--- title: Temperate gas giant summary: 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. science_status: [observed, model, sim] categories: [Gas giants, Planet classes, Giant planets] aliases: [Temperate gas giants, GGT, G3-T, Warm Jupiter, Warm Jupiters, Warm giant, Water-cloud giant, Clear-blue giant, Hazy giant, Transition giant, GGT-TN, GGT-WC, GGT-CB, GGT-HZ] infobox: type: planet_class name: Temperate gas giant image: File:Temperate_gas_giant_GGT-WC-PB_sim.png caption: "Sim render: a water-cloud temperate giant (GGT-WC-PB-2), pale bands of white and blue-white" code: GGT legacy_code: G3-T level: Type series: G (gas giant) science_status: "observed (warm Jupiters' orbits, masses, radii, some spectra); model (clouds and colour); sim (subtypes)" literature_equivalent: "Warm Jupiter (orbital periods of roughly 10 to 200 days); Sudarsky classes II and III" defining_criteria: "Sim: equilibrium temperature 150 to 800 K. Subtypes by temperature and haze: TN 150 to 250 K, WC 250 to 350 K, CB 350 K and above with haze optical depth below 0.05, HZ the same with more haze" mass: {value: "about 0.1 to 13", unit: M_Jup, source: observed, note: "Sim: log-normal about 1 M_Jup, clamped 0.16 to 11"} radius: {value: "about 0.8 to 1.2; not inflated", unit: R_Jup, source: observed} equilibrium_temperature: {value: "150 to 800", unit: K, source: sim} bond_albedo: {value: "0.10 to 0.81 (models)", unit: dimensionless, source: model, note: "Sim: WC 0.55 to 0.81, TN 0.45 to 0.65, HZ 0.15 to 0.30, CB 0.10 to 0.20"} dominant_gases: "H2 and He; methane the main carbon carrier below about 800 K; water vapour; ammonia" cloud_and_haze_species: "NH3 fading at the cool end; H2O ice clouds near 250 to 350 K; none in the upper atmosphere above about 350 K except photochemical haze" interior_structure: "As for cold giants; radius not inflated, so radius and mass together reveal the heavy-element content" tidal_state: "Mostly not tidally locked; eccentric orbits common" typical_orbit: "About 0.1 to 1 AU around Sun-like stars (periods of weeks to about a year); closer around M dwarfs" rings_moons: "Moons possible at the outer end; Hill spheres shrink closer in" frequency_in_sim: "260 of the 8,742 planets in the 5,159 generated systems (TN 149, HZ 73, CB 30, WC 2)" real_examples: "HD 80606 b (highly eccentric); WASP-80 b (825 K, methane, at the hot boundary); directly imaged GJ 504 b (about 510 K) and 51 Eridani b (600 to 750 K) have effective temperatures in this range" subtypes: "GGT-TN Transition, GGT-WC Water-Cloud, GGT-CB Clear-Blue, GGT-HZ Hazy (sim names)" sim_source: "Temperate gas giant physics engine and properties module; the temperate giant science reference" rendered_example: "GGT-WC-PB-2, GGT-CB-AZ-1 (sim renders); 16 temperate looks in the procedural generator" last_verified: "2026-09-27, writer B" sim: entity: planet_type.GGT refs: - id: sudarsky2000 type: article-journal author: [{family: Sudarsky, given: David}, {family: Burrows, given: Adam}, {family: Pinto, given: Philip}] title: "Albedo and Reflection Spectra of Extrasolar Giant Planets" container-title: The Astrophysical Journal volume: 538 page: 885-903 issued: 2000 DOI: 10.1086/309160 - id: cahoy2010 type: article-journal author: [{family: Cahoy, given: Kerri L.}, {family: Marley, given: Mark S.}, {family: Fortney, given: Jonathan J.}] title: "Exoplanet Albedo Spectra and Colors as a Function of Planet Phase, Separation, and Metallicity" container-title: The Astrophysical Journal volume: 724 page: 189-214 issued: 2010 DOI: 10.1088/0004-637X/724/1/189 - id: huang2016 type: article-journal author: [{family: Huang, given: Chelsea}, {family: Wu, given: Yanqin}, {family: Triaud, given: Amaury H. M. J.}] title: "Warm Jupiters Are Less Lonely than Hot Jupiters: Close Neighbors" container-title: The Astrophysical Journal volume: 825 page: 98 issued: 2016 DOI: 10.3847/0004-637X/825/2/98 - id: demory2011 type: article-journal author: [{family: Demory, given: Brice-Olivier}, {family: Seager, given: Sara}] title: "Lack of Inflated Radii for Kepler Giant Planet Candidates Receiving Modest Stellar Irradiation" container-title: The Astrophysical Journal Supplement Series volume: 197 page: 12 issued: 2011 DOI: 10.1088/0067-0049/197/1/12 - id: thorngren2016 type: article-journal author: [{family: Thorngren, given: Daniel P.}, {family: Fortney, given: Jonathan J.}, {family: Murray-Clay, given: Ruth A.}, {family: Lopez, given: Eric D.}] title: "The Mass-Metallicity Relation for Giant Planets" container-title: The Astrophysical Journal volume: 831 page: 64 issued: 2016 DOI: 10.3847/0004-637X/831/1/64 - id: udry2003 type: article-journal author: [{family: Udry, given: S.}, {family: Mayor, given: M.}, {family: Santos, given: N. C.}] title: "Statistical properties of exoplanets. I. The period distribution: Constraints for the migration scenario" container-title: Astronomy & Astrophysics volume: 407 page: 369-376 issued: 2003 DOI: 10.1051/0004-6361:20030843 - id: dawson2018 type: article-journal author: [{family: Dawson, given: Rebekah I.}, {family: Johnson, given: John Asher}] title: "Origins of Hot Jupiters" container-title: Annual Review of Astronomy and Astrophysics volume: 56 page: 175-221 issued: 2018 DOI: 10.1146/annurev-astro-081817-051853 - id: laughlin2009 type: article-journal author: [{family: Laughlin, given: Gregory}, {family: Deming, given: Drake}, {family: Langton, given: Jonathan}, {literal: "et al."}] title: "Rapid heating of the atmosphere of an extrasolar planet" container-title: Nature volume: 457 page: 562-564 issued: 2009 DOI: 10.1038/nature07649 - id: bell2023 type: article-journal author: [{family: Bell, given: Taylor J.}, {family: Welbanks, given: Luis}, {family: Schlawin, given: Everett}, {literal: "et al."}] title: "Methane throughout the atmosphere of the warm exoplanet WASP-80b" container-title: Nature volume: 623 page: 709-712 issued: 2023 DOI: 10.1038/s41586-023-06687-0 - id: kuzuhara2013 type: article-journal author: [{family: Kuzuhara, given: M.}, {family: Tamura, given: M.}, {family: Kudo, given: T.}, {literal: "et al."}] title: "Direct Imaging of a Cold Jovian Exoplanet in Orbit around the Sun-like Star GJ 504" container-title: The Astrophysical Journal volume: 774 page: 11 issued: 2013 DOI: 10.1088/0004-637X/774/1/11 - id: macintosh2015 type: article-journal author: [{family: Macintosh, given: B.}, {family: Graham, given: J. R.}, {family: Barman, given: T.}, {literal: "et al."}] title: "Discovery and spectroscopy of the young jovian planet 51 Eri b with the Gemini Planet Imager" container-title: Science volume: 350 page: 64-67 issued: 2015 DOI: 10.1126/science.aac5891 - id: matthews2024 type: article-journal author: [{family: Matthews, given: Elisabeth C.}, {family: Carter, given: Aarynn L.}, {family: Pathak, given: Prashant}, {literal: "et al."}] title: "A temperate super-Jupiter imaged with JWST in the mid-infrared" container-title: Nature volume: 633 page: 789-792 issued: 2024 DOI: 10.1038/s41586-024-07837-8 - id: heller2013 type: article-journal author: [{family: Heller, given: René}, {family: Barnes, given: Rory}] title: "Exomoon Habitability Constrained by Illumination and Tidal Heating" container-title: Astrobiology volume: 13 page: 18-46 issued: 2013 DOI: 10.1089/ast.2012.0859 images_wanted: - file: File:Temperate_gas_giant_GGT-WC-PB_sim.png subject: "The sim's pale-banded water-cloud giant: soft white and blue-white bands, a bright polar hood" source: sim source_ref: "GGQA:ggt_temperate_clear_blue_water_cloud_final/GGT-WC-PB-2_sphere_20.png" credit: "Pax Abyssi (sim render, procedural gas giant generator)" - file: File:Temperate_gas_giant_sequence_sim.png subject: "Four temperate giants side by side, cool to warm: the Transition look (pale grey-white bands), Water-Cloud (white and blue-white), Clear-Blue (featureless azure) and Hazy (featureless tawny)" source: sim source_ref: "GGQA:common_types_variant_final_sheets/GGT-TN-FD-3_sphere_20.png + GGQA:ggt_temperate_clear_blue_water_cloud_final/GGT-WC-PB-2_sphere_20.png + GGQA:ggt_temperate_clear_blue_water_cloud_final/GGT-CB-AZ-1_sphere_20.png + GGQA:common_types_variant_final_sheets/GGT-HZ-TN-3_sphere_20.png" credit: "Pax Abyssi (sim renders, procedural gas giant generator)" note: "Compose the four 900 x 900 spheres into one 3600 x 900 strip, left to right in the order given, each labelled with its temperature band." --- A **temperate gas giant** is a giant planet warmer than Jupiter but cooler than a [[Hot Jupiter|hot Jupiter]], with an equilibrium temperature of roughly 150 to 800 K. Around a Sun-like star such planets orbit from about 0.1 AU out to a little beyond 1 AU, with years of a few weeks to a few years; astronomers call the inner ones **warm Jupiters**. This is the temperature range in which a giant's clouds change most. Ammonia clouds thin and disappear, water clouds form, and then the water evaporates too, leaving the upper atmosphere clear. The [[Sudarsky classification]] predicts that the same planet moved inward through this range would turn from a brilliant white to a dark, featureless blue, which gives temperate giants the widest range of looks of any giant. ## Characteristics ### From ammonia to water to clear air The clouds a giant shows depend on which gases can condense in its upper atmosphere (see [[Cold gas giant]] for the three decks of Jupiter and Saturn). As a giant warms past about 150 K, the ammonia deck forms deeper and fades from view. Around 250 K, in the models, water condenses high enough to become the top cloud, and a giant covered in water-ice cloud would be the most reflective planet of any kind: Sudarsky's Class II model reflects 81% of the light that reaches it :cite[sudarsky2000]. It would look like a larger, whiter Venus with faint pale-blue bands and none of Jupiter's browns, because the coloured compounds that stain Jupiter's belts form above or among ammonia clouds, not water. Above about 350 K, water no longer condenses in the upper atmosphere. Starlight penetrates deep. Hydrogen molecules scatter blue light back out, and sodium, potassium, methane and water absorb the red and near-infrared, so the model planet turns dark and blue, reflecting only about 12% of the incoming energy around a Sun-like star :cite[sudarsky2000]. With no cloud tops to trace the winds, it would look nearly featureless. Photochemical hazes, made by ultraviolet light breaking up methane and other molecules high in the atmosphere, can dull that blue toward grey or brown, and later models show how haze, metallicity and viewing angle move the colours of such planets around :cite[cahoy2010]. ::figure{src="File:Temperate_gas_giant_sequence_sim.png" size=wide alt="Four gas giants side by side: pale grey-white and banded, white and blue-white banded, featureless azure, and featureless tawny brown" caption="Sim renders: the sim's four temperate looks from cool to warm, Transition, Water-Cloud, Clear-Blue and Hazy."} ### Normal sizes, useful densities Many hot Jupiters are inflated beyond Jupiter's size by heat deposited in their interiors, but the effect switches off below an orbit-averaged stellar flux of about 2 × 10⁸ erg s⁻¹ cm⁻², roughly 150 times the sunlight Earth receives and an equilibrium temperature near 1,000 K :cite[demory2011]. Temperate giants therefore have the radii their mass and composition predict. That makes them the best giants for weighing heavy elements: comparing a warm giant's measured mass and radius with structure models reveals how much rock and ice it contains, and more massive giants turn out to hold more heavy elements in total but a smaller fraction of their mass :cite[thorngren2016]. ### Eccentric orbits and neighbours Warm Jupiters have more varied orbits than hot Jupiters. Many are eccentric, and about half of those found by Kepler have small planets orbiting close by, while hot Jupiters almost never do :cite[huang2016]. That difference is one of the strongest clues to how giants reach the inner parts of their systems (below). The most extreme case is HD 80606 b, whose orbit is so elongated (eccentricity 0.93) that its distance from its star changes by a factor of about 30 over its 111-day year. The Spitzer Space Telescope watched its atmosphere heat rapidly as it swung past the star :cite[laughlin2009]; for most of its orbit it is a temperate giant and for a few days it is a hot Jupiter. ## Formation and migration Radial-velocity surveys found fewer giants with periods of about 3 to 10 days than with shorter or longer periods, a gap between hot and warm Jupiters called the period valley :cite[udry2003]. Warm Jupiters are thought to reach their orbits in more than one way. Those with close, low-mass neighbours and circular orbits probably formed where they are, or migrated gently through the gas disc, since a violent history would have scattered their companions. Eccentric warm Jupiters may be hot Jupiters caught partway through high-eccentricity migration, in which a giant is flung onto an elongated orbit by another body and has its orbit slowly shrunk and circularised by tides raised at each close pass :cite[huang2016] :cite[dawson2018]. ## How we know Warm Jupiters are found by radial-velocity surveys and, less often, by transits: a planet with a 100-day orbit is less likely to be aligned to transit and transits less often than one with a 3-day orbit. Their atmospheres are just starting to be measured. JWST detected methane throughout the atmosphere of WASP-80 b, an 825 K giant at the hot edge of this range, the gas the models expect to carry most of a temperate giant's carbon :cite[bell2023]. Direct imaging reaches the same temperatures by another route: young giants still warm from formation reach the same temperatures by their own heat: GJ 504 b, at about 510 K, has colours that suggest a largely cloud-free atmosphere :cite[kuzuhara2013], and 51 Eridani b, at 600 to 750 K, shows strong methane and water absorption :cite[macintosh2015]. One of the coldest giants imaged, epsilon Indi Ab at about 275 K, sits where water clouds might form, though it is warmed from inside rather than by its star :cite[matthews2024]. No temperate giant has yet had its reflected colour measured, so the white and blue worlds remain predictions. A temperate giant at the right distance from its star could also host large moons in its star's habitable zone, whose habitability would depend on the planet's shadow, reflected light and tidal heating as well as on the star :cite[heller2013]. ## Notable examples | Planet | Notes | |---|---| | HD 80606 b | Eccentricity 0.93, 111-day orbit; its atmosphere heats rapidly at each close pass :cite[laughlin2009] | | WASP-80 b | 825 K; methane detected by JWST in both transmission and emission :cite[bell2023] | | GJ 504 b | Young giant imaged directly; about 510 K and about 4 Jupiter masses, with colours that suggest few clouds :cite[kuzuhara2013] | | 51 Eridani b | Young giant imaged directly; 600 to 750 K, strong methane and water absorption :cite[macintosh2015] | | epsilon Indi Ab | About 275 K from internal heat; one of the coldest giants imaged, and a candidate for water clouds :cite[matthews2024] | :::callout{type=sim title="In Pax Abyssi"} The sim's temperate gas giants (GGT) are giants whose equilibrium temperature is 150 to 800 K. The physics engine computes temperature and photochemical haze first and assigns the subtype afterwards: **Transition** (GGT-TN, 150 to 250 K, fading ammonia with pale bands), **Water-Cloud** (GGT-WC, 250 to 350 K, Bond albedo up to 0.81), **Clear-Blue** (GGT-CB, 350 K and above with a haze optical depth below 0.05, Bond albedo 0.10 to 0.20) and **Hazy** (GGT-HZ, the same temperatures under thicker haze, which the engine grows with the star's ultraviolet output and the planet's metallicity). Most temperate giants are placed by the warm-Jupiter system architecture. There are 260 among the 8,742 planets of the 5,159 generated systems. The procedural gas giant generator (BUILT, awaiting the owner's verdict) has 16 temperate looks; the four in the figure above are among them, from pale banded white to featureless tawny haze. ::: ## See also - [[Sudarsky classification]] - [[Gas giant]] - [[Cold gas giant]] - [[Hot Jupiter]] - [[Habitable zone]] - [[Moons]]