2. IQ We now know of how many planets? A. 5 B. 9 C. 8 D. more than 100

3. IQ That’s right! D. is the correct answer! We now know of about 100 planets, most of which orbit other stars! This panel shows that most of the extrasolar planets are massive (like Jupiter) and orbit closer to their star than the Earth orbits the Sun (1 AU).

5. IQ The two major classes of planets are terrestrial (Earth-like), and lunar (Moon-like). True False

6. IQ False. The two major classes of planets are terrestrial (Earth- like) and gas giants, or Jovian (Jupiter-like). What are the major differences?

7. IQ All of the planets formed from the same material that formed the Sun. T F

8. IQ T. is the correct answer. The planets formed from a disk of material that surrounded the proto-Sun. This same mechanism is seen in other, newly-forming stars

9. IQ The terrestrial planets are rocky, because they are close to the sun, warmer, and therefore the gases constituting the Jovian planets “boiled away.” T F

10. IQ T. The statement is true. The vast majority of the gases (hydrogen, helium, and others) that constitute the Jovian planets has evaporated from the terrestrial planets because of the Sun’s heat.