1. Enceladus and Titan: Prime targets in the search for life

2. Enceladus

3. Enceladus is a moon of Saturn, 1000 times smalller than Europa, with jets emanating from hot crevasses. The jets are icy particles frozen from salty water.

5. Titan 2nd largest moon in the sol sys Density 1.88 g/cm 3 --> rock+ice Dense N 2 -CH 4 atmosphere. Surface 89-94 K; pressure 1.5 atm.

6. NB – 1D radiative transfer codes are able to produce matching temperature profiles by including what we know about Titan’s composition

7. Cassini-Huygens

8. INMS shows complex chemistry in the region above 900 km (probably below, too). Cassini-Huygens

9. Surface mass spectrum from Huygens

10. methane ethane acetylene nitrogen HCN Photochemistry at the heart of Titan’s surface-atmosphere evolution λ < 1450 Å λ ≈ 2000 Å

11. Quantification of the methane consumption (simplified) Net photochemical destruction rate of CH 4 (Lavvas, et al. 2008) p-l= -3.5 x 10 -13 g cm -2 s -1 referred to the surface Mass per area of methane in atmosphere ~ P/g = 370 g cm -2 Lifetime of atmospheric methane: -P/g(p-l) = 35 million years Amount of methane that must be supplied to the surface over time Need 4.5 x 10 9 years /3.5 x 10 7 years ~ 100 x present atmospheric methane over the age of the solar system. or 100P/g = 3.7 x 10 4 g cm -2 / (0.7, 0.4 g cm -3 ) = (0.5, 0.9) km thick layer of (C 2 H 6, CH 4 ) over the age of the solar system Methane must be resupplied through time by outgassing from the interior.

12. 12

13. Ligeia Mare: One of Titan’s great seas 100 km

15. 20092005 Ontario Lacus

16. Hayes et al, 2009 Loss of liquid of ~ 86 km 3, av. depth 5 meters  5 m layer lost over 5 years

18. Moriconi et al 2010. Cassini VIMS data.

19. Titan’s Milankovitch cycles: precession of Saturn’s eccentric orbit

20. Cycling of lakes/seas on Titan Seasonal 30 years Methane-rich Ethane/propane-rich Croll-Milankovitch 50,000 years Ethane/propane-rich Precipitates (C 2 H 2, HCN…) Lower viscosity  waves Higher viscosity  smooth “Hydration/d ehydration” cycling SeasonalCroll-Milankovitch No analog exists in Earth’s hydrologic cycle for this kind of complexity

22. Methanogenic C 2 H 2 +3H 2  2CH 4 Chemistry 3C 2 H 2  C 6 H 6 Titan surface reactions? + 334 kJoules/mole (McKay and Smith, 2005)

26. Could this Titan host life on its surface? At -180 C liquid water is not stable at the surface. However, should one rule out a priori a form of life that exists in ethane and methane….?

28. Steve Benner and colleagues

29. Life in ethane-methane seas on Titan is a far more stringent test of a separate second origin than life found on Mars, Europa, or Enceladus. Impact exchange of material between bodies in our solar system implies a fundamental difficulty in proving that life “like us” had a separate origin. Life in a hydrocarbon sea is so fundamentally different-- at the molecular level— that it immediately would imply a second, separate origin of life. Titan has a big advantage over other astrobiological targets ? Titan No planetary protection issues: landing in the hydrocarbon lakes sterilizes the probe. Easy access to the lakes: no radiation, no drilling, just repeat Huygens mission....

30. LPL/JPL/NASA/USGS “ If life is an intrinsic property of chemical reactivity, life should exist on Titan. “Indeed, for life not to exist on Titan, we would have to argue that life is not an intrinsic property of the reactivity of carbon-containing molecules under conditions where they are stable.” Limits of Organic Life, National Research Council 2007

31. TiME: The Titan Mare Explorer A Discovery Mission to an Extraterrestrial Sea

32. We must go back to the Saturn system...if we want to test whether the origin of life is a common cosmic phenomenon