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44-474: In 2007 the gas giant exoplanet XO-3b was discovered by the XO Telescope using the transit method . This object may be classed as brown dwarf because of its high mass. This main-sequence-star-related article is a stub . You can help Misplaced Pages by expanding it . Gas giant A gas giant is a giant planet composed mainly of hydrogen and helium . Jupiter and Saturn are

88-532: A class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods ( P < 10 days ). The close proximity to their stars and high surface-atmosphere temperatures resulted in their informal name "hot Jupiters". Hot Jupiters are the easiest extrasolar planets to detect via the radial-velocity method, because the oscillations they induce in their parent stars' motion are relatively large and rapid compared to those of other known types of planets. One of

132-527: A dayside temperature greater than 2,200 K (1,930 °C; 3,500 °F). In such dayside atmospheres, most molecules dissociate into their constituent atoms and circulate to the nightside where they recombine into molecules again. One example is TOI-1431b , announced by the University of Southern Queensland in April 2021, which has an orbital period of just two and a half days. Its dayside temperature

176-528: A different team found that every time they observe the exoplanet at a certain position in its orbit, they also detected X-ray flares. In 2019, astronomers analyzed data from Arecibo Observatory , MOST , and the Automated Photoelectric Telescope, in addition to historical observations of the star at radio, optical, ultraviolet, and X-ray wavelengths to examine these claims. They found that the previous claims were exaggerated and

220-442: A hot Jupiter's passage would be particularly water-rich. According to a 2011 study, hot Jupiters may become disrupted planets while migrating inwards; this could explain an abundance of "hot" Earth-sized to Neptune-sized planets within 0.2 AU of their host star. One example of these sorts of systems is that of WASP-47 . There are three inner planets and an outer gas giant in the habitable zone. The innermost planet, WASP-47e,

264-533: A large radius and very low density are sometimes called "puffy planets" or "hot Saturns", due to their density being similar to Saturn 's. Puffy planets orbit close to their stars so that the intense heat from the star combined with internal heating within the planet will help inflate the atmosphere . Six large-radius low-density planets have been detected by the transit method . In order of discovery they are: HAT-P-1b , CoRoT-1b , TrES-4b , WASP-12b , WASP-17b , and Kepler-7b . Some hot Jupiters detected by

308-475: A layer of liquid metallic hydrogen , with probably a molten rocky core inside. The outermost portion of their hydrogen atmosphere contains many layers of visible clouds that are mostly composed of water (despite earlier consensus that there was no water anywhere in the Solar System besides Earth) and ammonia . The layer of metallic hydrogen located in the mid-interior makes up the bulk of every gas giant and

352-588: A number of ways, most notably the possibility of accreting material from the stellar winds of their stars and, assuming a fast rotation (not tidally locked to their stars), a much more evenly distributed heat with many narrow-banded jets. Their detection using the transit method would be much more difficult due to their tiny size compared to the stars they orbit, as well as the long time needed (months or even years) for one to transit their star as well as to be occulted by it. Theoretical research since 2000 suggested that "hot Jupiters" may cause increased flaring due to

396-415: 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

440-481: A radius resembling that of a gas giant if it has the right temperature. Heat that is funneled upward by local storms is a major driver of the weather on gas giants. Much, if not all, of the deep heat escaping the interior flows up through towering thunderstorms. These disturbances develop into small eddies that eventually form storms such as the Great Red Spot on Jupiter. On Earth and Jupiter, lightning and

484-454: A substantially larger fraction of the planet's mass. No such objects have been found yet and they are still hypothetical. Simulations have shown that the migration of a Jupiter-sized planet through the inner protoplanetary disk (the region between 5 and 0.1 AU from the star) is not as destructive as expected. More than 60% of the solid disk materials in that region are scattered outward, including planetesimals and protoplanets , allowing

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528-504: Is 2,700 K (2,430 °C; 4,400 °F), making it hotter than 40% of stars in our galaxy. The nightside temperature is 2,600 K (2,330 °C; 4,220 °F). Ultra-short period planets (USP) are a class of planets with orbital periods below one day and occur only around stars of less than about 1.25 solar masses . Confirmed transiting hot Jupiters that have orbital periods of less than one day include WASP-18b , Banksia , Astrolábos , and WASP-103b . Gas giants with

572-518: Is a high-pressure system located in Jupiter's southern hemisphere. The GRS is a powerful anticyclone, swirling at about 430 to 680 kilometers per hour counterclockwise around the center. The Spot has become known for its ferocity, even feeding on smaller Jovian storms. Tholins are brown organic compounds found within the surface of various planets that are formed by exposure to UV irradiation. The tholins that exist on Jupiter's surface get sucked up into

616-581: Is a large terrestrial planet of 6.83 Earth masses and 1.8 Earth radii; the hot Jupiter, b, is little heavier than Jupiter, but about 12.63 Earth radii; a final hot Neptune, c, is 15.2 Earth masses and 3.6 Earth radii. A similar orbital architecture is also exhibited by the Kepler-30 system. Several hot Jupiters, such as HD 80606 b , have orbits that are misaligned with their host stars, including several with retrograde orbits such as HAT-P-14b . This misalignment may be related to

660-408: Is insoluble allow the denser helium to form droplets and act as a source of energy, both through the release of latent heat and by descending deeper into the center of the planet. This phase separation leads to helium droplets that fall as rain through the liquid metallic hydrogen until they reach a warmer region where they dissolve in the hydrogen. Since Jupiter and Saturn have different total masses,

704-599: 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 "rocks". In this terminology, since Uranus and Neptune are primarily composed of ices, not gas, they are more commonly called ice giants and distinct from

748-690: Is orbited by at least 1 large exomoon . It has been proposed that gas giants orbiting red giants at distances similar to that of Jupiter could be hot Jupiters due to the intense irradiation they would receive from their stars. It is very likely that in the Solar System Jupiter will become a hot Jupiter after the transformation of the Sun into a red giant. The recent discovery of particularly low density gas giants orbiting red giant stars supports this hypothesis. Hot Jupiters orbiting red giants would differ from those orbiting main-sequence stars in

792-401: Is referred to as "metallic" because the very large atmospheric 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 [19,700  °C ; 35,500  °F ]) and pressures that their properties are not yet completely understood. The placement of the solar system's gas giants can be explained by

836-490: The Grand tack hypothesis . The defining differences between a very low-mass brown dwarf (which can have a mass as low as roughly 13 times that of Jupiter ) and a gas giant 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. The term gas giant

880-423: The frost line , from rock, ice, and gases via the core accretion method of planetary formation . The planet then migrates inwards to the star where it eventually forms a stable orbit. The planet may have migrated inward smoothly via type II orbital migration. Or it may have migrated more suddenly due to gravitational scattering onto eccentric orbits during an encounter with another massive planet, followed by

924-406: The radial-velocity method may be puffy planets. Most of these planets are around or below Jupiter mass as more massive planets have stronger gravity keeping them at roughly Jupiter's size. Indeed, hot Jupiters with masses below Jupiter, and temperatures above 1800 Kelvin, are so inflated and puffed out that they are all on unstable evolutionary paths which eventually lead to Roche-Lobe overflow and

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968-432: The atmosphere by storms and circulation; it is hypothesized that those tholins that become ejected from the regolith get stuck in Jupiter's GRS, causing it to be red. Condensation of helium creates liquid helium rain on gas giants. On Saturn, this helium condensation occurs at certain pressures and temperatures when helium does not mix in with the liquid metallic hydrogen present on the planet. Regions on Saturn where helium

1012-420: The atmospheric ionization, and thus the greater the magnitude of the interaction and the larger the electric current, leading to more heating and expansion of the planet. This theory matches the observation that planetary temperature is correlated with inflated planetary radii. Theoretical research suggests that hot Jupiters are unlikely to have moons , due to both a small Hill sphere and the tidal forces of

1056-421: The best-known hot Jupiters is 51 Pegasi b . Discovered in 1995, it was the first extrasolar planet found orbiting a Sun-like star . 51 Pegasi b has an orbital period of about 4 days. Though there is diversity among hot Jupiters, they do share some common properties. There are three schools of thought regarding the possible origin of hot Jupiters. One possibility is that they were formed in-situ at

1100-565: The circularization and shrinking of the orbits due to tidal interactions with the star. A hot Jupiter's orbit could also have been altered via the Kozai mechanism , causing an exchange of inclination for eccentricity resulting in a high eccentricity low perihelion orbit, in combination with tidal friction. This requires a massive body—another planet or a stellar companion —on a more distant and inclined orbit; approximately 50% of hot Jupiters have distant Jupiter-mass or larger companions, which can leave

1144-486: The cores of the hot Jupiters began as more common super-Earths which accreted their gas envelopes at their current locations, becoming gas giants in situ . The super-Earths providing the cores in this hypothesis could have formed either in situ or at greater distances and have undergone migration before acquiring their gas envelopes. Since super-Earths are often found with companions, the hot Jupiters formed in situ could also be expected to have companions. The increase of

1188-422: The distances at which they are currently observed. Another possibility is that they were formed at a distance but later migrated inward. Such a shift in position might occur due to interactions with gas and dust during the solar nebula phase. It might also occur as a result of a close encounter with another large object destabilizing a Jupiter's orbit. In the migration hypothesis, a hot Jupiter forms beyond

1232-407: The evaporation and loss of the planet's atmosphere. Even when taking surface heating from the star into account, many transiting hot Jupiters have a larger radius than expected. This could be caused by the interaction between atmospheric winds and the planet's magnetosphere creating an electric current through the planet that heats it up , causing it to expand. The hotter the planet, the greater

1276-554: The formation of in situ hot Jupiters is not entirely in situ . If the atmosphere of a hot Jupiter is stripped away via hydrodynamic escape , its core may become a chthonian planet . The amount of gas removed from the outermost layers depends on the planet's size, the gases forming the envelope, the orbital distance from the star, and the star's luminosity. In a typical system, a gas giant orbiting at 0.02 AU around its parent star loses 5–7% of its mass during its lifetime, but orbiting closer than 0.015 AU can mean evaporation of

1320-717: The gas giants of the Solar System . The term "gas giant" was originally synonymous with " giant planet ". However, in the 1990s, it became known that Uranus and Neptune are really a distinct class of giant planets, 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 elements such as hydrogen and helium, with heavier elements making up between 3 and 13 percent of their mass. They are thought to consist of an outer layer of compressed molecular hydrogen surrounding

1364-591: The gas giants. Theoretically, gas giants can 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. A cold hydrogen-rich gas giant more massive than Jupiter but less than about 500  M E ( 1.6   M J ) will only be slightly larger in volume than Jupiter. For masses above 500  M E , gravity will cause

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1408-450: The heat of the photosphere the hot Jupiter is orbiting. There are several proposed hypotheses as to why this might occur. One such hypothesis involves tidal dissipation and suggests there is a single mechanism for producing hot Jupiters and this mechanism yields a range of obliquities. Cooler stars with higher tidal dissipation damps the obliquity (explaining why hot Jupiters orbiting cooler stars are well aligned) while hotter stars do not damp

1452-406: The host star failed to display many of the brightness and spectral characteristics associated with stellar flaring and solar active regions , including sunspots. Their statistical analysis also found that many stellar flares are seen regardless of the position of the exoplanet, therefore debunking the earlier claims. The magnetic fields of the host star and exoplanet do not interact, and this system

1496-427: The hot Jupiter with an orbit inclined relative to the star's rotation. The type II migration happens during the solar nebula phase, i.e. when gas is still present. Energetic stellar photons and strong stellar winds at this time remove most of the remaining nebula. Migration via the other mechanism can happen after the loss of the gas disk. Instead of being gas giants that migrated inward, in an alternate hypothesis

1540-541: The hydrologic cycle are intimately linked together to create intense thunderstorms. During a terrestrial thunderstorm, condensation releases heat that pushes rising air upward. This "moist convection" engine can segregate electrical charges into different parts of a cloud; the reuniting of those charges is lightning. Therefore, we can use lightning to signal to us where convection is happening. Although Jupiter has no ocean or wet ground, moist convection seems to function similarly compared to Earth. The Great Red Spot (GRS)

1584-463: The interaction of the magnetic fields of the star and its orbiting exoplanet, or because of tidal forces between them. These effects are called "star–planet interactions" or SPIs. The HD 189733 system is the best-studied exoplanet system where this effect was thought to occur. In 2008, a team of astronomers first described how as the exoplanet orbiting HD 189733 A reaches a certain place in its orbit, it causes increased stellar flaring . In 2010,

1628-406: The mass of the locally growing hot Jupiter has a number of possible effects on neighboring planets. If the hot Jupiter maintains an eccentricity greater than 0.01, sweeping secular resonances can increase the eccentricity of a companion planet, causing it to collide with the hot Jupiter. The core of the hot Jupiter in this case would be unusually large. If the hot Jupiter's eccentricity remains small

1672-410: The obliquity (explaining the observed misalignment). Another hypothesis is that the host star sometimes changes rotation early in its evolution, rather than the orbit changing. Yet another hypothesis is that hot Jupiters tend to form in dense clusters, where perturbations are more common and gravitational capture of planets by neighboring stars is possible. Ultra-hot Jupiters are hot Jupiters with

1716-517: 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. 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

1760-416: The planet-forming disk to reform in the gas giant's wake. In the simulation, planets up to two Earth masses were able to form in the habitable zone after the hot Jupiter passed through and its orbit stabilized at 0.1 AU. Due to the mixing of inner-planetary-system material with outer-planetary-system material from beyond the frost line, simulations indicated that the terrestrial planets that formed after

1804-501: The stars they orbit, which would destabilize any satellite's orbit, the latter process being stronger for larger moons. This means that for most hot Jupiters, stable satellites would be small asteroid -sized bodies. Furthermore, the physical evolution of hot Jupiters can determine the final fate of their moons: stall them in semi-asymptotic semimajor axes, or eject them from the system where they may undergo other unknown processes. In spite of this, observations of WASP-12b suggest that it

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1848-511: The sweeping secular resonances could also tilt the orbit of the companion. Traditionally, the in situ mode of conglomeration has been disfavored because the assembly of massive cores, which is necessary for the formation of hot Jupiters, requires surface densities of solids ≈ 10 g/cm , or larger. Recent surveys, however, have found that the inner regions of planetary systems are frequently occupied by super-Earth type planets. If these super-Earths formed at greater distances and migrated closer,

1892-831: The thermodynamic conditions in the planetary interior could be such that this condensation process is more prevalent in Saturn than in Jupiter. Helium condensation could be responsible for Saturn's excess luminosity as well as the helium depletion in the atmosphere of both Jupiter and Saturn. Solar System   → Local Interstellar Cloud   → Local Bubble   → Gould Belt   → Orion Arm   → Milky Way   → Milky Way subgroup   → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster   → Local Hole   → Observable universe   → Universe Each arrow ( → ) may be read as "within" or "part of". Hot Jupiter Hot Jupiters (sometimes called hot Saturns ) are

1936-406: 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

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