Chemistry of Planetary Atmospheres– Observations, Experiments, Computations and Modeling

1. Chemistry of Planetary Atmospheres– Observations, Experiments, Computations and Modeling Yuk Ling Yung (翁玉林） Caltech Seminar at NSRRC 19 July 2012

2. Cheng, B. M., E. P. Chew, C. P. Liu, M. Bahou, Y. P. Lee, Y. L. Yung, and M. F. Gerstell. (1999). "Photo-induced Fractionation of Water Isotopomers in the Martian Atmosphere." Geophysical Research Letters26(24): 3657-3660. • Lee, A. Y. T., Y. L. Yung, B. M. Cheng, M. Bahou, C. Y. Chung, and Y. P. Lee. (2001). "Enhancement of Deuterated Ethane on Jupiter." Astrophysical Journal551(1): L93-L96. • Bahou, M., C. Y. Chung, Y. P. Lee, B. M. Cheng, Y. L. Yung, and L. C. Lee. (2001). "Absorption Cross Sections of HCl and DCl at 135-232 Nanometers: Implications for Photodissociation on Venus." Astrophysical Journal559(2): L179-L182. • Cheng, B. M., H. C. Liu, H. K. Chen, M. Bahou, Y. P. Lee, A. M. Mebel, L. C. Lee, M. C. Liang, and Y. L. Yung. (2006). “Absorption cross sections of NH3, NH2D and ND3 in the spectral range 140-220 nm and its implication for planetary isotopic fractionation.” Astrophys. J.647 1535-1542. • Liang, M. C., B. M. Cheng, H. C. Lu, H. K. Chen, M. S. Alam, Y. P. Lee and Y. L. Yung. (2007). “Isotopic fractionation of nitrogen in ammonia in the troposphere of Jupiter.” Astrophys. J. Lett. 657 L117-120, doi:0004-637X.

3. Dr. Liang Mao-Chang Academia Sinica 3

5. Cheng, B. M., E. P. Chew, C. P. Liu, M. Bahou, Y. P. Lee, Y. L. Yung, and M. F. Gerstell. (1999). "Photo-induced Fractionation of Water Isotopomers in the Martian Atmosphere." Geophysical Research Letters26(24): 3657-3660. • Lee, A. Y. T., Y. L. Yung, B. M. Cheng, M. Bahou, C. Y. Chung, and Y. P. Lee. (2001). "Enhancement of Deuterated Ethane on Jupiter." Astrophysical Journal551(1): L93-L96. • Bahou, M., C. Y. Chung, Y. P. Lee, B. M. Cheng, Y. L. Yung, and L. C. Lee. (2001). "Absorption Cross Sections of HCl and DCl at 135-232 Nanometers: Implications for Photodissociation on Venus." Astrophysical Journal559(2): L179-L182. • Cheng, B. M., H. C. Liu, H. K. Chen, M. Bahou, Y. P. Lee, A. M. Mebel, L. C. Lee, M. C. Liang, and Y. L. Yung. (2006). “Absorption cross sections of NH3, NH2D and ND3 in the spectral range 140-220 nm and its implication for planetary isotopic fractionation.” Astrophys. J.647 1535-1542. • Liang, M. C., B. M. Cheng, H. C. Lu, H. K. Chen, M. S. Alam, Y. P. Lee and Y. L. Yung. (2007). “Isotopic fractionation of nitrogen in ammonia in the troposphere of Jupiter.” Astrophys. J. Lett. 657 L117-120, doi:0004-637X.

8. Today’s Outline • What Drives Evolution? () • Mars (Isotopes) • Venus (Loss of Ocean) • Titan and Enceladus • Exoplanets(Life?) • Conclusions

13. Today’s Outline • What Drives Evolution? () • Mars (Isotopes) • Venus (Loss of Ocean) • Titan and Enceladus • Exoplanets(Life?) • Conclusions

14. Mars: Gone with the (Solar) Wind • Isotopic Fractionation • Kass and Yung Science 1995

20. Today’s Outline • What Drives Evolution? () • Mars (Isotopes) • Venus (Loss of Ocean) • Titan and Enceladus • Exoplanets(Life?) • Conclusions

21. Venus (Loss of Ocean) Yung and DeMore Icarus 1982 Yung et al. JGR 2008

25. Today’s Outline • What Drives Evolution? () • Mars (Isotopes) • Venus (Loss of Ocean) • Titan and Enceladus • Exoplanets(Life?) • Conclusions

26. Titan/Enceladus Yung, Allen, Pinto ApJ 1984 Liang et al. ApJL 2007 Parkinson et al. 2008

27. Enter Cassini • Launched in 1997 • Arrived in Saturn system in 2004 • Wide array of instruments • Ultraviolet Imaging Spectrograph (UVIS)

29. Lorenz + Mitton 02

30. [Moses et al., JGR, 2005]

31. Titan • Atmosphere: Mostly nitrogen (98%), with methane and various hydrocarbons • Surface pressure of ~1.5 atm • Temperature of atmosphere ranges from 80K to 180K

32. Hidden in Haze • Thick layers of haze obscure the surface • Photochemistry drives complex suite of organic reactions • These organics have distinct absorption features in the UV region of spectrum

33. Hidden in Haze • Motivation: • What chemistry occurs on Titan, and where? • How might the products of this chemistry vary in space and time? • Connection to lower atmosphere/surface?

34. Stargazing with Cassini UVIS • Cassini UVIS instrument • EUV Spectrograph used for solar and stellar occultations • FUV Spectrograph used for stellar occultations • Measures integrated UV photon flux (from Esposito et al. 2003)

35. Stargazing with Cassini UVIS • Cassini UVIS instrument • EUV Spectrograph used for solar and stellar occultations • FUV Spectrograph used for stellar occultations • Measures integrated UV photon flux • Occultations with UVIS can probe atmospheric regions that no other instruments can easily observe

37. Photon Counts to Optical Depth • Process in two steps: • Calculate Io (λ) spectrum from above atmosphere • Optical depth is calculated as: τ (λ,h) = - ln [I (λ,h) / Io (λ)] where I (λ,h) is the integrated photon flux at each wavelength λ and occultation ray height h

40. Optical Depth to Abundance • Species absorption cross-sections • From laboratory measurements • Instrument response function • For given species abundance (cm-2), can calculate contribution to optical depth as seen by UVIS • Rodgers retrieval methodology • Finds best fit parameters of forward model in iterative process that minimizes cost function • J(x) = (x-xa)T Sa-1 (x-xa) + (y-Kx)TSe-1(y-Kx)

45. Abundance to Density • Assume spherically symmetric atmosphere • Convert line of sight abundance to local density using inverse Abel transform

49. Tholins and Haze