In the 1990s, astronomers found that Uranus and Neptune were actually gas giant The difference is that only 20% of them are hydrogen, while gas giant planets such as Jupiter and Saturn are up to 90% hydrogen. The main component of these ice giants is "ice", which is heavier than hydrogen and helium. These materials exist in solid state during the formation of ice giant stars, but now they only exist in certain conditions, such as Supercritical fluid 。 Although the surface of the ice giant is still hydrogen Mainly, but the internal area below this range is generally in a "frozen" state. These "ice" mainly consists of water 、 ammonia And methane Composition, so the water state equation It plays a very important role in the formation of ice giants. Unlike gas giants, these ice giants lack cores Metallic hydrogen 。 [1] Ice giants are smaller than gas giants, but still larger than terrestrial planet Large. The size of ice giants is constrained by an important factor: the formation of gas giant planets must be faster than Earth like planets, because they must prevent Protoplanetary disk The gas in is dissipated. According to the observation of protoplanetary disks in young star clusters, ice giants must form within 30 to 100 thousand years, after which the protoplanetary disks will begin to dissipate. [2] Ice giants have extremely variable atmospheres, including Polar vortex , strong zonal wind, and large-scale circulation 。 There is no model that can accurately explain the causes of these climate systems [1] 。 Because of their huge scale and low Thermal conductivity The pressure inside the planet can reach hundreds of GPa and the temperature can reach thousands of degrees. In March 2012, astronomers found that the compressibility of water in ice giants may be less than one third of normal. This data will help to model ice giants and help astronomers have a better understanding of them. In addition to Uranus and Neptune, other systems outside the solar system also have ice giants. [3] The magnetic fields of Uranus and Neptune are both abnormally shifted and tilted. The magnetic field intensity of these ice giants lies between the gas giant planets and the earth like planets, that is Geomagnetic field Tens of times the strength. Uranus and Neptune have magnetic fields 50 and 25 times stronger than Earth's, respectively. The magnetic field of these ice giants comes from their ionizing convection melting ice mantle. [1] The volume of an ice giant is significantly smaller than that of a gas giant planet: the equatorial radii of Jupiter and Saturn are 71492km and 60268km respectively, but Uranus and Neptune are only 25559km and 24764km. Nevertheless, ice giants are still much larger than Earth like planets. Their mass, rotation period and number of satellites are also between gas giant planets and earth like planets. [4]
2022 ， An international team led by Germany's Dresden Rosendorf Helmholtz Center (HZDR), Rostock University and France's Federal Institute of Technology carried out a novel experiment, which confirmed their earlier view that "rock drilling rain" would indeed fall in the ice giant stars outside the solar system [5] 。
