Glossary term: 巨行星

Description: 巨行星是主要由氢、氦，或水、甲烷，或氨等更复杂的分子组成的巨大天体。类地行星主要由铁或岩石等沸点很高的物质组成，而巨行星则被认为有一个被其他物质包围的固态内核。巨行星的质量远远大于地球，因此其引力足够强大，可以维持由氢和氦等轻元素组成的扩展气态大气层。

巨行星分为两类：气态巨行星和冰质巨行星，前者主要由氢和氦组成，而后者主要由水、甲烷和氨组成，周围环绕着氢和氦组成的大气层。这两个名称可能会引起混淆，因为气态巨行星中的大部分物质并不是气态的，而冰质巨行星包含的也并不是固态冰，而是先在寒冷的外太阳系中冻结、后被吸积到行星上的物质。

太阳系中最大的四颗行星（木星、土星、海王星和天王星）都是巨行星。

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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

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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