. The journey to the moon had been the first step toward future exploration(探险) in space. The distance between the Moon and Earth is very short indeed when compared with the distances between Earth and the other planets. Mars, the nearest planet to Earth is millions of miles away. Traveling to the planets will be man’s next aim. Such travels will be more challenging than the trip to the moon and certainly more adventurous. Recently, two American spaceships, Vikings 1 and 2, landed on Mars trying to discover whether that planet has any life on it. So far the signs of life on Mars