It is one thing to land science instruments on Mars;however,it is quite 1_
another to establish a basc for humans to explore planet.Daytime temeratures 2_
can be rise above freezing,but,because of the extremely thin atmosphere, 3_
the sun heat rediates back into space.Even at the equator,the temerature 4_
drops 50℃ at night.In fact,there is no ozone layer to keep out 5_
ultraviolet radiation,and hardly some oxygen for either breathing 6_
and burning conventional fuels.But despit all these problems,scientists are 7_
currently working transport and clothing for Mars and artificial environment 8_
in which colonists could live.However,the potential cost make the ides of 9_
human life on Mars nothing othore then a fantastic dream.10_
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