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So far space scientists have discovered about seventy planets outside the solar system,
據認為，外層空間有10億億億顆行星。
out of the ten billion trillion or so that are thought to be out there, so humans can hardly claim to speak with authority on the matter,
迄今為止，太空科學家已經在太陽系之外發現了其中的70顆左右，因此人類在這個問題上幾乎無話可說。
but it appears that if you wish to have a planet suitable for life, you have to be just awfully lucky,
但是，看來，若要找到顆適合于生命的行星，你非得運氣極好；
and the more advanced the life, the luckier you have to be.
若想找到顆適合與高級生命的行星，你非得福星高照。
Various observers have identified about two dozen particularly helpful breaks we have had on Earth,
各方面的研究人員已經確認，我們地球上享有20來條特別值得慶幸的機緣，
but this is a flying survey so we'll distill them down to the principal four. They are:
但本書不作深入研究，因此僅將其歸納成以下的主要4條：
Excellent location. We are, to an almost uncanny degree, the right distance from the right sort of star,
優越的位置。我們有個合適的恒星，與這個恒星相隔合適的距離，
one that is big enough to radiate lots of energy, but not so big as to burn itself out swiftly.
這個恒星大得足以輻射大量熱量，又不是大得很快自燃殆盡。這一切都異乎尋常地恰到好處。
It is a curiosity of physics that the larger a star the more rapidly it burns.
恒星越大，燃燒的越快，這是一種有趣的物理現象。
Had our sun been ten times as massive, it would have exhausted itself after ten million years instead of ten billion and we wouldn't be here now.
假如我們的太陽是現在的10倍之大，它會在1 000萬年之后，而不是在100億年之后消耗干凈，我們現在就不會在這里。
We are also fortunate to orbit where we do.
還很幸運的是，我們在現在的軌道上運行。
Too much nearer and everything on Earth would have boiled away.
離太陽太近，地球上的一切都會化為蒸汽；
Too much farther away and everything would have frozen.
離太陽太遠，一切都會結成冰塊。
In 1978, an astrophysicist named Michael Hart made some calculations
1978年，天體物理學家邁克爾·哈特做了一些測算后得出結論，
and concluded that Earth would have been uninhabitable had it been just 1 percent farther from or 5 percent closer to the Sun.
只要地球離太陽再遠1%，或再近5%，地球就不適于居住。
That's not much, and in fact it wasn't enough.
幅度不算很大，其實還可以再大一點。
