1			2			3
											4
										5
								6
															7
						8				9
	10					11
																			12
13											14			15
			16											17
				18
														19
			20
													21

Across 1. Any of numerous small, often irregularly shaped rocky bodies that orbit the Sun, primarily in the belt between Mars and Jupiter. 4. For a period of 20 years out of every 248, Pluto's highly elliptical orbit crosses within that of this planet, makin git the farthest planet from the Sun. 6. Planet closest to the sun. 7. Reddish planet that is the last of the terrestrial planets. 9. The hottest planet in the Solar System, due to the greenhouse effect. 11. The distance that light travels in a vaccum in one year. 13. An extremely dense celestial object whose gravitational field is so strong, that not even light can escape from its vicinity. 15. A small piece of rock or metal that has entered the Earth's atmoshpere from space. 16. The planets Mars, Jupiter, Saturn, Uranus, and Neptune. 18. A celestial body that orbits a planet. 19. A cloud layer of frozen methane gives this planet a faint bluish-green color. 20. Was discovered that the planets did not orbit in circles, but ____. 21. Planet encircled by a large, flat system of rings made up of rock fragments and tiny ice crystals.

Down 2. The only planet yet discovered with a viable atmosphere. 3. The planets Mercury and Venus. 5. The natural force of attraction exerted by a celestial body upon objects at or near its surface, tending to draw them towards the center of the body. 8. Relating to a model of the Solar System or universe having the Sun as the center. 10. The partial or complete obscuring of one celestial body by another. 12. The path of a celestial body or an artificial satellite as it revolves around another body. 14. The largest planet in the Solar System. 17. A visible, thinly spread cloud of interstellar gas and dust.