然而，如今的类地行星与木星不同，几乎没有轻气体和冰。

However, unlike Jupiter, the terrestrial planets today are nearly void of light gases and ices.

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这两组行星的构成物质根据熔点分为三类：气体、岩石和冰。

The substances that make up both groups of planets are divided into three groups—gases, rocks, and ices—based on their melting points.

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那是一类包含冰和机化合物的特殊物质，而这些物质只有被粉碎的彗星才能产生。

It's the particular type of material, which also included grains of ice and organic chemicals - just what you'd expect from a pulverized comet.

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