From the earth: Greetings
来自地球：问候
Which life forms are most likely to develop on a distant planet?
哪些生命形式最有可能在遥远的星球上发展？
Recent developments in astronomy have made it possible to detect planets in our own Milky Way and in other galaxies.
天文学的最新发展使得在我们自己的银河系和其他星系中探测行星成为可能。
This is a major achievement because, in relative terms, planets are very small and do not emit light.
这是一项重大成就，因为相对而言，行星非常小，不发光。
Finding planets is proving hard enough, but finding life on them will prove infinitely more difficult.
寻找行星已经足够困难了，但是在它们上面找到生命将变得更加困难。
The first question to answer is whether a planet can actually support life.
首先要回答的问题是，一颗行星是否真的可以支持生命。
In our own solar system, for example, Venus is far to hot and Mars is far too cold to support life.
例如，在我们自己的太阳系中，金星远热，火星太冷，无法维持生命。
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，即使在这里，植物和动物的生命也需要超过四十亿年的时间才能进化。
Whether a planet can support life depends on the size and brightness of its star, that is its 'sun'.
一颗行星能否维持生命取决于它的恒星的大小和亮度，那就是它的"太阳"。
Imagine a star up to twenty times larger, brighter and hotter than our own sun.
想象一下，一颗比我们自己的太阳大二十倍，更亮，更热的恒星。
A planet would have to be a very long way from it to be capable of supporting life.
一颗行星必须离它有很长的路要走才能支撑生命。
Alternatively, if the star were small,
或者，如果恒星很小,
the life-supporting planet would have to have a close orbit round it and also provide the perfect conditions for life forms to develop.
维持生命的行星必须围绕它有一个紧密的轨道，并为生命形式的发展提供完美的条件。
But how would we find such a planet?
但我们如何才能找到这样一个星球呢？
At present, there is no telescope in existence that is capable of detecting the presence of life.
目前，还没有望远镜能够探测到生命的存在。
The development of such a telescope will be one of the great astronomical projects of the 21st century.
这种望远镜的开发将是21世纪伟大的天文项目之一。
It is impossible to look for life on another planet using earth-based telescopes.
使用基于地球的望远镜在另一个星球上寻找生命是不可能的。
Our own warm atmosphere and the heat generated by the telescope
我们自己温暖的大气层和望远镜产生的热量
would make it impossible to detect objects as small as planets.
这将使我们无法探测到像行星一样小的物体。
Even a telescope in orbit round the earth,
即使是绕地球轨道运行的望远镜,
like the very successful Hubble telescope,
就像非常成功的哈勃望远镜,
would not be suitable because of the dust particles in our solar system.
因为太阳系里有尘埃颗粒,所以不适合.
A telescope would have to be as far away as the planet Jupiter to look for life in outer space,
望远镜必须与木星一样远，才能在外太空寻找生命,
because the dust becomes thinner the further we travel towards the outer edges of our own solar system.
因为灰尘变得更薄，我们进一步前往我们自己的太阳系的外边缘。
Once we detected a planet,
一旦我们发现了一颗行星,
we would have to find a way of blotting out the light from its star,
我们得想办法把它的星星上的光遮住,
so that we would be able to 'see' the planet properly and analyse its atmosphere.
这样我们就能正确地"看到"这个星球并分析它的大气层。
In the first instance, we would be looking for plant life, rather than 'little green men'.
首先，我们会寻找植物生命，而不是"小绿人"。
The life forms most likely to develop on a planet would be bacteria.
最有可能在地球上发展的生命形式将是细菌。
It is bacteria that have generated the oxygen we breathe on earth.
正是细菌产生了我们在地球上呼吸的氧气。
For most of the earth's history they have been the only form of life on our planet.
在地球历史上的大部分时间里，它们一直是我们这个星球上唯一的生命形式。
As Earth-dwellers, we always cherish the hope that we will be visited by little green men
作为地球居民，我们总是珍惜希望能被小绿人访问
and that we will be able to communicate with them.
我们将能够与他们沟通。
But this hope is always in the realms of science fiction.
但这种希望总是在科幻小说的领域。
If we were able to discover lowly forms of life like bacteria on another planet,
如果我们能在另一个星球上发现卑微的生命形式，就像细菌一样,
it would completely change our view of ourselves.
这将彻底改变我们对自己的看法。
As Daniel Goldin of NASA observed,
正如美国宇航局的丹尼尔*戈丁所观察到的那样,
'Finding life elsewhere would change everything.
在别处寻找生活会改变一切。
No human endeavour or thought would be unchanged by it.'
任何人类的努力或思想都不会因此而改变。'
