Life around Saturn, and beyond

1. Life around Saturn,and beyond ASTR 1420 Lecture 15 Sections 9.3

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. 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+ Titan, the Masked! 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. 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 ! Interior of Titan

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. 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 Origin of Atmosphere 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! • interesting to see if we can find right- and left-handed amino acids in life!

15. Titan Complex organic aerosols consisting of CHN and hydrogen gas (H2), which escapes into space. Ethane and methane partly condense, forming clouds and hazes that precipitate, replenishing the lakes and bearing many organic species in solution. (Nature 454, 587-589; 31 July 2008)

16. Tiger stripes = fresh ices  cracks or grooves Active Enceladus • 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

17. Enceladus

18. Enceladus creates Saturn’s E-ring Cassini (2006) : 2007-03-27 APOD

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

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

21. Iapetus = Alien’s Starship? ?

22. IapetusDeathstar!

23. Cryovolcanism… Triton: Surprising possibility of potential habitability largest moon of Neptune

24. Triton’s cantalope skin • Possibly formed by diapirism (i.e., slow boiling pattern)

25. Triton: Surprising possibility of potential habitability • Retrograde motion = Triton orbits Neptune “backward”  captured moon! • Crater count  Triton’s surface is 10-100 million years old. • Active ice geysers!! • Remnant internal heat from the capture may drive the geological activity… • possible subsurface liquid ocean • even at -230°C, possible habitable world!

26. Cosmic Messengers

27. Signal from Pioneer • A signal from the Pioneer 10 spacecraft, sent from a distance of more than 6 billion kilometers. The spacecraft transmitted the signal with a power of only one watt (about the power of X-mas tree light)!

28. In summary… Important Concepts Important Terms icy volcanism (cryo-volcanism) • At least six potentially habitable jovian moons! • Europa, Ganymede, Callisto, Titan, Enceladus, and Triton • Origin of Titan’s atmosphere • Prominent characteristics of Titan, Enceladus, Iapetus, and Triton. • Chapter/sections covered in this lecture : 9.3 • Next lecture : Exo-planets!