Across
- 4. the collection of eight planets and their moons in orbit around the sun, together with smaller bodies in the form of asteroids, meteoroids, and comets.
- 8. a portion of a meteor that survives passage through an atmosphere and strikes the ground
- 10. the "red" planet and farthest of the terrestrial planets from the sun
- 11. measure of the deformity of a solid object from a perfect spherical shape
- 17. a small body of icy and dusty matter that revolves about the Sun; when a comet comes near the Sun, some of its material vaporizes, forming a large head of tenuous gas and often a tail
- 18. only planet known to have life
- 19. planet any of the planets Mercury, Venus, Earth, or Mars; sometimes the Moon is included in the list
- 20. gravitational separation of materials of different density into layers in the interior of a planet or moon
Down
- 1. any of the planets Jupiter, Saturn, Uranus, and Neptune in our solar system, or planets of roughly that mass and composition in other planetary systems
- 2. objects, from tens to hundreds of kilometers in diameter, that formed in the solar nebula as an intermediate step between tiny grains and the larger planetary
- 3. the cloud of gas and dust from which the solar system formed
- 5. first planet from the sun
- 6. largest of all the planets
- 7. time required for half of the radioactive atoms in a sample to disintegrate
- 9. process by which certain kinds of atomic nuclei decay naturally, with the spontaneous emission of subatomic particles and gamma rays
- 12. farthest planet from the sun and also a gas giant
- 13. a stony or metallic object orbiting the Sun that is smaller than a planet but that shows no evidence of an atmosphere or of other types of activity associated with comets
- 14. we see today; the comets and some asteroids may be leftover planetesimals
- 15. measure of the shape of an orbit. Lower values are circular where larger numbers are more oval
- 16. a small piece of solid matter that enters Earth’s atmosphere and burns up, popularly called a shooting star because it is seen as a small flash of light
