发布时间：2016-03-30 来源：中学网校 发布人：tusya
Scientists think that there has been life on Earth for millions of year. However, we haven’t found life on other planets yet. Because none of them has an environment with air, people and things can’t grow.
The Earth is a planet and it goes around the sun. The sun and its planets are called the solar system. It's a small part of our galaxy.
Scientists have sent lots of spacecraft to look at other planets in our solar system, and some spacecraft have gone beyond it. However, no one has discovered any life in space yet.