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Which life forms are most likely to develop on a distant planet?
Recent developments in astronomy have made it possible to detect planets in
our own Milky 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 taken more than 4 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 20 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 21st century.
It is impossible to look for life on another planet using earth-based
telescopes. 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 detected 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 analyze 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 bacteria. 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 science
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 生词与短语
astronomy
n. 天文学
relative
adj. 相对的
infinitely
adv. 无限地，无穷地
solar
adj. 太阳系的
Venus
n. 金星
Mars
n. 火星
orbit
n. 运行轨道
astronomical
adj. 天文学的
generate
v. 产生
particle
n. 微粒，粒子
Jupiter
n. 木星
blot
v. 遮暗
analyse
v. 分析
bacteria
n. 细菌
oxygen
n. 氧气
realm
n. 领域
endeavour
v. 努力
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发表于 2016-7-11 23:04:28