1. Saturn’s Satellites

3. Discussion What does the density of Saturn’s satellites tell you about their composition?

4. Discussion Why don’t the satellites of Saturn show a density gradient like the Galilean satellites of Jupiter?

5. Epimetheus

7. Janus

8. Mimas

10. Enceladus

14. Enceladus backlit

16. South pole composite image

17. Heat map of South pole region

18. Geysers

20. Tethys

21. Telesto & Calypso

23. Dione

24. Helene

25. Rhea

26. Titan

27. Hyperion

28. Iapetus

29. Leading side

30. Trailing side

31. Discussion Can you think of a reason why one side of Iapetus should be so much brighter than the other?

32. Tenuous ring near Phoebe

34. Equatorial ridge

35. 10 km high equatorial mountain

37. Phoebe

38. Titan

39. Methane absorption lines Reflected light spectrum from Titan

40. Discussion How can Titan have an atmosphere, whereas the more massive Mercury does not?

41. Voyager 1 Composition: 90% nitrogen – 1.5 atm With trace amounts of methane (CH 4 ), argon, hydrogen, carbon monoxide, ethane (C 2 H 6 ), acetylene (C 2 H 2 ), propane (C 2 H 8 ), hydrogen cyanide (HCN).

42. Discussion Why does Titan have hydrogen in its atmosphere? I thought hydrogen couldn’t be held by anything less massive than a Jovian sized planet.

43. Discussion With all the flammable gasses in Titan’s atmosphere why doesn’t the satellite explode?

44. Why does Titan still have methane in its atmosphere? At the present rate of destruction, all of the methane now in Titan’s atmosphere should be gone in a few million years. Thus, there must be some source of methane such as comets, volcanoes, or underground springs.

45. Discussion Why is there no carbon dioxide in Titan’s atmosphere? Hint: surface temperature on Titan is -180 C

46. Discussion Why doesn’t Ganymede have an atmosphere? Escape velocity 2.7 km/s Surface temperature 110 K about the same as on Titan

49. Discussion Why does the atmosphere around Titan appear blue?

50. The aerosols cannot stay suspended forever As the polymers grow longer they will precipitate out of the atmosphere and onto the surface. Titan may have bodies of liquid ethane on its surface.

52. Huygens probe

56. Earth Sand dunes Titan Frozen ethane dunes?

57. Ice Giants

58. Discussion Both Uranus and Neptune have about the same size, 4 times the radius of the Earth, but Neptune has more mass than Uranus, 17.2 M e and 14.5 M e respectively. What does this tell you about Neptune?

59. Atmospheres Both planets have about the same atmospheric composition: UranusNeptune Hydrogen82.5%80% Helium15.2%19% Methane2.3%2% And the same temperature at their cloud tops -360 F or 55 K.

60. Discussion How can Uranus and Neptune both have the same temperature, when Neptune is much farther from the Sun?

61. Differences Neptune is denser and has a significant internal heat source while Uranus does not. Neptune’s atmosphere has belts, storms and high clouds, while Uranus’s atmosphere is bland and featureless.

63. Uranus

64. Neptune

67. Discussion The blue/green color of Uranus and Neptune are caused by methane. What do you think happens when ultraviolet light breaks up this methane?

68. Discussion Why is Uranus’s atmosphere so plain compared to Neptune’s?

69. Uranus

70. Discussion How do you think we got the previous plot of the density profile of Uranus’s atmosphere?

71. Uranus and the seasons

73. Uranus false color

74. Uranus HST infrared image

76. Neptune HST infrared image