1. Organic Synthesis in the Atmosphere of Titan: Modeling and Recent Observations
Yuk Yung (Caltech),
M. C. Liang (Academia Sinica), X. Zhang (Caltech),
J. Kammer (Caltech), D. Shemansky (SET)
NAI Titan Team Meeting May 2011, Pasadena, CA

2. Outline of Today’s Talk
Titan: gas phase chemistry
Aerosol formation
Surface chemistry
Synergism with lab data

3. Solar Scattering
Stellar Occultation
J. Ajello

4. Mixing Ratios of Selected Species from Occultations

5. UVIS spectrum
tholin
CH4
Impact: 514 km
Liang et al. 2007

6. Optical Depth Images
Figs must expand!

7. Auto-catalytic process
EUV
FUV
Auto-catalytic process
auto
Lavvas et al. 2008

8. Hydrocarbon Abundances from TB Encounter
Tholin scale heights above 540 km are larger than any other species indicating formation at high altitudes and downward diffusion.

9. Photochemical results
HCN
CH4; hydrostatic
HC3N
CH4; non-hydrostatic
C6N2
C6H6
C6N2; condensation line
Liang, Yung, Shemansky ApJ 2007

10. Gu et al. 2009

11. Model without Haze

13. C6Hx

15. Model with Haze Formation

17. C6Hx

19. [Vuitton, et al., 2006]

20. [Vuitton, et al., 2006]

21. Ion observation
[Vuitton, et al., 2006]

22. Outline of Today’s Talk
Titan: gas phase chemistry
Aerosol formation
Surface chemistry
Synergism with lab data

23. Solar Scattering
Stellar Occultation
J. Ajello

24. Stellar Occultation
tholin
CH4
Impact: 514 km
Liang et al. 2007

25. Single Scattering Albedo (SSA):
Important Parameters
Single Scattering Albedo (SSA):
SSA = Qs/Qe
Goody and Yung 1989

26. Refractive Index from Khare and Sagan (1984)
SSA at 1875 Å
Obs:
0.118
16 nm
Refractive Index from Khare and Sagan (1984)

27. Shemansky et al. 2010

28. . 2 Comparisons Tomasko et al. 2008: ~100 km 50 nm radius 3000 monmers
Trainer, et al 2006
Tomasko et al. 2008: ~100 km
50 nm radius 3000 monmers

29. Comparison of radius of tholins
Tholin Radius at 1040 km: 16 nm
Liang et al. (2007) “guessed” 12.5 nm from Stellar Occultation only
Comparable to 25 nm (in radius) from Trainer et al. (2006) ; 40 nm from Bar- Nun et al. (2008)
Lavvas et al. (2008) at 520 km (ISS):
~40 nm

30. T
Tomasko et al. 2008

31. Outline of Today’s Talk
Titan: gas phase chemistry
Aerosol formation
Surface chemistry
Synergism with lab data

32. What happens to the Unsaturated Hydrocarbons at the Surface?
COSMIC-RAY-MEDIATED FORMATION OF BENZENE ON THE SURFACE OF SATURN’S MOON TITAN
Zhou et al. 2010

33. Benzene (PAH) Production on Surface
Cosmic-ray flux on Titan’s surface (φCR =1e9 eV cm−2 s−1)
Yield of benzene from solid acetylene (from lab: Y = 5.6e-3 eV−1)
Fraction of the surface of Titan covered by organics (Fo=0.2)
Fraction of organics that is acetylene (Fa=0.2)
Time for turnover of the surface by geological processes (τ=2e6 yrs, lowest estimate )
We get: M = 1.4e19 molecules cm−2
3.4 e−17 g cm−2 s−1

34. Outline of Today’s Talk
Titan: gas phase chemistry
Aerosol formation
Surface chemistry
Synergism with lab data

35. Forward and adjoint models
Inverse Model
Optimization
Improved
Estimate
Parameter Estimate
Gradients
(sensitivities)
Forward Model
Adjoint Model t0 tf tf t0
Predictions
Adjoint Forcing -
Observations
<-- time evolution profiles

36. Lab: Adamkovics et al. (2003)
Liang et al. (submitted)

38. Jupiter (Moses 2005)

39. Titan (Moses 2005)

40. References
Yung, Y. L., M. Allen, and J. P. Pinto. (1984). "Photochemistry of the Atmosphere of Titan: Comparison between Model and Observations." Astrophysical Journal Supplement Series 55(3):
Goody, R. M., and Y.L. Yung, Atmospheric Radiation: Theoretical Basis, 1989, Oxford University Press.
Yung, Y. L., and W. D. DeMore, Photochemistry of Planetary Atmospheres, 1999, Oxford University Press.

41. Acknowledgements
We appreciate discussions with kinetics groups of Ralf Kaiser and Stan Sander, Mark Allen, Bob West, and support from NASA Cassini, OPR, NAI and PATM.