Transneptunian object

Illustration at scale of the largest transneptunian objects.

A trans-Neptunian object (also, trans-Neptunian object) is any object in the solar system whose orbit lies partly or entirely beyond the orbit of the planet Neptune. Some specific subdivisions of that space are called the Kuiper belt and the Oort cloud. By a resolution of the International Astronomical Union on June 11, 2008, the trans-Neptunian dwarf planets were renamed plutoids.

To refer to a trans-Neptunian object, the abbreviation TNO (from English trans neptunian object) is often used. In many cases, it is used interchangeably with the abbreviation KBO (from English Kuiper belt object), which is not entirely correct. TNOs include, among others, Oort cloud bodies and KBOs. The latter, in turn, are also subdivided into plutinos and cubewanos.^{[citation required]}

Due to changes in the orbits of the known planets in the early 1900s, and attributed to the action of gravity (the attractive force between all matter) on the planets themselves, it was assumed that there were one or more more planets beyond Neptune that had not been identified (see planet X). A similar hypothesis had led to the discovery of Neptune, from distortions in the orbit of Uranus. The search for these theoretical bodies led to the discovery of Pluto, and a few significant objects have since been found. However, they are still too small to explain the disturbances, and revised calculations of Neptune's mass showed that the problem was fictitious.^{[citation needed]}

Notable trans-Neptunian objects

In June 2005, the number of these objects was over a thousand, of which a hundred had a precisely determined orbit, and therefore a definitive numbering of the Minor Planet Center.

Kuiper Belt

Kuiper belt objects are often subclassified based on their orbital characteristics. On the one hand, there are objects that orbit in some kind of resonance with Neptune, 2:3, 1:2, 3:5, 4:7, etc. On the other hand, those that are not orbitally linked to Neptune, without orbital resonance of any kind, which are called cubewanos or classical Kuiper belt objects.^{[citation needed]}

2:3 Resonance (plutinos)

With a period of ~250 years, the 2:3 resonance at 39.4 AU is by far the dominant category among resonant objects, with 92 confirmed and 104 possible members. The following objects orbiting in this resonance plutinos are named after Pluto, the first to be discovered. Some important plugins are:

Relevant Plutinos

Name	Diameter (km)	Perihelio (ua)	Afelio (ua)	Discovery	Year	Image
Pluto	2306±20	29,67	48,83	Clyde William Tombaugh	1930
Caronte	1207±3			James W. Christy	1978
Nix	46-137			Hubble Space Telescope	2005
Hydra	61-167				2005
Cerbero	13-34				2011
Stigia	10-25				2012
1993 RO	90	31,462	46.628	David C. Jewitt and Jane X. Luu	1993
1993 RP	70	34,863	43.795	David C. Jewitt and Jane X. Luu	1993
1993 SB	130	26.719	51,572	I.P. Williams, A. Fitzsimmons and D. O'Ceallaigh	1993
1993 SC	363	32,095	46.7	I.P. Williams, A. Fitzsimmons and D. O'Ceallaigh	1993
Ixion	822	30,0009	49,0773	Deep Ecliptic Survey	2001
Haumea	1300–1900	43,339	51.524	José L. Ortiz and Michael E. Brown	2003
Namaka	170			Brown, Trujillo, Rabinowitz	2005
Hiiakaka	310			Brown, Trujillo, Rabinowitz	2005
Orcus	917±25	30.53	48,31	Brown, Trujillo, Rabinowitz	2004
Makemake	1430±14	38.590	52.840	Brown, Trujillo, Rabinowitz	2005
2003 VS2	523+35.1 −34.4	36.427	42,104	NEAT	2003
2003 AZ84	730	32,309	46,554	Brown, Trujillo	2003
Huya	458,0±9.2	28.520	50.363	Ignacio Ferrín	2000

3:5 Resonance

As of October 2008, 10 of these objects had been found. They have a period of ~275 years. These are the three most important:

Resonance 4:7

With a period of ~290 years, another important group (as of October 2008 about 20 objects found) orbiting the Sun at 43.7 AU (in the middle of classical objects). The objects are quite small (with one exception, H>6) and most of them follow orbits close to the ecliptic. Objects with well-known orbits include:

1:2 Resonance (twotinos)

With a period of ~330 years, this resonance at 47.8 AU is often considered the outer edge of the Kuiper belt, and objects in this resonance are sometimes called twotinos. Twotinos have tilts of less than 15 degrees and eccentricities generally moderate (0.1 < and <0.3). An unknown number of 1:2 resonants probably did not originate from a disk of planetesimals that was swept by the resonance during the Neptune migration, but were captured after they had dispersed.

There are far fewer objects in this resonance (a total of 14 since October 2008) than plutinos. Long-term orbital integration shows that the 1:2 resonance is less stable than the 2:3 resonance; only 15% of objects in 1:2 resonance were stable after 4 billion years, compared to 28% for plutinos. Consequently, twotinos could originally have been as numerous as plutinos, but their populations have fallen. well below that of plutinos ever since.

2:5 Resonance

They have an orbit of ~410 years. In total, the orbits of 11 objects are classified in 2:5 resonance as of October 2008. Objects with well-established orbits at 55.4 AU include:

Name	Diameter (km)	Perihelio (ua)	Afelio (ua)	Discovery	Year	Image
2002 TC302	584,1+105.6 −88.0	39.199	71.870	Brown, Trujillo, Rabinowitz	2002
2003 UY117					2003
2001 KC77	201	35.418	76,001	Marc Buie	2001
2002 GG32					2002
1998 WA31	139	31,473	78.179	Marc Buie	1998

1:1 Resonance (Neptune Trojans)

Some objects have been discovered with a semi-major axis similar to that of Neptune, near the Sun-Neptune Lagrange Points. These Neptune Trojans are in a 1:1 resonance with Neptune. Nine such objects have been discovered as of October 2012:

• 2001 QR322
• 2004 UP10
• 2005 TN53
• 2005 TO74
• 2006 RJ103
• 2007 VL305
• 2008 LC18
• 2004 KV18
• 2011 HM102

Only the last three are near Neptune's L5, the rest are at L4.

Other resonances

The nominal Pound 7:12 of Haumea in a diagram where Neptune remains static. The color changes from red to green where the ecliptic crosses.

So-called higher order resonances are known for a limited number of objects, including the following:

• 4:5 (35 UA, ~205 years old) 2001 XH255
• 3:4 (36.5 UA, ~220 years) (143685) 2003 SS317, (15836) 1995 DA2
• 5:9 (44,5 UA, ~295 years) 2002 GD32
• 4:9 (52 UA, ~370 years) (42301) 2001 UR163, (182397) 2001 QW297
• 3:7 (53 UA, ~385 years) 2001 XT254, (95625) 2002 GX32, (183964) 2004 DJ71, (181867) 1999 CV118
• 5:12 (55 UA, ~395 years) (79978) 1999 CC158, (119878) 2001 CY224(84% probability according to Emel’yanenko)
• 3:8 (57 UA, ~440 years) 2000 YW134 (82075)(84% probability according to Emel’yanenko)
• 3:10 (67 AU, ~549 years) (225088) 2007 OR10
• 2:7 (70 UA, ~580 years) (471143) Dziewanna, 2006 HX122(The preliminary orbit suggests a weak 2:7 resonance. Further observations are required.)

Some objects are in distant resonances

• 1:3 (62.5 UA, ~495 years) (136120) 2003 LG7, (385607) 2005 EO297
• 1:4 (76 UA, ~660 years) 2003 LA7
• 1:5 (88 UA, ~820 years) 2003 YQ179 (apparently coincidental)

Some notable unproven resonances (which could be coincidence) of dwarf planets are:

• 7:12 (43 UA, ~283 years) Haumea (highly probable nominal orbit in resonance)
• 6:11 (45 UA, ~302 years) Makemake(182294) 2001 KU76 seems also to be in resonance 6:11)
• 5:17 (67 AU, ~560 years) Eris (2007 OR10 is in a similar orbit)

No resonance (cubewanos)

A cubewano, also called a "classic Kuiper belt object" or, in English, classical Kuiper belt object (CKBO), is a trans-Neptunian object that does not meet any type of orbital resonance with Neptune. The peculiar name is derived from the first object of this class, the 1992 QB1; Pronounced in English: /kju:bi wʌn/.

Relevant Cubewanos

Name	Diameter (km)	Perihelio (ua)	Afelio (ua)	Discovery	Year	Image
Albion	160	40,8754	46,5925	David C. Jewitt, Jane X. Luu	1992
1998 WW31	133±15	41,045	48,472	M. W. Buie	1998
S/(WW31) 1	110±12			Christian Veillet, Alain Doressoundiram	2000
Varuna	757	40,494	45,313	R. McMillan	2000
Quaoar	1110	41.695	45.116	Chad Trujillo, Michael Brown	2002
Logos	77±18	39.675	50.50	C. A. Trujillo, J. Chen, D. C. Jewitt, J. X. Luu	1997
Zoe.	66			several	2001
Varda	705+81 −75	39.622	52.284	J. A. Larsen	2003
Chaos	612	40.929	50.269	Deep Ecliptic Survey	1998
2002 TX300	320	38.1057	48.954	NEAT	2002
2002 AW197	768	41,066	53,503	several	2002
2002 UX25	650	36.815	48,923	Spacewatch	2002

Scattered Disc

Relevant objects of the scattered disk

Name	Diameter (km)	Perihelio (ua)	Afelio (ua)	Discovery	Year	Image
2004 XR190	425-850	51,394	64,032	Lynne Jones, Brett Gladman, John J. Kavelaars, Jean-Marc Petit, Joel Parker, Phil Nicholson.	2004
2007 OR10	1280 ± 210	33,62	100.79	M. E. Brown, Schwamb, David Lincoln Rabinowitz	2007
1996 TL66	339±20	35,010	132.87	David C. Jewitt, Jane X. Luu, Jun Chen, C. A. Trujillo	1996
Eris	2326	35	97	M. E. Brown, C. A. Trujillo, David Lincoln Rabinowitz	2005
Disnomia	350			M. E. Brown, M. A. van Dam, A. H. Bouchez, D. Le Mignant	2005

Separate Objects

Sometimes considered as outer scattered disk objects. This is a list of known separate objects, which could not be easily dispersed by Neptune's orbit and are therefore likely to be separate objects, but lie within perihelion distance ≈50-75 AU, boundary used that would define the sednoids.

Inner Oort Cloud

The Hills cloud, also called the inner Oort cloud and Inner Cloud, is, in astronomy, a vast and spherical hypothetical inner body in the Oort cloud, the outer edge of which is located at a distance of 2 to 3× 10⁴ AU from the Sun, and whose inner edge, not so sharp, is hypothetically located between 100 and 3000 AU.

Relevant objects of the inner cloud

Name	Diameter (km)	Perihelio (ua)	Afelio (ua)	Discovery	Year	Image
Sedna	995±80	76.0917	≈ 936	Michael E. Brown, C. Trujillo, D. Rabinowitz	2003
2012 VP113	~ 500	80.5 ± 0.6	446 ± 13	Scott Sheppard, Chad Trujillo	2012
2015 TG387	≈300	65±1	≈2300	Scott Sheppard, Chad Trujillo	2015

Oort Cloud

The hypothetical companion star Nemesis would fit the definition of a trans-Neptunian object, although its existence has not been proven.

Plutino and plutoid

Do not confuse the terms plutino and plutoid. Each one of these categories groups trans-Neptunian objects that, although they may belong to both at the same time, each one has different characteristics as a requirement:

• Pluto-like orbital features are transneptunian objects, regardless of their size.
• Plutoids are transneptunian objects with a size similar to Pluto, regardless of the orbital group to which they belong.