《新版新概念英语第三册(英音)Lesson (55)》歌词

[00:00:01] --- lesson 55 from the earth: greetings

[00:00:07] --- listen to the tape then answer the question below.

[00:00:13] --- which life forms are most likely to develop on a distant planet?

[00:00:20] recent developments in astronomy have made it possible to detect planets in our own milky way and in other galaxies.

[00:00:28] this is a major achievement because, in relative terms, planets are very small and do not emit light.

[00:00:37] finding planets is proving hard enough, but finding life on them will prove infinitely more difficult.

[00:00:44] the first question to answer is whether a planet can actually support life.

[00:00:50] in our own solar system, for example, venus is far too hot and mars is far too cold to support life.

[00:01:00] only the earth provides ideal conditions, and even here it has taken more than four billion years for plant and animal life to evolve.

[00:01:10] whether a planet can support life depends on the size and brightness of its star, that is its 'sun'.

[00:01:19] imagine a star up to twenty times larger, brighter and hotter than our own sun.

[00:01:26] a planet would have to be a very long way from it to be capable of supporting life.

[00:01:32] alternatively, if the star were small, the life-supporting planet would have to have a close orbit round it and also provide the perfect conditions for life forms to develop.

[00:01:43] but how would we find such a planet?

[00:01:47] at present, there is no telescope in existence that is capable of detecting the presence of life.

[00:01:53] the development of such a telescope will be one of the great astronomical projects of the twenty-first century.

[00:02:01] it is impossible to look for life on another planet using earth-based telescopes.

[00:02:06] our own warm atmosphere and the heat generated by the telescope would make it impossible to detect objects as small as planets.

[00:02:16] even a telescope in orbit round the earth, like the very successful hubble telescope, would not be suitable because of the dust particles in our solar system.

[00:02:27] a telescope would have to be as far away as the planet jupiter to look for life in outer space,

[00:02:34] because the dust becomes thinner the further we travel towards the outer edges of our own solar system.

[00:02:41] once we detected a planet, we would have to find a way of blotting out the light from its star,

[00:02:47] so that we would be able to 'see' the planet properly and analyse its atmosphere.

[00:02:52] in the first instance, we would be looking for plant life, rather than 'little green men'.

[00:02:59] the life forms most likely to develop on a planet would be bacteria.

[00:03:04] it is bacteria that have generated the oxygen we breathe on earth.

[00:03:09] for most of the earth's history they have been the only form of life on our planet.

[00:03:15] as earth-dwellers, we always cherish the hope that we will be visited by little green men and that we will be able to communicate with them.

[00:03:25] but this hope is always in the realms of science fiction.

[00:03:29] if we were able to discover lowly forms of life like bacteria on another planet, it would completely change our view of ourselves.

[00:03:38] as daniel goldin of nasa observed, 'finding life elsewhere would change everything.

[00:03:45] no human endeavor or thought would be unchanged by it.'