Hilda_asteroid - Wikiparency

# Hilda asteroid  **Microsim — three.js (Wikitube framework):** *The Hilda asteroids in the Solar System explorer* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?obj=hildas&embed=1" data-title="The Hilda asteroids in the Solar System explorer"></div> *The Solar System explorer locked on this article's state (`?obj=hildas`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.*  *Try: set the speed to 1 year/s and watch the Hilda points gather into a rounded triangle whose corners stay fixed relative to Jupiter as the planet goes round; press l to turn on labels, pick out 153 Hilda and count three of its laps for every two of Jupiter's; then set show to small bodies to see the triangle wrapped around the main belt without the planets in the way.* The **Hilda asteroids** (adjective Hildian) are a dynamical group of more than 6,000 [[Asteroid|asteroids]] orbiting beyond the [[Asteroid_belt|asteroid belt]] and inside the orbit of [[Jupiter]], locked in a 3:2 [[Resonance|resonance]] with the planet: each Hilda goes around the [[Sun]] three times while Jupiter goes around twice.[^mpc-hilda][^broz2008] The group takes its name from 153 Hilda, its largest member, about 171 km across on an [[Orbit|orbit]] with a semi-major axis of 3.97 [[Astronomical_unit|AU]].[^jpl-sbdb] Hilda orbits are moderately eccentric (up to about 0.3) and inclined by less than about 20°.[^ohtsuka2008] The resonance makes the whole group behave as a single pattern. Each Hilda reaches aphelion, its farthest point from the Sun and its closest approach to Jupiter's orbit, only near one of three places that keep pace with Jupiter: the planet's L4 and L5 Lagrange points and the point opposite it, L3. At any moment, therefore, the Hildas together outline a triangle with rounded sides whose corners sit at those points.[^busch-hildas][^lvov2004] Two collisional families are known in the group, the Hilda family and the Schubart family, the second named after 1911 Schubart.[^broz2008] Most Hildas are dark D-type and P-type bodies with a minority of C-types, surfaces that resemble those of [[Comet|comet]] nuclei.[^gilhutton2008][^grav2012] The explorer at the top of this page draws the Hilda triangle turning with Jupiter; its points are ILLUSTRATIVE, placed to show how the aphelia cluster at L3, L4 and L5, while 153 Hilda follows its real orbit from the JPL Small-Body Database.[^jpl-sbdb] ## Dynamics A 3:2 resonance fixes both the period and the size of a Hilda orbit. With Jupiter's sidereal period of 11.86 years, two-thirds of it is 7.91 years, and [[Kepler's_laws_of_planetary_motion|Kepler's third law]] then gives a semi-major axis of 5.20 × (2/3)^(2/3) ≈ 3.97 AU (derived), exactly where 153 Hilda and 1911 Schubart are found.[^nasa-fs][^jpl-sbdb] Brož and Vokrouhlický counted 1,197 multi-opposition asteroids in this resonance in 2008; the Minor Planet Center now lists more than 6,000 objects of Hilda orbit type.[^broz2008][^mpc-hilda] The triangle follows from the same arithmetic. During one Hilda orbit Jupiter covers two-thirds of its own circuit, 240°. In a frame turning with [[Jupiter]], the Hilda's aphelion, nearly fixed in space, therefore moves back 240°, which is the same as moving forward 120° (derived). Its successive aphelia fall at three places 120° apart, and the resonance holds them where they avoid the planet: one at L3, opposite Jupiter, and one each at L4 and L5, 60° ahead and behind.[^lvov2004] The conjunctions with Jupiter then happen while the asteroid is near perihelion, as far inside the planet's orbit as it goes, which is why Hildas can take up any longitude relative to Jupiter and still never meet it closely.[^lvov2004][^ohtsuka2008] Each individual orbit is an ordinary ellipse; it is the population, seen at one instant, that draws the triangle. L'vov and colleagues describe the resulting stream as about 1 AU wide along the sides and 20–40% wider at the corners.[^lvov2004] [[Kepler's_laws_of_planetary_motion|Kepler's second law]] explains why the corners are crowded. An asteroid moves slowest near aphelion, so each Hilda lingers at a corner and then hurries along a side on the inner part of its orbit, and the density of objects at the corners is correspondingly higher than along the sides.[^openstax][^lvov2004] The pattern is not perfectly symmetric, because Jupiter's own orbit is eccentric (0.048): the side joining L4 and L5 is traversed at slightly different speeds from the other two sides depending on whether Jupiter is near perihelion or aphelion.[^lvov2004][^nasa-fs] At the L4 and L5 corners the Hildas share space with the [[Jupiter_trojan|Jupiter trojans]], and along the middles of the sides they come close to the outer [[Asteroid_belt|asteroid belt]]. The trojans are spread more widely in inclination, so the two populations overlap only partly.[^lvov2004] The resonance has also shaped the group's history. Brož and Vokrouhlický found that primordial bodies in the 3:2 resonance would have been cleared out when Jupiter and [[Saturn]] crossed their mutual 1:2 resonance, so the present Hildas were probably captured during or after the migration of the giant planets described by the [[Nice_model|Nice model]].[^broz2008] Inside the resonance the [[Thermal_radiation|thermal]] Yarkovsky push changes a body's eccentricity rather than its semi-major axis, which lets family ages be estimated: about 1.7 billion years for the Schubart family and more than 4 billion years for the Hilda family.[^broz2008] A family that old, from a parent about 200 km across, is unlikely to have formed at today's low collision rates, which suggests the Hilda family formed during the [[Late_Heavy_Bombardment|Late Heavy Bombardment]].[^broz2011] The edge of the stable zone is a route in and out. Quasi-Hilda comets move near the 3:2 resonance on unstable orbits and are the main source of temporary captures by Jupiter: comet 147P/Kushida–Muramatsu, for example, orbited Jupiter twice between 1949 and 1961, and comet Shoemaker–Levy 9, captured before it broke apart and struck the planet, may have come the same way.[^ohtsuka2008] ## Research Most of what is known about Hilda motion was first worked out from a few hundred objects,[^lvov2004] and surveys since then have multiplied the sample. Hildas are easiest to observe when [[Earth]] lines up with the middle of one side of the triangle, where the asteroids are near perihelion and at opposition, closest to Earth and fully lit. The triangle turns with Jupiter, so Earth passes one of its three sides once every third of the Earth–Jupiter synodic period of 398.9 days, about every 133 days or four and a half months (derived).[^nasa-fs] The gain in brightness is large: for 153 Hilda, at opposition near perihelion (3.42 AU from the Sun) the asteroid is about 1.4 magnitudes brighter than at opposition near aphelion (4.52 AU), and more eccentric Hildas gain more (derived).[^jpl-sbdb] Infrared surveys have measured the population's physical properties directly. The NEOWISE survey observed 1,023 Hildas between about 3 and 200 km across and found them uniformly dark, with a weighted mean albedo of 0.055 ± 0.018 and no dependence of albedo on size.[^grav2012] The two families differ: the Hilda family is somewhat brighter (0.061) and dominated by D-types, while the Schubart family is darker (0.039). Among Hildas larger than 30 km, about two-thirds are D-types and about a quarter C- or P-types, most of those P-types.[^grav2012] Colours from the Sloan Digital Sky Survey point the same way, and link the group's surfaces with those of comet nuclei, consistent with an origin among icy planetesimals of the outer Solar System.[^gilhutton2008] Open questions remain. With eccentricities up to about 0.3, Hilda orbits reach in to about 2.8 AU at perihelion (derived from 3.97 × 0.7) and out towards [[Jupiter]]'s orbit at aphelion, crossing the neighbourhoods of the outer belt and the trojans, so their orbits and families are a test of how and when the giant planets moved; further discoveries may revise the present picture.[^broz2011][^lvov2004] ## References [^mpc-hilda]: Minor Planet Center. "Objects with orbit type Hilda – database query". https://minorplanetcenter.net/db_search/show_by_orbit_type?&orbit_type=8 [^broz2008]: Brož, M.; Vokrouhlický, D. (2008). "Asteroid families in the first-order resonances with Jupiter". *Monthly Notices of the Royal Astronomical Society* 390: 715–732. https://doi.org/10.1111/j.1365-2966.2008.13764.x [^jpl-sbdb]: JPL Small-Body Database: 153 Hilda and 1911 Schubart (orbital elements and physical parameters). https://ssd.jpl.nasa.gov/tools/sbdb_lookup.html (elements fetched 2026-09-18). [^ohtsuka2008]: Ohtsuka, K.; Ito, T.; Yoshikawa, M.; Asher, D. J.; Arakida, H. (2008). "Quasi-Hilda comet 147P/Kushida-Muramatsu: another long temporary satellite capture by Jupiter". *Astronomy & Astrophysics* 489: 1355–1362. https://doi.org/10.1051/0004-6361:200810321 [^busch-hildas]: Busch, M. "The triangle formed by the Hilda asteroids". *EasySky*. http://www.easysky.de/eng/screenshots/Hildas.htm [^lvov2004]: L'vov, V. N.; Smekhacheva, R. I.; Smirnov, S. S.; Tsekmejster, S. D. (2004). "Some peculiarities in the Hildas motion". *Izvestiya Glavnoj Astronomicheskoj Observatorii v Pulkove* 217: 318–324 (in Russian). [^gilhutton2008]: Gil-Hutton, R.; Brunini, A. (2008). "Surface composition of Hilda asteroids from the analysis of the Sloan Digital Sky Survey colors". *Icarus* 193: 567–571. https://doi.org/10.1016/j.icarus.2007.08.026 [^grav2012]: Grav, T.; Mainzer, A. K.; Bauer, J.; et al. (2012). "WISE/NEOWISE observations of the Hilda population: preliminary results". *The Astrophysical Journal* 744: 197. https://doi.org/10.1088/0004-637X/744/2/197 [^nasa-fs]: NASA NSSDCA. Jupiter Fact Sheet (sidereal period, eccentricity, synodic period). https://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html (fetched 2026-09-18). [^openstax]: Ling, S. J.; Sanny, J.; Moebs, W. (2016). *University Physics Volume 1*, ch. 13 "Gravitation" (Kepler's laws). OpenStax. https://open.umn.edu/opentextbooks/textbooks/university-physics-volume-1 [^broz2011]: Brož, M.; Vokrouhlický, D.; Morbidelli, A.; Nesvorný, D.; Bottke, W. F. (2011). "Did the Hilda collisional family form during the late heavy bombardment?". *Monthly Notices of the Royal Astronomical Society* 414: 2716–2727. https://doi.org/10.1111/j.1365-2966.2011.18587.x ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Hilda_asteroid) : [Wikitube](https://en.wikitube.io/wiki/Hilda_asteroid) · pinned revision [1370779974](https://en.wikipedia.org/w/index.php?oldid=1370779974) · 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-054 · explorer state `?obj=hildas`.*