# Sednoid <!-- SOLSIM:BEGIN g31 — Solar System explorer state (hand-built on wt-core, specs/solar/); do not hand-edit inside --> **Microsim — three.js (Wikitube framework):** *Extreme trans-Neptunian objects in the Solar System explorer* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=etno&embed=1" data-title="Extreme trans-Neptunian objects in the Solar System explorer"></div> *The Solar System explorer locked on this article's state (`?obj=etno`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.* <!-- SOLSIM:END --> *Try: press l and pick out the three real sednoid orbits, Sedna, 2012 VP113 and Leleākūhonua, among the sampled points; drag to look down on the plane of the planets and compare the directions in which their near ends point; then scroll out until Leleākūhonua's orbit, reaching beyond 2,000 AU, fits in the view.* A **sednoid** is a [[Trans-Neptunian_object|trans-Neptunian object]] on a long, highly eccentric orbit whose perihelion lies so far from the [[Sun]] that [[Neptune]] cannot have put it there, like the orbit of the dwarf planet [[Sedna_(dwarf_planet)|Sedna]] after which the group is named. Four objects are generally accepted as sednoids: Sedna, 2012 VP113, 541132 Leleākūhonua and 2023 KQ14 ("Ammonite"), all with perihelia beyond 60 [[Astronomical_unit|AU]].[^chen2025] Because Neptune's pull on them is weak, sednoids are also counted as [[Detached_object|detached objects]], and some astronomers regard them as members of the inner [[Oort_cloud|Oort cloud]], or [[Hills_cloud|Hills cloud]], placed at 1,000–10,000 AU from the Sun.[^huang2024][^sheppard-ioc][^nesvorny2025] There is no agreed formal definition. Trujillo and Sheppard proposed perihelion greater than 50 AU and semi-major axis greater than 150 AU.[^trujillo2014][^sheppard-list] That rule also admits 2013 SY99, 2020 MQ53 and 2021 RR205, whose perihelia exceed 50 AU and whose semi-major axes exceed 700 AU, but most astronomers leave them out: at such wide orbits the [[Tide|galactic tide]] and Neptune's weak influence still make the orbits drift slowly, so they are not frozen in the way the sednoids are.[^mpc-q50][^bannister2017][^chen2025] High eccentricity, above about 0.7, also separates the sednoids from a set of distant objects with moderate eccentricities, such as 2015 KQ174, 2015 FJ345 and 2004 XR190, which Neptune does not disturb either.[^sheppard2016] The explorer at the top of this page shows the [[Extreme_trans-Neptunian_object|extreme trans-Neptunian objects]]: a cloud of ILLUSTRATIVE points with semi-major axes of 150 to 1,000 AU, and among them the real orbits of three sednoids from the JPL Small-Body Database. 2023 KQ14 is not drawn.[^jpl-sbdb] ## Unexplained orbits The problem the sednoids pose is one of mechanics. An object scattered by a planet keeps an orbit that returns to where the scattering happened, so a body flung out by Neptune ends with a perihelion near 30–40 AU and an aphelion far out. The known giant planets cannot raise such a perihelion to 65–80 AU, and the tide of the [[Milky_Way]] is too weak at these distances to do it either.[^brown2004][^trujillo2014] Nor can the sednoids have formed where they are now on their present orbits. Accretion, the gradual sticking together of small bodies, needs low collision speeds; on crossing, eccentric orbits the relative velocities between planetesimals would have been too high, so a sednoid formed in place must have started on a nearly circular orbit and been stretched later.[^sheppard-jewitt2005] Four broad explanations are discussed. The first is a close passage of another star while the Sun was still in the cluster where it formed, which would have raised the perihelia of bodies already on wide orbits.[^morbidelli2004][^pfalzner2018] The second is capture: the sednoids could be planetesimals taken from the disc of another star during such an encounter, most likely a sibling from the same birth cluster.[^brown2004][^jilkova2015] The third is an undiscovered planet beyond the [[Kuiper_belt|Kuiper belt]], such as the proposed [[Planet_Nine]], whose gravity would keep lifting and shepherding distant perihelia.[^gomes2006][^lykawka2008] The fourth is a rogue planet that passed through the outer Solar System early on and was later lost, raising perihelia during its stay.[^gladman2006][^huang2024] These are not exclusive, and each has supporters. What distinguishes them is how they would shape the population as a whole, which is why each new sednoid is used as a test. ## Known members The table gives barycentric elements for the four accepted sednoids, computed by JPL Horizons at the epoch of 18 September 2026. Barycentric elements refer the orbit to the centre of mass of the [[PORTAL_Solar_System|Solar System]], which moves as [[Jupiter]] and [[Saturn]] go round; for orbits this long they are steadier than heliocentric ones, but they still vary slightly with epoch.[^horizons] | Sednoid | Perihelion (AU) | Semi-major axis (AU) | Aphelion (AU) | Eccentricity | Inclination (°) | Period (years) | Discovered | |---|---|---|---|---|---|---|---| | Sedna | 76.2 | 506 | 937 | 0.85 | 11.9 | 11,400 | 2003 | | 2012 VP113 | 80.5 | 262 | 444 | 0.69 | 24.1 | 4,250 | 2012 | | Leleākūhonua | 64.8 | 1,213 | 2,361 | 0.95 | 11.7 | 42,200 | 2015 | | 2023 KQ14 | 65.9 | 252 | 438 | 0.74 | 11.0 | 4,000 | 2023 | The periods follow [[Kepler's_laws_of_planetary_motion|Kepler's third law]], P = a^1.5 in years and AU; for 2023 KQ14, 252^1.5 ≈ 4,000 years (derived). Estimated diameters range from about 900 km for Sedna to a few hundred kilometres for the others.[^lellouch2013][^chen2025] The first three sednoids share, with the other most distant detached objects, a clustering of the argument of perihelion near 0°. Trujillo and Sheppard showed that this cannot be an observational bias, and it is unexpected, because the giant planets should randomise the argument of perihelion through precession on timescales of 40 to 650 million years, and about 1.5 billion years for Sedna.[^trujillo2014][^jilkova2015] One or more undiscovered perturbers could maintain it: Trujillo and Sheppard found that a super-Earth near 250 AU could hold these objects around ω = 0° for billions of years while staying too faint for the all-sky surveys of the time, the idea later developed as Planet Nine.[^trujillo2014][^dlfm2014] Leleākūhonua, then called 2015 TG387, was announced on 1 October 2018, with a perihelion of 65 AU and an orbit reaching more than 2,000 AU.[^sheppard2019] An earlier candidate, V774104, presented at the 2015 Division for Planetary Sciences meeting, had too short an arc to show whether its perihelion was beyond Neptune's reach.[^witze2015] The group may not share one origin: 2012 VP113's spectral slope differs sharply from Sedna's.[^deleon2017] A search of TESS images by Rice and Laughlin recovered Sedna but has not yet added confirmed members.[^rice2020][^dlfm2022tess] ## Theoretical population Each origin leaves a signature. Megan Schwamb set out the predictions in 2007: if a planet beyond Neptune lifted the perihelia, all such objects should share roughly the same perihelion, near 80 AU; if they were captured from a star whose disc turned the same way as the Solar System's, they should have low inclinations and semi-major axes of about 100–500 AU, while capture from a counter-rotating system would give two groups, one of low and one of high inclination; and a series of passing stars would leave a wide spread of perihelia and inclinations.[^schwamb2007] The four known sednoids already span perihelia from 65 to 80 AU and inclinations from about 11° to 24°, too few to decide between these patterns.[^horizons] Michael Brown called Sedna "a fossil record of the earliest Solar System".[^fussman2006] Schwamb, Brown and Rabinowitz searched for more in 2007–2008 with a survey sensitive to motion out to 1,000 AU; it found the dwarf planet [[Gonggong_(dwarf_planet)|Gonggong]] but no new sednoid. Modelling that null result, they estimated that about 40 Sedna-sized bodies probably exist in the region, the brightest about as bright as [[Eris_(dwarf_planet)|Eris]].[^schwamb2009] The discovery of Leleākūhonua gave a second estimate. Sheppard and colleagues concluded that it implies about 2 million inner Oort cloud objects larger than 40 km, with a total mass of order 10²² kg, comparable to [[Pluto]] and several times the mass of the [[Asteroid_belt|asteroid belt]].[^sheppard2019] Such bodies are faint because they are only seen near perihelion: sunlight reflected back to [[Earth]] fades roughly as the fourth power of distance (derived), so an object at 80 AU is about 16 times fainter than the same object at 40 AU. The explorer's sampled points stand in for that unseen population and are not individual orbits. ## See also - [[Sedna_(dwarf_planet)]] - [[Extreme_trans-Neptunian_object]] - [[Detached_object]] · [[Hills_cloud]] · [[Oort_cloud]] - [[Planet_Nine]] - [[Trans-Neptunian_object]] ## Notes Derived values are marked "(derived)". Periods follow Kepler's third law, P = a^1.5 (P in years, a in AU). Reflected light from a body seen near the Sun scales roughly as 1/r⁴, since sunlight falls as 1/r² on the way out and again on the way back; 2⁴ = 16. ## References [^chen2025]: Chen, Y.-T.; Lykawka, P. S.; Huang, Y.; Kavelaars, J. J.; Fraser, W. C.; Bannister, M. T.; et al. (2025). "Discovery and dynamics of a Sedna-like object with a perihelion of 66 au". *Nature Astronomy* 9: 1309–1316. https://doi.org/10.1038/s41550-025-02595-7 [^huang2024]: Huang, Y.; Gladman, B. (2024). "Primordial orbital alignment of sednoids". *The Astrophysical Journal Letters* 962: L33. https://doi.org/10.3847/2041-8213/ad2686 [^sheppard-ioc]: Sheppard, S. S. "Beyond the edge of the Solar System: the inner Oort cloud population". Carnegie Institution for Science, Department of Terrestrial Magnetism. http://home.dtm.ciw.edu/users/sheppard/inner_oort_cloud/ [^nesvorny2025]: Nesvorný, D.; Dones, L.; Vokrouhlický, D.; Levison, H. F.; et al. (2025). "A spiral structure in the inner Oort cloud". *The Astrophysical Journal* 983: 74. https://doi.org/10.3847/1538-4357/adbf9b [^trujillo2014]: Trujillo, C. A.; Sheppard, S. S. (2014). "A Sedna-like body with a perihelion of 80 astronomical units". *Nature* 507: 471–474. https://doi.org/10.1038/nature13156 [^sheppard-list]: Sheppard, S. S. "Known extreme outer Solar System objects". Carnegie Institution for Science, Department of Terrestrial Magnetism. http://home.dtm.ciw.edu/users/sheppard/inner_oort_cloud/sednoids.html [^mpc-q50]: Minor Planet Center. "List of objects with q > 50 AU and a > 150 AU". https://minorplanetcenter.net/db_search/show_by_properties?perihelion_distance_min=50&semimajor_axis_min=150 [^bannister2017]: Bannister, M. T.; Shankman, C.; Volk, K.; et al. (2017). "OSSOS. V. Diffusion in the orbit of a high-perihelion distant Solar System object". *The Astronomical Journal* 153: 262. https://doi.org/10.3847/1538-3881/aa6db5 [^sheppard2016]: Sheppard, S. S.; Trujillo, C.; Tholen, D. J. (2016). "Beyond the Kuiper belt edge: new high perihelion trans-Neptunian objects with moderate semimajor axes and eccentricities". *The Astrophysical Journal Letters* 825: L13. https://doi.org/10.3847/2041-8205/825/1/L13 [^jpl-sbdb]: JPL Small-Body Database (elements for 90377 Sedna, (2012 VP113), 541132 Leleākūhonua, fetched 2026-09-18). NASA Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html [^brown2004]: Brown, M. E.; Trujillo, C.; Rabinowitz, D. (2004). "Discovery of a candidate inner Oort cloud planetoid". *The Astrophysical Journal* 617: 645–649. https://doi.org/10.1086/422095 [^sheppard-jewitt2005]: Sheppard, S. S.; Jewitt, D. (2005). "Small bodies in the outer Solar System". *Frank N. Bash Symposium*. http://www.dtm.ciw.edu/users/sheppard/pub/Sheppard06smallbodies.pdf [^morbidelli2004]: Morbidelli, A.; Levison, H. F. (2004). "Scenarios for the origin of the orbits of the trans-Neptunian objects 2000 CR105 and 2003 VB12 (Sedna)". *The Astronomical Journal* 128: 2564–2576. https://doi.org/10.1086/424617 [^pfalzner2018]: Pfalzner, S.; Bhandare, A.; Vincke, K.; Lacerda, P. (2018). "Outer Solar System possibly shaped by a stellar fly-by". *The Astrophysical Journal* 863: 45. https://doi.org/10.3847/1538-4357/aad23c [^jilkova2015]: Jílková, L.; Portegies Zwart, S.; Pijloo, T.; Hammer, M. (2015). "How Sedna and family were captured in a close encounter with a solar sibling". *Monthly Notices of the Royal Astronomical Society* 453: 3158–3163. https://doi.org/10.1093/mnras/stv1803 [^gomes2006]: Gomes, R. S.; Matese, J. J.; Lissauer, J. J. (2006). "A distant planetary-mass solar companion may have produced distant detached objects". *Icarus* 184: 589–601. https://doi.org/10.1016/j.icarus.2006.05.026 [^lykawka2008]: Lykawka, P. S.; Mukai, T. (2008). "An outer planet beyond Pluto and the origin of the trans-Neptunian belt architecture". *The Astronomical Journal* 135: 1161–1200. https://doi.org/10.1088/0004-6256/135/4/1161 [^gladman2006]: Gladman, B.; Chan, C. (2006). "Production of the extended scattered disk by rogue planets". *The Astrophysical Journal* 643: L135–L138. https://doi.org/10.1086/505214 [^horizons]: JPL Horizons On-Line Ephemeris System, barycentric osculating orbital elements at epoch 2026-09-18 (retrieved 2026-09-18). NASA Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/horizons/ [^lellouch2013]: Lellouch, E.; Santos-Sanz, P.; Lacerda, P.; Mommert, M.; et al. (2013). "'TNOs are Cool': a survey of the trans-Neptunian region. IX. Thermal properties of Kuiper belt objects and Centaurs from combined Herschel and Spitzer observations". *Astronomy & Astrophysics* 557: A60. https://doi.org/10.1051/0004-6361/201322047 [^dlfm2014]: de la Fuente Marcos, C.; de la Fuente Marcos, R. (2014). "Extreme trans-Neptunian objects and the Kozai mechanism: signalling the presence of trans-Plutonian planets". *Monthly Notices of the Royal Astronomical Society: Letters* 443: L59–L63. https://doi.org/10.1093/mnrasl/slu084 [^sheppard2019]: Sheppard, S. S.; Trujillo, C. A.; Tholen, D. J.; Kaib, N. (2019). "A new high perihelion trans-Plutonian inner Oort cloud object: 2015 TG387". *The Astronomical Journal* 157: 139. https://doi.org/10.3847/1538-3881/ab0895 [^witze2015]: Witze, A. (10 November 2015). "Astronomers spy most distant Solar System object ever". *Nature News*. https://doi.org/10.1038/nature.2015.18770 [^deleon2017]: de León, J.; de la Fuente Marcos, C.; de la Fuente Marcos, R. (2017). "Visible spectra of (474640) 2004 VN112–2013 RF98 with OSIRIS at the 10.4 m GTC: evidence for binary dissociation near aphelion among the extreme trans-Neptunian objects". *Monthly Notices of the Royal Astronomical Society: Letters* 467: L66–L70. https://doi.org/10.1093/mnrasl/slx003 [^rice2020]: Rice, M.; Laughlin, G. (2020). "Exploring trans-Neptunian space with TESS: a targeted shift-stacking search for Planet Nine and distant TNOs in the galactic plane". *The Planetary Science Journal* 1: 81. https://doi.org/10.3847/PSJ/abc42c [^dlfm2022tess]: de la Fuente Marcos, C.; de la Fuente Marcos, R.; Vaduvescu, O.; Stanescu, M. (2022). "Distant trans-Neptunian object candidates from NASA's TESS mission scrutinized: fainter than predicted or false positives?". *Monthly Notices of the Royal Astronomical Society: Letters* 513: L78–L82. https://doi.org/10.1093/mnrasl/slac036 [^schwamb2007]: Schwamb, M. E. (2007). "Searching for Sedna's sisters: exploring the inner Oort cloud". California Institute of Technology. http://www.astro.caltech.edu/~george/option/candex07/schwamb_report.pdf [^fussman2006]: Fussman, C. (May 2006). "The man who finds planets". *Discover*. http://discovermagazine.com/2006/may/cover [^schwamb2009]: Schwamb, M. E.; Brown, M. E.; Rabinowitz, D. L. (2009). "A search for distant Solar System bodies in the region of Sedna". *The Astrophysical Journal Letters* 694: L45–L48. https://doi.org/10.1088/0004-637X/694/1/L45 ## External links - Sheppard, S. S. "Known extreme outer Solar System objects". Carnegie Science. https://sites.google.com/carnegiescience.edu/sheppard/home/discoveries - Carnegie Institution for Science (2 October 2018). "New extremely distant Solar System object found during hunt for Planet X". https://carnegiescience.edu/news/new-extremely-distant-solar-system-object-found-during-hunt-planet-x - JPL Small-Body Database lookup. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Sednoid) : [Wikitube](https://en.wikitube.io/wiki/Sednoid) · pinned revision [1355644321](https://en.wikipedia.org/w/index.php?oldid=1355644321) · 2026-09-18 ## Previous hub tags Hubs: `Life_Physics`. Portals: [[PORTAL_Solar_System]]. --- *Solar System portal child articles, wave 1 · 2026-09-18 · drafted · row SOL-077 · explorer state `?obj=etno`.* <!-- hub_tags: Life_Physics · PORTAL_Solar_System -->