在太阳系中,除地球以外,无论哪一个天体上都还没有发现有生命存在的迹象,因为它们不是太热,就是太冷,再不然,就是缺少生命存在所必需的各种条件。尽管其他星球的物理化学环境对地球上的生命来说,是过于严酷了,但航宇事业的成就以及地球上存在许许多多的实际困难,则要求人类寻找一个新的、更广阔的生活场所。当然,这许许多多的困难, In the solar system, there is no sign of existence on any celestial body except Earth because they are neither too hot nor too cold, or else they lack the necessary conditions for the existence of life. Although the physical and chemical environment of other planets is too harsh for life on Earth, the achievements of the aerospace industry and the many practical difficulties on Earth require mankind to find a new and broader place to live . Of course, this many and many difficulties,