2 Complete the sentences. ► There are billions of stars in the universe . 1 Is it important to send rockets into ____? 2 The earth revolves around the sun: in other , earth is a planet in our solar system. 3 The Venus Express rocket took ____ five months to ____ the planet Venus. 4 The idea of human life on Mars is far-____. 5 We have ____ a lot of knowledge about the solar system in recent years. 6 The earth ____ around the sun every 365 days. 7 My ____ of space is very limited. I'd like to learn more about it. 8 The moon is a ____ of the earth.