Home » Astronomy » Planets » Planets: Gas giants and Ice giants

Planets: Gas giants and Ice giants

Jupiter, Saturn, Uranus and Neptune

A gas giant is a giant planet composed mainly of hydrogen and helium. Jupiter and Saturn are the Solar System’s gas giants.

By the 1990s it became known that Uranus and Neptune are a distinct class of giant planet, composed mainly of heavier volatile substances ( ‘ices’), and therefore are now increasingly referred to as ice giants.

Gas giants: Jupiter and Saturn

Jupiter and Saturn consist mostly of hydrogen and helium, with heavier elements making up between 3 and 13 percent of the mass.

Their structures are thought to consist of an outer layer of molecular hydrogen, surrounding a layer of liquid metallic hydrogen, with probably a molten core with a rocky composition.

The outermost portion of the hydrogen atmosphere is characterized by 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 large 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.  {Gas giant, Wikipedia}

Moons of Jupiter

Possible habitat for life on Enceladus, a moon of Saturn


Ice planets: Uranus and Neptune

An ice giant is a giant planet composed mainly of ices—volatile substances heavier than hydrogen and helium, such as water, methane, and ammonia—as opposed to gas (hydrogen and helium).

It became known in the 1990s that Uranus and Neptune were really a distinct class of giant planet, composed of about 20% hydrogen, compared to the heavier gas giants’ 90%. These materials were actually ices during the ice giants’ formation, but now they exist in different phases, primarily super-critical fluids.

The ice is primarily  H2O. Ice giants are thought to lack metallic hydrogen at their cores, unlike the gas giants. Different atmospheric patterns have been observed, including polar vortices, strong zonal winds, and large-scale circulation.

{adapted from Ice giant, Wikipedia}

A view through their cores.




Uranus’s moons




%d bloggers like this: