55 From the earth: Greetings

Recent developments in astronomy have made it possible to detect planets in our own Milky Way and in other galaxies.

天文学方面的最新发展使得我们能够在银河系和其他星系发现行星。

This is a major achievement because, in relative terms, planets are very small and do not emit light.

这是一个重要的成就，因为相对来说,行星很小,而且也不发光。

Finding planets is proving hard enough, but finding life on them will prove infinitely more difficult.

寻找行星证明相当困难,但是要在行星上发现生命会变得无比艰难。

The first question to answer is whether a planet can actually support life.

第一个需要解答的问题是一颗行星是否有能够维持生命的条件。

In our own solar system, for example, Venus is far too hot and Mars is far too cold to support life.

举例来说,在我们的太阳系里,对于生命来说,金星的温度太高,而火星的温度则太低。

Only the Earth provides ideal conditions, and even here it has taken more than four billion years for plant and animal life to evolve.

只有地球提供了理想的条件,而即使在这里,植物和动物的进化也用了40亿年的时间。