Glossary term: Géantes gazeuses

Description: Une géante gazeuse est une planète géante composée principalement d'hydrogène et d'hélium, qui sont des gaz présents dans l'espace interstellaire et interplanétaire. Ceci explique son nom. Cependant, la plupart de l'hydrogène et de l'hélium des géantes gazeuses sont en fait à l'état liquide.

On pense que les géantes gazeuses ont un noyau rocheux entouré d'épaisses couches d'hydrogène et d'hélium. Dans les parties les plus profondes de la planète, ces gaz sont comprimés sous forme liquide et on pense que les couches les plus profondes contiennent un océan d'hydrogène métallique. Dans les couches extérieures, l'hydrogène et l'hélium sont sous forme de gaz. D'autres éléments présents dans l'atmosphère peuvent former des nuages et de la pluie. Dans les géantes gazeuses les plus froides, les nuages de la couche supérieure peuvent être constitués de vapeur d'eau ou d'ammoniac. Dans les couches plus profondes et plus chaudes des géantes gazeuses plus froides et dans les couches extérieures des géantes gazeuses plus chaudes, les nuages peuvent être constitués de fer et de minéraux qui sont solides à température ambiante.

Les deux plus grosses planètes du Système solaire, Jupiter et Saturne, sont des géantes gazeuses.

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Term and definition status: The original definition of this term in English have been approved by a research astronomer and a teacher
The translation of this term and its definition is still awaiting approval

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Related Media

The planet Jupiter with the two of the four Galilean moons (visible as bright dots) orbiting it.

Jupiter's Rotation, by Vishal Sharma, India

Caption: Third place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons: Jupiter’s Rotation, by Vishal Sharma, India. This time-lapse beautifully shows the rotation of Jupiter and the passage of two Galilean moons on the right side of the frame. Jupiter completes one rotation in just under 10 hours and we see as the Great Red Spot makes its way from left to right. The two moons travel a noticeable fraction of their orbit in this short time. This image was taken in 2020 in the North of India.
Credit: Vishal Sharma/IAU OAE

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

The planet Jupiter, seen here as a bright disk, is orbited by the four Galilean moons, seen here as bright dots

Jupiter Moons Movie2, by Nicolas Hurez, Paul-Antoine Matrangolo, and Carl Pennypacker, United States of America

Caption: Second place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons. This sequence shows the orbit of the four Galilean moons around the planet Jupiter. Almost two entire orbits of the innermost moon, Io, can be seen, with the other moons (Europa and Ganymede, but in particular Callisto) being further away, orbiting noticeably slower. The images were obtained in 2018 with the Las Cumbres Global Observatory at different locations on Earth, allowing a continuous sequence of images over approximately half a week without gaps during the day. With clear skies and over the course of several nights, the motion of the Galilean moons can also be observed with binoculars (ideally steady your elbows on a surface).
Credit: Nicolas Hurez, Paul-Antoine Matrangolo and Carl Pennypacker/IAU OAE

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

Jupiter with coloured horizontal bands of clouds. The shadow of the moon Io is seen as a dark circle in the top left

Jupiter, Io and its shadow, by Ralf Burkart, Germany

Caption: First place in the 2021 IAU OAE Astrophotography Contest, category Galilean moons. This time-lapse of Jupiter taken in 2017 from Germany beautifully illustrates the transit of one of the Galilean moons, Io, in front of Jupiter. As this is simply a moon casting a shadow on a planet it is equivalent to a lunar eclipse on Earth observed from further away. While the shadow of the moon is clearly visible from the beginning, it might be difficult to spot the moon itself against the background of the beautiful atmospheric bands of Jupiter the first time the video is seen. Watching it repeatedly allows appreciating the rapid motion and rotation in this fantastic observation.
Credit: Ralf Burkart/IAU OAE

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

Jupiter

Caption: Cette vue du disque complet de Jupiter a été obtenue le 21 avril 2014 avec la Camera 3 à grand champ (WFC3) de Hubble. Elle montre la grande tâche rouge proéminente, un gigantesque cyclone. Des bandes de nuages couvrent la surface, dont les couleurs proviennent de gaz comme l'ammoniac et d'autres composés chimiques.
Credit: NASA, ESA, et A. Simon (Goddard Space Flight Center) credit link

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

Saturne

Caption: La caméra à grand champ 3 du télescope spatial Hubble de la NASA/ESA a observé Saturne le 20 juin 2019, alors que la planète s'approchait au plus près de la Terre, à une distance d'environ 1,36 milliard de kilomètres. L'image montre des bandes colorées de gaz à la surface de la planète ainsi que ses anneaux proéminents composés de glace et de matériaux rocheux.
Credit: NASA, ESA, A. Simon (Goddard Space Flight Center), et M.H. Wong (Université de Californie, Berkeley) credit link

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

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