Fifth Workshop on Titan Chemistry April 2011, Kauai, Hawaii 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)

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

Lorenz + Mitton 02

[Moses et al., JGR, 2005]

Solar Scattering Stellar Occultation J. Ajello

Mixing Ratios of Selected Species from Occultations

UVIS spectrum Liang et al tholin CH 4 Impact: 514 km

Optical Depth Images

c Lavvas et al EUV FUV autoauto Auto-catalytic process

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.

Photochemical results Liang, Yung, Shemansky ApJ 2007 CH 4 ; hydrostatic CH 4 ; non-hydrostatic HC 3 N HCN C6N2C6N2 C6H6C6H6 C 6 N 2 ; condensation line

Gu et al. 2009

Model without Haze

C6HxC6Hx

Model with Haze

C6HxC6Hx

[Vuitton, et al., 2006]

Ion observation

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

Solar Scattering Stellar Occultation J. Ajello

Liang et al tholin CH 4 Impact: 514 km Stellar Occultation

Single Scattering Albedo (SSA): SSA = Q s /Q e Important Parameters Goody and Yung 1989

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

Shemansky et al. 2010

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

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 Comparison of radius of tholins

T Tomasko et al. 2008

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

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

Benzene (PAH) Production on Surface Cosmic-ray flux on Titan’s surface (φ CR =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 (F o =0.2) Fraction of organics that is acetylene (F a =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

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

Inverse Model Parameter Estimate Predictions Adjoint Forcing Gradients (sensitivities) Optimization Forward Model Adjoint Model Observations Improved Estimate - t0t0 tftf tftf t0t0 Forward and adjoint models <-- time evolution profiles

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

Jupiter (Moses 2005)

Titan (Moses 2005)

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.

Acknowledgements We appreciate discussions with kinetics groups of Prof Kaiser and Dr Sander, Mark Allen, Bob West, and support from NASA Cassini, OPR and PATM.