【正确答案】On October, 1957, the Soviet Union successfully launched the first artificial satellite, which turned the first page in human history of entering the space. During the half century coming after, humans' explorations in outer space have grown by leaps and bounds and have made brilliant a-chievements. Humans not only successfully landed on the moon, but also reached toward even more distant planet such as Mars. At the end of 2006, the number of the various types of artificial objects flying around the Earth, including satellites, space shuttles, international space stations, space laboratories, etc. is already close to 6,000.