Across
- 3. a comet or asteroid whose path intersects the orbit of Earth
- 8. dark, smooth looking portions covering 17% or the moon
- 11. “shooting star”
- 12. intermediate step between tiny grains and larger planetary objects
- 15. the lighter, heavily cratered regions of the moon
- 18. extraterrestrial rock
- 19. the region of the solar system between the orbits of mars and Jupiter
- 20. source for short-period comets
- 22. Description of planets without rocky surfaces Jupiter, Saturn, Uranus, Neptune
- 23. the solid chunk of ice and dust in the head of a comet
- 24. dust and ion points away from sun
- 25. the large spherical region around the Sun from which most “new” comets come
Down
- 1. an asteroid whose orbit could bring it on a collision course with Earth
- 2. Material that is forced or thrown out
- 4. orbits the sun and is smaller than a planet bigger than a meteor with no head or tail
- 5. extinction level event
- 6. gravitational separation of materials of different density into layers in the interior of a planet or moon
- 7. time required for half the radioactive atoms to decay
- 8. produced when Earth passes through a cometary dust stream
- 9. Plural of mare
- 10. the cloud of gas and dust from which the solar system formed
- 13. the gradual accumulation of mass
- 14. dirty snowball
- 16. the sudden disappearance in the fossil record of a large number of species
- 17. Description of planets with a rocky surface: Mercury, Venus, Earth or Mars
- 21. bright streaks starting from a crater and extending away for great distances