Terminology[edit | edit source]

Ice giants are considerably larger than terrestrial planets and they are composed mainly of elements heavier than hydrogen and helium, such as oxygen, carbon, nitrogen, and sulfur.

As opposed to gas giants, helium and hydrogen make up only about 20% of an ice giant's mass. Although during the formation of ice giants most of the volatile compounds that are incorporated can be described as "ices", in later stages of their existence the volatiles are mainly found in the form of supercritical fluids[1].

Interior structure[edit | edit source]

Like gas giants, ice giants usually have a rocky core composed of silicates, iron and nickel at their centre. This core only accounts for a fraction of the total planetary mass[2].

The bulk of the planet is usually located in the intermediate layer, which is referred to as mantle. The mantle comprises an extremely dense and hot mixture of water, ammonia and other volatiles. In this layer pressures can reach up to several hundred Gigapascals, which accounts for the unusual properties of the fluid encountered at these depths, like increased solubility and electric conductivity.

An atmosphere containing hydrogen, helium and methane gases sorrounds the mantle. This atmosphere can account for a significant portion of an ice giant's radius but because of its low density it usually increases the total planetary mass by only a small amount.

Interior structure of an ice giant

Atmosphere[edit | edit source]

The outer regions of the atmosphere may contain clouds, band structures and storms similar to those found in gas giants. There are also ice giants lacking these features either because the elements responsible for cloud formation are absent in their atmospheres or because they have no internal energy source which results in lower altitude and decreased visibility of their cloud structures.[3]

View of Asmodeus, a ringed ice giant with nine moons.

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