Our Solar System

1. the planet that is often called Earth's twin.
3. An imaginary straight line that runs from the North Pole to the South Pole.
6. the smallest planet in our solar system.
10. the planet known as the Red Planet.
11. the planet that is almost the same size as Uranus.
13. The spin of a body on its axis.
15. the only planet in the solar system that has the combination of factors needed to support life.
17. The motion of a body that travels around another body in space; one complete trip along an orbit.
19. The average distance between Earth and the sun.
20. a flattened circle in the solar system is also called an ________________.

2. the planetary ring that circles this planet's equator is its most spectacular feature.
4. The sun and all of the planets and other bodies that travel around it.
5. A force of attraction between objects that is due to their masses.
7. A disk of matter that encircles a planet that consists of numerous particles in orbit, which range in size from dust grains up to objects tens of meters across.
8. the atmosphere of this planet is composed mostly of hydrogen and helium.
9. The highly dense planets nearest to the sun; Mercury, Venus, Earth, and Mars.
12. A mixture of gases that surrounds a planet, moon, or other celestial body.
14. The path that a body follows as it travels around another body in space.
16. The planets that have deep, massive atmosphere, such as Jupiter, Saturn, Uranus, and Neptune.
18. the planet that has the most moons orbiting around it.