Detached objects are a dynamical class of minor planets in the outer reaches of the Solar System and belong to the broader family of trans-Neptunian objects (TNOs). These objects have orbits whose points of closest approach to the Sun (perihelion) are sufficiently distant from the gravitational influence of Neptune that they are only moderately affected by Neptune and the other known planets: This makes them appear to be "detached" from the rest of the Solar System, except for their attraction to the Sun.[1][2]

Trans-Neptunian objects plotted by their distance and inclination. Objects beyond a distance of 100 AU display their designation.   Resonant TNO & Plutino
  Cubewanos (classical KBO)
  Scattered disc object
  Detached object

In this way, detached objects differ substantially from most other known TNOs, which form a loosely defined set of populations that have been perturbed to varying degrees onto their current orbit by gravitational encounters with the giant planets, predominantly Neptune. Detached objects have larger perihelia than these other TNO populations, including the objects in orbital resonance with Neptune, such as Pluto, the classical Kuiper belt objects in non-resonant orbits such as Makemake, and the scattered disk objects like Eris.

Detached objects have also been referred to in the scientific literature as extended scattered disc objects (E-SDO),[3] distant detached objects (DDO),[4] or scattered–extended, as in the formal classification by the Deep Ecliptic Survey.[5] This reflects the dynamical gradation that can exist between the orbital parameters of the scattered disk and the detached population.

At least nine such bodies have been securely identified,[6] of which the largest, most distant, and best known is Sedna. Those with large semi-major axes and high perihelion orbits similar to that of Sedna are termed sednoids. As of 2024, there are three known sednoids: Sedna, 2012 VP113, and Leleākūhonua.[7] These objects exhibit a highly statistically significant asymmetry between the distributions of object pairs with small ascending and descending nodal distances that might be indicative of a response to external perturbations; asymmetries such as this one are sometimes attributed to perturbations induced by unseen planets.[8][9]

Orbits

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Detached objects have perihelia much larger than Neptune's aphelion. They often have highly elliptical, very large orbits with semi-major axes of up to a few hundred astronomical units (AU, the radius of Earth's orbit). Such orbits cannot have been created by gravitational scattering by the giant planets, not even Neptune. Instead, a number of explanations have been put forward, including an encounter with a passing star[10] or a distant planet-sized object,[4] or Neptune migration (which may once have had a much more eccentric orbit, from which it could have tugged the objects to their current orbit)[11][12][13][14][15] or ejected rogue planets (present in the early Solar System that were ejected).[16][17][18]

The classification suggested by the Deep Ecliptic Survey team introduces a formal distinction between scattered-near objects (which could be scattered by Neptune) and scattered-extended objects (e.g. 90377 Sedna) using a Tisserand's parameter value of 3.[5]

The Planet Nine hypothesis suggests that the orbits of several detached objects can be explained by the gravitational influence of a large, unobserved planet between 200 AU and 1200 AU from the Sun and/or the influence of Neptune.[19]

Classification

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Detached objects are one of four distinct dynamical classes of TNO; the other three classes are classical Kuiper-belt objects, resonant objects, and scattered-disc objects (SDO).[20] Sednoids also belong to detached objects. Detached objects generally have a perihelion distance greater than 40 AU, deterring strong interactions with Neptune, which has an approximately circular orbit about 30 AU from the Sun. The boundary between the scattered and detached regions can be defined using an analytical resonance overlap criterion.[21][22]

The discovery of 90377 Sedna in 2003, together with a few other objects discovered around that time such as (148209) 2000 CR105 and (612911) 2004 XR190, has motivated discussion of a category of distant objects that may also be inner Oort cloud objects or (more likely) transitional objects between the scattered disc and the inner Oort cloud.[2]

Although Sedna is officially considered a scattered-disc object by the MPC, its discoverer Michael E. Brown has suggested that because its perihelion distance of 76 AU is too distant to be affected by the gravitational attraction of the outer planets it should be considered an inner-Oort-cloud object rather than a member of the scattered disc.[23] This classification of Sedna as a detached object is accepted in recent publications.[24]

This line of thinking suggests that the lack of a significant gravitational interaction with the outer planets creates an extended–outer group starting somewhere between Sedna (perihelion 76 AU) and more conventional SDOs like 1996 TL66 (perihelion 35 AU), which is listed as a scattered–near object by the Deep Ecliptic Survey.[25]

Influence of Neptune

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One of the problems with defining this extended category is that weak resonances may exist and would be difficult to prove due to chaotic planetary perturbations and the current lack of knowledge of the orbits of these distant objects. They have orbital periods of more than 300 years and most have only been observed over a short observation arc of a couple years. Due to their great distance and slow movement against background stars, it may be decades before most of these distant orbits are determined well enough to confidently confirm or rule out a resonance. Further improvement in the orbit and potential resonance of these objects will help to understand the migration of the giant planets and the formation of the Solar System. For example, simulations by Emel'yanenko and Kiseleva in 2007 show that many distant objects could be in resonance with Neptune. They show a 10% likelihood that 2000 CR105 is in a 20:1 resonance, a 38% likelihood that 2003 QK91 is in a 10:3 resonance, and an 84% likelihood that (82075) 2000 YW134 is in an 8:3 resonance.[26] The likely dwarf planet (145480) 2005 TB190 appears to have less than a 1% likelihood of being in a 4:1 resonance.[26]

Influence of hypothetical planet(s) beyond Neptune

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Mike Brown—who made the Planet Nine hypothesis—makes an observation that "all of the known distant objects which are pulled even a little bit away from the Kuiper seem to be clustered under the influence of this hypothetical planet (specifically, objects with semimajor axis > 100 AU and perihelion > 42 AU)".[27] Carlos de la Fuente Marcos and Ralph de la Fuente Marcos have calculated that some of the statistically significant commensurabilities are compatible with the Planet Nine hypothesis; in particular, a number of objects[a] which are called extreme trans-Neptunian object (ETNOs)[29] may be trapped in the 5:3 and 3:1 mean-motion resonances with a putative Planet Nine with a semimajor axis ~700 AU.[30]

Possible detached objects

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This is a list of known objects by discovery date that could not be easily scattered by Neptune's current orbit and therefore are likely to be detached objects, but that lie inside the perihelion gap of ≈50–75 AU that defines the sednoids.[31][32][33][34][35][36]

Objects listed below have a perihelion of more than 40 AU, and a semi-major axis of more than 47.7 AU (the 1:2 resonance with Neptune, and the approximate outer limit of the Kuiper Belt):[37]

Designation Diameter[38]
(km)
H q
(AU)
a
(AU)
Q
(AU)
ω (°) Discovery
Year
Discoverer Notes & Refs
2000 CR105 243 6.3 44.252 221.2 398 316.93 2000 M. W. Buie [39]
2000 YW134 216 4.7 41.207 57.795 74.383 316.481 2000 Spacewatch ≈3:8 Neptune resonance
2001 FL193 81 8.7 40.29 50.26 60.23 108.6 2001 R. L. Allen, G. Bernstein, R. Malhotra orbit extremely poor, might not be a TNO
2001 KA77 634 5.0 43.41 47.74 52.07 120.3 2001 M. W. Buie borderline classical KBO
2002 CP154 222 6.5 42 52 62 50 2002 M. W. Buie orbit fairly poor, but definitely a detached object
2003 UY291 147 7.4 41.19 48.95 56.72 15.6 2003 M. W. Buie borderline classical KBO
Sedna 995 1.5 76.072 483.3 890 311.61 2003 M. E. Brown, C. A. Trujillo, D. L. Rabinowitz Sednoid
2004 PD112 267 6.1 40 70 90 40 2004 M. W. Buie orbit very poor, might not be a detached object
Alicanto 222 6.5 47.308 315 584 326.925 2004 Cerro Tololo (unspecified) [40][41][42]
2004 XR190 612 4.1 51.085 57.336 63.586 284.93 2004 R. L. Allen, B. J. Gladman, J. J. Kavelaars
J.-M. Petit, J. W. Parker, P. Nicholson
very high inclination; Neptune Mean Motion Resonance (MMR) along with the Kozai Resonance (KR) modified the eccentricity and inclination of 2004 XR190 to obtain a very high perihelion[39][43][44]
2005 CG81 267 6.1 41.03 54.10 67.18 57.12 2005 CFEPS
2005 EO297 161 7.2 41.215 62.98 84.75 349.86 2005 M. W. Buie
2005 TB190 372 4.5 46.197 75.546 104.896 171.023 2005 A. C. Becker, A. W. Puckett, J. M. Kubica Neptune Mean Motion Resonance (MMR) along with the Kozai Resonance (KR) modified the eccentricity and inclination to obtain a high perihelion[44]
2006 AO101 168 7.1 2006 Mauna Kea (unspecified) orbit extremely poor, might not be a TNO
2007 JJ43 558 4.5 40.383 48.390 56.397 6.536 2007 Palomar (unspecified) borderline classical KBO
2007 LE38 176 7.0 41.798 54.56 67.32 53.96 2007 Mauna Kea (unspecified)
2008 ST291 640 4.2 42.27 99.3 156.4 324.37 2008 M. E. Schwamb, M. E. Brown, D. L. Rabinowitz ≈1:6 Neptune resonance
2009 KX36 111 8.0 100 100 2009 Mauna Kea (unspecified) orbit extremely poor, might not be a TNO
2010 DN93 486 4.7 45.102 55.501 65.90 33.01 2010 Pan-STARRS ≈2:5 Neptune resonance; Neptune Mean Motion Resonance (MMR) along with the Kozai Resonance (KR) modified the eccentricity and inclination to obtain a high perihelion[44]
2010 ER65 404 5.0 40.035 99.71 159.39 324.19 2010 D. L. Rabinowitz, S. W. Tourtellotte
2010 GB174 222 6.5 48.8 360 670 347.7 2010 Mauna Kea (unspecified)
2012 FH84 161 7.2 42 56 70 10 2012 Las Campanas (unspecified)
2012 VP113 702 4.0 80.47 256 431 293.8 2012 S. S. Sheppard, C. A. Trujillo Sednoid
2013 FQ28 280 6.0 45.9 63.1 80.3 230 2013 S. S. Sheppard, C. A. Trujillo ≈1:3 Neptune resonance; Neptune Mean Motion Resonance (MMR) along with the Kozai Resonance (KR) modified the eccentricity and inclination to obtain a high perihelion[44]
2013 FT28 202 6.7 43.5 310 580 40.3 2013 S. S. Sheppard
2013 GP136 212 6.6 41.061 155.1 269.1 42.38 2013 OSSOS
2013 GQ136 222 6.5 40.79 49.06 57.33 155.3 2013 OSSOS borderline classical KBO
2013 GG138 212 6.6 46.64 47.792 48.946 128 2013 OSSOS borderline classical KBO
2013 JD64 111 8.0 42.603 73.12 103.63 178.0 2013 OSSOS
2013 JJ64 147 7.4 44.04 48.158 52.272 179.8 2013 OSSOS borderline classical KBO
2013 SY99 202 6.7 50.02 694 1338 32.1 2013 OSSOS
2013 SK100 134 7.6 45.468 61.61 77.76 11.5 2013 OSSOS
2013 UT15 255 6.3 43.89 195.7 348 252.33 2013 OSSOS
2013 UB17 176 7.0 44.49 62.31 80.13 308.93 2013 OSSOS
2013 VD24 128 7.8 40 50 70 197 2013 Dark Energy Survey orbit very poor, might not be a detached object
2013 YJ151 336 5.4 40.866 72.35 103.83 141.83 2013 Pan-STARRS
2014 EZ51 770 3.7 40.70 52.49 64.28 329.84 2014 Pan-STARRS
2014 FC69 533 4.6 40.28 73.06 105.8 190.57 2014 S. S. Sheppard, C. A. Trujillo
2014 FZ71 185 6.9 55.9 76.2 96.5 245 2014 S. S. Sheppard, C. A. Trujillo ≈1:4 Neptune resonance; Neptune Mean Motion Resonance (MMR) along with the Kozai Resonance (KR) modified the eccentricity and inclination to obtain a very high perihelion[44]
2014 FC72 509 4.5 51.670 76.329 100.99 32.85 2014 Pan-STARRS ≈1:4 Neptune resonance; Neptune Mean Motion Resonance (MMR) along with the Kozai Resonance (KR) modified the eccentricity and inclination to obtain a very high perihelion[44]
2014 JM80 352 5.5 46.00 63.00 80.01 96.1 2014 Pan-STARRS ≈1:3 Neptune resonance; Neptune Mean Motion Resonance (MMR) along with the Kozai Resonance (KR) modified the eccentricity and inclination to obtain a high perihelion[44]
2014 JS80 306 5.5 40.013 48.291 56.569 174.5 2014 Pan-STARRS borderline classical KBO
2014 OJ394 423 5.0 40.80 52.97 65.14 271.60 2014 Pan-STARRS in 3:7 Neptune resonance
2014 QR441 193 6.8 42.6 67.8 93.0 283 2014 Dark Energy Survey
2014 SR349 202 6.6 47.6 300 540 341.1 2014 S. S. Sheppard, C. A. Trujillo
2014 SS349 134 7.6 45 140 240 148 2014 S. S. Sheppard, C. A. Trujillo ≈2:10 Neptune resonance; Neptune Mean Motion Resonance (MMR) along with the Kozai Resonance (KR) modified the eccentricity and inclination to obtain a high perihelion[45]
2014 ST373 330 5.5 50.13 104.0 157.8 297.52 2014 Dark Energy Survey
2014 UT228 154 7.3 43.97 48.593 53.216 49.9 2014 OSSOS borderline classical KBO
2014 UA230 222 6.5 42.27 55.05 67.84 132.8 2014 OSSOS
2014 UO231 97 8.3 42.25 55.11 67.98 234.56 2014 OSSOS
2014 WK509 584 4.0 40.08 50.79 61.50 135.4 2014 Pan-STARRS
2014 WB556 147 7.4 42.6 280 520 234 2014 Dark Energy Survey
2015 AL281 293 6.1 42 48 54 120 2015 Pan-STARRS borderline classical KBO
orbit very poor, might not be a detached object
2015 AM281 486 4.8 41.380 55.372 69.364 157.72 2015 Pan-STARRS
2015 BE519 352 5.5 44.82 47.866 50.909 293.2 2015 Pan-STARRS borderline classical KBO
2015 FJ345 117 7.9 51 63.0 75.2 78 2015 S. S. Sheppard, C. A. Trujillo ≈1:3 Neptune resonance; Neptune Mean Motion Resonance (MMR) along with the Kozai Resonance (KR) modified the eccentricity and inclination to obtain a very high perihelion[44]
2015 GP50 222 6.5 40.4 55.2 70.0 130 2015 S. S. Sheppard, C. A. Trujillo
2015 KH162 671 3.9 41.63 62.29 82.95 296.805 2015 S. S. Sheppard, D. J. Tholen, C. A. Trujillo
2015 KG163 101 8.3 40.502 826 1610 32.06 2015 OSSOS
2015 KH163 117 7.9 40.06 157.2 274 230.29 2015 OSSOS ≈1:12 Neptune resonance
2015 KE172 106 8.1 44.137 133.12 222.1 15.43 2015 OSSOS 1:9 Neptune resonance
2015 KG172 280 6.0 42 55 69 35 2015 R. L. Allen
D. James
D. Herrera
orbit fairly poor, might not be a detached object
2015 KQ174 154 7.3 49.31 55.40 61.48 294.0 2015 Mauna Kea (unspecified) ≈2:5 Neptune resonance; Neptune Mean Motion Resonance (MMR) along with the Kozai Resonance (KR) modified the eccentricity and inclination to obtain a very high perihelion[44]
2015 RX245 255 6.2 45.5 410 780 65.3 2015 OSSOS
Leleākūhonua 300 5.5 65.02 1042 2019 118.0 2015 S. S. Sheppard, C. A. Trujillo, D. J. Tholen Sednoid
2017 DP121 161 7.2 40.52 50.48 60.45 217.9 2017
2017 FP161 168 7.1 40.88 47.99 55.1 218 2017 borderline classical KBO
2017 SN132 97 5.8 40.949 79.868 118.786 148.769 2017 S. S. Sheppard, C. A. Trujillo, D. J. Tholen
2018 VM35 134 7.6 45.289 240.575 435.861 302.008 2018 Mauna Kea (unspecified)

The following objects can also be generally thought to be detached objects, although with slightly lower perihelion distances of 38–40 AU.

Designation Diameter[38]
(km)
H q
(AU)
a
(AU)
Q
(AU)
ω (°) Discovery
Year
Discoverer Notes & Refs
2003 HB57 147 7.4 38.116 166.2 294 11.082 2003 Mauna Kea (unspecified)
2003 SS422 168 7.04 39.574 198.181 356.788 206.824 2003 Cerro Tololo (unspecified)
2005 RH52 128 7.8 38.957 152.6 266.3 32.285 2005 CFEPS
2007 TC434 168 7.0 39.577 128.41 217.23 351.010 2007 Las Campanas (unspecified) 1:9 Neptune resonance
2012 FL84 212 6.6 38.607 106.25 173.89 141.866 2012 Pan-STARRS
2014 FL72 193 6.8 38.1 104 170 259.49 2014 Cerro Tololo (unspecified)
2014 JW80 352 5.5 38.161 142.62 247.1 131.61 2014 Pan-STARRS
2014 YK50 293 5.6 38.972 120.52 202.1 169.31 2014 Pan-STARRS
2015 DM319 8.78 39.491 272.302 505.113 43.227 2015 OSSOS
2015 GT50 88 8.6 38.46 333 627 129.3 2015 OSSOS

See also

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Notes

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  1. ^ 60 minor planets with a semi-major axis greater than 150 AU and perihelion greater than 30 AU are known.[28]

References

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  33. ^ "objects with perihelia between 40–55 AU and aphelion more than 100 AU".
  34. ^ "objects with perihelia between 40–55 AU and semi-major axis more than 50 AU".
  35. ^ "objects with perihelia between 40–55 AU and eccentricity more than 0.5".
  36. ^ "objects with perihelia between 37–40 AU and eccentricity more than 0.5".
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