Scientists think that there has been life on the earth for millions 【小题1】 years. However, we 【小题2】 found life on any other planets yet. The earth is a planet and it goes around the sun. And there are seven other planets that also go around the sun. The sun and 【小题3】 planets are called the solar system. The solar system is a small part of the universe.

Scientists has launched many spaceships to explore other planets in the solar system.Some spaceships have gone beyond the solar system. However, no one has discovered any life in space 【小题4】.

Why has no one from other planets sent us a message? Have they tried 【小题5】 send information to us? With so many stars in space, are we alone, or is there life on other planets in space?