Glossary term: Ice Giant

Description: In the Solar System there are four giant planets: Jupiter, Saturn, Uranus, and Neptune. The last two, Uranus and Neptune, are known as ice giants. They have solid rocky cores surrounded by a thick layer of water, ammonia, and methane. These chemicals are in a strange, high-pressure state of matter: not quite solid, not quite liquid. The outer atmosphere of both planets is a thick, puffy layer of hydrogen and helium.

In the early Solar System, in the regions far from the Sun, it was cold enough for water, methane, and ammonia to freeze into ices. Here "ices" is a general term for frozen chemicals made of molecules. The young planets Uranus and Neptune accreted these ices due to their gravitational pull. Because these ices were the source of such an important component of these two planets, they were named the ice giants.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

Related Media

Uranus showing a uniformly greenish-blue coloured appearance

Uranus in natural colours

Caption: This is an image of the planet Uranus taken by the spacecraft Voyager 2 in 1986. Its appearance is close to what the naked eye would see. The greenish-blue colour indicates an atmosphere containing methane.
Credit: NASA/JPL-Caltech credit link

License: PD Public Domain icons

Uranus appears as a light blue disk with and a pale polar region. Thin white rings surround the planet

Uranus with rings

Caption: The NASA/ESA Hubble Space Telescope’s ACS/HRC camera observed Uranus in August 2005. The surface depicts white clouds and a bright polar region. The rings around Uranus are narrow and contain rocky material from tiny dust particles up to metre-sized boulders.
Credit: NASA, ESA, and M. Showalter (SETI Institute) credit link

License: PD Public Domain icons

Neptune is spherical and blue with thin bands of white cloud and a slightly darker spot just below its equator


Caption: Voyager 2 Narrow Angle Camera image of Neptune taken in August 1989. The Great Dark Spot, flanked by cirrus clouds, is at center. A smaller dark storm, Dark Spot Jr., is rotating into view at bottom left. Additionally, a patch of white cirrus clouds to its north, named "Scooter" for its rapid motion relative to other features, is visible.
Credit: NASA / JPL / Voyager-ISS / Justin Cowart credit link

License: PD Public Domain icons