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reach, be, go, find, not know, discover, think, call, have, communicate, keep |
Scientists think that there has been life on the earth for hundreds of millions of years. However, we haven'tlife on any other planets yet.
The earth is a planet and itaround the sun. Seven other planets also go around the sun. None of them has an environment like that of the earth, so scientists do not they will find life on them. The sun and its planets are called the solar system, and our solar system is a small part of a much larger group of stars and planets, the Galaxy or the Milky Way. There billions of stars in the Galaxy, and our sun is only one of them.
Scientists many other galaxies in the universe already. They are very far away and their light to travel for many years to reach us. So how large is the universe? It is impossible to imagine.
Scientists have sent spaceships to the planet Mars to take photos. They have even sent spaceships to travel outside the solar system. However, no spaceship has travelled far enoughother stars in our Galaxy. Scientists have always asked the questions: With so many stars in the universe, are we alone or is there life in space? Have there been visitors to the earth from other planets? Why has no one with us? We the answers yet.
