英语听力：自然百科 已知的宇宙 接触外星人(3)（在线收听）

Those planets are all going to be so hot, and you can't develop something as complex as life.

那些星球都太热了，如生命这类复杂事物根本无法在那里诞生。

Scientists have gone back to the drawing board, looking to find worlds capable of supporting life, small rocky planets like earth.

科学家们重新开始了寻找，可支持生命的世界的工作，他们的目标是类似地球的小型岩石行星。

We don't know that life has to evolve on the surface of small rocket planets. But we know it did once here on earth. And so it's a reasonable place to start the search.

我们不知道生命是不是，只有在岩石行星上才能出现，但我们知道它在地球上诞生了，所以在这种地方开展搜索是很明智的。

Earth is important, because we know that this little planet had everything it needed to create life. And if a distant world has similar conditions, there's at least a possibility life could emerge there too.

地球很重要，因为我们知道，她刚好拥有一切创造生命所需的，如果一个遥远世界也有类似的条件，那么那里至少有可能也出现生命。

If you were to give a biologist a piece of paper and say write down on every line something you need for life.

如果你给生物学家一张纸，并让他列出他认为生命所需的东西。

He'll say you need energy source, you need oxygen, you need water, you need carbon, you need organic compounds, you need amino acids, you need all the stuff.

他们会说那需要能源，氧气，水，碳，有机化合物，氨基酸等等所有的一切。

There is a long list of factors that make our earth special and perfectly suited for life. But the most important is its distance from our energy source, the sun.

有一长串的东西使我们的地球与众不同并且适宜生命存在，但最重要的是地球和我们能量来源的距离—太阳。

At 93 million miles away the earth is at just the right place for water to exist as a liquid. So why is liquid water important?

离地球9300万英里远，地球所处的位置刚刚好，使得水能以液态形式存在，那么为什么液态水这么重要呢？

Imagine a world, so much hotter than the earth, there are no oceans, no liquid water all on its surface.

想象一个比地球热得多的地方，那里地表上根本没有海洋，没有液态水。

Such a place would be like a desert. Without water, there is nothing to let the grains in sand interact.

这样的地方会像一个沙漠，没有水，就没有东西可以使这些沙粒相互作用。

And in the same way without water, there is nothing to allow the atoms, the carbon and oxygen, and trace elements to form the molecules that would give rise to the chemistry of life.

同样的没有水就没有东西可以使原子，碳，氧气，和各种元素形成可产生生命的化学反应的分子。

On the other hand, on a world much colder than the earth, water can only exist as ice, and we have another problem.

但另一方面，在一个比地球冷得多的地方，水只能以冰的形式存在，这就产生了另一个问题。

This frozen block of sand has all the grains in sand locked together. They can't move around and interact.

这个冻住的沙块有许多被困住的沙粒，它们无法移动并相互作用。

Just the same way that on a frozen world, the atoms in molecules can't move around and interact to from the chemistry necessary for life.

同样在一个冰冻的世界，原子和分子无法移动或相互作用，来形成生命必须的化学反应。

But if temperatures and conditions are just right like here on earth, you get liquid water.

但如果温度和其他条件都很合适，比如在地球上就能有液态水。