Listen to the tape then answer the question below.
Which life forms are most likely to develope on a distant planet?
Recent developments in astronomy have made it possible to detect planets in our
own Millky Way and in other galaxies.This is a major achievement because, in
relative terms, planets are very small and do not emit light. Finding planets is
proving hard enough, but finding life on them will prove infinitely more difficult.The
first question to answer is whether a planet can actually support life.In our own
solar system,for example,Venus is far too hot and Mars is far too cold to support life
Only the Earth provides ideal conditions,and even here it has more than four billion
years for plant and animal life to evolve.
Whether a planet can support life depends on the size and brightness of its star,
that is its 'sun'. Imagine a star up to twenty times larger,brighter and hotter than
our own sun.A planet would have to be a very long way from it to be capable of
supporting life.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.But how would we find such a planet? At present, there is no
telescope in existence that is capable of detecting the presence of life. The development of such a telescope will be one of the great astronomical projects of the
twenty-first century.
It is impossible to look for lief on another planet using earth-based telescope. our
own warm atmosphere and the heat generated by the telescope would make it
impossible to detect objects as small as planets. 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. A telescope would have to be as far away as the
planet Jupiter to look for life in outer space, because the dust becomes thinner the
further we travel towards the outer edges of our own solar system. Once we detect a
planet, we would have to find a way of blotting out the light from its star,so that we
would be able to 'see' the planet properly and analves its atmosphere. In the first
instance , we would be looking for plant life,rather than ' little green men'.The life forms most likely to develop on a planet would be becteria. It is bacteria that have
generated the oxygen we breathe on earth. For most of the earth's history they have been the only form of life on our planet. 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. But this hope is always in the realms of scientic fiction. If
we were able to discover lowly forms of life like bacteria on another planet, it would
completely change our view of ourselves. As Daniel Goldin of NASA observed,'Finding
life elsewhere would change everything. No human endeavour or thought would be
unchanged by it.'
New words and expressions 生词和短语
astronomy n.天文学 particle n.微粒，粒子
relative adj.相对的 Jupiter n.木星
infinitely adv.无限地，无穷地 blot v.遮暗
solar adj.太阳系的 analyse v.分析
Venus n.金星 bacteria n.细菌
Mars n.火星 oxygen n.氧气
orbit n.运行轨道 realm n.领域
astronomical adj.天文学的 endeavour n.努力
generate v.产生
Notes on the text 课文注释
1、Milky Way,银河。
2、Whether a planet can support life depends on.......，一颗行星能否支持生命取决于....