The twenty-first century will be an age of exploration such as man has never known. There are eight planets， at least thirty moons， and thousands of asteroids to be explored①. Their total area is about 250 times that of the earth. Space-ships will not be able to land on some of them. But that still leaves to be explored an area ten times as great as the continents of the earth.
Exploring space may seem terrifying to some people. No doubt explorers of the past were terrified by the great empty oceans that lay before them. They conquered② their fears， crossed the oceans， and built the New World.
In the past when explorers set sail into the unknown， they had to say good-bye to everything they knew at home. Space explorers will not face such great loneliness. Even when they travel far beyond the sun， they will be able to send messages back.
① explorev. 探究，探索
② conquerv. 战胜，克服，征服，成功地登上
探险时代
21世纪将成为人类对向无所知的地方进行探险的时代。
可供探险的有8大行星，至少有30个月亮和数以千计的小行星，其总面积约为地球面积的250倍。宇宙飞船不能在其中的一些星球上降落。但是仍有相当于地球大陆10倍的面积可供探险。
对于某些人来说，空间探险也许很可怕。过去的探险家们无疑曾被横陈在他们面前的巨大而空漠的海洋所震慑，但他们战胜了恐惧，跨越了海洋，建立了美洲。
过去，当探险者们启航前往无人所知之处时，他们不得不与家中所熟悉的一切告别。空间探险家们将不会面临如此巨大的孤独。即使他们在远离太阳的地方旅行，他们也能够把信息发送回来。
