Out of This World Crossword for Astrophysicists

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Across
  1. 2. A space devoid of all matter
  2. 4. This orbits the Earth
  3. 7. The largest planet in our solar system
  4. 9. Aliens from Mars
  5. 11. Jean-Luc Picard's spaceship
  6. 13. The earth tilts on its --
  7. 15. A giant cloud of gas and dust in space
  8. 16. The scientific study of the stars
  9. 17. What ET wanted to do
  10. 18. A space rock that enters our atmosphere
Down
  1. 1. What was the ninth planet
  2. 3. Surname of the first person on the moon
  3. 5. The Earth orbits this
  4. 6. An earthling travelling in space
  5. 8. Device for examining far away objects in space
  6. 10. The closest planet to Earth
  7. 12. A pattern of stars that make a shape
  8. 14. First name of the person responsible for removing the ninth planet