Ice giant
In 1952, science fiction writer James Blish coined the term gas giant[3] and it was used to refer to the large non-terrestrial planets of the Solar System.
They are primarily composed of elements heavier than hydrogen and helium, forming a separate type of giant planet altogether.
The terrestrial planets of the Solar System are widely understood to have formed through collisional accumulation of planetesimals within the protoplanetary disk.
The gas giants—Jupiter, Saturn, and their extrasolar counterpart planets—are thought to have formed solid cores of around 10 Earth masses (ME) through the same process, while accreting gaseous envelopes from the surrounding solar nebula over the course of a few to several million years (Ma),[8][9] although alternative models of core formation based on pebble accretion have recently been proposed.
Such bodies, being swept up by the gas giants, would also have been likely to just be accreted into larger planets or thrown into cometary orbits.
[11] Observations of photoevaporation of protoplanetary disks in the Orion Trapezium Cluster by extreme ultraviolet (EUV) radiation emitted by θ1 Orionis C suggests another possible mechanism for the formation of ice giants.
Multiple-Jupiter-mass gas-giant protoplanets could have rapidly formed due to disk instability before having most of their hydrogen envelopes stripped off by intense EUV radiation from a nearby massive star.
The stronger EUV would increase the removal of the gas envelopes from protoplanets before they could collapse sufficiently to resist further loss.
[2] Although Uranus and Neptune are referred to as ice giant planets, it is thought that there is a supercritical water-ammonia ocean beneath their clouds, which accounts for about two-thirds of their total mass.
These include long-lived, high-speed equatorial winds, polar vortices, large-scale circulation patterns, and complex chemical processes driven by ultraviolet radiation from above and mixing with the lower atmosphere.
Their compositions promote different chemical processes and they receive far less sunlight in their distant orbits than any other planets in the Solar System (increasing the relevance of internal heating on weather patterns).
It forms and dissipates every few years, as opposed to the similarly sized Great Red Spot of Jupiter, which has persisted for centuries.
Of all known giant planets in the Solar System, Neptune emits the most internal heat per unit of absorbed sunlight, a ratio of approximately 2.6.
[2] Because of their large sizes and low thermal conductivities, the planetary interior pressures range up to several hundred GPa and temperatures of several thousand kelvins (K).
