(单词翻译:单击)
An exoplanet is a planet outside of our solar system.
系外行星是太阳系之外的行星。
Most exoplanets orbit different stars in the galaxy.
大多数系外行星围绕星系中的不同恒星运行。
However, astronomers have observed some planets that are independent of any star system.
但是，天文学家已经观测到一些独立于任何恒星系统的行星。
The first two exoplanets were discovered in 1992.
最初的两颗系外行星是在1992年发现的。
Since then, scientists have been searching for exoplanets that are similar to Earth.
从那时起，科学家们一直在寻找与地球相似的系外行星。
This might lead to the discovery of alien life.
或许在这个过程中，我们能发现外星生命。
However, Earth-like planets are difficult to find, because the resources necessary for life only exist under very specific conditions.
然而，类地行星很难找到，因为生命所需的资源只有在非常特殊的条件下才能存在。
Our planet happens to be in the solar system’s habitable zone, where the temperature allows water to exist in liquid form.
地球恰好位于太阳系的宜居带，其温度正好能使水以液态的形式存在。
There are over 1,700 known exoplanets, and only 16 of them are potentially habitable.
目前已知的系外行星有1700多颗，其中只有16颗可能适合人类居住。
