Plutino - Wikiparency

# Plutino  **Microsim — three.js (Wikitube framework):** *The Kuiper belt in the Solar System explorer* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=kuiper&embed=1" data-title="The Kuiper belt in the Solar System explorer"></div> *The Solar System explorer locked on this article's state (`?obj=kuiper`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.*  *Try: under show, choose small bodies and find the ring of points at 39.4 AU that marks the plutinos, just inside the main belt; then set show back to everything and the speed to 100 years/s and count Neptune's laps, about 1.6 seconds each: in the time Neptune goes round three times, about five seconds, a plutino goes round only twice.* The **plutinos** are the [[Trans-Neptunian_object|trans-Neptunian objects]] in the 2:3 mean-motion [[Resonance|resonance]] with [[Neptune]]: each completes two orbits of the [[Sun]] while Neptune completes three.[^jewitt-plutino][^malhotra1995] [[Pluto]] is the largest member and gives the group its name; the next largest include [[Orcus_(dwarf_planet)|Orcus]], Achlys and Ixion.[^jpl-sbdb] Under IAU rules, plutinos are named after beings of the underworld.[^wgsbn2025] The plutinos make up the inner edge of the [[Kuiper_belt|Kuiper belt]] and are the most populous known class of [[Resonant_trans-Neptunian_object|resonant trans-Neptunian objects]], roughly a quarter of known Kuiper belt objects.[^jewitt-plutino] The first found after Pluto, (385185) 1993 RO, was discovered by David Jewitt and Jane Luu in September 1993.[^jpl-sbdb] Their orbits are more eccentric and inclined than those of the [[Classical_Kuiper_belt_object|classical objects]] beyond them, and many cross Neptune's orbit, yet the resonance keeps them from ever meeting the planet. The pattern is widely explained by Neptune's outward migration early in the Solar System's history, which swept objects into the resonance.[^malhotra1995] The explorer at the top of this page is locked on the Kuiper belt and marks the plutinos with a ring at 39.4 AU, the distance of the 2:3 resonance. The ring and the belt's points are ILLUSTRATIVE: real plutinos move on eccentric, tilted orbits that spread them from inside Neptune's orbit to near the belt's outer edge.[^jpl-t1] ## Orbits A plutino's semi-major axis follows from [[Kepler's_laws_of_planetary_motion|Kepler's third law]]. A period 3/2 times Neptune's 164.8 years is 247.2 years, and the corresponding semi-major axis is 30.07 × 1.5^(2/3) ≈ 39.4 AU (both derived).[^jpl-t1][^nasa-fs-n] Known plutinos cluster tightly around this value: Pluto, Orcus, Ixion and Huya all have semi-major axes between 39.3 and 39.6 AU.[^jpl-sbdb] ### Origin The objects now in resonance with Neptune are thought to have begun on a variety of ordinary orbits. Renu Malhotra showed in 1995 that if Neptune migrated outward after it formed, driven by exchanges of angular momentum with the remaining planetesimals, its resonances would have moved outward with it. Objects overtaken by the advancing 2:3 resonance were caught and carried along, and as they were pushed outward their eccentricities grew.[^malhotra1995] The model accounts for Pluto's own eccentric, Neptune-crossing orbit and predicted that many other bodies should share it, as the discoveries since 1993 have borne out.[^jewitt-plutino] Migration of this kind is part of broader accounts of the early Solar System such as the [[Nice_model|Nice model]]. The 2:3 resonance is of low order, which makes it among the strongest and most stable of Neptune's resonances, and this is thought to be the main reason it holds more known objects than any other.[^almeida2009] In the space of orbital elements, the low-inclination cloud beyond 40 AU is the classical belt, whereas bodies with eccentricities of about 0.05–0.34 and semi-major axes close to 39.4 AU are mostly plutinos.[^lewis2004] ### Orbital characteristics Many plutinos have orbits like Pluto's, with inclinations of 10–25° and eccentricities of 0.2–0.25. With a = 39.4 AU and e = 0.25, the perihelion distance is q = a(1 − e) ≈ 29.6 AU, just inside Neptune's orbit, and the aphelion is a(1 + e) ≈ 49.3 AU, near the outer edge of the main belt where the 1:2 resonance lies (derived). Pluto itself has e = 0.25, q = 29.6 AU and i = 17°; Huya, with e = 0.27, comes to within 28.5 AU of the Sun.[^jpl-sbdb] Orbital periods of plutinos vary only by a few years around 247 years. Some plutinos are unusual. 15810 Arawn follows a nearly circular orbit, with e = 0.12, and in the frame rotating with Pluto it moves as a quasi-satellite of Pluto, lingering near it for long intervals.[^delafuente2016][^jpl-sbdb] 47171 Lempo, by contrast with Pluto, has an inclination of only 8°.[^jpl-sbdb] ### Long-term stability Pluto's own influence on the other plutinos was long neglected because its mass is small. The resonance, however, is narrow: the range of semi-major axes it can hold is only a few times wider than Pluto's [[Hill_sphere|Hill sphere]], the region where Pluto's gravity dominates. Over time, depending on its eccentricity, a plutino can be nudged out of the resonance by Pluto.[^wan2001] Simulations by Qingjuan Yu and Scott Tremaine found that plutinos with eccentricities 10–30% smaller or larger than Pluto's are not stable over billions of years.[^yu1999] Objects leaking from the resonance in this way may become [[Centaur_(small_Solar_System_body)|centaurs]].[^wan2001] ## Orbital diagrams The key to a plutino's safety is where it is when it reaches perihelion. Because the period ratio is exactly 3:2, the configuration repeats every 494 years (two plutino orbits, three Neptune orbits; derived), and the resonance keeps each perihelion passage far from Neptune. For Pluto, the direction of perihelion oscillates slowly about a point roughly 90° away from Neptune, so Neptune is always about a quarter of an orbit away when Pluto comes to perihelion.[^cohen1965][^malhotra1995] The two therefore never come close, even though Pluto's perihelion lies inside Neptune's orbit and its path crosses Neptune's in projection; its perihelion distance of 29.6 AU also takes it far inside the orbits of the classical objects but well outside that of [[Uranus]], at 19.2 AU.[^malhotra1995][^jpl-sbdb][^jpl-t1] Seen from above the plane of the Solar System, a plutino's path is an ellipse that dips inside Neptune's orbit on one side and swings out to near 50 AU on the other. Seen edge-on, the same orbit tilts 10–20° or more out of the plane, so plutinos form a thick ring rather than a thin one. Plotted as eccentricity against semi-major axis, plutinos form a vertical stripe at 39.4 AU spanning a wide range of eccentricities, while the classical objects cluster at low eccentricity beyond 42 AU.[^lewis2004][^jewitt-plutino] The explorer's ring at 39.4 AU marks only the resonance's semi-major axis; it does not show these individual ellipses.[^jpl-t1] ## Brightest objects The table lists some of the brightest plutinos, with orbital elements (semi-major axis a, perihelion q, inclination i) and absolute magnitude H from the JPL Small-Body Database, together with the discovery year and discoverers it records. Lower H means a brighter, generally larger object.[^jpl-sbdb] | Object | a (AU) | q (AU) | i (°) | H | Discovered | Discoverers | |---|---|---|---|---|---|---| | 134340 Pluto | 39.6 | 29.6 | 17.1 | −0.55 | 1930 | Clyde Tombaugh | | 90482 Orcus | 39.4 | 30.7 | 20.6 | 2.13 | 2004 | M. Brown, C. Trujillo | | 28978 Ixion | 39.3 | 29.8 | 19.7 | 3.47 | 2001 | M. W. Buie | | 208996 Achlys | 39.7 | 32.7 | 13.5 | 3.71 | 2003 | C. Trujillo, M. Brown | | 38628 Huya | 39.3 | 28.5 | 15.5 | 4.79 | 2000 | I. Ferrín | | 47171 Lempo | 39.7 | 30.6 | 8.4 | 4.94 | 1999 | E. P. Rubenstein, L.-G. Strolger | Pluto, a [[Dwarf_planet|dwarf planet]] with a diameter of about 2,376 km and five known moons, the largest being [[Charon_(moon)|Charon]], dwarfs the rest.[^nasa-fs-p] Sizes of the others depend on albedos that are poorly known, so H is the more reliable ranking.[^jewitt-plutino] ## See also - [[Resonant_trans-Neptunian_object]] - [[Kuiper_belt]] · [[Classical_Kuiper_belt_object]] - [[Pluto]] · [[Orcus_(dwarf_planet)]] - Twotino ## References [^jewitt-plutino]: Jewitt, D. (2004). "The plutinos". University of Hawaii. http://www.ifa.hawaii.edu/~jewitt/kb/plutino.html [^malhotra1995]: Malhotra, R. (1995). "The origin of Pluto's orbit: implications for the Solar System beyond Neptune". *The Astronomical Journal* 110: 420–429. https://doi.org/10.1086/117532 [^jpl-sbdb]: JPL Solar System Dynamics. "Small-Body Database" (elements, absolute magnitudes and discovery circumstances of 134340 Pluto, 90482 Orcus, 28978 Ixion, 208996 Achlys, 38628 Huya, 47171 Lempo, 385185 (1993 RO) and 15810 Arawn), fetched 2026-09-18. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html [^wgsbn2025]: IAU Working Group for Small Bodies Nomenclature (22 February 2025). "Rules and guidelines for naming non-cometary small Solar-System bodies". https://www.wgsbn-iau.org/documentation/NamesAndCitations.pdf [^jpl-t1]: JPL Solar System Dynamics. "Approximate Positions of the Planets", Table 1. https://ssd.jpl.nasa.gov/planets/approx_pos.html [^nasa-fs-n]: Williams, D. R. "Neptune Fact Sheet". NASA NSSDCA (last updated 3 October 2024). https://nssdc.gsfc.nasa.gov/planetary/factsheet/neptunefact.html (fetched 2026-09-18). [^nasa-fs-p]: Williams, D. R. "Pluto Fact Sheet". NASA NSSDCA. https://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html (fetched 2026-09-18). [^almeida2009]: Almeida, A. J. C.; Peixinho, N.; Correia, A. C. M. (2009). "Neptune Trojans and Plutinos: colors, sizes, dynamics, and their possible collisions". *Astronomy & Astrophysics* 508: 1021–1030. https://doi.org/10.1051/0004-6361/200911943 [^lewis2004]: Lewis, J. S. (2004). *Physics and Chemistry of the Solar System* (2nd ed.). Academic Press, pp. 409–412. ISBN 0-12-446744-X. [^delafuente2016]: de la Fuente Marcos, C.; de la Fuente Marcos, R. (2016). "The analemma criterion: accidental quasi-satellites are indeed true quasi-satellites". *Monthly Notices of the Royal Astronomical Society* 462: 3344–3349. https://doi.org/10.1093/mnras/stw1833 [^wan2001]: Wan, X.-S.; Huang, T.-Y. (2001). "The orbit evolution of 32 plutinos over 100 million years". *Astronomy and Astrophysics* 368: 700–705. https://doi.org/10.1051/0004-6361:20010056 [^yu1999]: Yu, Q.; Tremaine, S. (1999). "The dynamics of plutinos". *The Astronomical Journal* 118: 1873–1881. https://doi.org/10.1086/301045 [^cohen1965]: Cohen, C. J.; Hubbard, E. C. (1965). "Libration of the close approaches of Pluto to Neptune". *The Astronomical Journal* 70: 10–13. https://doi.org/10.1086/109674 ## External links - David Jewitt: the plutinos. http://www.ifa.hawaii.edu/~jewitt/kb/plutino.html - Minor Planet Center: list of trans-Neptunian objects. https://minorplanetcenter.net/iau/lists/TNOs.html - JPL Small-Body Database. https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Plutino) : [Wikitube](https://en.wikitube.io/wiki/Plutino) · pinned revision [1370787614](https://en.wikipedia.org/w/index.php?oldid=1370787614) · 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-067 · explorer state `?obj=kuiper`.*