Gas_giant - Wikiparency

# Gas giant  **Microsim — three.js (Wikitube framework):** *Rock inside, gas and ice outside (Solar System explorer)* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/solar/Solar_System.html?view=composition&embed=1" data-title="Rock inside, gas and ice outside (Solar System explorer)"></div> *The Solar System explorer locked on this article's state (`?view=composition`); every object and population of the [[PORTAL_Solar_System|Solar System portal]] has its own state in the same scene.*  *Try: press l to show the labels and find Jupiter and Saturn, the two gas giants, just beyond the asteroid belt; drag to a view from above and compare their orbits with the ice giants' farther out and the tight group of rocky planets inside the frost line; then set the speed to 10 years/s and watch Jupiter complete roughly five circuits while Saturn completes two.* A **gas giant** is a giant planet made mainly of [[Hydrogen|hydrogen]] and [[Helium|helium]].[^dangelo2018] The Solar System has two, [[Jupiter]] and [[Saturn]]. The term once covered all four giant planets, but from the 1970s and 1980s it became usual to treat [[Uranus]] and [[Neptune]] as a separate class, the [[Ice_giant|ice giants]], made largely of heavier volatile compounds.[^marley2019] Jupiter and Saturn are mostly hydrogen and helium, with heavier elements making up between 3 and 13% of their mass. Beneath a deep atmosphere of molecular hydrogen lies a layer of liquid metallic hydrogen, which holds most of each planet's mass, and within that a core of heavier elements at temperatures near 20,000 K and pressures at which their behaviour is not well understood; the outer atmosphere contains layered clouds, mostly of ammonia and water.[^guillot2004] Where a gas giant ends and a brown dwarf begins is debated: one definition uses how the object formed, another only the physics of its interior, and objects above about 13 Jupiter masses can burn deuterium.[^burgasser2008][^bodenheimer2013] The explorer at the top of this page opens on the composition view, which colours the two gas giants apart from the rocky planets inside the [[Frost_line_(astrophysics)|frost line]] and from the ice giants beyond them. Jupiter and Saturn together hold more than 90% of the mass orbiting the [[Sun]]: (1,898 + 568) / 2,670 × 10²⁴ kg ≈ 92% of the planets' combined mass (derived).[^nasa-fs] ## Terminology The phrase "gas giant" first appears in 1952, in James Blish's rewritten version of his science-fiction story "Solar Plexus"; the story originally appeared in 1941 without it.[^hdsf] It was applied at first to all the giant planets. In a strict sense it is a misnomer. Through most of a giant planet's volume the pressure is so high that the hydrogen is not a gas: apart from the core and the upper atmosphere, the material is above its critical point, where liquid and gas can no longer be distinguished.[^dangelo2011][^dangelo2021] The name survived because planetary scientists use "gas", "ice" and "rock" as shorthand for classes of material rather than for physical states. In the outer Solar System, "gases" are hydrogen and helium; "ices" are [[Water|water]], methane and ammonia; and "rocks" are silicates and metals, whatever phase each happens to be in inside a planet. By that convention Jupiter and Saturn, made mostly of hydrogen and helium, are gas giants, while [[Uranus]] and [[Neptune]], whose bulk is mostly ices, are [[Ice_giant|ice giants]].[^marley2019] The difference shows in density. Saturn's mean density, 687 kg/m³, is below that of water, and Jupiter's is 1,326 kg/m³, both far below the 5,514 kg/m³ of [[Earth]].[^nasa-fs] Uranus and Neptune, with 1,270 and 1,638 kg/m³, are denser than Saturn despite being much less massive, because ices are heavier than hydrogen and helium and these planets are less compressed than Jupiter.[^nasa-fs] Density alone does not fix composition, since the more massive a hydrogen planet is the more it squeezes itself, but the contrast between Saturn and Neptune shows how differently the two kinds of giant are built. ## Classification Gas giants can be classified by the clouds that form in their atmospheres, which depend mainly on temperature and therefore on distance from the star. In the scheme of David Sudarsky, Adam Burrows and colleagues, a cold giant with an effective temperature below about 150 K has upper clouds of ammonia (class I); a somewhat warmer one, up to about 250 K, has water clouds (class II); between roughly 350 and 800 K the atmosphere is too warm for water clouds and too cool for anything else, and is largely cloudless (class III); above about 900 K alkali metals such as sodium and potassium dominate the spectrum (class IV); and in the hottest, above about 1,400 K, clouds of silicate and iron condense high in the atmosphere (class V).[^sudarsky2000][^sudarsky2003] The classes differ strongly in appearance. Cloud decks reflect starlight, so class I and II planets are bright, while the cloudless class III and alkali-dominated class IV planets absorb most visible light and would look dark; silicate clouds in class V brighten the hottest planets again.[^sudarsky2000] [[Jupiter]] and [[Saturn]], with ammonia clouds at the top of their atmospheres, are class I. The hot Jupiters found close to other stars fall into classes IV and V.[^sudarsky2003] The scheme is based on model atmospheres rather than observed spectra of many planets, and real atmospheres complicate it with hazes, chemistry driven by starlight and winds that carry heat from the day side to the night side. ## Extrasolar Gas giants were among the first exoplanets found in other [[Planetary_system|planetary systems]], because their large masses and sizes make them easy to detect, and many orbit far closer to their stars than Jupiter does to the Sun.[^dangelo2018] Their formation is usually explained by core accretion: a solid core of about ten Earth masses forms first and then captures gas from the [[Protoplanetary_disk|protoplanetary disk]].[^dangelo2018] ### Cold gas giants A cold, hydrogen-rich gas giant more massive than Jupiter is only slightly larger in volume. Adding mass compresses the interior more, and beyond a few Jupiter masses the planet's radius stops growing and then shrinks, because the pressure that supports it comes increasingly from degenerate electrons rather than from heat.[^seager2007] Gas giants also cool and contract slowly over billions of years, converting gravitational energy into heat by the Kelvin–Helmholtz mechanism, so that they can emit more energy than they receive from their star.[^irwin2003][^bagenal2004] [[Jupiter]] radiates about 1.7 times the solar energy it absorbs.[^hanel1981] ### Gas dwarfs Hydrogen planets need not be giants. Planets with rocky cores and thick envelopes of hydrogen, helium and other volatiles, with radii between about 1.7 and 3.9 Earth radii, have been called gas dwarfs.[^buchhave2014][^dangelo2016] Small gas planets, especially those close to their stars, lose their atmospheres faster than large or distant ones through hydrodynamic escape, in which heating drives the upper atmosphere off as a wind.[^tian2005][^swift2012] One of the smallest likely gas planets known, KOI-314c, has about the mass of Earth but a radius about 60% larger, a density that requires a thick gaseous envelope.[^cowen2014][^kipping2014] A low-mass gas planet can even reach a radius like a gas giant's if it is hot enough.[^batygin2013] ## Precipitation and meteorological phenomena ### Jovian weather Much of the weather on the gas giants is powered from below. Heat escaping from the deep interior rises through towering thunderstorms, and these storms feed small eddies that grow into larger systems.[^kerr2000] The engine is the same moist convection that drives thunderstorms on [[Earth]]: when water vapour condenses in rising air it releases latent heat, which pushes the air higher still, and the churning separates electric charges within the cloud until they recombine as lightning. Because lightning marks where convection is active, spacecraft can use it to map the storms; Jupiter has no ocean, but moist convection appears to work there much as it does on Earth.[^kerr2000] ### Jupiter's Red Spot The Great Red Spot is a high-pressure storm, an anticyclone, in [[Jupiter]]'s southern hemisphere. Its winds circle counterclockwise at about 430 to 680 km/h, and it absorbs smaller storms that drift into it.[^paoletta2021] The spot has been shrinking: in the Voyager era about three Earths could fit across it, and it is now only slightly wider than one.[^paoletta2021] At its outer edge its winds sped up by about 8% over an eleven-year span of observations, while near its centre they are much slower.[^paoletta2021] ### Helium rain on Saturn and Jupiter At the pressures and temperatures inside [[Saturn]], [[Helium|helium]] does not fully mix with liquid metallic [[Hydrogen|hydrogen]]. Where it separates, it forms droplets that fall as rain through the hydrogen until they reach warmer depths and dissolve again.[^mcintosh2007] Falling helium releases energy, both as latent heat and as gravitational energy as it sinks toward the centre.[^morales2009] Because Saturn is less massive and cooler inside than Jupiter, conditions favour the separation more strongly there. The process could explain why Saturn emits more energy than models of simple cooling predict, and why the atmospheres of both planets are depleted in helium relative to the Sun.[^morales2009] ## See also - [[Ice_giant]] - [[Terrestrial_planet]] - [[Jupiter]] · [[Saturn]] - [[Formation_and_evolution_of_the_Solar_System]] - Hot Jupiter · Brown dwarf · Super-Jupiter ## References [^dangelo2018]: D'Angelo, G.; Lissauer, J. J. (2018). "Formation of giant planets". In Deeg, H. J.; Belmonte, J. A. (eds.), *Handbook of Exoplanets*. Springer, pp. 2319–2343. https://doi.org/10.1007/978-3-319-55333-7_140 [^marley2019]: Marley, M. (2 April 2019). "Not a heart of ice". The Planetary Society. https://www.planetary.org/articles/not-a-heart-of-ice [^guillot2004]: Guillot, T.; Stevenson, D. J.; Hubbard, W. B.; Saumon, D. (2004). "The interior of Jupiter". In Bagenal, F.; Dowling, T. E.; McKinnon, W. B. (eds.), *Jupiter: The Planet, Satellites and Magnetosphere*. Cambridge University Press, pp. 35–58. ISBN 978-0-521-81808-7. [^burgasser2008]: Burgasser, A. J. (June 2008). "Brown dwarfs: failed stars, super Jupiters". *Physics Today*. http://astro.berkeley.edu/~gmarcy/astro160/papers/brown_dwarfs_failed_stars.pdf [^bodenheimer2013]: Bodenheimer, P.; D'Angelo, G.; Lissauer, J. J.; Fortney, J. J.; Saumon, D. (2013). "Deuterium burning in massive giant planets and low-mass brown dwarfs formed by core-nucleated accretion". *The Astrophysical Journal* 770: 120. https://doi.org/10.1088/0004-637X/770/2/120 [^nasa-fs]: NASA NSSDCA. "Planetary Fact Sheet". https://nssdc.gsfc.nasa.gov/planetary/factsheet/ (fetched 2026-09-18). [^hdsf]: Sheidlower, J. (ed.). "Gas giant". *Historical Dictionary of Science Fiction*. https://sfdictionary.com/view/52/gas-giant [^dangelo2011]: D'Angelo, G.; Durisen, R. H.; Lissauer, J. J. (2010). "Giant planet formation". In Seager, S. (ed.), *Exoplanets*. University of Arizona Press, pp. 319–346. ISBN 978-0-8165-2945-2. [^dangelo2021]: D'Angelo, G.; Weidenschilling, S. J.; Lissauer, J. J.; Bodenheimer, P. (2021). "Growth of Jupiter: formation in disks of gas and solids and evolution to the present epoch". *Icarus* 355: 114087. https://doi.org/10.1016/j.icarus.2020.114087 [^sudarsky2000]: Sudarsky, D.; Burrows, A.; Pinto, P. (2000). "Albedo and reflection spectra of extrasolar giant planets". *The Astrophysical Journal* 538: 885–903. https://doi.org/10.1086/309160 [^sudarsky2003]: Sudarsky, D.; Burrows, A.; Hubeny, I. (2003). "Theoretical spectra and atmospheres of extrasolar giant planets". *The Astrophysical Journal* 588: 1121–1148. https://doi.org/10.1086/374331 [^seager2007]: Seager, S.; Kuchner, M.; Hier-Majumder, C. A.; Militzer, B. (2007). "Mass–radius relationships for solid exoplanets". *The Astrophysical Journal* 669: 1279–1297. https://doi.org/10.1086/521346 [^irwin2003]: Irwin, P. G. J. (2003). *Giant Planets of Our Solar System: Atmospheres, Composition, and Structure*. Springer, p. 63. ISBN 978-3-540-00681-7. [^bagenal2004]: Bagenal, F. (2004). "Class 12 – Giant planets – heat and formation". ASTR 3750 *Planets, Moons & Rings*, University of Colorado. http://lasp.colorado.edu/~bagenal/3750/ClassNotes/Class12/Class12.html [^hanel1981]: Hanel, R. A.; Conrath, B. J.; Herath, L. W.; Kunde, V. G.; Pirraglia, J. A. (1981). "Albedo, internal heat, and energy balance of Jupiter: preliminary results of the Voyager infrared investigation". *Journal of Geophysical Research: Space Physics* 86: 8705–8712. https://doi.org/10.1029/JA086iA10p08705 [^buchhave2014]: Buchhave, L. A.; Bizzarro, M.; Latham, D. W.; et al. (2014). "Three regimes of extrasolar planet radius inferred from host star metallicities". *Nature* 509: 593–595. https://doi.org/10.1038/nature13254 [^dangelo2016]: D'Angelo, G.; Bodenheimer, P. (2016). "In situ and ex situ formation models of Kepler 11 planets". *The Astrophysical Journal* 828: 33. https://doi.org/10.3847/0004-637X/828/1/33 [^tian2005]: Tian, F.; Toon, O. B.; Pavlov, A. A.; De Sterck, H. (2005). "Transonic hydrodynamic escape of hydrogen from extrasolar planetary atmospheres". *The Astrophysical Journal* 621: 1049–1060. https://doi.org/10.1086/427204 [^swift2012]: Swift, D. C.; Eggert, J. H.; Hicks, D. G.; et al. (2012). "Mass–radius relationships for exoplanets". *The Astrophysical Journal* 744: 59. https://doi.org/10.1088/0004-637X/744/1/59 [^cowen2014]: Cowen, R. (2014). "Earth-mass exoplanet is no Earth twin". *Nature* (news). https://doi.org/10.1038/nature.2014.14477 [^kipping2014]: Kipping, D. M.; Nesvorný, D.; Buchhave, L. A.; et al. (2014). "The hunt for exomoons with Kepler (HEK). IV. A search for moons around eight M dwarfs". *The Astrophysical Journal* 784: 28. https://doi.org/10.1088/0004-637X/784/1/28 [^batygin2013]: Batygin, K.; Stevenson, D. J. (2013). "Mass–radius relationships for very low mass gaseous planets". *The Astrophysical Journal Letters* 769: L9. https://doi.org/10.1088/2041-8205/769/1/L9 [^kerr2000]: Kerr, R. A. (2000). "Deep, moist heat drives Jovian weather". *Science* 287: 946–947. https://doi.org/10.1126/science.287.5455.946b [^paoletta2021]: Paoletta, R. (7 October 2021). "The shape of Jupiter's Great Red Spot is changing. Here's why." The Planetary Society. https://www.planetary.org/articles/why-jupiter-great-red-spot-changing-shape [^mcintosh2007]: McIntosh, G. (2007). "Precipitation in the Solar System". *The Physics Teacher* 45: 502–505. https://doi.org/10.1119/1.2798364 [^morales2009]: Morales, M. A.; Schwegler, E.; Ceperley, D.; et al. (2009). "Phase separation in hydrogen–helium mixtures at Mbar pressures". *Proceedings of the National Academy of Sciences* 106: 1324–1329. https://doi.org/10.1073/pnas.0812581106 ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Gas_giant) : [Wikitube](https://en.wikitube.io/wiki/Gas_giant) · pinned revision [1370256844](https://en.wikipedia.org/w/index.php?oldid=1370256844) · 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-039 · explorer state `?view=composition`.*