Glossary term: Giant Planet

Description: A giant planet is a large body mostly composed of hydrogen, helium, or more complex molecules such as water, methane, or ammonia. While a terrestrial planet is mostly composed of material with a very high boiling point such as iron or rock, giant planets are thought to have a solid core surrounded by other material. The mass of a giant planet is substantially higher than that of Earth, so its gravity is strong enough to retain the extended gaseous atmosphere made up of light elements like hydrogen and helium.

Giant planets fall into two categories: gas giants which are mostly made up of hydrogen and helium, and ice giants which are mostly made up of water, methane, and ammonia surrounded by an atmosphere of hydrogen and helium. In both cases the names can be confusing as most of the material in gas giants is not in a gaseous state and ice giants do not contain solid ice, rather material that was frozen in the cold outer Solar System before it was accreted onto the planet.

The four largest planets in the Solar System (Jupiter, Saturn, Neptune, and Uranus) are all giant planets.

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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".

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Credit: NASA, ESA, and A. Simon (Goddard Space Flight Center) credit link

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

The planet Saturn with pale brownish cloud ribbons and its thin and extended greyish rings


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Credit: NASA, ESA, A. Simon (Goddard Space Flight Center), and M.H. Wong (University of California, Berkeley) credit link

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons

Uranus showing a uniformly greenish-blue coloured appearance

Uranus in natural colours

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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

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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