绝知此事要躬行

In the early part of the last century, speculation about ilfe life on Mars was more florid, particularly by the American astronaut astronomer Percival Lowell. Through his telescope in Arizona, Lowell convinced himself he saw swaths sways of vegetation come and go with the seasons. Of course, he didn't. What he really saw was shifted were shifting areas of sand dunes. But he also believed he'd found evidence of an advanced civilizationcivilisation.

" The canals are of various lengthlengths. Some stretch 2,500 miles from end to end. We are looking upon the results result of the world of some sort of intelligent beings.

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Lowell's canals were just an optical illusion. , the results result of the imperfect image in his telescope and his over-excited imagination.

We got a better feeling for Mars as a life-friendly or unfriendly world. , when the first space probes visited in the 1960s and 70s, . It had a really thin atmosphere, and therefore hardly any shielding against radiation coming from space. It was a desert world with no liquid water on the surface, let alone canals.

But there was evidence that water had in the distant past, float in great volumes, and that it might still be there as ice undergroundunder ground. So even in 1972, scientists like NASA's Gerald Soffen entertained the possibility of quite fancy organisms alive on the surface today.

• Words worth to be remembered:
  • speculation [,spekjʊ'leɪʃn]: n. 推测；eg:Every induction is a speculation. 所有归纳推理都是一种猜测。
  • florid ['flɒrɪd] adj. 绚丽的 eg: The senator gave a florid speech.议员作了一番词藻华美的演说。
  • dune [djuːn] n. （由风吹积而成的）沙丘 eg: Large dunes make access to the beach difficult in places. 在有些地方大沙丘使得靠近海滩很难。

譯文

上个世纪初期，对于火星上存在生命这样的猜测有点言过其词，尤其是美国天文学家帕西瓦尔·罗威尔的猜测。通过他在亚利桑那州的望远镜，他确信自己看到了植物随着季节的变化而变化。显然，他并没有看到什么植物。他真正看到的其实是随风移动的沙丘。但是他相信自己找到了火星上存在先进文明的证据。

“火星上有不同长度的运河。有些绵延2500英里。我们把这看作是火星世界里存在某种智慧生命才有的结果。”

罗威尔所说的运河只不过是视觉幻影，因为望远镜里的影像并不完整，还有他的过度兴奋导致了空想。

在20世纪60年代到70年代，当第一批太空探测器着陆火星，对于火星能否适合生存我们有了更好的了解。它的大气层很薄，因此几乎不能屏蔽来自太空的辐射。它的地表没有水，是一片荒漠，更不要说有运河了。

但是有证据显示在遥远的过去，火星上有过水的存在，有过大量水的流动，也许这些水还以冰的形式存在地下。所以甚至在1972年，像NASA的杰拉德索芬这样的科学家们都认为如今在火星表面还有相当奇特的生命体存在的可能。