Giant planet

Last updated
Jupiter and its shrunken Great Red Spot.jpg
Saturn during Equinox (rot45).jpg
Uranus Voyager2 color calibrated.png
Neptune Voyager2 color calibrated.png
The four giant planets of the Solar System: Shown in order from the Sun and in true color. Sizes are not to scale.

A giant planet, sometimes referred to as a jovian planet (Jove being another name for the Roman god Jupiter), is a diverse type of planet much larger than Earth. Giant planets are usually primarily composed of low-boiling point materials (volatiles), rather than rock or other solid matter, but massive solid planets can also exist. There are four such planets in the Solar System: Jupiter, Saturn, Uranus, and Neptune. Many extrasolar giant planets have been identified.

Contents

Giant planets are sometimes known as gas giants, but many astronomers now apply the term only to Jupiter and Saturn, classifying Uranus and Neptune, which have different compositions, as ice giants. Both names are potentially misleading; the Solar System's giant planets all consist primarily of fluids above their critical points, where distinct gas and liquid phases do not exist. Jupiter and Saturn are principally made of hydrogen and helium, whilst Uranus and Neptune consist of water, ammonia, and methane .

The defining differences between a very low-mass brown dwarf and a massive gas giant (~13  MJ) are debated. One school of thought is based on planetary formation; the other, on the physics of the interior of planets. Part of the debate concerns whether brown dwarfs must, by definition, have experienced nuclear fusion at some point in their history. [1]

Terminology

The term gas giant was coined in 1952 by science fiction writer James Blish and was originally used to refer to all giant planets. Arguably it is something of a misnomer, because throughout most of the volume of these planets the pressure is so high that matter is not in gaseous form. [2] Other than the upper layers of the atmosphere, [3] all matter is likely beyond the critical point, where there is no distinction between liquids and gases. Fluid planet would be a more accurate term. Jupiter also has metallic hydrogen near its center, but much of its volume is hydrogen, helium, and traces of other gases above their critical points. The observable atmospheres of all these planets (at less than a unit optical depth) are quite thin compared to their radii, only extending perhaps one percent of the way to the center. Thus, the observable parts are gaseous (in contrast to Mars and Earth, which have gaseous atmospheres through which the crust can be seen).

The rather misleading term has 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 the matter's phase. In the outer Solar System, hydrogen and helium are referred to as gas; water, methane, and ammonia as ice; and silicates and metals as rock. When deep planetary interiors are considered, it may not be far off to say that, by ice astronomers mean oxygen and carbon, by rock they mean silicon, and by gas they mean hydrogen and helium. The many ways in which Uranus and Neptune differ from Jupiter and Saturn have led some to use the term only for planets similar to the latter two. With this terminology in mind, some astronomers have started referring to Uranus and Neptune as ice giants to indicate the predominance of the ices (in fluid form) in their interior composition. [4]

The alternative term jovian planet refers to the Roman god Jupiter—the genitive form of which is Jovis, hence Jovian—and was intended to indicate that all of these planets were similar to Jupiter.

Objects large enough to start deuterium fusion (above 13 Jupiter masses for solar composition) are called brown dwarfs, and these occupy the mass range between that of large giant planets and the lowest-mass stars. The 13-Jupiter-mass (MJ) cutoff is a rule of thumb rather than something of precise physical significance. Larger objects will burn most of their deuterium and smaller ones will burn only a little, and the 13  MJ value is somewhere in between. [5] The amount of deuterium burnt depends not only on the mass but also on the composition of the planet, especially on the amount of helium and deuterium present. [6] The Extrasolar Planets Encyclopaedia includes objects up to 60 Jupiter masses, and the Exoplanet Data Explorer up to 24 Jupiter masses. [7] [8]

Description

Cut-away illustrations of the interior of the giant planets. Jupiter is shown with a rocky core overlaid by a deep layer of metallic hydrogen. Gas Giant Interiors.jpg
Cut-away illustrations of the interior of the giant planets. Jupiter is shown with a rocky core overlaid by a deep layer of metallic hydrogen.

A giant planet is a massive planet and has a thick atmosphere of hydrogen and helium. They may have a dense molten core of rocky elements, or the core may have completely dissolved and dispersed throughout the planet if the planet is hot enough. [9] In "traditional" giant planets such as Jupiter and Saturn (the gas giants) hydrogen and helium make up most of the mass of the planet, whereas they only make up an outer envelope on Uranus and Neptune, which are instead mostly composed of water, ammonia, and methane and therefore increasingly referred to as "ice giants".

Extrasolar giant planets that orbit very close to their stars are the exoplanets that are easiest to detect. These are called hot Jupiters and hot Neptunes because they have very high surface temperatures. Hot Jupiters were, until the advent of space-borne telescopes, the most common form of exoplanet known, due to the relative ease of detecting them with ground-based instruments.

Giant planets are commonly said to lack solid surfaces, but it is more accurate to say that they lack surfaces altogether since the gases that form them simply become thinner and thinner with increasing distance from the planets' centers, eventually becoming indistinguishable from the interplanetary medium. Therefore, landing on a giant planet may or may not be possible, depending on the size and composition of its core.

Subtypes

Gas giants

Saturn's north polar vortex Saturn north polar vortex 2012-11-27.jpg
Saturn's north polar vortex

Gas giants consist mostly of hydrogen and helium. The Solar System's gas giants, Jupiter and Saturn, have heavier elements making up between 3 and 13 percent of their mass. [10] Gas giants are thought to consist of an outer layer of molecular hydrogen, surrounding a layer of liquid metallic hydrogen, with a probable molten core with a rocky composition.

Jupiter and Saturn's outermost portion of the hydrogen atmosphere has 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 high pressure turns hydrogen into an electrical conductor. The core is thought to consist of heavier elements at such high temperatures (20,000 K) and pressures that their properties are poorly understood. [10]

Ice giants

Ice giants have distinctly different interior compositions from gas giants. The Solar System's ice giants, Uranus and Neptune, have a hydrogen-rich atmosphere that extends from the cloud tops down to about 80% (Uranus) or 85% (Neptune) of their radius. Below this, they are predominantly "icy", i.e. consisting mostly of water, methane, and ammonia. There is also some rock and gas, but various proportions of ice–rock–gas could mimic pure ice, so that the exact proportions are unknown. [11]

Uranus and Neptune have very hazy atmospheric layers with small amounts of methane, giving them aquamarine colors; light blue and ultramarine respectively. Both have magnetic fields that are sharply inclined to their axes of rotation.

Unlike the other giant planets, Uranus has an extreme tilt that causes its seasons to be severely pronounced. The two planets also have other subtle but important differences. Uranus has more hydrogen and helium than Neptune despite being less massive overall. Neptune is therefore denser and has much more internal heat and a more active atmosphere. The Nice model, in fact, suggests that Neptune formed closer to the Sun than Uranus did, and should therefore have more heavy elements.

Massive solid planets

Massive solid planets can also exist.

Solid planets up to thousands of Earth masses may be able to form around massive stars (B-type and O-type stars; 5–120 solar masses), where the protoplanetary disk would contain enough heavy elements. Also, these stars have high UV radiation and winds that could photoevaporate the gas in the disk, leaving just the heavy elements. For comparison, Neptune's mass equals 17 Earth masses, Jupiter has 318 Earth masses, and the 13 Jupiter-mass limit used in the IAU's working definition of an exoplanet equals approximately 4000 Earth masses. [12]

Super-Puffs

A super-puff is a type of exoplanet with a mass only a few times larger than Earth’s but a radius larger than Neptune, giving it a very low mean density. They are cooler and less massive than the inflated low-density hot-Jupiters. The most extreme examples known are the three planets around Kepler-51 which are all Jupiter-sized but with densities below 0.1 g/cm3. [13]

Extrasolar giant planets

An artist's conception of 79 Ceti b, the first extrasolar giant planet found with a minimum mass less than Saturn. Plan79ceti.jpg
An artist's conception of 79 Ceti b, the first extrasolar giant planet found with a minimum mass less than Saturn.

Because of the limited techniques currently available to detect exoplanets, many of those found to date have been of a size associated, in the Solar System, with giant planets. Because these large planets are inferred to share more in common with Jupiter than with the other giant planets, some have claimed that "jovian planet" is a more accurate term for them. Many of the exoplanets are much closer to their parent stars and hence much hotter than the giant planets in the Solar System, making it possible that some of those planets are a type not observed in the Solar System. Considering the relative abundances of the elements in the universe (approximately 98% hydrogen and helium) it would be surprising to find a predominantly rocky planet more massive than Jupiter. On the other hand, models of planetary-system formation have suggested that giant planets would be inhibited from forming as close to their stars as many of the extrasolar giant planets have been observed to orbit.

Atmospheres

The bands seen in the atmosphere of Jupiter are due to counter-circulating streams of material called zones and belts, encircling the planet parallel to its equator. The zones are the lighter bands, and are at higher altitudes in the atmosphere. They have an internal updraft and are high-pressure regions. The belts are the darker bands, are lower in the atmosphere, and have an internal downdraft. They are low-pressure regions. These structures are somewhat analogous to the high and low-pressure cells in Earth's atmosphere, but they have a very different structure—latitudinal bands that circle the entire planet, as opposed to small confined cells of pressure. This appears to be a result of the rapid rotation and underlying symmetry of the planet. There are no oceans or landmasses to cause local heating and the rotation speed is much higher than that of Earth.

There are smaller structures as well: spots of different sizes and colors. On Jupiter, the most noticeable of these features is the Great Red Spot, which has been present for at least 300 years. These structures are huge storms. Some such spots are thunderheads as well.

See also

Related Research Articles

<span class="mw-page-title-main">Exoplanet</span> Planet outside the Solar System

An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not then recognized as such. The first confirmation of the detection occurred in 1992. A different planet, first detected in 1988, was confirmed in 2003. As of 1 April 2024, there are 5,653 confirmed exoplanets in 4,161 planetary systems, with 896 systems having more than one planet. The James Webb Space Telescope (JWST) is expected to discover more exoplanets, and to give more insight into their traits, such as their composition, environmental conditions, and potential for life.

<span class="mw-page-title-main">Planet</span> Large, round non-stellar astronomical object

A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a young protostar orbited by a protoplanetary disk. Planets grow in this disk by the gradual accumulation of material driven by gravity, a process called accretion. The Solar System has at least eight planets: the terrestrial planets Mercury, Venus, Earth, and Mars, and the giant planets Jupiter, Saturn, Uranus, and Neptune.

<span class="mw-page-title-main">Nebular hypothesis</span> Astronomical theory about the Solar System

The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System. It suggests the Solar System is formed from gas and dust orbiting the Sun which clumped up together to form the planets. The theory was developed by Immanuel Kant and published in his Universal Natural History and Theory of the Heavens (1755) and then modified in 1796 by Pierre Laplace. Originally applied to the Solar System, the process of planetary system formation is now thought to be at work throughout the universe. The widely accepted modern variant of the nebular theory is the solar nebular disk model (SNDM) or solar nebular model. It offered explanations for a variety of properties of the Solar System, including the nearly circular and coplanar orbits of the planets, and their motion in the same direction as the Sun's rotation. Some elements of the original nebular theory are echoed in modern theories of planetary formation, but most elements have been superseded.

<span class="mw-page-title-main">Super-Jupiter</span> Class of planets with more mass than Jupiter

A super-Jupiter is a gas giant exoplanet that is more massive than the planet Jupiter. For example, companions at the planet–brown dwarf borderline have been called super-Jupiters, such as around the star Kappa Andromedae.

The definition of the term planet has changed several times since the word was coined by the ancient Greeks. Greek astronomers employed the term ἀστέρες πλανῆται, 'wandering stars', for star-like objects which apparently moved over the sky. Over the millennia, the term has included a variety of different celestial bodies, from the Sun and the Moon to satellites and asteroids.

<span class="mw-page-title-main">Ice giant</span> Giant planet primarily consisting of compounds with freezing points exceeding 100°K

An ice giant is a giant planet composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur. There are two ice giants in the Solar System: Uranus and Neptune.

<span class="mw-page-title-main">Sudarsky's gas giant classification</span>

Sudarsky's classification of gas giants for the purpose of predicting their appearance based on their temperature was outlined by David Sudarsky and colleagues in the paper Albedo and Reflection Spectra of Extrasolar Giant Planets and expanded on in Theoretical Spectra and Atmospheres of Extrasolar Giant Planets, published before any successful direct or indirect observation of an extrasolar planet atmosphere was made. It is a broad classification system with the goal of bringing some order to the likely rich variety of extrasolar gas-giant atmospheres.

<span class="mw-page-title-main">Formation and evolution of the Solar System</span> Modelling its structure and composition

There is evidence that the formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary disk out of which the planets, moons, asteroids, and other small Solar System bodies formed.

<span class="mw-page-title-main">Gliese 436 b</span> Hot Neptune exoplanet orbiting Gliese 436

Gliese 436 b is a Neptune-sized exoplanet orbiting the red dwarf Gliese 436. It was the first hot Neptune discovered with certainty and was among the smallest-known transiting planets in mass and radius, until the much smaller Kepler exoplanet discoveries began circa 2010.

<span class="mw-page-title-main">Super-Earth</span> Planet with a mass between Earth and Uranus

A Super-Earth is a type of exoplanet with a mass higher than Earth's, but substantially below those of the Solar System's ice giants, Uranus and Neptune, which are 14.5 and 17 times Earth's, respectively. The term "super-Earth" refers only to the mass of the planet, and so does not imply anything about the surface conditions or habitability. The alternative term "gas dwarfs" may be more accurate for those at the higher end of the mass scale, although "mini-Neptunes" is a more common term.

<span class="mw-page-title-main">Extraterrestrial atmosphere</span> Area of astronomical research

The study of extraterrestrial atmospheres is an active field of research, both as an aspect of astronomy and to gain insight into Earth's atmosphere. In addition to Earth, many of the other astronomical objects in the Solar System have atmospheres. These include all the gas giants, as well as Mars, Venus and Titan. Several moons and other bodies also have atmospheres, as do comets and the Sun. There is evidence that extrasolar planets can have an atmosphere. Comparisons of these atmospheres to one another and to Earth's atmosphere broaden our basic understanding of atmospheric processes such as the greenhouse effect, aerosol and cloud physics, and atmospheric chemistry and dynamics.

A substellar object, sometimes called a substar, is an astronomical object, the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained. This definition includes brown dwarfs and former stars similar to EF Eridani B, and can also include objects of planetary mass, regardless of their formation mechanism and whether or not they are associated with a primary star.

This page describes exoplanet orbital and physical parameters.

<span class="mw-page-title-main">Hot Neptune</span> Planet with a mass similar to Uranus or Neptune orbiting close to its star

A hot Neptune or Hoptune is a type of giant planet with a mass similar to that of Uranus or Neptune orbiting close to its star, normally within less than 1 AU. The first hot Neptune to be discovered with certainty was Awohali in 2007, an exoplanet about 33 light years away. Recent observations have revealed a larger potential population of hot Neptunes in the Milky Way than was previously thought. Hot Neptunes may have formed either in situ or ex situ.

<span class="mw-page-title-main">Helium planet</span> Planet with helium-dominated atmosphere

A helium planet is a planet with a helium-dominated atmosphere. This contrasts with ordinary gas giants such as Jupiter and Saturn, whose atmospheres consist primarily of hydrogen, with helium as a secondary component only. Helium planets might form in a variety of ways. Gliese 436 b is a possible helium planet.

<span class="mw-page-title-main">Tyche (hypothetical planet)</span> Hypothetical gas giant in the Oort cloud

Tyche was a hypothetical gas giant located in the Solar System's Oort cloud, first proposed in 1999 by astrophysicists John Matese, Patrick Whitman and Daniel Whitmire of the University of Louisiana at Lafayette. They argued that evidence of Tyche's existence could be seen in a supposed bias in the points of origin for long-period comets. More recently, Matese and Whitmire re-evaluated the comet data and noted that Tyche, if it existed, would be detectable in the archive of data that was collected by NASA's Wide-field Infrared Survey Explorer (WISE) telescope. In 2014, NASA announced that the WISE survey had ruled out any object with Tyche's characteristics, indicating that Tyche as hypothesized by Matese, Whitman, and Whitmire does not exist.

<span class="mw-page-title-main">Mini-Neptune</span> Planet smaller than Neptune with a gas atmosphere

A Mini-Neptune is a planet less massive than Neptune but resembling Neptune in that it has a thick hydrogen-helium atmosphere, probably with deep layers of ice, rock or liquid oceans.

<span class="mw-page-title-main">Gas giant</span> Giant planet mainly composed of light elements

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". 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. For this reason, Uranus and Neptune are now often classified in the separate category of ice giants.

Kepler-1625b is a super-Jupiter exoplanet orbiting the Sun-like star Kepler-1625 about 2,500 parsecs away in the constellation of Cygnus. The large gas giant is approximately the same radius as Jupiter, and orbits its star every 287.4 days. In 2017, hints of a Neptune-sized exomoon in orbit of the planet was found using photometric observations collected by the Kepler Mission. Further evidence for a Neptunian moon was found the following year using the Hubble Space Telescope, where two independent lines of evidence constrained the mass and radius to be Neptune-like. The mass-signature has been independently recovered by two other teams. However, the radius-signature was independently recovered by one of the teams but not the other. The original discovery team later showed that this latter study appears affected by systematic error sources that may influence their findings.

References

  1. ↑ Burgasser, Adam J. (June 2008). "Brown dwarfs: Failed stars, super Jupiters" (PDF). Physics Today . Archived from the original (PDF) on 8 May 2013. Retrieved 11 January 2016.
  2. ↑ D'Angelo, G.; Durisen, R. H.; Lissauer, J. J. (2011). "Giant Planet Formation". In S. Seager. (ed.). Exoplanets. University of Arizona Press, Tucson, AZ. pp. 319–346. arXiv: 1006.5486 . Bibcode:2010exop.book..319D.
  3. ↑ 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. arXiv: 2009.05575 . Bibcode:2021Icar..35514087D. doi:10.1016/j.icarus.2020.114087. S2CID   221654962.
  4. ↑ Jack J. Lissauer; David J. Stevenson (2006). "Formation of Giant Planets" (PDF). NASA Ames Research Center; California Institute of Technology. Archived from the original (PDF) on 2009-02-26. Retrieved 2006-01-16.
  5. ↑ 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 (2): 120 (13 pp.). arXiv: 1305.0980 . Bibcode:2013ApJ...770..120B. doi:10.1088/0004-637X/770/2/120. S2CID   118553341.
  6. ↑ Spiegel, David S.; Burrows, Adam; Milsom, John A. (2011-01-20). "The Deuterium-Burning Mass Limit for Brown Dwarfs and Giant Planets". The Astrophysical Journal. 727 (1): 57. arXiv: 1008.5150 . Bibcode:2011ApJ...727...57S. doi:10.1088/0004-637X/727/1/57. ISSN   0004-637X. S2CID   118513110.
  7. ↑ Schneider, Jean (2016). "III.8 Exoplanets versus brown dwarfs: The CoRoT view and the future". Exoplanets versus brown dwarfs: the CoRoT view and the future. p. 157. arXiv: 1604.00917 . doi:10.1051/978-2-7598-1876-1.c038. ISBN   978-2-7598-1876-1. S2CID   118434022.
  8. ↑ Wright, J. T.; Fakhouri, O.; Marcy, G. W.; Han, E.; Feng, Y.; Johnson, John Asher; Howard, A. W.; Fischer, D. A.; Valenti, J. A.; Anderson, J.; Piskunov, N. (2010). "The Exoplanet Orbit Database". Publications of the Astronomical Society of the Pacific. 123 (902): 412–422. arXiv: 1012.5676 . Bibcode:2011PASP..123..412W. doi:10.1086/659427. S2CID   51769219.
  9. ↑ Wilson, Hugh F.; Militzer, Burkhard (2012-03-14). "Rocky core solubility in Jupiter and giant exoplanets". Physical Review Letters. 108 (11): 111101. arXiv: 1111.6309 . Bibcode:2012PhRvL.108k1101W. doi:10.1103/PhysRevLett.108.111101. ISSN   0031-9007. PMID   22540454. S2CID   42226611.
  10. 1 2 The Interior of Jupiter, Guillot et al., in Jupiter: The Planet, Satellites and Magnetosphere, Bagenal et al., editors, Cambridge University Press, 2004
  11. ↑ L. McFadden; P. Weissman; T. Johnson (2007). Encyclopedia of the Solar System (2nd ed.) . Academic Press. ISBN   978-0-12-088589-3.
  12. ↑ Seager, S.; Kuchner, M.; Hier-Majumder, C. A.; Militzer, B. (2007). "Mass-Radius Relationships for Solid Exoplanets". The Astrophysical Journal. 669 (2): 1279–1297. arXiv: 0707.2895 . Bibcode:2007ApJ...669.1279S. doi:10.1086/521346. S2CID   8369390.
  13. ↑ Libby-Roberts, Jessica E.; Berta-Thompson, Zachory K.; Desert, Jean-Michel; Masuda, Kento; Morley, Caroline V.; Lopez, Eric D.; Deck, Katherine M.; Fabrycky, Daniel; Fortney, Jonathan J.; Line, Michael R.; Sanchis-Ojeda, Roberto; Winn, Joshua N. (2020-01-20). "The Featureless Transmission Spectra of Two Super-Puff Planets". The Astronomical Journal. 159 (2): 57. arXiv: 1910.12988 . Bibcode:2020AJ....159...57L. doi: 10.3847/1538-3881/ab5d36 . ISSN   1538-3881. S2CID   204950000.

Bibliography

This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.