4s

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Across
  1. 4. - Bright celestial object in the sky (4 letters, four)
  2. 5. - Celestial object with a tail of gas and dust (5 letters, five)
  3. 6. - Extraterrestrial being (5 letters, five)
  4. 8. - Relating to the sun (5 letters, five)
  5. 9. - Red planet in our solar system (4 letters, four)
  6. 11. - Center of our solar system (3 letters, three)
  7. 13. - Celestial body orbiting a star (6 letters, six)
Down
  1. 1. - Vast expanse beyond Earth's atmosphere (5 letters, five)
  2. 2. - Small rocky body orbiting the sun (8 letters, eight)
  3. 3. - Massive system of stars and other matter (6 letters, six)
  4. 5. - Universe as a whole (6 letters, six)
  5. 7. - American space agency (4 letters, four)
  6. 9. - Earth's natural satellite (4 letters, four)
  7. 10. - Vehicle for space travel (6 letters, six)
  8. 12. - Cloud of gas and dust in space (6 letters, six)