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--- lesson 55 From the earth: Greetings |
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--- Listen to the tape then answer the question below. |
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--- Which life forms are most likely to develop on a distant planet? |
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Recent developments in astronomy have made it possible to detect planets in our own Milky Way and in other galaxies. |
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This is a major achievement because, in relative terms, planets are very small and do not emit light. |
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Finding planets is proving hard enough, but finding life on them will prove infinitely more difficult. |
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The first question to answer is whether a planet can actually support life. |
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In our own solar system, for example, Venus is far too hot and Mars is far too cold to support life. |
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Only the Earth provides ideal conditions, and even here it has taken more than four billion years for plant and animal life to evolve. |
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Whether a planet can support life depends on the size and brightness of its star, that is its 'sun'. |
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Imagine a star up to twenty times larger, brighter and hotter than our own sun. |
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A planet would have to be a very long way from it to be capable of supporting life. |
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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. |
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But how would we find such a planet? |
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At present, there is no telescope in existence that is capable of detecting the presence of life. |
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The development of such a telescope will be one of the great astronomical projects of the twenty-first century. |
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It is impossible to look for life on another planet using earth-based telescopes. |
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Our own warm atmosphere and the heat generated by the telescope would make it impossible to detect objects as small as planets. |
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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. |
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A telescope would have to be as far away as the planet Jupiter to look for life in outer space, |
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because the dust becomes thinner the further we travel towards the outer edges of our own solar system. |
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Once we detected a planet, we would have to find a way of blotting out the light from its star, |
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so that we would be able to 'see' the planet properly and analyse its atmosphere. |
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In the first instance, we would be looking for plant life, rather than 'little green men'. |
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The life forms most likely to develop on a planet would be bacteria. |
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It is bacteria that have generated the oxygen we breathe on earth. |
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For most of the earth's history they have been the only form of life on our planet. |
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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. |
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But this hope is always in the realms of science fiction. |
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If we were able to discover lowly forms of life like bacteria on another planet, it would completely change our view of ourselves. |
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As Daniel Goldin of NASA observed, 'Finding life elsewhere would change everything. |
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No human endeavor or thought would be unchanged by it.' |
