Glossary term: 冥王星
Description: 冥王星是太阳系中的天体之一。它位于柯伊伯带，在海王星轨道之外。它曾被称为太阳系第九大行星，但在 2006 年被重新归类为矮行星。它于 1930 年被克莱德-汤博发现。冥王星与太阳的平均距离为 60 亿千米，半径为 1185 千米（比地球的卫星还小）。冥王星上的一年相当于地球上的 247.9 年，一天相当于地球上的 6.4 天。
2015年，美国国家航空航天局的 "新视野 "号飞船成为第一个飞越冥王星的航天器，并首次提供了冥王星表面及其大气层的详细信息。冥王星表面非常寒冷，几乎没有氢可以以气态形式存在。冥王星仅有的一点大气主要是氮气，表面有大片冰冻的氮气平原。它的大气层延伸到1600千米的距离。冥王星由岩石（70%）和冰（30%）组成。它有五颗已知的卫星：卡戎（Charon）、斯提克斯（Styx）、尼克斯（Nix）、刻耳柏洛斯（Kerberos）和海德拉（Hydra）。
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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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