Saturn—God of Agriculture

1. Saturn—God of Agriculture Saturn: Son of Uranus and Gaia—After castrating his father, his 6th son, Jupiter, overthrew him and the rest of the Titans and seized power for the Olympian gods.

2. Saturn—As Seen From Earth

3. Saturn—Voyager 2 in 1981

4. Notice:

5. Internal Structure Note: ‘liquid metallic hydrogen’ on Saturn, also. How do we know that Saturn has a larger core to overall mass ratio (10%) compared to Jupiter’s (2.6%)?

6. The core to overall mass ratio is about 2.6% for Jupiter, but is much larger for Saturn … about 10%. An observation supporting this conclusion is that _____. Saturn is more massive than Jupiter and its center is more gravitationally compressed. Saturn’s ring system is more extensive than Jupiter’s Saturn is less oblate than Jupiter, even though it is more massive and rotates at approximately the same speed. Saturn is more oblate than Jupiter—but not as oblate as it would be if it had the same core to overall mass ratio as Jupiter

7. Saturn has lower atmospheric temperature than Jupiter. Saturn has lower ‘g’ so its cloud layers are more spread out.

8. Jupiter Saturn Ultraviolet image superimposed on visible image

9. SATURN’S NORTH POLE • First seen by Voyager 1980

10. Saturn’s Hexagon • 30 years later—Cassini looks at north pole after Saturn emerged from 15 years of winter. • Hexagonal ‘jet stream’ is still there!

11. Saturn from Voyager Titan Rhea Enceladus Mimas Tethys Dione

12. Orbits of Saturn’s Moons Inner, large moons Outer, captured moons Hyperion Notice inclined, elliptical orbit

13. Views of Saturn’s Rings

14. Saturn’s Ring System

15. The Cassini division is _____. an elite division of WWII Italian soldiers that fought off the German landing at Anzio a major division in the rings of Saturn that is visible from Earth the division between terrestrial and Jovian planets a gap between two mountain ranges on Saturn

16. Saturn’s Satellites and Rings

17. Saturn's Major Satellites Diameter LunarUnits NameOrbital RadiusPeriod (days) Mimas 0.12 3.08 0.9Enceladus 0.14 3.95 1.4Tethys 0.30 4.89 1.9Dione 0.32 6.26 2.7Rhea 0.44 8.75 4.5Titan 1.48 (0.75 Mars) 20.27 15.9 Hyperion328×260×214 km 24.90 21.3 Iapetus 0.42 59.08 79.3 Phoebe230×220×210 km 214.84 -545.1

18. Saturn’s Ring Structure

19. The Roche Limit ≈ 2.4 Planetary Radii

20. Planetary Rings and Roche Limit

21. A planet’s Roche limit is ______. the distance beyond which matter cannot be captured by the planet the distance within which any solid satellite (e.g., a fragment of rock) will be pulled apart by tidal forces the outer extent of the magnetic field of the planet, or the magnetospheric boundary the distance within which tidal forces will overcome the mutual gravitational forces that hold a large object together in a spherical shape and pull it apart into small, irregularly fragments held together primarily by molecular forces

22. Cassini Division and Encke Gap

23. View of Rings Away from Sun Cassini Division is not empty

24. Ring Structure

25. Rings—Natural Color Different chemical compositions?

26. Ring Spokes

27. Spokes—Close Up Spokes rotate at same rate as Saturn’s magnetic field Clouds of electrically charged dust raised from rings by magnetic forces

28. Cassini approaches Saturn

29. Cassini sees Prometheus & Pandora Prometheus and Pandora are ‘shepherd’ satellites

31. F-Ring and Prometheus Prometheus’ gravitation creates ‘drape’ in F-Ring

32. The F-Ring Shepherds Prometheus Pandora

33. Two tiny but significant satellites, Prometheus and Pandora, that follow nearly identical orbits around Saturn are called shepherd satellites because they ______. trigger volcanoes or geysers on the surfaces of larger moons by gravitational interaction. give off a sound like the ‘woof’ of a dog. when ring particles try to move past them concentrate particles in the narrow, twisted F ring of Saturn. clear out particles from the Cassini division in Saturn's rings.

34. Daphnis and the Keeler Gap in the A-Ring As Daphnis orbits, its gravity induces scalloping along the edges of the Keeler gap

35. Outer Edge of B-Ring

36. Mimas Mimas orbits Saturn in a 2:1 period resonance with particles in the Cassini Division

37. Tethys…Telesto & Calypso not shown • Size (km): • Telesto: 29 x 22 x 20 • Calypso: 30 x 23 x 14 Diameter: 1066 km

38. Orbit of Tethys, Telesto, Calypso

39. Saturn's Major Satellites Diameter LunarUnits NameOrbital RadiusPeriod (days) Mimas 0.12 3.08 0.9Enceladus 0.14 3.95 1.4Tethys 0.30 4.89 1.9Dione 0.32 6.26 2.7Rhea 0.44 8.75 4.5Titan 1.48 (0.75 Mars) 20.27 15.9 Hyperion328×260×214 km 24.90 21.3 Iapetus 0.42 59.08 79.3 Phoebe230×220×210 km 214.84 -545.1

40. Phoebe • Retrograde orbit in ecliptic plane—not in Saturn’s equatorial plane. • Primitive object similar to Pluto and Triton (ice and rock—very dark) in composition. • Ancient planetesimalwhich accreted into cores of Jovian planets—most were ‘thrown’ intoKuiper belt.

41. Iapetus • Very dark, reddish ‘leading’ side • Might be a thin layer of organic material similar to complex substances found in primitive meteorites. • Dark material might have originated from Phoebe. Micrometeor impacts could kick dark matter off Phoebe which is then swept up by Iapetus.

42. Iapetus’ Equatorial Ridge But…the dark material seems to be concentrated in crater floors— indicates an internal origin. Iapetus is far from Saturn — might have formed with methane or ammonia ice in its interior. Dark material explained by eruptions of methane from its interior? Such rings formed on Moon and Mars when dark volcanic material flowed into impact craters and filled around the central peak. Hypothesis supported by a dark ring of material about 100 kilometers (62 miles) in diameter that straddles the border between the leading and trailing hemispheres of Iapetus.

43. Chaotic Hyperion • Heavily cratered, spongy-like reddish surface • Largest, irregularly-shaped satellite • Tumbles chaotically in eccentric orbit

44. Enceladus Orbits in E-Ring

45. Enceladus The geologically youthful terrains came as a great surprise to the scientific community, because no theory was then able to predict that such a small and cold moon compared to Jupiter's highly active moon Io) could exhibit signs of such activity.

46. Enceladus Enceladus’ Surface • Almost 100% reflective • Geological resurfacing—liquid interior? • Areas where no craters

47. Ejection from Enceladus

48. Plume Vent Model

50. Some astronomers suspect that Saturn's satellite Enceladus is heated enough by tidal flexing, which produces active geysers of water imaged by the Cassini spacecraft flyby. This is similar to the mechanism that causes Io’s ‘volcanoes.’ Which one of the following observations supports this conjecture? Enceladus orbits within Saturn’s faint E ring, which lies outside Saturn’s Roche limit and might be made up of ice particles ejected from the geysers. Enceladus is a “shepherd satellite” for Saturn’s braided F ring, which could be made up of ice particles from the geysers. A strong electric current flows from Enceladus to Saturn along Saturn's magnetic lines of force. Enceladus lies within Saturn’s Roche limit and is in the process of breaking up.