inner planets

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Across
  1. 2. second planet
  2. 3. like earth in some ways
  3. 5. gases that surround the planet
  4. 7. celestial object that moves around a planet
  5. 8. most dense of them all
  6. 9. moved repeatedly around
Down
  1. 1. smaller planets with shorter orbit
  2. 4. made of rocky cores and dense
  3. 6. red planet
  4. 7. keeps thing simple