010 GB174 at 48.5 AU, and 2004 VN112 at 47.3 AU. Data thus far suggests than there is indeed a cutoff to the classical TNO population at 47 AU, although the discoveries of Sedna and 2004 XR190 suggest an unrecognized population of much more distant objects (see below).

Of the 1,805 outer solar system objects counted above, 51 have inclinations from 40° to 90°, and 52 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 38 largest known TNOs (plus two satellites) 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 50 TNOs appear to be at least 500 km in diameter and 136 at least 300 km. The total volume of known TNOs (including Pluto) is estimated at 152% of that of the Moon (35% in Pluto/Charon and 31% in Eris/Dysnomia). (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). Data for the 79 known TNO binary or multiple systems are given below:

TNOcompanion(s)component diameters (km)separation (km)orbital period (d)year
reported
(134340) PlutoCharon 23501210 19,571 6.3871978
Styx 15 42,490 20.16 2012
Nix 70 48,840 24.85 2005
Kerberos 25 57,730 32.17 2011
Hydra 60 64,740 38.20 2005
(26308) 1998 SM165 S/2001 (26308) 1 290100 11,370 130.2 2002
(38628) Huya   430220 1,700? 2.6? 2012
(42355) Typhon Echidna 150 80 1,630 18.9712006
(47171) 1999 TC36 310260 870 1.9072007
S/2001 (1999 TC36) 1 140 7,410 50.38 2002
(48939) 1995 TL8   330150 420? 0.5? 2005
(50000) Quaoar Weywot 1030 80 14,500 12.44 2007
(55637) 2002 UX25   670190 4,800? 8? 2007
(58534) Logos Zoe 80 70 8,220 309.9 2002
(60458) 2000 CM114   170130 2,200? 15? 2006
(60621) 2000 FE8   150110 1,200? 8? 2007
(65489) Ceto Phorcys 200150 1,840 9.5542006
(66652) Borasisi Pabu 130100 4,530 46.29 2003
(79360) Sila-Nunam Nunam 250240 2,780 12.5 2005
(80806) 2000 CM105   160120 2,700? 23? 2005
(82075) 2000 YW134   470160 1,900? 3? 2005
(82157) 2001 FM185   140120 3,100? 33? 2011
(88611) TeharonhiawakoSawiskera 160120 27,700 828.8 2001
(90482) Orcus Vanth 880270 9,010 9.5392007
(119067) 2001 KP76   150150 8,900? 130? 2008
(119979) 2002 WC19   440140 2,800? 6? 2007
(120347) Salacia Actaea 870290 5,600 5.4942006
(123509) 2000 WK183   110100 2,370 30.92 2007
(134860) 2000 OJ67   140110 2,360 22.04 2005
(136108) HaumeaNamaka 1390160 25,660 18.2782005
Hi'iaka 320 49,900 49.46 2005
(136199) Eris Dysnomia 2330660 37,600 15.7722005
(139775) 2001 QG298   140120 170 0.5742004
(148780) Altjira   220200 9,900 139.6 2007
(160091) 2000 OL67   150120 7,800? 120? 2008
(160256) 2002 PD149   190160 24,000? 470? 2007
(174567) Varda   700360 4,200? 4? 2011
(182933) 2002 GZ31   200120 2,100? 12? 2007
(208996) 2003 AZ84   770 80 7,200? 13? 2007
(229762) 2007 UK126   590100 3,600? 6? 2011
(275809) 2001 QY297   160140 9,960 138.1 2007
(303712) 2005 PR21   230140 3,600? 22? 2008
(341520) 2007 TY430   100100 21,000 961.2 2008
(364171) 2006 JZ81   120 80 32,000 1,500 2011
(385446) 2003 QW111   140 80 6,670 110.2 2006
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   130120 5,900? 90? 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 XP254   110 80 1,200? 12? 2011
2001 XR254   160130 9,300 125.6 2007
2002 VF130   120110 22,000? 760? 2009
2002 VT130   190150 2,500? 15? 2009
2002 XH91   300180 20.000? 190? 2009
2003 FE128   180130 2,100? 14? 2012
2003 HG57   160160 13,000? 210? 2012
2003 QA91   190180 1,900? 6? 2007
2003 QR91   210190 1,800? 11? 2007
2003 QY90   80 80 8,500 309.7 2003
2003 TJ58   60 50 3,800 137.3 2007
2003 UN284   120 80 56,000?3,190 2003
2003 WU188   180130 1,300? 4? 2007
2003 YS179   130110 7,800? 150? 2011
2003 YU179   150 80 2,000? 18? 2009
2004 KH19   180130 13,000? 210? 2011
2004 PB108   240130 10,400 97.02 2007
2005 EF298   140110 3,300? 38? 2011
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]   140 ? 16,000? 135? 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 79 binary/multiple TNOs (or SDOs/centaurs) (through March 2014) in a population of 1,657 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:


© 2001-2012, 2014 by Wm. Robert Johnston.
Last modified 5 April 2014.
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