1. Revised tholin profile for the atmosphere of Titan Mao-Chang Liang 1, J. A. Kammer, X. Zhang 3, D. Shemansky 4, Y. L. Yung 2 1 Research Center for Environmental Change, Academia Sinica 2 Division of Geological and Planetary Sciences, California Institute of Technology 3 University of Arizona 4 Space Environment Technologies

2.  Stellar occulations  Aerosol extinction profiles  Tb  Vi, Tb Sco, T21  Eri, T41  CMa (ingress & egress), T47  Uma  Solar occulation  T0  Scattering spectrum at 1040 km Cassini UVIS

3. Lorenz + Mitton 2002

4. Solar Scattering Stellar Occultation J. Ajello

5. T0 olar reflection spectrum  High resolution slit; Integration time 14910 sec;  Red line: Effective altitude 1040 km; mid pixel 1203 km  Green line: Effective altitude 1612 km  Cyan line: best fitting model spectrum

6. T0 UVIS extinction spectrum Liang et al. 2007 tholin CH 4 Impact: 514 km

7. UVIS extinction profiles

8. Modeling – No production/loss 10 -15 g cm -2 76 A ~10 -3 g cm -3 eddy 10 -2 g cm -3 10 -3 g cm -3

9. Solution #1 – C 2 H 2 -> tholin 10 -15 g cm -2 3  10 -15 g cm -2 size increase 76 A -> 3300 A

10. Extinction coefficient Particle radius (A)

11. Fractal particles  Aggregate of molecules at ~1000 km  monomer: 10 A  Mie radius: 76 A  density: ~10 -3 g cm -3  -> fractal dimension: ~1.5  Main haze (<300 km)  monomer: 66 nm  fractional dimension: 2

12.  Low density fractal particle  ~10 -3 g cm -3 abve ~800 km  Particle size of 76 A at 1040 km  Increase to ~3300 A below ~500 km, compared to 660 A monomer size below 300 km  Mass flux from the top is ~10 -15 g cm -2  No net production between 400-800 km Summary