Alien crossword by Wojciech Sondej & Bach Thomas Tran

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Across
  1. 5. between stars
  2. 8. antonym to contaminate
  3. 9. very advanced, complex
  4. 10. existing since the beginning of the universe
Down
  1. 1. (people) who prefer staying at home rather than going out
  2. 2. proposed idea to state sth not yet proven
  3. 3. creatures from outside the Earth
  4. 4. happening after sth else (adverb)
  5. 6. related to the study of stars and other objects in space using physical laws
  6. 7. deserted, empty, uninhabited