Description: 海王星是第八大行星，也是距离太阳最远的行星。和它的邻居天王星一样，海王星也是一颗冰巨行星。海王星的半径略小于 2.5 万公里，是地球半径的四倍。海王星有一个坚固的岩石核心，周围有一层高压水、甲烷和氨。在太阳系外的早期，这些化学物质被冻结并吸附在年轻的海王星上，因此被称为 "冰巨行星"。海王星的外部大气层是一层厚厚的、蓬松的氢和氦。

它与太阳的典型距离约为 45 亿千米，约为 30 个天文单位（地球-太阳距离）。海王星至少有 14 颗卫星和一个微弱的行星环。作为最外层的主行星，海王星的引力在塑造柯伊伯带中较小天体的轨道方面起着关键作用。

肉眼看不到海王星。最初发现海王星是因为它的引力对天王星轨道的影响。数学家约翰-库奇-亚当斯（John Couch Adams）和乌尔班-勒威耶（Urbain Le Verrier）都在 19 世纪 40 年代初预测了海王星的存在和位置。根据勒威耶的计算，约翰-戈特弗里德-加勒于 1846 年首次确认了海王星。海王星以罗马海神的名字命名。

Related Terms:

• 天文单位
• 巨行星
• 冰雪巨人
• 柯伊伯带
• 外行星
• 太阳系
• 天王星

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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