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Saturn’s Moons

Saturn’s Moons. Lecture 24. Saturn’s Moons. 62 Moons, 53 named (18 above). Mostly icy, some with rocky cores. Titan is the 2 nd largest moon in our Solar System & only one with a “real” atmosphere with N 2 , CH 4 , CO 2 (1.5 bar!) 98% of N 2 : (N 2 =77% at Earth) No appreciable O 2.

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Saturn’s Moons

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  1. Saturn’s Moons Lecture 24

  2. Saturn’s Moons • 62 Moons, 53 named (18 above). Mostly icy, some with rocky cores. • Titan is the 2nd largest moon in our Solar System & only one with a “real” atmosphere with N2, CH4, CO2 (1.5 bar!) • 98% of N2 : (N2=77% at Earth) • No appreciable O2

  3. Titan, the Masked! sunlight 1/100 of Earth -180°C A lot of organic molecules CH4, C2H2, C2H6, C3H8, …, argon, CO2, etc. Always covered with thick haze/smog Cassini/Huygens in 2004+ Voyager 2 image of Titan

  4. Cassini + Huygens (2004- )

  5. Titan’s landscape from Huygens descending image… looks like a dry streambed! Water ice as rocks…

  6. Interior of Titan Satellite gravity measurement… Similar to Callisto, Titan’s interior is not differentiated! It has a subsurface ocean at very low temperature  mixture of water and ammonia Controversial… : some believe that it should have a rocky core + icy mantle… A lot of NH3 !

  7. Titan’s Atmosphere • Multi-layer of haze • Titan once was believed to be the largest moon in the solar system because of its extended haze layer (~200 km). • Titan’s solid surface is only 60km smaller than Ganymede… • NH3 + CH4 + solar UV photons organic molecules… • Drizzle of methane and ethane. Possible lakes/oceans of methane

  8. Liquid Flow Methane river  A feature most likely formed by a liquid methane flow. Taken by Huygens probe. Theoretical models predict that a single methane rainstorm can produce several inches of rain…

  9. Methane World Cassini pictures of Saturn's moon Titan taken in 2004 and 2005 show that a large methane lake suddenly appeared after what looked like a heavy rainstorm

  10. Sea of Methane on Titan A Cassini radar image juxtaposed with an image of the Lake Superior

  11. Lots of Natural Gases, but no Oxygen to burn with! • Temperature range for liquid: water: 0 to 100C, methane: -182C to -164C, ethane: -183C to -89C Possible ethane world?

  12. Origin of Atmosphere 10 times more extended than Earth’s Key factor  size (gravity) How does Titan have an atmosphere when even a larger moon Ganymede doesn’t? distance from the Sun effect of their host planets Image of Titan taken from Cassini orbiter • Ganymede does not have an atmosphere  at Jupiter’s distance, only water ice could condense…, but at Saturn’s distance, ices such as methane and ammonia could condense! • Due to the stronger gravity of Jupiter, impacts were generally stronger at Jupiter’s moons than Saturn’s moon. Stronger impacts more easily blew away atmospheres…

  13. More surface feature : Sand Dunes Windblown dunes Namib desert from Space Shuttle

  14. Titan : summary • Very similar features with very different composition and temperature! • A lot of liquid hydrocarbons! about 200°C colder than liquid water  much slower chemical reaction  slower metabolism • A lot of organic material (e.g., organic sand dunes!) • Possible life in the upper atmosphere (acetylene [C2H2] based) or in the subsurface liquid ocean!

  15. Mimas

  16. Enceladus

  17. Active Enceladus Tiger stripes = fresh ices  cracks or grooves • Ice geysers  subsurface liquid water + ammonia mixture • Although we expect some tidal heating, it is hard to explain all these activities. • possible subsurface habitable zone! 6th largest moon of Saturn

  18. Enceladus

  19. Tethys

  20. Dione

  21. Rhea

  22. Iapetus

  23. Iapetus : An Intelligence Test for Earthlings? 3rd largest moon of Saturn

  24. Strange Surface Equatorial bulge (how???) • Heavily terraformed?

  25. Iapetus = Alien’s Starship? ?

  26. IapetusDeathstar!

  27. In summary… Important Concepts Important Terms Ice geysers • Titan: • thick atmosphere • origin of the atmosphere • methane world • similarities and dissimilarities compared to Earth • Other moons of Saturn: What’s special about these? • Enceladus • Iapetus • Chapter/sections covered in this lecture : sections 13-8 through 13-10

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