Terminology[ edit ] The term gas giant was coined in 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.
Gas giant Saturn's north polar vortex Gas giants consist mostly of hydrogen and helium. The Solar System's gas giants, Jupiter and Saturnhave heavier elements making up between 3 and 13 percent of their mass.
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, K and pressures that their properties are poorly understood. Ice giant Ice giants have distinctly different interior compositions from gas giants. Below this, they are predominantly "icy", i. 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.
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 modelin fact, suggests that Neptune formed closer to the Sun than Uranus did, and should therefore have more heavy elements.
Massive solid planets[ edit ] 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— solar masseswhere 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.
Comparison of sizes of planets of a given mass with different compositions See also: Hot JupiterSuper-JupiterSub-brown dwarfand Brown dwarf Because of the limited techniques currently available to detect exoplanetsmany 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.
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[ edit ] 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.Terrestrial and Jovian Planets.
With the exception of Pluto, planets in our solar system are classified as either terrestrial (Earth-like) or Jovian (Jupiter-like) planets. The planets of the solar system as depicted by a NASA computer illustration.
Orbits and sizes are not shown to scale. Credit: NASA A gas giant is a large planet composed mostly of gases, such as. Jovian planet n. One of the four gas giant planets in the solar system, Jupiter, Saturn, Uranus, and Neptune, which have very large masses and are farther from the sun than.
Giant planets are also sometimes called jovian planets, after Jupiter.
They are also sometimes known as gas giants. However, many astronomers apply the latter term only to Jupiter and Saturn, classifying Uranus and Neptune, which have different compositions, as . Jovian Planets A Jovian planet is a gas giant, the term is derived from Jupiter which describes the three other gas giants in the Solar System as Jupiter-like.
Though the name may imply it, a gas giant is not composed only of gas. After size, perhaps the most noticeable difference between the jovian and terrestrial planets involves moons and rings.
The terrestrial planets are nearly isolated worlds, with only Earth (1 moon) and Mars (2 moons) orbited by any moons at all.