Astronomy Puzzle

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Across
  1. 5. Planet similar in size to Venus
  2. 6. 99.8% of mass of our solar system
  3. 7. Burning balls of gas
  4. 9. Closest planet to the sun
Down
  1. 1. Planetesimals that formed orbits around planets
  2. 2. The hottest planet
  3. 3. Force that holds our solar system together
  4. 4. Gives Mars it's "reddish" color
  5. 8. First four planets are the inner _____ planets