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There are four gas giants in our solar system: Jupiter, Saturn, Uranus, and Neptune. These are also known as the Jovian planets.
The four solar system gas giants share a number of features in common. All have atmospheres that are mostly hydrogen and helium, and that blend into the liquid interior at pressures greater than the critical pressure, so that there is no clear boundary between atmosphere and body. They have very hot interiors, ranging from about 5000 k for Neptune to over 20,000 k for Jupiter. This great heat means that, beneath their atmospheres, the planets are most likely entirely liquid. When discussions refer to a "rocky core", one should not picture a ball of solid granite, or even, at 20,000 k, liquid granite. Rather, what is meant is a region in which the concentration of heavier elements such as iron and silicon is greater than that in the rest of the planet.
All four planets rotate relatively rapidly, which causes wind patterns to break up into east-west bands or stripes. These bands are prominent in Jupiter, muted in Saturn and Neptune, and barely detectable at all in Uranus.
Finally, all four are accompanied by elaborite systems of rings and moonMoons The common noun moon (not capitalized) is used to mean any natural satellite of the other planets. There are, at least, 140 moons within Earth's solar system, and presumably many others orbiting the planets of other stars. Typically the larger gas gs. Saturn's rings are the most spectacular, and the only ones known before the 1970s. As of 2004, Jupiter was thought to have the most moons, with more than 60 found.
The Jovian planets further can be divided into one group consisting of Jupiter and Saturn, and another consisting of Uranus and Neptune.
These consist almost entirely of hydrogen and helium, and they are so large that one can still say this even though both are thought to have several Earth masses of heavier elements. Their deep interiors consist of liquid metallic hydrogen, a form of hydrogen distinguished by the fact that it conducts electricity.
Both have magnetic fields oriented fairly close to their axes of rotation.
Uranus and Neptune have distinctly different interior compositions, with the bulk of their interiors thought to consist of a mixture (or layered assortment) of rock, water, methane, and ammonia. Both have magnetic fields that are sharply inclined to their axes of rotation.
The term was coined by the science fiction writer James BlishJames Blish ( East Orange, New Jersey, May 23, 1921 Henley-on-Thames, July 29, 1975) was an American author of fantasy and science fiction. Blish also wrote criticism of science fiction using the pen-name William Atheling Jr. Blish trained as a biologist. Arguably it is a misnomer, since all of these planets are primarily liquid and not gaseous. In fact, for Jupiter and Saturn, the gaseous atmospheres are quite thin compared to the planetary radii -- only extending perhaps one percent of the way to the center. However, at least for Jupiter and Saturn, the name is defensible because their compositions are dominated by hydrogen and helium, which are gases in the outer solar system when not under pressure.
Planetary scientists often use 'rock', 'gas', and 'ice' as shorthands for classes of elements and compounds commonly found as planetary constituents, irrespective of what phase they appear in. In the outer solar system, hydrogen and helium are "gases"; water, methane, and ammonia are "ices"; and silicates are 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.
Wthh this terminology in mind, some astronomers are starting to refer to Uranus and Neptune as "ice giants", to indicate the apparent predominance of the "ices" (in liquid form) in their interior composition.
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