Space travel

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Across
  1. 3. take air into their lungs and let it out again
  2. 6. very far away
  3. 7. the layer of air or other gases around a planet
  4. 11. an extremely large group of stars and planets that extends over many billions of light years
  5. 12. the curved path in space that is followed by an object going round and round a planet, moon, or star
  6. 13. the whole of space and all the stars, planets, and other forms of matter and energy in it
Down
  1. 1. substances that help plants and animals to grow
  2. 2. the use of natural resources when this use is kept at a steady level that is not likely to damage the environment
  3. 4. a scientific test which is done in order to discover what happens to something in particular conditions
  4. 5. increase in size and change physically over a period of time
  5. 8. gradually change and develop into different forms
  6. 9. what people and animals eat
  7. 10. a being from another planet