Detached object

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

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 Solar System.^[1][2]

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 perihelia greater than 75 AU are termed sednoids. As of 2016, there are two known sednoids, Sedna and 2012 VP113.

Orbits

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 (in particular, Neptune). Instead, a number of explanations have been put forward, including an encounter with a passing star^[7] or a distant planet-sized object,^[4] or Neptune itself (which may once have had a much more eccentric orbit, from which it could have tugged the objects to their current orbit)^{[8][9][10][11][12]} or ejected planets (present in the early Solar System that were ejected).^[13][14][15]

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.^[16]

Classification

Detached objects are one of five distinct dynamical classes of TNO; the other four classes are classical Kuiper-belt objects, resonant objects, scattered-disc objects (SDO), and sednoids. 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. However, there are no clear boundaries between the scattered and detached regions, since both can coexist as TNOs in an intermediate region with perihelion distance between 37 and 40 AU.^[6] One such intermediate body with a well determined orbit is (120132) 2003 FY128.

The discovery of 90377 Sedna in 2003, together with a few other objects discovered around that time such as 2000 CR105 and 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.^[17] This classification of Sedna as a detached object is accepted in recent publications.^[18]

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.^[19]

Influence of Neptune

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.^[20] The likely dwarf planet (145480) 2005 TB190 appears to have less than a 1% likelihood of being in a 4:1 resonance.^[20]

Influence of hypothetical planet(s) beyond Neptune

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)."^[21] 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^{[upper-alpha 1]} may be trapped in the 5:3 and 3:1 mean-motion resonances with a putative Planet Nine with a semimajor axis ∼700 AU.^[24]

Possible detached objects

This is a list of known objects by decreasing perihelion, 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:^{[25][26][27][28][29][30]}

Designation number[lower-alpha 1]	Name	Diameter (km)	H	Perihelion (AU)	Semi-major axis (AU)	Aphelion (AU)	Argument of perihelion (°)	Discovery Year	Discoverer	Method[lower-alpha 2]	Refs
48639	1995 TL8	≈ 350	5.2	40.0	52.5	64.5		1995	A. Gleason	assumed
148209	2000 CR105	≈ 250	6.1	44.0	224	403	316.5	2000	Lowell Observatory	assumed	[31]
	2004 XR190	335–850	4.4	51.5	57.7	64		2004	Lynne Jones et al.	assumed	[31][32]
	2004 VN112	130–300	6.4	47.3	329	610	327.2	2004	CTIO	assumed	[33][34][35]
145480	2005 TB190	≈ 500	4.7	46.2	76.4	106.5		2005	Becker, A. C. et al.	assumed
	2008 ST291	≈ 612	4.2	42.5	98.6	154.8		2008	Meg Schwamb et al.
	2010 GB174	242	6.6	48.5	361	673	347.3	2010	Canada–France–Hawaii Telescope
	2010 ER65		5.4	40	99.77	159.5	324	2010	European Southern Observatory, La Silla		[36]
	2013 GP136		6.6	41.1	151.75	262.38	42	2013	Mauna Kea		[37]
	2013 JD64		8.0	42.6	72.6	102.6	177.5	2013	Mauna Kea		[38]
	2014 WT69		5.7	44.5	76.7	108.8	139.56	2014	Pan-STARRS 1, Haleakala		[39]
	2014 FC69	300–700	4.6	40.2	73.57	106.9	191.3	2014	Cerro Tololo Observatory, La Serena		[40]

See also

• Classical Kuiper belt object
• List of Solar System objects by greatest aphelion
• List of trans-Neptunian objects
• Planets beyond Neptune

Notes

1. Objects with a Minor Planet Center designation number have an orbit with more observations taken over a longer period of time, which is therefore better determined and more securely known, than the orbit of objects with only a provisional designation.
2. Method of diameter calculation: "Assumed" means the albedo of the object is assumed to be 0.04, and the object's diameter is calculated accordingly.

1. Twelve minor planets with a semi-major axis greater than 150 AU and perihelion greater than 30 AU are known,^{[22][nb 1]} which are called Extreme trans Neptunian objects (ETNOs).^[23]

1. 2003 SS422 is excluded from the count because it has an observation arc of only 76 days and hence its semi-major axis is not securely known.

References

1. P. S. Lykawka; T. Mukai (2008). "An Outer Planet Beyond Pluto and the Origin of the Trans-Neptunian Belt Architecture". Astronomical Journal 135: 1161. arXiv:0712.2198. Bibcode:2008AJ....135.1161L. doi:10.1088/0004-6256/135/4/1161.
2. D.Jewitt, A.Delsanti The Solar System Beyond The Planets in Solar System Update : Topical and Timely Reviews in Solar System Sciences , Springer-Praxis Ed., ISBN 3-540-26056-0 (2006) Preprint of the article (pdf)
3. B. Gladman et al. (2002): Evidence for an Extended Scattered Disk. Icarus 157, p. 269–279, doi:10.1006/icar.2002.6860 (PDF).
4. Rodney S. Gomes; Matese, J; Lissauer, J (2006). "A distant planetary-mass solar companion may have produced distant detached objects". Icarus (Elsevier) 184 (2): 589–601. Bibcode:2006Icar..184..589G. doi:10.1016/j.icarus.2006.05.026.
5. J. L. Elliot, S. D. Kern, K. B. Clancy, A. A. S. Gulbis, R. L. Millis, M. W. Buie, L. H. Wasserman, E. I. Chiang, A. B. Jordan, D. E. Trilling, and K. J. Meech (2006). "The Deep Ecliptic Survey: A Search for Kuiper Belt Objects and Centaurs. II. Dynamical Classification, the Kuiper Belt Plane, and the Core Population" (PDF). The Astronomical Journal 129: 1117. Bibcode:2005AJ....129.1117E. doi:10.1086/427395.
6. Lykawka, Patryk Sofia & Mukai, Tadashi (July 2007). "Dynamical classification of trans-neptunian objects: Probing their origin, evolution, and interrelation". Icarus 189 (1): 213–232. Bibcode:2007Icar..189..213L. doi:10.1016/j.icarus.2007.01.001.
7. Morbidelli, Alessandro; Levison, Harold F. (November 2004). "Scenarios for the Origin of the Orbits of the Trans-Neptunian Objects 2000 CR₁₀₅ and 2003 VB₁₂". The Astronomical Journal 128 (5): 2564–2576. arXiv:astro-ph/0403358. Bibcode:2004AJ....128.2564M. doi:10.1086/424617. Retrieved 2008-07-02.
8. "Evidence for an extended scattered disk". arXiv:astro-ph/0103435. Bibcode:2002Icar..157..269G. doi:10.1006/icar.2002.6860.
9. "Mankind's Explanation: 12th Planet".
10. "A comet's odd orbit hints at hidden planet".
11. "Is There a Large Planet Orbiting Beyond Neptune?".
12. "Signs of a Hidden Planet?".
13. "A Moment With ... Dr. Brett Gladman".
14. "Production of the Extended Scattered Disk by Rogue Planets". Bibcode:2006ApJ...643L.135G. doi:10.1086/505214.
15. "The long and winding history of Planet X".
16. Batygin, Konstantin; Brown, Michael E. (20 January 2016). "Evidence for a distant giant planet in the Solar system". The Astronomical Journal 151 (2). arXiv:1601.05438. Bibcode:2016AJ....151...22B. doi:10.3847/0004-6256/151/2/22.
17. Brown, Michael E. "Sedna (The coldest most distant place known in the solar system; possibly the first object in the long-hypothesized Oort cloud)". California Institute of Technology, Department of Geological Sciences. Retrieved 2008-07-02.
18. D.Jewitt, A. Moro-Martın, P.Lacerda The Kuiper Belt and Other Debris Disks to appear in Astrophysics in the Next Decade, Springer Verlag (2009). Preprint of the article (pdf)
19. Marc W. Buie (2007-12-28). "Orbit Fit and Astrometric record for 15874". SwRI (Space Science Department). Retrieved 2011-11-12.
20. Emel’yanenko, V. V (2008). "Resonant motion of trans-Neptunian objects in high-eccentricity orbits". Astronomy Letters 34: 271–279. Bibcode:2008AstL...34..271E. doi:10.1134/S1063773708040075.(subscription required)
21. Mike Brown. "Why I believe in Planet Nine".
22. "Minor Planets with semi-major axis greater than 150 AU and perihelion greater than 30 AU".
23. C. de la Fuente Marcos; R. de la Fuente Marcos (September 1, 2014). "Extreme trans-Neptunian objects and the Kozai mechanism: signalling the presence of trans-Plutonian planets". Monthly Notices of the Royal Astronomical Society 443 (1): L59–L63. arXiv:1406.0715. Bibcode:2014MNRAS.443L..59D. doi:10.1093/mnrasl/slu084.
24. de la Fuente Marcos, Carlos (20 Apr 2016). "Commensurabilities between ETNOs: a Monte Carlo survey". arXiv:1604.05881.
25. Michael E. Brown (10 September 2013). "How many dwarf planets are there in the outer solar system? (updates daily)". California Institute of Technology. Retrieved 2013-05-27. Diameter: 242km
26. "objects with perihelia between 40–55 AU and aphelion more than 60 AU".
27. "objects with perihelia between 40–55 AU and aphelion more than 100 AU".
28. "objects with perihelia between 40–55 AU and semi-major axis more than 50 AU".
29. "objects with perihelia between 40–55 AU and eccentricity more than 0.5".
30. "objects with perihelia between 37–40 AU and eccentricity more than 0.5".
31. E. L. Schaller and M. E. Brown (2007). "Volatile loss and retention on Kuiper belt objects" (PDF). Astrophysical Journal 659: I.61–I.64. Bibcode:2007ApJ...659L..61S. doi:10.1086/516709. Retrieved 2008-04-02.
32. R. L. Allen, B. Gladman (2006). "Discovery of a low-eccentricity, high-inclination Kuiper Belt object at 58 AU". The Astrophysical Journal 640. arXiv:astro-ph/0512430. Bibcode:2006ApJ...640L..83A. doi:10.1086/503098.
33. Marc W. Buie (2007-11-08). "Orbit Fit and Astrometric record for 04VN112". SwRI (Space Science Department). Retrieved 2008-07-17.
34. "JPL Small-Body Database Browser: (2004 VN112)". Retrieved 2015-02-24.
35. "List Of Centaurs and Scattered-Disk Objects". Retrieved 2011-07-05. Discoverer: CTIO
36. "IAU Minor Planet Center – 2010_ER65".
37. "IAU Minor Planet Center – 2013_GP136".
38. "IAU Minor Planet Center – 2013_JD64".
39. "IAU Minor Planet Center – 2014_WT69".
40. "IAU Minor Planet Center – 2014_FC69".