Across
- 3. A substance that flows
- 6. Natural environment
- 7. A group of two or more atoms
- 9. What's left when a meteorite hits Mars
- 12. To turn from a solid directly into a gas
- 13. The study of life on planets
- 14. The distance between two peaks of a wave
- 17. Space craft that lands
- 18. The building blocks of some human-made materials
- 19. Removing harmful gases
- 20. This layer of the atmosphere is protective
Down
- 1. Tiny planet-like body
- 2. The path Mars takes around the Sun
- 4. The force that keeps our feet on the ground
- 5. What a rocket carries
- 8. The Milky Way is one
- 10. The smallest part of an element
- 11. A small celestial body
- 15. Something that lives in an extreme environment
- 16. Indigestible part of a plant
- 19. Something that dissolves substances