Gas giant - wikipedia Gas giant For the band, see Gas Giants ( band ). Jupiter photographed by New Horizons in January 2007 Saturn at equinox, photographed by Cassini in August 2009 A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the gas giants of the Solar System. The term `` gas giant '' was originally synonymous with `` giant planet '', but in the 1990s it became known that Uranus and Neptune are really a distinct class of giant planet, being composed mainly of heavier volatile substances ( which are referred to as `` ices '' ). For this reason, Uranus and Neptune are now often classified in the separate category of ice giants. Jupiter and Saturn consist mostly of hydrogen and helium, with heavier elements making up between 3 and 13 percent of the mass. They are thought to consist of an outer layer of molecular hydrogen surrounding a layer of liquid metallic hydrogen, with probably a molten rocky core. The outermost portion of their hydrogen atmosphere is characterized by many layers of visible clouds that are mostly composed of water and ammonia. The layer of metallic hydrogen makes up the bulk of each planet, and is referred to as `` metallic '' because the very large pressure turns hydrogen into an electrical conductor. The gas giants ' cores are thought to consist of heavier elements at such high temperatures ( 20,000 K ) and pressures that their properties are poorly understood. The defining differences between a very low - mass brown dwarf and a gas giant ( estimated at about 13 Jupiter masses ) are debated. One school of thought is based on formation ; the other, on the physics of the interior. Part of the debate concerns whether `` brown dwarfs '' must, by definition, have experienced nuclear fusion at some point in their history. Contents 1 Terminology 2 Classification 3 Extrasolar 3.1 Cold gas giants 3.2 Gas dwarfs 4 See also 5 References Terminology The term gas giant was coined in 1952 by the science fiction writer James Blish and was originally used to refer to all giant planets. It is, arguably, something of a misnomer because throughout most of the volume of all giant planets, the pressure is so high that matter is not in gaseous form. Other than solids in the core and the upper layers of the atmosphere, all matter is above the critical point, where there is no distinction between liquids and gases. The term has nevertheless caught on, because planetary scientists typically use `` rock '', `` gas '', and `` ice '' as shorthands for classes of elements and compounds commonly found as planetary constituents, irrespective of what phase the matter may appear in. In the outer Solar System, hydrogen and helium are referred to as `` gases '' ; water, methane, and ammonia as `` ices '' ; and silicates and metals as `` rock ''. Because Uranus and Neptune are primarily composed of, in this terminology, ices, not gas, they are increasingly referred to as ice giants and separated from the gas giants. Classification Main article : Sudarsky 's gas giant classification Gas giants can, theoretically, be divided into five distinct classes according to their modeled physical atmospheric properties, and hence their appearance : ammonia clouds ( I ), water clouds ( II ), cloudless ( III ), alkali - metal clouds ( IV ), and silicate clouds ( V ). Jupiter and Saturn are both class I. Hot Jupiters are class IV or V. Extrasolar Cold gas giants A cold hydrogen - rich gas giant more massive than Jupiter but less than about 500 M ( 1.6 M ) will only be slightly larger in volume than Jupiter. For masses above 500 M, gravity will cause the planet to shrink ( see degenerate matter ). Kelvin -- Helmholtz heating can cause a gas giant to radiate more energy than it receives from its host star. Gas dwarfs Main article : Gas dwarf See also : Mini-Neptune Although the words `` gas '' and `` giant '' are often combined, hydrogen planets need not be as large as the familiar gas giants from the Solar System. However, smaller gas planets and planets closer to their star will lose atmospheric mass more quickly via hydrodynamic escape than larger planets and planets farther out. A gas dwarf could be defined as a planet with a rocky core that has accumulated a thick envelope of hydrogen, helium and other volatiles, having as result a total radius between 1.7 and 3.9 Earth - radii. The smallest known extrasolar planet that is likely a `` gas planet '' is Kepler - 138d, which has the same mass as Earth but is 60 % larger and therefore has a density that indicates a thick gas envelope. A low - mass gas planet can still have a radius resembling that of a gas giant if it has the right temperature. See also List of gravitationally rounded objects of the Solar System List of planet types Hot Jupiter References ^ Jump up to : The Interior of Jupiter, Guillot et al., in Jupiter : The Planet, Satellites and Magnetosphere, Bagenal et al., editors, Cambridge University Press, 2004 ^ Jump up to : Burgasser, A.J. ( June 2008 ). `` Brown dwarfs : Failed stars, super Jupiters '' ( PDF ). Physics Today. Retrieved 11 January 2016. Jump up ^ Science Fiction Citations, Citations for gas giant n. Jump up ^ D'Angelo, G. ; Durisen, R.H. ; Lissauer, J.J. ( 2011 ). `` Giant Planet Formation ''. In S. Seager. Exoplanets. University of Arizona Press, Tucson, AZ. pp. 319 -- 346. Bibcode : 2010exop. book... 319D. arXiv : 1006.5486. ^ Jump up to : Seager, S. ; Kuchner, M. ; Hier - Majumder, C.A. ; Militzer, B. ( 2007 ). `` Mass - Radius Relationships for Solid Exoplanets ''. The Astrophysical Journal. 669 ( 2 ) : 1279 -- 1297. Bibcode : 2007ApJ... 669.1279 S. arXiv : 0707.2895. doi : 10.1086 / 521346. Jump up ^ Patrick G.J. Irwin ( 2003 ). Giant Planets of Our Solar System : Atmospheres, Composition, and Structure. Springer. ISBN 3 - 540 - 00681 - 8. Jump up ^ `` Class 12 -- Giant Planets -- Heat and Formation ''. 3750 -- Planets, Moons & Rings. Colorado University, Boulder. 2004. Retrieved 2008 - 03 - 13. Jump up ^ Feng Tian ; Toon, Owen B. ; Pavlov, Alexander A. ; De Sterck, H. ( March 10, 2005 ). `` Transonic hydrodynamic escape of hydrogen from extrasolar planetary atmospheres ''. The Astrophysical Journal. 621 ( 2 ) : 1049 -- 1060. Bibcode : 2005ApJ... 621.1049 T. CiteSeerX 10.1. 1.122. 9085. doi : 10.1086 / 427204. Jump up ^ Mass - radius relationships for exoplanets, Damian C. Swift, Jon Eggert, Damien G. Hicks, Sebastien Hamel, Kyle Caspersen, Eric Schwegler, and Gilbert W. Collins Jump up ^ Three regimes of extrasolar planets inferred from host star metallicities, Buchhave et al. Jump up ^ D'Angelo, G. ; Bodenheimer, P. ( 2016 ). `` In Situ and Ex Situ Formation Models of Kepler 11 Planets ''. The Astrophysical Journal. 1606 : in press. Bibcode : 2016arXiv160608088D. arXiv : 1606.08088. Jump up ^ Cowen, Ron ( 2014 ). `` Earth - mass exoplanet is no Earth twin ''. Nature. doi : 10.1038 / nature. 2014.14477. Jump up ^ * Mass - Radius Relationships for Very Low Mass Gaseous Planets, Konstantin Batygin, David J. 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Exoplanetology Planet Definition IAU Planetary science Main topics Accretion Exoplanet Methods of detecting exoplanets Planetary system Sizes and types Terrestrial Carbon planet Coreless planet Desert planet Dwarf planet Ice planet Iron planet Lava planet Mega-Earth Ocean planet Sub-Earth Super-Earth Gaseous Chthonian planet Eccentric Jupiter Gas dwarf Helium planet Hot Jupiter Hot Neptune Ice giant Mini-Neptune Super-Jupiter Other types Brown dwarf Circumbinary planet Double planet Mesoplanet Planemo Planetesimal Protoplanet Pulsar planet Sub-brown dwarf Ultra-cool dwarf Formation and evolution Merging stars Nebular hypothesis Planetary migration Systems Exocomet Exomoon Interstellar comet Mean - motion resonances Retrograde planet Rogue planet Titius -- Bode laws Trojan planet Host stars Binary star Brown dwarfs Extragalactic planet F / Yellow - white dwarfs G / Yellow dwarfs Herbig Ae / Be K / Orange dwarfs M / Red dwarfs Planets in globular clusters Pulsar Red giant Subdwarf B Subgiant T Tauri White dwarfs Yellow giant Detection Astrometry Direct imaging list Microlensing list Polarimetry Pulsar timing list Radial velocity list Transit method list Transit - timing variation Habitability Astrobiology Circumstellar habitable zone Earth analog Extraterrestrial liquid water Habitability of natural satellites Superhabitable planet Catalogues Catalog of Nearby Habitable Systems Exoplanet Data Explorer Extrasolar Planets Encyclopaedia NASA Exoplanet Archive NASA Star and Exoplanet Database Lists Exoplanetary systems Host stars Multiplanetary systems Stars with proplyds Exoplanets List of exoplanets Discoveries Extremes Firsts Nearest Largest Most massive Terrestrial candidates Kepler Potentially habitable Other Exoplanet phase curves Nexus for Exoplanet System Science Planets in science fiction Sudarsky 's gas giant classification Discoveries of exoplanets Search projects Retrieved from `` https://en.wikipedia.org/w/index.php?title=Gas_giant&oldid=791888740 '' Categories : Gas giants Types of planet Talk Contents About Wikipedia Afrikaans Alemannisch Avañe'ẽ বাংলা Беларуская Беларуская ( тарашкевіца ) ‎ Български Català Čeština Cymraeg Dansk Deutsch Eesti Ελληνικά Español Esperanto Euskara فارسی Français Frysk Gaelg Galego 한국어 Հայերեն हिन्दी Hrvatski Bahasa Indonesia Ирон Íslenska Italiano עברית ქართული Kurdî Latina Latviešu Lëtzebuergesch Lietuvių Lumbaart Magyar മലയാളം मराठी Bahasa Melayu Монгол မြန်မာဘာသာ Nederlands नेपाली 日本 語 Norsk ਪੰਜਾਬੀ پنجابی Piemontèis Polski Português Română Русский Simple English Slovenčina Slovenščina Soomaaliga Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska Tagalog தமிழ் Татарча / tatarça ไทย Türkçe Українська اردو Tiếng Việt Winaray 粵語 中文 Edit links This page was last edited on 23 July 2017, at 02 : 43. 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Question: what planet is the big blue gas planet
Answer: Jupiter and Saturn