lecture delivered in class on 16 Feb 2011

1. Saturn

2. Orbital and Physical Properties Mass: 5.7 × 10 26 kg (97 times Earth) Radius: 60,000 km (9.5 times Earth, .8 times Jupiter) Density: 700 kg/m 3 – less than water! Rotation: rapid and differential, enough to flatten Saturn considerably Rings: very prominent; wide but extremely thin

5. Saturn’s Cloud Structure

6. Saturn’s Atmosphere Wind patterns on Saturn are similar to those on Jupiter, with zonal flow :

7. Saturn’s Atmosphere Jupiter-style “ spots ” rare on Saturn; don’t form often and quickly dissipate if they do

8. A Storm on Saturn

9. Saturn, False Color

10. Saturn’s Interior and Magnetosphere Interior structure similar to Jupiter’s:

12. Saturn’s Interior and Magnetosphere Saturn also has a strong magnetic field , but only 5% as strong as Jupiter’s Creates aurorae :

13. Saturn’s Spectacular Ring System Saturn has an extraordinarily large and complex ring system , which was visible even to the first telescopes

14. Saturn’s Spectacular Ring System Ring features visible from Earth:

15. Saturn’s rings are not in order

16. Saturn's rings change their appearance to terrestrial observers as the tilted ring plane orbits the Sun.

18. Roche Limit

19. Saturn’s Spectacular Ring System Closest distance that moon could survive is called Roche limit ; ring systems are all inside this limit

20. Saturn’s Spectacular Ring System Voyager probes showed Saturn’s rings to be much more complex than originally thought Earth is shown on the same scale as the rings

21. Saturn’s Spectacular Ring System Voyager also found radial “ spokes ” that formed and then dissipated; this probably happens frequently

22. Saturn’s Spectacular Ring System Cassini division turns out not to be completely empty: It is caused by an orbital resonance with other ring particles and Saturn’s innermost moon

23. Saturn’s Spectacular Ring System Strangest ring is outermost, F ring: It appears to have braids and kinks .

24. Saturn’s Spectacular Ring System F ring’s oddities probably caused by two shepherd moons , one of which can be seen here:

26. The Moons of Saturn Saturn’s many moons appear to be made of water ice Besides the small moons, Saturn has: Six medium-sized moons ( Mimas , Enceladus , Tethys , Dione , Rhea , and Iapetus ) One large moon ( Titan ) which is almost as large as Ganymede

28. The Moons of Saturn: Titan Titan has been known for many years to have an atmosphere thicker and denser than Earth’s; mostly nitrogen and argon Makes surface impossible to see; the picture at right was taken from only 4000 km away:

29. The Moons of Saturn: Titan Trace chemicals in Titan’s atmosphere make it chemically complex

30. The Moons of Saturn: Titan Due to difficulty of getting information, little is known about either the surface or the interior structure of Titan. This image, taken with an infrared telescope, shows some indication of surface features :

31. Cassini–Huygens Probe

33. Huygens to Titan

34. The Moons of Saturn: The Medium-Sized Moons

36. The Moons of Saturn: The Medium-Sized Moons Rhea , the largest, has a highly reflective, heavily cratered surface: Wispy features are on trailing side but not leading; origin not yet understood:

37. The Moons of Saturn: The Medium-Sized Moons Dione and Tethys are similar, having icy, heavily cratered surfaces:

38. The Moons of Saturn: The Medium-Sized Moons Mimas is the closest moon to Saturn, and has a crater covering one-third of its surface, the result of an impact that must have almost destroyed the moon: That’s no moon! Oh, no. It totally is a moon.

39. The Moons of Saturn: The Medium-Sized Moons Enceladus orbits close to Mimas, but is very shiny , indicating a surface covered with ice crystals:

40. The Moons of Saturn: The Medium-Sized Moons Iapetus is two-faced: its leading side is very dark (reflects 3% of incoming light), while its trailing side is bright (reflects 50% of incoming light). Cause is unknown.

41. Iapetus

46. The Other Side of Saturn