海王星是太阳系中唯一一颗先由精确的数学推导预测出来，再通过观察确定的行星。
Neptune is the only planet in our Solar System whose existence and location was mathematically predicted before the planet was actually observed.
我还亲自摸索到了一块正在清洗之中的钻石——人们告诉我说，这是在美国发现的唯一一颗真正的钻石。
I searched in the washings for a diamond and found it myself-the only true diamond, they said, that was ever found in the United States.
土卫六一直以来都是这项探测任务的主要聚焦点，因其体积比水星还要大，是唯一一颗拥有浓密大气层的卫星。
Titan was a major focus of the mission all along, since it's bigger than the planet Mercury and the only moon massive enough to have a significant atmosphere.
一年后，黎明号探测器将离开灶神星的轨道，计划在2015年到达谷神星，它是小行星带中唯一一颗比灶神星大的小行星。
After a year of studying Vesta, Dawn is scheduled to leave orbit and, in 2015, approach the only asteroid-belt object that is larger: Ceres.
海卫一温度极低(约为- 235摄氏度，一个大气压下- 210度左右氮气凝固——译者注)，以至其大部分的氮气都凝聚到了其表面形成霜，这使海卫一成为太阳系内唯一一颗以“氮冰”为主要地表成分的星球。
Triton is so cold that most of its nitrogen is condensed as frost, making it the only satellite in the solar system known to have a surface made mainly of nitrogen ice.
海卫一温度极低(约为- 235摄氏度，一个大气压下- 210度左右氮气凝固——译者注)，以至其大部分的氮气都凝聚到了其表面形成霜，这使海卫一成为太阳系内唯一一颗以“氮冰”为主要地表成分的星球。
Triton is so cold that most of its nitrogen is condensed as frost, making it the only satellite in the solar system known to have a surface made mainly of nitrogen ice.
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