Gas giant

A gas giant (sometimes also known as a jovian planet after the planet Jupiter, or giant planet) is a large planet that is not primarily composed of rock or other solid matter. There are two gas giants in the Solar System: Jupiter and Saturn. The other two giant planets, Uranus and Neptune, are not gas giants but ice giants. Many extrasolar gas giants have been identified orbiting other stars. Planets above 10 Earth masses are termed giant planets.[1] Lower-mass gassy planets are sometimes called "gas dwarfs".[2] 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 gas giants 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. The amount of deuterium burnt depends not only on mass but also on the composition of the planet, especially on the amount of helium and deuterium present.[3] The Extrasolar Planets Encyclopaedia includes objects up to 25 Jupiter masses, and the Exop

anet Data Explorer up to 24 Jupiter masses. Brown dwarfs are sub-stellar objects too low in mass to sustain hydrogen-1 fusion reactions in their cores, unlike main sequence stars, which can. They occupy the mass range between the heaviest gas giants and the lightest stars, with an upper limit around 75[1] to 80 Jupiter masses (). Brown dwarfs heavier than about 13 are thought to fuse deuterium and those above ~65 , fuse lithium as well. However, for some years now there has been debate concerning what criterion to use for defining the separation between a brown dwarf and a giant planet at very low brown dwarf masses (~13 Jupiter masses).[2] One school of thought is based on formation, and another on interior physics.[2] Dwarfs are categorized by spectral classification, with the major types being M, L, T, and Y.[2] Despite their name, most brown dwarfs would appear magenta to the human eye.[2] Another debate is whether brown dwarfs are required to have experienced fusion at some point in their history. Some planets are known to orbit brown dwarfs: 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144b. Brown dwarfs may have fully convective surfaces and interiors, with no chemical differentiation by depth.