1. Chapter 18 Inner and Outer Planets

2. universe All of space and everything in it

3. galaxy A system of dust, gas, and many millions of stars held together by gravity

4. astronomy The study of the Sun, Moon, stars, and other objects in space

5. solar system Includes the Sun, the planets, their moons, and other objects

6. craters Dents shaped like bowls that are made when meteorites crash into a surface

7. space probe A vehicle that carries cameras and other tools for studying different objects in space

8. satellite An object that orbits another object in space