Sedna_(dwarf_planet) - Wikiparency

# Sedna (dwarf planet)  **Microsim — three.js (Wikitube framework):** *Sedna in the Solar System explorer* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=Sedna&embed=1" data-title="Sedna in the Solar System explorer"></div> *The Solar System explorer locked on this article's state (`?obj=Sedna`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.*  *Try: set scale to true and see Sedna's orbit at its real proportions, with the orbits of the planets shrunk to a small knot at the centre; set scale back to log, press l for labels, and drag the year slider from 1800 to 2050 to watch Sedna close in on the perihelion it reaches in 2076; then set the speed to 100 years/s and see how little of its orbit it covers while Neptune laps the Sun.* **Sedna** (minor-planet number 90377) is a [[Dwarf_planet|dwarf planet]] on one of the widest known orbits in the [[PORTAL_Solar_System|Solar System]], a long ellipse that never brings it closer to the [[Sun]] than about 76 [[Astronomical_unit|AU]], two and a half times the distance of [[Neptune]], and carries it out to roughly 940 AU.[^horizons-sedna][^brown2004] Discovered in November 2003, it is about 900–1,000 km across; its surface is among the reddest in the Solar System, a mixture of water, carbon dioxide and ethane ices with reddish organic compounds.[^pal2012][^emery2024] It has no known moon, so its mass and density are unknown.[^bettati2025] Sedna takes about 11,400 years to go round the Sun once, and it is now close to the inner end of its orbit, 83 AU away in 2026 and due at perihelion in 2076.[^horizons-sedna][^horizons-2076] Its perihelion is too distant for Neptune to have placed it there, so its orbit is taken as evidence of some other early influence: a passing star, a planet not yet found, or capture from another star's disc. It is the prototype of the [[Sednoid|sednoids]], the most detached of the [[Extreme_trans-Neptunian_object|extreme trans-Neptunian objects]], and has been proposed as the first known member of the inner [[Oort_cloud|Oort cloud]].[^brown2004][^huang2024] The explorer at the top of this page is locked on Sedna and draws its orbit from the JPL Small-Body Database solution, with ticks at perihelion and aphelion.[^jpl-sbdb] ## History ### Discovery Michael Brown of Caltech, Chad Trujillo of the Gemini Observatory and David Rabinowitz of Yale University found Sedna on 14 November 2003, in a survey begun in 2001 with the Samuel Oschin telescope at Palomar Observatory and Yale's 160-megapixel Palomar Quest camera.[^brown2004][^mpec2004] Its motion, 4.6 arcseconds against the stars in 3.1 hours, pointed to a distance near 100 AU.[^brown2004] Most of that apparent motion is parallax: over a few hours the Earth's own movement shifts the line of sight to a distant object, and the farther the object the smaller the shift, so a slow crawl marks a remote body. Follow-up observations in November and December 2003 used the SMARTS telescope at Cerro Tololo in Chile, the Tenagra IV telescope in Arizona and the Keck Observatory on Mauna Kea. Together with earlier images from Palomar in August 2003 and from the Near-Earth Asteroid Tracking programme in 2001–2002, they fixed an orbit that was both very distant and very eccentric, with the object then about 90 AU from the [[Sun]].[^brown2004][^mpec2004] Images in the Palomar Digitized Sky Survey have since taken its observed arc back to 25 September 1990.[^jpl-sbdb] ### Naming Brown's team at first called the object "the Flying Dutchman", after the ghost ship of legend, because it moved so slowly that it had slipped past their searches.[^brown2012] The name they proposed comes from Sedna, the Inuit goddess of the sea, who lives at the bottom of the cold Arctic Ocean; Brown linked her home to the object's remoteness from the Sun, and suggested that future finds in the same region be named from Arctic mythologies.[^brown-sedna] Announcing the name before the object had been numbered broke the usual procedure, and Brian Marsden of the Minor Planet Center said so publicly.[^bbc2004][^mpec2004s73] No competing name was put forward, however, and the Committee on Small Body Nomenclature of the International Astronomical Union accepted "Sedna" in September 2004, noting that it might allow similar early announcements in cases of extraordinary interest.[^mpec2004s73][^mpc52733] ## Orbit and rotation Sedna's orbit has a barycentric semi-major axis of about 506 AU and an eccentricity of about 0.85: it comes to 76.2 AU from the Sun at perihelion and recedes to about 937 AU at aphelion, some 19 times [[Pluto]]'s greatest distance.[^horizons-sedna][^nasa-fs] [[Kepler's_laws_of_planetary_motion|Kepler's third law]] turns that semi-major axis into a period of about 506^1.5 ≈ 11,400 years (derived), the longest known for an object of its size.[^horizons-sedna] Speed changes enormously around such an orbit. From the vis-viva equation, v² = GM(2/r − 1/a), Sedna moves at about 4.6 km/s at perihelion and only about 377 m/s at aphelion, 1.3% of [[Earth]]'s mean orbital speed of 29.8 km/s (derived).[^horizons-sedna][^nasa-fs] Sunlight falls off as the square of distance, so at 76 AU the Sun delivers about 0.24 W/m² and at 937 AU about 0.0016 W/m², against 1,361 W/m² at Earth (derived).[^nasa-fs] Even near perihelion the Sun seen from Sedna is only a brilliant point, too small to show a disc to the eye; near aphelion, beyond the heliosphere's termination shock, the surface stays colder than −240 °C.[^hubble2004][^nasa2004] When it was found, about 90 AU away and moving inward, Sedna was the most distant Solar System object ever observed. [[Eris_(dwarf_planet)|Eris]], found by the same survey near its aphelion at 97 AU, overtook it, and because Sedna is near perihelion, both Eris and [[Gonggong_(dwarf_planet)|Gonggong]] are currently farther from the Sun though their orbits are smaller.[^astdys-sedna][^astdys-eris][^astdys-gonggong] Perihelion falls in mid-2076.[^horizons-2076] Early photometry suggested a slow rotation of 20–50 days, possibly braked by a large moon, but Hubble Space Telescope images taken in March 2004 found no companion.[^hubble2004b] Light curves from the MMT telescope then gave a period of about 10 hours, ordinary for a body of this size; an 18-hour solution was judged less likely.[^gaudi2005] In the explorer, Sedna's orbit comes from the JPL Small-Body Database's heliocentric solution, which places aphelion at about 1,010 AU; the barycentric value of 937 AU used above refers the orbit to the Solar System's centre of mass instead of the Sun, and suits an orbit this long.[^jpl-sbdb][^horizons-sedna] ## Physical characteristics Sedna's absolute magnitude of about 1.8 and a visual albedo near 0.41 imply a diameter of roughly 900 km.[^pal2012][^lellouch2013] Earlier estimates were far larger: the discoverers set an upper limit of 1,800 km in 2004, and Spitzer Space Telescope data reduced it to under 1,600 km by 2007.[^grundy2005][^stansberry2008] Thermal measurements from the Herschel Space Observatory gave 995 ± 80 km in 2012, and a reanalysis with a better thermophysical model gave 906 km a year later.[^pal2012][^lellouch2013] A stellar occultation observed from Australia in 2013 produced chords of 1,025 and 1,305 km, consistent with a body of this size.[^rommel2020] Without a moon to weigh it, its mass is unknown; Hubble's 2004 images are the only published search for a satellite.[^hubble2004b] In visible light Sedna is one of the reddest objects known, almost as red as [[Mars]].[^brown-sedna] Trujillo and colleagues attribute the colour to tholins, organic compounds built from simpler molecules such as methane by billions of years of ultraviolet light and energetic particles; its uniform colour suggests that few impacts expose fresh ice.[^trujillo2005] They set upper limits of 60% methane ice and 70% water ice on the surface.[^trujillo2005] Barucci and colleagues compared its spectrum with that of [[Triton_(moon)|Triton]] and fitted weak methane and nitrogen bands, and Spitzer infrared photometry later confirmed methane and water ice.[^barucci2005][^emery2007] Sedna shares its colour with the outer classical [[Kuiper_belt|Kuiper belt]] objects, which hints at a common region of origin.[^sheppard2010] The James Webb Space Telescope changed that picture in 2022. Its near-infrared spectra, from 0.7 to 5 μm, show abundant ethane ice and complex organics, with traces of ethylene, acetylene and possibly carbon dioxide, but little sign of methane or nitrogen.[^emery2024] A body of Sedna's size may have differentiated, and Emery and colleagues considered a subsurface ocean possible; if nitrogen is present, a thin atmosphere might form during the two centuries around perihelion, but none of substance is expected.[^emery2007][^emery2024] ## Origin Brown and his colleagues called Sedna the first observed member of the Oort cloud, the theorised reservoir of comets extending nearly a light-year from the Sun. They noted that its 76 AU perihelion lies far beyond the reach of [[Neptune]]'s scattering, which shapes the orbits of [[Scattered_disc|scattered disc]] objects such as [[Eris_(dwarf_planet)|Eris]]. Because Sedna is much closer than a classical Oort cloud body and its orbit is only modestly inclined, they placed it in an inner cloud between the Kuiper belt and the spherical outer cloud.[^brown2004][^lykawka2007] Sedna could not have formed on its present orbit. Accretion needs slow, near-circular relative motions; if Sedna formed in place, the Sun's disc must have reached at least 75 AU and its first orbit must have been nearly circular, so something later stretched it.[^stern2005][^sheppard-jewitt2005] Brown's team named three candidates: an unseen planet, a single passing star, or a star in the Sun's birth cluster.[^brown2004] They favoured the cluster, because an aphelion of about 1,000 AU is too close for passing field stars to affect it at present.[^brown2004] Morbidelli and Levison found the most likely cause to be a passage of another star at about 800 AU within the first 100 million years or so; Kenyon and Bromley modelled similar encounters.[^morbidelli2004][^kenyon2004] The planet hypothesis has several forms. Gomes and colleagues found in 2006 that a Jupiter-mass body at up to 5,000 AU, a Neptune-mass body at 2,000 AU or an Earth-mass body at 1,000 AU could reproduce Sedna's orbit, and Lykawka and Mukai modelled an Earth-sized body scattered outward by Neptune onto an orbit between about 80 and 170 AU.[^gomes2006][^lykawka2008] Batygin and Brown's [[Planet_Nine]], perhaps six Earth masses on an eccentric orbit about 15 times as far out as Neptune, would shepherd Sedna together with other ETNOs.[^batygin2016][^brown2022] A third idea is capture: Morbidelli and Levison, and Kenyon and Bromley, suggested that Sedna was taken from the disc of a passing star or brown dwarf, most likely within the Sun's first 100 million years.[^morbidelli2004][^kenyon2004] ## Population Sedna's discovery looked lucky. It is bright enough to be seen with current surveys only near perihelion, so the chance of catching it was about 1 in 80, and unless that was a fluke some 40–120 similar objects should exist.[^brown2004][^brown2008] A 2007–2008 survey by Schwamb, Brown and Rabinowitz, sensitive to motion out to 1,000 AU, found Gonggong but no second sednoid; modelled against that result, about 40 Sedna-sized bodies probably exist in the region, the brightest near Eris's magnitude.[^schwamb2009] Each origin predicts a different population. A distant planet would give sednoids similar perihelia, near 80 AU; capture from a star turning the same way as the Solar System would give low inclinations and semi-major axes of 100–500 AU; a series of stellar passes would give a wide scatter of perihelia and inclinations.[^schwamb2007] Brown called Sedna "a fossil record of the earliest Solar System".[^fussman2006] The sample has grown slowly. Trujillo and Sheppard announced 2012 VP113 in 2014, about half Sedna's size, on a 4,200-year orbit with a perihelion near 80 AU.[^trujillo2014] Sheppard's team announced Leleākūhonua (2015 TG387) in 2018, with a perihelion of 65 AU and a period of about 40,000 years, and estimated about 2 million inner Oort cloud objects larger than 40 km, totalling about 10²² kg.[^sheppard2019] Sedna itself was recovered in data from the Transiting Exoplanet Survey Satellite in 2020.[^rice2020] ## Classification The announcement of Sedna in March 2004 fed the debate that ended with the International Astronomical Union's [[IAU_definition_of_planet|2006 definition of a planet]].[^nasa2004] Under that definition a planet must have cleared the neighbourhood of its orbit, which Sedna has not; bodies large enough to be rounded by their own gravity but not dominant in their zones are dwarf planets.[^lakdawalla2020] Sedna is bright, and so large, enough that it is expected to be in hydrostatic equilibrium, and most astronomers count it as a dwarf planet, although the IAU's own list has not changed since 2006.[^rambaux2017][^tancredi2008][^pinilla2019] By orbit it is harder to place. The Minor Planet Center lists it simply as a [[Trans-Neptunian_object|trans-Neptunian object]], as does the JPL Small-Body Database.[^mpc-tno][^jpl-sbdb] Proposed finer categories include extended scattered disc object, [[Detached_object|detached object]] and distant detached object, and the Deep Ecliptic Survey places it in its "scattered-extended" class.[^delsanti2006][^gomes2006][^elliot2005] ## Exploration Sedna reaches perihelion around July 2076, and it will not be as close again for more than 11,000 years.[^horizons-2076] It spends most of its orbit beyond the heliopause, where the [[Solar_wind|solar wind]] gives way to the [[Interstellar_medium|interstellar medium]], so its surface records exposure to interstellar radiation.[^zubko2022] A 2011 study found that a flyby using a [[Jupiter]] gravity assist could reach Sedna in 24.48 years, launching on 6 May 2033 or 23 June 2046 and arriving in 2057 or 2070.[^mcgranaghan2011] Later work has explored gravity assists from [[Venus]], Earth, [[Saturn]] and Neptune, and a 2025 feasibility study found that a fusion rocket could put a large spacecraft into orbit around Sedna in about 10 years, or a solar sail could fly a small probe past it in about 7.[^zubko2021][^ancona2025] The explorer draws the heliosphere as simplified ILLUSTRATIVE shells, including a heliopause at about 121 AU, so Sedna's orbit can be seen passing well outside it. ## Notes Derived values are marked "(derived)". The period follows from Kepler's third law with the barycentric semi-major axis of 506 AU. Speeds follow from the vis-viva equation with GM of the Sun and the barycentric perihelion (76.19 AU) and aphelion (937 AU); Earth's mean orbital speed, 29.78 km/s, and the solar constant, 1,361 W/m², are from the NASA fact sheet. ## References [^horizons-sedna]: JPL Horizons On-Line Ephemeris System. "Barycentric osculating orbital elements for 90377 Sedna (2003 VB12)". NASA Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/horizons/ [^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 [^pal2012]: Pál, A.; Kiss, C.; Müller, T. G.; Santos-Sanz, P.; et al. (2012). "'TNOs are Cool': a survey of the trans-Neptunian region. VII. Size and surface characteristics of (90377) Sedna and (55636) 2002 TX300". *Astronomy & Astrophysics* 541: L6. https://doi.org/10.1051/0004-6361/201218874 [^emery2024]: Emery, J. P.; Wong, I.; Brunetto, R.; Cook, J. C.; Pinilla-Alonso, N.; Stansberry, J. A.; et al. (2024). "A tale of 3 dwarf planets: ices and organics on Sedna, Gonggong, and Quaoar from JWST spectroscopy". *Icarus* 414: 116017. https://doi.org/10.1016/j.icarus.2024.116017 [^bettati2025]: Bettati, A.; Lunine, J. (2025). "Atmospheric escape explains diverse surface compositions of Pluto vs Sedna". *Icarus* 430: 116482. https://doi.org/10.1016/j.icarus.2025.116482 [^horizons-2076]: JPL Horizons On-Line Ephemeris System. "Horizons batch output for Sedna, July 2076". NASA Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/horizons/ [^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 [^jpl-sbdb]: JPL Small-Body Database, 90377 Sedna (2003 VB12) (elements fetched 2026-09-18). NASA Jet Propulsion Laboratory. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=90377 [^mpec2004]: Minor Planet Center (15 March 2004). "MPEC 2004-E45: 2003 VB12". https://minorplanetcenter.net/mpec/K04/K04E45.html [^brown2012]: Brown, M. E. (2012). *How I Killed Pluto and Why It Had It Coming*. Spiegel & Grau, p. 96. ISBN 978-0-385-53110-8. [^brown-sedna]: Brown, M. E. "Sedna". California Institute of Technology. http://www.gps.caltech.edu/~mbrown/sedna/ [^bbc2004]: Walker, D. (16 March 2004). "How do planets get their names?". *BBC News*. http://news.bbc.co.uk/1/hi/magazine/3515658.stm [^mpec2004s73]: Minor Planet Center (2004). "MPEC 2004-S73: editorial notice". https://minorplanetcenter.net/mpec/K04/K04S73.html [^mpc52733]: Minor Planet Center (28 September 2004). *Minor Planet Circulars* 52733. http://www.minorplanetcenter.org/iau/ECS/MPCArchive/2004/MPC_20040928.pdf [^nasa-fs]: NASA NSSDCA. "Planetary fact sheet" (fetched 2026-09-18). https://nssdc.gsfc.nasa.gov/planetary/factsheet/ [^hubble2004]: Space Telescope Science Institute (2004). "Long view from a lonely planet" (STScI-2004-14). https://hubblesite.org/contents/media/images/2004/14/1514-Image.html [^nasa2004]: NASA Jet Propulsion Laboratory (15 March 2004). "Most distant object in Solar System discovered". https://www.jpl.nasa.gov/news/most-distant-object-in-solar-system-discovered [^astdys-sedna]: AstDyS. "(90377) Sedna ephemerides". Department of Mathematics, University of Pisa. https://newton.spacedys.com/astdys/index.php?pc=1.1.3.1&n=90377 [^astdys-eris]: AstDyS. "(136199) Eris ephemerides". 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"Analysis of mission opportunities to Sedna in 2029–2034". *Advances in Space Research* 68: 2752–2775. https://doi.org/10.1016/j.asr.2021.05.035 [^ancona2025]: Ancona, E.; Kezerashvili, R. Ya.; Longo, S. (2025). "Feasibility study of a mission to Sedna: nuclear propulsion and advanced solar sailing concepts". *Aerotecnica Missili & Spazio* 105: 365–378. https://doi.org/10.1007/s42496-025-00281-5 ## Further reading - Brown, M. E. (2012). *How I Killed Pluto and Why It Had It Coming*. Spiegel & Grau. ISBN 978-0-385-53110-8. - Barucci, M. A.; Boehnhardt, H.; Cruikshank, D. P.; Morbidelli, A. (eds.) (2008). *The Solar System Beyond Neptune*. University of Arizona Press. ISBN 978-0-8165-2755-7. ## External links - NASA Science. "Sedna". https://science.nasa.gov/dwarf-planets/ - Brown, M. E. "Sedna" (discoverer's page). http://www.gps.caltech.edu/~mbrown/sedna/ - JPL Small-Body Database: 90377 Sedna. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html#/?sstr=90377 ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Sedna_(dwarf_planet)) : [Wikitube](https://en.wikitube.io/wiki/Sedna_(dwarf_planet)) · pinned revision [1373458166](https://en.wikipedia.org/w/index.php?oldid=1373458166) · 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-076 · explorer state `?obj=Sedna`.*