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

Yuk Ling Yung (翁玉林）Caltech

Seminar at NSRRC19 July 2012

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 Letters 26(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 Journal 551(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 Journal 559(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.

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Dr. Liang Mao-Chang

Academia Sinica

4

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 Letters 26(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 Journal 551(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 Journal 559(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.

What Drives Evolution? () Mars (Isotopes) Venus (Loss of Ocean) Titan and Enceladus Exoplanets (Life?) Conclusions

Today’s Outline

What Drives Evolution? () Mars (Isotopes) Venus (Loss of Ocean) Titan and Enceladus Exoplanets (Life?) Conclusions

Today’s Outline

Mars: Gone with the (Solar) Wind

Isotopic Fractionation

Kass and Yung Science 1995

What Drives Evolution? () Mars (Isotopes) Venus (Loss of Ocean) Titan and Enceladus Exoplanets (Life?) Conclusions

Today’s Outline

Venus (Loss of Ocean)

Yung and DeMore Icarus 1982

Yung et al. JGR 2008

What Drives Evolution? () Mars (Isotopes) Venus (Loss of Ocean) Titan and Enceladus Exoplanets (Life?) Conclusions

Today’s Outline

Titan/Enceladus

Yung, Allen, Pinto ApJ 1984

Liang et al. ApJL 2007

Parkinson et al. 2008

Enter Cassini

• Launched in 1997• Arrived in Saturn

system in 2004• Wide array of

instruments– Ultraviolet Imaging

Spectrograph (UVIS)

Lorenz + Mitton 02

[Moses et al., JGR, 2005]

Titan

• Atmosphere: Mostly nitrogen (98%), with methane and various hydrocarbons

• Surface pressure of ~1.5 atm

• Temperature of atmosphere ranges from 80K to 180K

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

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?

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)

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

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

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)T Se

-1 (y-Kx)

Abundance to Density

• Assume spherically symmetric atmosphere

• Convert line of sight abundance to local density using inverse Abel transform

Tholins and Haze

Invited Talk (AGU 2007) Yung et al., Oxidants on Small Icy Bodies and Snowball Earth

H2O: need 20000 resolution 900 -1300 A5000 resolution 550 -900 A

N2: Glenn Stark has been doing a lot of work on this; 800 - 1000ANeed resolution of at least 100000.

What Drives Evolution? () Mars (Isotopes) Venus (Loss of Ocean) Titan and Enceladus Exoplanets (Life?) Conclusions

Today’s Outline

Are We Alone in the Universe?

There is life out there in the universe which is smarter than we are, or we're the most intelligent life in the universe. Either way, it's a mighty sobering thought.

Library of Helaxandria, 2007

Extrasolar Planets (HD 189733b )

Tinetti et al. Nature 2007

Molecules in Exoplanets

H2O, CO, CO2, CH4

Tinetti et al., Nature, 448, 163, 2007

Water, T-P at the terminator

Water line list: BT2Barber et al., 2006

HD 209458b

Hydrocarbons

CO + h C + OC + H2 + M 3CH2 + M2 3CH2 C2H2 + 2HC2H2 + H + M C2H3 + MC2H3 + H2 C2H4 + HC2H4 + H + M C2H5 + MC2H5 + H 2CH3

CH3 + H + M CH4 + M

CH4 Production

bottleneck

Li et al. PNAS 2008

What Drives Evolution? () Mars (Isotopes) Venus (Loss of Ocean) Titan and Enceladus Exoplanets (Life?) Conclusions

Today’s Outline

Planets have evolved

Isotopic composition provides clues

Exoplanets provide testbeds for evolution

Biological evolution is possible in exoplanets

Conclusions: Unifying Theme

夢中遇外星人 夜深闌靜後      獨步上小丘驀見山盡處      鋩鋩七火球划破長空過      飛向一母舟稍待齊集合      即去不復留余生也有幸      遇此外星儔伊人竟是誰      莫非織與牛羽化宇宙間      遨與造物遊彼族之文明      豈我所能究乍見一伊鐵      大頭又大眸

深邃不可測      似懷千歲憂我乃漢族人      唯知仁德修敦睦安天命      亙古寡敵仇惜哉輕科學      昧於新潮流百年遭萬劫      國難無止休頻頻被魚肉      不如奴與囚爾族識天機      必有濟世謀拯民於水火      復我唐漢周欲答已驚醒      但見光柔柔頃刻電光逝      仰望空悵惆遙思遠一方      朝暉撫神州

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Backup Slides

x: Machida et al. [1995] +: Bernard et al. [2006]