木星、土星、天王星和海王星。这些都是气体行星，是太阳系的四个重量级。但曾经存在第五个行星吗？
Jupiter, Saturn, Uranus, and Neptune. Those are the gas giants, the four heavyweights of the solar system. But was there once a fifth?
这些都是气体行星，太阳系的四个重量级。
Those are the gas giants, the four heavyweights of the solar system.
它是巨型气体行星与我们找寻的目标之间的一颗过渡性星体。
This is a transitional planet somewhere between a gas giant and what we've been hoping to find.
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