1. Helium rain lower temperatures of Saturn's interior allow helium to come out of solution with hydrogen and form droplets, these droplets fall toward the center of Saturn depleting the outer layers of helium and producing the excess heat that is radiated by Saturn.

2. Tidal stability limit the distance from a planet within which a moon will be torn apart by the gravitational pull, believed to be the cause of the rings of the Jovian planets, also called the Roche limit.

3. Roche limit --the distance from a planet within which a moon will be torn apart by the gravitational pull, believed to be the cause of the rings of the Jovian planets, also called the tidal stability limit.

4. ringlets smaller rings that actually make the ring structure of Saturn, discovered by the Voyager spacecraft, numbering in the tens of thousands.

5. Ring gaps areas of very little or no ring material between the rings

6. moonlets small moons that scoop up ring material as the moon moves through its orbit leaving a gap in its wake

7. resonance repeated gravitational pull in certain areas of the ring by small moons (Mimas, for example) that produces gaps in the rings

8. shepherd satellites -the two small moons which keep the F-ring in place, Prometheus and Pandora

9. spokes dark lines extending outward through the rings, caused by small particles suspended above the plane of the rings

10. Titan largest moon of Saturn, has an atmosphere

11. Odysseus huge impact crater on Tethys

12. wispy terrain prominent, light-colored streaks on trailing face of Rhea

13. Cassini regio dark area on leading face of Iapetus

14. F-ring thin, braid-like ring held in place by shepherd satellites

15. coorbital satellites Janus and Epimethius, have the same orbit, one slightly closer to Saturn than the other; every 4 Earth years they switch places

16. LaGrange points points where smaller moons accompany larger moons in their orbits, 60 degree angles to the larger moon

17. chaotic rotation orbit of Hyperion, because of gravitational pull of Saturn and Titan the orbit is not circular; moon constantly changes rotational speed and and axis

1. Why is Saturn's polar radius shorter than its equatorial radius? Saturn has a low density and a high rotation rate. This causes Saturn to be flattened. The term for this is oblateness.

2. Which two elements make up most of Saturn? How does this compare to Jupiter? Hydrogen and Helium, same as Jupiter.

3. Why is Saturn's surface appearance so much more uniform than Jupiter's? Saturn's weaker gravity results in a thicker atmosphere, so holes in the upper atmosphere don't show the lower darker layers as on Jupiter.

4. What is similar about all the Jovian planets? They are all gas giants, and they all have rings.

5. What is the tidal stability limit (Roche limit)? The distance from a planet within which a moon will be torn apart by the gravitational pull of the planet.

6. List two ways Saturn's moons affect Saturn's rings. Some moons sweep through the rings plowing out gaps. Other moons produce gaps due to gravitational pull on the rings.

7. What are shepherd satellites? Two moons (Prometheus and Pandora) that form the "braided" F-ring.

8. How many rings are there? Tens of thousands of narrow ringlets.

9. What is unique about Titan, Saturn's largest moon? It has an atmosphere.

10. List Saturn's medium sized moons. Mimas Enceladus Tethys Dione Rhea Iapetus

11. What is unique about the orbits of Hyperion and Phoebe? Hyperion has a chaotic orbit because of Titan's gravity, constantly changing its rotation speed and axis. Phoebe is Saturn's only moon with a retrograde orbit.

12. Describe the orbits of Janus and Epimethius. They are coorbital satellites. One is slightly closer to the planet, so it orbits slightly faster. When the inner moon "laps" the outer one, they switch places.