Frozen giant


May 25, 2022

An ice giant, or ice giant, is a type of giant planet composed primarily of less volatile elements than hydrogen and helium, such as water, methane, or ammonia. These materials are called "ice" in astrophysics, regardless of their state (solid, liquid ..), in contrast to the usual definition of the term. Such a distinction between gas giants was made starting from 1990, when the increased chemical-physical knowledge more remote giants led to distinguish the more massive giants, such as Jupiter and Saturn from Uranus and Neptune. The latter contain intermediate elements heavier than "gas" (hydrogen and helium), but lighter than "rocks" (silicon) and "metals" (iron, nickel). Uranus and Neptune are classified as ice giants in that only about 20% of hydrogen is present in their total mass, compared to almost 90% of the presence of this gas in the more massive Jupiter and Saturn. water, however, which is in the supercritical state, that is, under particular pressure and temperature conditions in the equation of state diagram, which must be taken into account when modeling the structure of these celestial bodies. Frozen giants are believed to lack a metallic hydrogen core, unlike gas giants. Several discovered exoplanets have been included in this class that likely have similar characteristics to those of Uranus and Neptune, with some classified into further division into hot icy giants, such as hot Neptunian planets.


The frozen giants probably formed in the first million years of the solar system's life, when the protoplanetary disk still contained a significant amount of gas, immediately captured by the star or by more massive giant planets such as Jupiter. This also has implications for the possibility of the formation of icy giants, which must form relatively quickly before the gas from the protoplanetary disk is dissipated. Observations on protoplanetary disks around young stars suggest that the gas disk in the initial phase of the formation of a planetary system can last from 3 to 10 million years.

Magnetic fields

The magnetic fields of Uranus and Neptune are both unusually inclined and asymmetrical. The intensity of the magnetic fields of Uranus and Neptune are intermediate between those of the major gas giants (Jupiter and Saturn) and those of the terrestrial planets, moreover they are not generated by the nuclei but by the compression and ionization of the melted ice mantle.

Frozen giant exoplanets

In December 2019, the first cold Neptunian orbiting a white dwarf was detected. The exoplanet orbits the star WD J0914 + 1914, located about 1500 light years away in the constellation of Cancer with an estimated temperature of about 28000 degrees Celsius (five times the temperature of the Sun). The planet would orbit its own celestial body at a distance of 10 million kilometers, about 15 times the solar radius. The conclusion that the planet is of the frozen Neptunian type is supported by the presence of chemical elements such as hydrogen, oxygen and sulfur in the disc of material that rotates in a whirlwind fall around the white dwarf.


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External links

(EN) Gas and Ice Giants, on ESO, First Giant Planet Found Around White Dwarf, on YouTube, 4 December 2019.