Hello, I'm an expert in planetary science with a keen interest in the study of the outer planets in our solar system. Let's dive into the question of why Neptune is sometimes referred to as a "Green Planet."

Neptune is not actually green in color. It's often depicted as blue, which is due to the presence of methane in its atmosphere. Methane absorbs red light, which makes the planet appear more blue to the human eye. However, the term "Green Planet" in reference to Neptune is a bit of a misnomer and is not commonly used by astronomers or planetary scientists. It's possible that this term might be used in a metaphorical or poetic sense to describe the planet's remote and mysterious nature, or perhaps in the context of its discovery, which was predicted before it was observed, a feat that was considered a great leap in scientific understanding at the time.

Now, let's translate that into Chinese:

你好，我是行星科学的专家，对研究我们太阳系中的外行星特别感兴趣。让我们深入探讨为什么海王星有时被称为“绿色行星”。

海王星实际上并不是绿色的。它通常被描绘成蓝色，这是因为其大气中存在甲烷。甲烷吸收红光，这使得这颗行星在人眼中看起来更蓝。然而，将海王星称为“绿色行星”实际上是有点用词不当，天文学家或行星科学家并不常用这个术语。这个术语可能是在比喻或诗意上用来描述这颗行星的遥远和神秘性质，或者可能是在其发现的背景下使用的，海王星的发现是在它被观测到之前就预测到了，这在当时被认为是科学理解上的巨大飞跃。

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The color comes from methane clouds. In some photos released after the Voyager 2 flyby (in 1986), Uranus looked green, but that color was artificial. ... As in the case of Uranus, the color is due to methane. Neptune would appear darker than Uranus due to dimmer illumination (greater distance from the Sun).read more >>