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So far space scientists have discovered about seventy planets outside the solar system,
据认为，外层空间有10亿亿亿颗行星。
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,
迄今为止，太空科学家已经在太阳系之外发现了其中的70颗左右，因此人类在这个问题上几乎无话可说。
but it appears that if you wish to have a planet suitable for life, you have to be just awfully lucky,
但是，看来，若要找到颗适合于生命的行星，你非得运气极好；
and the more advanced the life, the luckier you have to be.
若想找到颗适合与高级生命的行星，你非得福星高照。
Various observers have identified about two dozen particularly helpful breaks we have had on Earth,
各方面的研究人员已经确认，我们地球上享有20来条特别值得庆幸的机缘，
but this is a flying survey so we'll distill them down to the principal four. They are:
但本书不作深入研究，因此仅将其归纳成以下的主要4条：
Excellent location. We are, to an almost uncanny degree, the right distance from the right sort of star,
优越的位置。我们有个合适的恒星，与这个恒星相隔合适的距离，
one that is big enough to radiate lots of energy, but not so big as to burn itself out swiftly.
这个恒星大得足以辐射大量热量，又不是大得很快自燃殆尽。这一切都异乎寻常地恰到好处。
It is a curiosity of physics that the larger a star the more rapidly it burns.
恒星越大，燃烧的越快，这是一种有趣的物理现象。
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.
假如我们的太阳是现在的10倍之大，它会在1 000万年之后，而不是在100亿年之后消耗干净，我们现在就不会在这里。
We are also fortunate to orbit where we do.
还很幸运的是，我们在现在的轨道上运行。
Too much nearer and everything on Earth would have boiled away.
离太阳太近，地球上的一切都会化为蒸汽；
Too much farther away and everything would have frozen.
离太阳太远，一切都会结成冰块。
In 1978, an astrophysicist named Michael Hart made some calculations
1978年，天体物理学家迈克尔·哈特做了一些测算后得出结论，
and concluded that Earth would have been uninhabitable had it been just 1 percent farther from or 5 percent closer to the Sun.
只要地球离太阳再远1%，或再近5%，地球就不适于居住。
That's not much, and in fact it wasn't enough.
幅度不算很大，其实还可以再大一点。
