The universe is really mystical(神秘的）.Scientists have done lots of study about it but there is still much they haven't discovered.
Scientists think that there1life on the earth for hundreds of millions of years. However, we have not found life on any other planets2.
There are eight planets going around the sun. The earth is one of them. There are humans, animals, and many other kinds of life on the earth. There is water and air, too. And compared to other planets, the earth is not too3or too cold. None of seven other planets has an environment like that of the earth.
The sun and its planets are called the solar system, and our solar system is a small part of a4larger group of stars and planets, called the Galaxy or the Milky Way. There are5stars in the Galaxy, and our sun is only one of them.
Scientists have also discovered many other galaxy in the universe. They are very far away and their light has to travel for many years to reach us. So 6is the universe? It is impossible to imagine.
Scientists have sent spaceships to the planet Mars to7photos. They have even sent spaceships to travel outside 8 .However, no spaceship has traveled9to reach other stars in our Galaxy.
When we see stars twinkling(闪耀）in the sky at night, we may think a lot:10so many stars in the universe, are we alone, or is there life out there in space? Have there been visitors to the earth from other planets? Why has no one communicated with us? We do not know the answer...
