--- title: Cold gas giant canonical_url: https://paxabyssi.com/wiki/Cold_gas_giant markdown_url: https://paxabyssi.com/wiki/Cold_gas_giant.md type: wiki-page revision_id: 83 revision_view: stable last_updated: 2026-09-27 license: CC BY-SA 4.0 license_url: https://creativecommons.org/licenses/by-sa/4.0/ science_status: - observed - model - sim summary: A gas giant far enough from its star that ammonia freezes into clouds high in its atmosphere, like Jupiter and Saturn. Its own internal heat rivals the sunlight it absorbs, and it can keep large families of moons and rings. categories: - Gas giants - Planet classes - Giant planets aliases: - Cold gas giants - GGC - G1-C - Cold Jupiter - Cold Jupiters - Jupiter analogue - Jupiter-like planet - Ammonia-banded cold gas giant - Sulfur-golden cold gas giant - Phosphine-ruddy cold gas giant - Quiescent-pale cold gas giant - GGC-AB - GGC-SG - GGC-PR - GGC-QP infobox: type: planet_class code: GGC mass: note: "Sim: log-normal about 1 M_Jup, clamped 0.16 to 11" unit: M_Jup value: about 0.1 to 13 (Saturn 0.30, Jupiter 1.00) source: observed name: Cold gas giant image: File:Cold_gas_giant_GGC-AB-TU_sim.png level: Type radius: unit: R_Jup value: about 0.8 to 1.1 (Saturn 0.84, Jupiter 1.00) source: observed series: G (gas giant) caption: "Sim render: the sim's Jupiter-class cold giant (GGC-AB-TU-1) in the game's look-development stage, four radii out" subtypes: GGC-AB Ammonia-Banded, GGC-SG Sulfur-Golden, GGC-PR Phosphine-Ruddy, GGC-QP Quiescent-Pale (sim names) sim_source: Cold gas giant physics engine and properties module; the cold gas giant science references bond_albedo: note: Sim subtypes 0.35 to 0.65 unit: dimensionless value: Jupiter 0.503 (Cassini), Saturn 0.342 source: observed legacy_code: G1-C rings_moons: Jupiter 101 and Saturn 285 known moons (IAU Minor Planet Center, 26 March 2026); both ringed tidal_state: Not tidally locked; rotation 9.9 h (Jupiter), 10.7 h (Saturn) wind_speeds: unit: m/s value: Jupiter's fastest jets about 150; Saturn's equatorial jet 370 to 450 source: observed bulk_density: unit: g/cm³ value: Saturn 0.687, Jupiter 1.326 source: observed last_verified: 2026-09-27, writer B real_examples: Jupiter, Saturn; Kepler-167 e (a transiting Jupiter analogue); epsilon Indi Ab typical_orbit: Beyond about 1 AU around Sun-like stars; Jupiter 5.2 AU dominant_gases: H2 about 90 to 96%, He 3 to 10% by volume; CH4 0.3 to 0.45%; NH3 125 to 260 ppm (upper atmospheres of Saturn and Jupiter) science_status: observed (Jupiter, Saturn); sim (subtypes) escape_velocity: unit: km/s value: Jupiter 59.5, Saturn 35.5 source: observed frequency_in_sim: 900 of the 8,742 planets in the 5,159 generated systems gravity_at_1_bar: unit: m/s² value: Jupiter 23.1, Saturn 9.0 (equatorial) source: observed rendered_example: GGC-AB-TU-1 (sim render); 21 cold giant looks in the procedural generator defining_criteria: "Sim: equilibrium temperature below 150 K. Subtypes by trace-gas abundance (the sim's own scheme): QP if NH3, PH3 and H2S are all low; PR if PH3 is at least 2 ppm; SG if H2S is at least about 16 ppm; otherwise AB" interior_structure: Molecular hydrogen over metallic hydrogen; dilute heavy-element core; helium rain under way temperature_at_1_bar: unit: K value: Jupiter 165, Saturn 134 source: observed literature_equivalent: Cold Jupiter; Sudarsky class I (ammonia clouds) cloud_and_haze_species: NH3 ice near 0.7 bar; NH4SH near 2 bar; H2O near 5 bar; photochemical haze and unidentified chromophores above equilibrium_temperature: unit: K value: below 150; Jupiter about 102 source: observed related: - https://paxabyssi.com/wiki/Hot_Jupiter.md - https://paxabyssi.com/wiki/Gas_giant.md - https://paxabyssi.com/wiki/Temperate_gas_giant.md - https://paxabyssi.com/wiki/Ice_giant.md - https://paxabyssi.com/wiki/Sudarsky_classification.md - https://paxabyssi.com/wiki/Arid_world.md --- # Cold gas giant > Source: https://paxabyssi.com/wiki/Cold_gas_giant > > Licence: [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/). Text by Pax Abyssi Wiki contributors; history at https://paxabyssi.com/wiki/Cold_gas_giant/history > > Revision 83, 27 September 2026 A **cold gas giant** is a gas giant far enough from its star that its upper atmosphere is cold enough, below about 150 K, for ammonia to freeze into clouds. Jupiter and Saturn are the two in the Solar System, and they are the planets on which almost everything known about giant planets was learned. A cold giant's own internal heat is comparable to the sunlight it absorbs, its weather is organised into bands by rapid rotation, and it can keep a large family of moons and rings. In the [Sudarsky classification](https://paxabyssi.com/wiki/Sudarsky_classification.md) these are Class I, the "Jovian" giants. Among exoplanets they are called cold Jupiters, and around Sun-like stars they are the most common kind of giant. ## Characteristics ### A planet heated from within Jupiter orbits at 5.2 AU, where sunlight is about 27 times weaker than at Earth. Its equilibrium temperature, the temperature sunlight alone would give it, is about 102 K. Yet Jupiter radiates 7.5 watts per square metre of its own heat on top of the sunlight it re-emits, a little more than it absorbs from the Sun, so its effective temperature is about 125 K [1]. That heat is left over from formation and is released as the planet slowly contracts and as helium settles out of its interior. The Galileo probe found helium depleted in Jupiter's upper atmosphere, a sign that helium is raining out below [2]; Saturn, smaller and colder, has lost more of its helium to the depths [3]. Internal heat keeps the deep atmosphere convecting and so drives the weather and the magnetic field. ### Three cloud decks A cold giant's atmosphere gets warmer with depth, and three clouds form where the temperature crosses the condensation point of a trace gas [4] [5]. | Deck | Approximate pressure (Jupiter) | Composition | Appearance | | ------ | ------------------------------ | ----------------------------------------------------------------------- | --------------------------------------------------- | | Upper | about 0.7 bar | Ammonia (NH3) ice | White; the visible cloud tops of the zones | | Middle | about 2 bar | Ammonium hydrosulfide (NH4SH), formed from ammonia and hydrogen sulfide | Seen through gaps in the belts | | Lower | about 5 bar | Water ice and liquid water | Home of the deepest convective storms and lightning | Saturn has the same decks, but because Saturn is colder each forms deeper, under a thicker layer of haze, which is one reason Saturn looks softer and more muted than Jupiter. Juno's microwave instrument can see below the clouds and found water at about 2.5 times the solar proportion at Jupiter's equator, with a wide uncertainty [6], and ammonia depleted to surprising depths, which may be carried down by slushy hailstones of ammonia and water called "mushballs" [7]. The colours are the least understood part. Pure ammonia ice is white, and the tans, browns and reds of the belts and the Great Red Spot come from small amounts of coloured material called chromophores, whose chemistry has not been identified. A leading laboratory candidate forms when sunlight breaks up ammonia and the fragments react with acetylene, making a reddish material whose spectrum matches the Great Red Spot's [8]. Sulfur and phosphorus compounds are other candidates. Because these absorbers darken the planet at blue and ultraviolet wavelengths, Jupiter reflects about half of the sunlight that reaches it (a Bond albedo of 0.503) rather than the higher value a clean ammonia cloud would give [1]. (Image pending: Temperature against pressure in a cold giant's atmosphere with ammonia, ammonium hydrosulfide and water cloud decks marked where the profile crosses each condensation curve) *Figure 1.* Diagram: the three cloud decks of a cold giant form where its temperature profile crosses each gas's condensation curve. ### Belts, zones and jets A cold giant spins fast: Jupiter's day is 9.9 hours and Saturn's 10.7 [9] [10]. The rotation stretches the weather into bands. Bright **zones** and darker **belts** alternate with latitude, separated by jet streams that blow alternately east and west. Jupiter's fastest jets blow at about 150 m/s [11]; Saturn's reaches 370 to 450 m/s, among the fastest steady winds in the Solar System [12]. The jets are not a thin surface layer. Juno measured the slight north-south asymmetry they impose on Jupiter's gravity field and found that they extend about 3,000 km down [13]. ### Storms and polar vortices Long-lived storms sit between the jets. The Great Red Spot, an anticyclone larger than Earth, has been watched for more than 150 years; it is shrinking in length by about 0.19 degrees of longitude a year and drifting westward faster than it did in the 1980s [14]. Juno found Jupiter's poles unlike anything seen before: eight cyclones arranged in a ring around one at the north pole and five around one at the south [15]. Saturn's north pole is circled by a jet that meanders into a six-sided wave, the hexagon, first seen in Voyager images [16]. ![Jupiter's south pole from above, crowded with oval cyclones and swirling cloud bands](https://media.paxabyssi.com/public/3cc3149ef86dbf4ba3b0beb3ee55aaa92b14de2e5b449f714a7b2ce522aa1b8a/2560.webp "Observation: Jupiter's south pole from Juno, 52,000 km up; the ovals are cyclones up to 1,000 km across. Credit: enhanced image by Betsy Asher Hall and Gervasio Robles based on images provided courtesy of NASA/JPL-Caltech/SwRI/MSSS.") *Figure 2.* Observation: Jupiter's south pole from Juno, 52,000 km up; the ovals are cyclones up to 1,000 km across. Credit: enhanced image by Betsy Asher Hall and Gervasio Robles based on images provided courtesy of NASA/JPL-Caltech/SwRI/MSSS. Credit: Enhanced image by Betsy Asher Hall and Gervasio Robles based on images provided courtesy of NASA/JPL-Caltech/SwRI/MSSS. Licence: Public domain (NASA). ### Moons and rings Far from their stars, cold giants have large Hill spheres, the regions where their gravity dominates, and they can hold many moons. As of 26 March 2026 the International Astronomical Union's Minor Planet Center lists 101 known moons of Jupiter and 285 of Saturn; most are small, distant captured bodies, and the count rises every year [17]. Both planets have rings. Saturn's bright rings are almost pure water ice, and their age is disputed: the slow rain of dark micrometeoroid dust measured by Cassini suggests they are no more than a few hundred million years old [18], while impact simulations suggest that much of that dust vaporises and is removed, which would allow the rings to be as old as the planet [19]. ## Formation and evolution Cold giants are thought to form by core accretion beyond the snow line, where ice adds to the solid material available to build a core of about ten Earth masses before the gas disc disperses (see [Gas giant](https://paxabyssi.com/wiki/Gas_giant.md)). Most stay where they formed or near it. Radial-velocity surveys find giant planets about four times more common beyond 1 AU than inside it, with about 14 per 100 Sun-like stars between 2 and 8 AU [20]. After formation, a cold giant cools and contracts for billions of years; its internal heat fades, its helium rains inward, and its cloud decks settle slowly deeper. ## How we know Almost everything known in detail comes from the Solar System: Pioneer and Voyager flybys, the Galileo orbiter and its atmospheric probe, Cassini's thirteen years at Saturn, and Juno at Jupiter since 2016, alongside decades of telescope monitoring. Around other stars, cold giants are hard to find. Their orbits take years, so radial-velocity surveys need long baselines, and few transit. Kepler-167 e is one that does: a Jupiter-sized planet on a 1,071-day orbit around a K dwarf [21]. Direct imaging can see giants that still glow with youth or internal heat; JWST imaged epsilon Indi Ab, a cold giant of about six Jupiter masses whose effective temperature of about 275 K comes almost entirely from its interior [22]. ## Notable examples | Planet | Mass | Radius | Orbit | Notes | | --------------- | ------------------ | --------------- | --------------- | ---------------------------------------------------- | | Jupiter | 317.8 Earth masses | 71,492 km | 5.20 AU | Bond albedo 0.503; 101 known moons [9] [1] [17] | | Saturn | 95.2 Earth masses | 60,268 km | 9.6 AU | Less dense than water; 285 known moons [10] [17] | | Kepler-167 e | | about 0.9 R_Jup | 1,071 days | A transiting Jupiter analogue around a K dwarf [21] | | epsilon Indi Ab | about 6 M_Jup | | about 200 years | Imaged by JWST; about 275 K [22] | > **In Pax Abyssi** > > The sim's cold gas giants (GGC) are giants whose equilibrium temperature at the time they are placed is below 150 K. They are split into four subtypes of the sim's own naming, chosen from the abundances of three trace gases: **Quiescent-Pale** (QP) when ammonia, phosphine and hydrogen sulfide are all scarce, **Phosphine-Ruddy** (PR) when phosphine is at least 2 parts per million, **Sulfur-Golden** (SG) when hydrogen sulfide is high, and **Ammonia-Banded** (AB) otherwise, with looks modelled on a pale, a rust-hazed, a Saturn-like and a Jupiter-like giant. Tying each colour to one gas is a convention of the game: the real chromophores are unidentified. Each subtype carries its own Bond albedo range, from 0.35 to 0.45 for Phosphine-Ruddy to 0.50 to 0.65 for Quiescent-Pale. There are 900 cold giants among the 8,742 planets of the 5,159 generated systems. > > The procedural gas giant generator (BUILT, awaiting the owner's verdict) has 21 cold-giant looks. It grows the bands from a simulated flow: Gaussian jets at every belt edge, eastward on the poleward side of each zone, rows of vortices along each jet, named storms that drift with their latitude's wind, and festoons pulled from belt into zone; ammonia-ice zones are drawn over stained, deeper belts. The first flyable stops put the ship four radii and 1.6 radii from a Jupiter-class giant generated for the real F-type star 14 Ceti. ## See also - [Gas giant](https://paxabyssi.com/wiki/Gas_giant.md) - [Sudarsky classification](https://paxabyssi.com/wiki/Sudarsky_classification.md) - [Temperate gas giant](https://paxabyssi.com/wiki/Temperate_gas_giant.md) - [Hot Jupiter](https://paxabyssi.com/wiki/Hot_Jupiter.md) - [Ice giant](https://paxabyssi.com/wiki/Ice_giant.md) - [Moons](https://paxabyssi.com/wiki/Moons.md) - [Sol](https://paxabyssi.com/wiki/Sol.md) ## References 1. Li, L. et al. (2018). Less absorbed solar energy and more internal heat for Jupiter. Nature Communications 9, 3709. 2. von Zahn, U., Hunten, D. M. and Lehmacher, G. (1998). Helium in Jupiter's atmosphere: Results from the Galileo probe Helium Interferometer Experiment. Journal of Geophysical Research: Planets 103, 22815-22829. 3. Mankovich, C. R. and Fortney, J. J. (2020). Evidence for a Dichotomy in the Interior Structures of Jupiter and Saturn from Helium Phase Separation. The Astrophysical Journal 889, 51. 4. Weidenschilling, S. J. and Lewis, J. S. (1973). Atmospheric and cloud structures of the Jovian planets. Icarus 20, 465-476. 5. Atreya, S. K. et al. (1999). A comparison of the atmospheres of Jupiter and Saturn: deep atmospheric composition, cloud structure, vertical mixing, and origin. Planetary and Space Science 47, 1243-1262. 6. Li, C. et al. (2020). The water abundance in Jupiter's equatorial zone. Nature Astronomy 4, 609-616. 7. Guillot, T. et al. (2020). Storms and the Depletion of Ammonia in Jupiter: I. Microphysics of "Mushballs". Journal of Geophysical Research: Planets 125, e2020JE006403. 8. Carlson, R. W. et al. (2016). Chromophores from photolyzed ammonia reacting with acetylene: Application to Jupiter's Great Red Spot. Icarus 274, 106-115. 9. NASA Space Science Data Coordinated Archive. Jupiter Fact Sheet. 10. NASA Space Science Data Coordinated Archive. Saturn Fact Sheet. 11. Tollefson, J. et al. (2017). Changes in Jupiter's Zonal Wind Profile preceding and during the Juno mission. Icarus 296, 163-178. 12. García-Melendo, E. et al. (2011). Saturn's zonal wind profile in 2004-2009 from Cassini ISS images and its long-term variability. Icarus 215, 62-74. 13. Kaspi, Y. et al. (2018). Jupiter's atmospheric jet streams extend thousands of kilometres deep. Nature 555, 223-226. 14. Simon, A. A. et al. (2018). Historical and Contemporary Trends in the Size, Drift, and Color of Jupiter's Great Red Spot. The Astronomical Journal 155, 151. 15. Adriani, A. et al. (2018). Clusters of cyclones encircling Jupiter's poles. Nature 555, 216-219. 16. Godfrey, D. A. (1988). A hexagonal feature around Saturn's north pole. Icarus 76, 335-356. 17. International Astronomical Union (2026). IAU Minor Planet Center Confirms New Moons of Saturn and Jupiter. 18. Kempf, S. et al. (2023). Micrometeoroid infall onto Saturn's rings constrains their age to no more than a few hundred million years. Science Advances 9, eadf8537. 19. Hyodo, R., Genda, H. and Madeira, G. (2025). Pollution resistance of Saturn's ring particles during micrometeoroid impact. Nature Geoscience 18, 44-49. 20. Fulton, B. J. et al. (2021). California Legacy Survey. II. Occurrence of Giant Planets beyond the Ice Line. The Astrophysical Journal Supplement Series 255, 14. 21. Kipping, D. M. et al. (2016). A Transiting Jupiter Analog. The Astrophysical Journal 820, 112. 22. Matthews, E. C. et al. (2024). A temperate super-Jupiter imaged with JWST in the mid-infrared. Nature 633, 789-792. ## Infobox (planet class) | Field | Value | | --- | --- | | Code | GGC | | Mass | about 0.1 to 13 (Saturn 0.30, Jupiter 1.00) M_Jup | | Name | Cold gas giant | | Image | File:Cold_gas_giant_GGC-AB-TU_sim.png | | Level | Type | | Radius | about 0.8 to 1.1 (Saturn 0.84, Jupiter 1.00) R_Jup | | Series | G (gas giant) | | Caption | Sim render: the sim's Jupiter-class cold giant (GGC-AB-TU-1) in the game's look-development stage, four radii out | | Subtypes | GGC-AB Ammonia-Banded, GGC-SG Sulfur-Golden, GGC-PR Phosphine-Ruddy, GGC-QP Quiescent-Pale (sim names) | | Sim source | Cold gas giant physics engine and properties module; the cold gas giant science references | | Bond albedo | Jupiter 0.503 (Cassini), Saturn 0.342 dimensionless | | Legacy code | G1-C | | Rings moons | Jupiter 101 and Saturn 285 known moons (IAU Minor Planet Center, 26 March 2026); both ringed | | Tidal state | Not tidally locked; rotation 9.9 h (Jupiter), 10.7 h (Saturn) | | Wind speeds | Jupiter's fastest jets about 150; Saturn's equatorial jet 370 to 450 m/s | | Bulk density | Saturn 0.687, Jupiter 1.326 g/cm³ | | Last verified | 2026-09-27, writer B | | Real examples | Jupiter, Saturn; Kepler-167 e (a transiting Jupiter analogue); epsilon Indi Ab | | Typical orbit | Beyond about 1 AU around Sun-like stars; Jupiter 5.2 AU | | Dominant gases | H2 about 90 to 96%, He 3 to 10% by volume; CH4 0.3 to 0.45%; NH3 125 to 260 ppm (upper atmospheres of Saturn and Jupiter) | | Science status | observed (Jupiter, Saturn); sim (subtypes) | | Escape velocity | Jupiter 59.5, Saturn 35.5 km/s | | Frequency in sim | 900 of the 8,742 planets in the 5,159 generated systems | | Gravity at 1 bar | Jupiter 23.1, Saturn 9.0 (equatorial) m/s² | | Rendered example | GGC-AB-TU-1 (sim render); 21 cold giant looks in the procedural generator | | Defining criteria | Sim: equilibrium temperature below 150 K. Subtypes by trace-gas abundance (the sim's own scheme): QP if NH3, PH3 and H2S are all low; PR if PH3 is at least 2 ppm; SG if H2S is at least about 16 ppm; otherwise AB | | Interior structure | Molecular hydrogen over metallic hydrogen; dilute heavy-element core; helium rain under way | | Temperature at 1 bar | Jupiter 165, Saturn 134 K | | Literature equivalent | Cold Jupiter; Sudarsky class I (ammonia clouds) | | Cloud and haze species | NH3 ice near 0.7 bar; NH4SH near 2 bar; H2O near 5 bar; photochemical haze and unidentified chromophores above | | Equilibrium temperature | below 150; Jupiter about 102 K | ## Related pages - [Hot Jupiter](https://paxabyssi.com/wiki/Hot_Jupiter.md): A gas giant orbiting so close to its star that its year lasts days and its dayside is hotter than lava. Hot Jupiters were the first planets found around Sun-like stars and remain the best-studied exoplanet atmospheres, though fewer than one Sun-like star in a hundred has one. - [Gas giant](https://paxabyssi.com/wiki/Gas_giant.md): A planet made mostly of hydrogen and helium, with no solid surface, from about a tenth of Jupiter's mass up to the brown dwarf boundary near 13 Jupiter masses. Jupiter and Saturn are the Solar System's two; thousands more are known around other stars. - [Temperate gas giant](https://paxabyssi.com/wiki/Temperate_gas_giant.md): A gas giant warmer than Jupiter but cooler than a hot Jupiter, roughly 150 to 800 K, where ammonia clouds give way to water clouds and then to clear air. It spans the widest range of looks of any giant, from brilliant white to dark blue. - [Ice giant](https://paxabyssi.com/wiki/Ice_giant.md): A giant planet made mostly of water, methane and ammonia rather than hydrogen and helium, like Uranus and Neptune. Their interiors are hot, dense fluids, their magnetic fields are lopsided, and planets of about their mass may be among the commonest in the Galaxy. - [Sudarsky classification](https://paxabyssi.com/wiki/Sudarsky_classification.md): A theoretical scheme from 2000 that sorts giant planets into five classes by the temperature of their upper atmospheres, which decides what clouds can form and so how much light, and what colour, the planet reflects. - [Arid world](https://paxabyssi.com/wiki/Arid_world.md): A rocky planet with a thin, cold atmosphere and no stable liquid water at the surface, only ice and the traces of ancient rivers. Mars is the Solar System's example. Categories: [Gas giants](https://paxabyssi.com/wiki/Category:Gas_giants.md), [Planet classes](https://paxabyssi.com/wiki/Category:Planet_classes.md), [Giant planets](https://paxabyssi.com/wiki/Category:Giant_planets.md)