Gas giant

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").

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.

[3] The defining differences between a very low-mass brown dwarf (which can have a mass as low as roughly 13 times that of Jupiter[4]) and a gas giant are debated.

[5] Part of the debate concerns whether brown dwarfs must, by definition, have experienced nuclear fusion at some point in their history.

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.

[7] Other than solids in the core and the upper layers of the atmosphere, all matter is above the critical point, where there is no distinction between liquids and gases.

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".

[12][13] A gas dwarf could be defined as 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.

[18] These disturbances develop into small eddies that eventually form storms such as the Great Red Spot on Jupiter.

[19] Tholins are brown organic compounds found within the surface of various planets that are formed by exposure to UV irradiation.