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New Insights into the Atmospheric Chemistry of Venus from Venus Express Yuk L. Yung Caltech

New Insights into the Atmospheric Chemistry of Venus from Venus Express Yuk L. Yung Caltech GISS Seminar, Mar 24 2012. Outline. Why Venus Venus Express Mesosphere Troposphere Unsolved Problems. Different Twins. Upper Atmosphere. DeMore and Yung, Science, 1982. Outline. Why Venus

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New Insights into the Atmospheric Chemistry of Venus from Venus Express Yuk L. Yung Caltech

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  1. New Insights into the Atmospheric Chemistry of Venus from Venus Express Yuk L. Yung Caltech GISS Seminar, Mar 24 2012

  2. Outline • Why Venus • Venus Express • Mesosphere • Troposphere • Unsolved Problems

  3. Different Twins

  4. Upper Atmosphere DeMore and Yung, Science, 1982

  5. Outline • Why Venus • Venus Express • Mesosphere • Troposphere • Unsolved Problems

  6. Venus Express Payloads Titov et al., 2009

  7. “Firsts” by Venus Express (1) • First global monitoring of the composition of the lower atmosphere in the near IR spectral windows from orbit; • This has been done very well by VIRTIS. Abundance of CO, SO2, COS, H2O at ~35 km and H2O at the surface at all latitudes. Indeed pioneering results. • First coherent study of the atmospheric temperature and dynamics at different levels of the atmosphere up to the top of the cloud layer; • We have now a survey of temperature structures in the 40-120 km altitude range. From this the thermal wind field in 50-80km range has been derived. This is complemented by direct wind tracking (clouds) at 70 km, ~60 km, and 50 km. • First measurements of global surface temperature distribution from orbit; • VIRTIS has almost completely covered the Southern hemisphere. VMC is building surface maps from ~20 S to ~50 N. • First study of the middle and upper atmosphere dynamics from O2, O, and NO emissions; • These emissions originating around the mesopause (~90-110 km) have been observed and mapped. The regions of maximum brightness of NO and O2 airglow are slightly displaced, leading to new insights to the dynamics in this region. Svedhem

  8. “Firsts” by Venus Express (2) • First measurements of the non-thermal atmospheric escape • Great results from ASPERA: escape of O+, H+, and He++ ions is measured as well as spatial distribution of fluxes. The escape of O and H corresponds to water. • First coherent observations of Venus in the spectral range from UV to thermal infrared; • Accomplished, but thermal range is limited to λ< 5 µm due to the non operational PFS. • First application of the solar/stellar occultation technique at Venus; • Yes, the technique implemented by SOIR and SPICAV has proven to be extremely effective in sounding the mesosphere (70-120 km). • Firsts use of 3D ion mass analyzer, high energy resolution electron spectrometer, and energetic neutral atom imager; • Very good results on characterization of the plasma environment. Comparative studies with both ASPERA-3 on MEX and ASPERA-4 on VEX. • First complete monitoring of the electromagnetic environment of the planet. • MAG is providing excellent data on the structure and variability of the induced magnetosphere as well as on lightning. Particularly impressive as VEX has only one field instrument Svedhem

  9. SO2 SOIR/ SPICAV VIRTIS SO2 H2O CO H2SO4 VIRTIS H2O Atmospheric composition results

  10. Outline • Why Venus • Venus Express • Mesosphere • Troposphere • Unsolved Problems

  11. SO & SO2 Belyaev et al., Icarus, 2011

  12. Why there is a problem Yung and DeMore, Icarus, 1982 Mills, 1998

  13. Volcanism? Smrekar et al., Science, 2010 Glaze et al., 2010, LPSC

  14. Latitudinal Transport?

  15. Temperature Profiles Patzold et al., Science, 2007 Bertaux et al., Nature, 2007

  16. Global Circulation Regimes Troposphere • Zonal superrotation (>100 m/s) • Poleward winds v ~ 10 m/s Thermosphere • Zonal superrotation (~100 m/s) • Solar-antisolarcirculation (~200 m/s) Titovet al., 2009

  17. Aerosol Profiles Wilquetet al., JGR, 2009

  18. H2SO4 Photolysis?

  19. Sulfur Chemistry above 80 km Or…

  20. H2SO4 Case Zhang et al., Icarus, 2011

  21. H2SO4V.S. Sx

  22. Summary • A sulfur source is required to explain the SO2 inversion layer above 80 km. • The evaporation of the aerosols composed of sulfuric acid or polysulfurabove 90 km could provide the sulfur source. • Measurements of SO3 and SO (a1∆→X3∑) emission at 1.7 μm may be the key to distinguish between the two models.

  23. Conclusions (1) • Recent observations of enhanced amounts of SO2 at 100 km by Venus Express suggest a hitherto unknown source of gaseous sulfur species in the upper atmosphere of Venus. Highly variable correlated with temperature. • The photolysis of H2SO4 vapor derived from evaporation of H2SO4 aerosols provides a source of SO3, which upon photolysis yields SO2. • The predicted concentrations of SO and SO3could be detected by future measurements.

  24. Conclusions (2) • More experimental work is needed to investigate the molecular dynamics of the photolysis of H2SO4 and its hydrates, as well as the saturation vapor pressure of H2SO4 in the low temperature range (150-300 K). • A more detailed microphysical aerosol coupled photochemical model is needed. • The proposed mechanism may play an important role in the recycling of H2SO4 in the terrestrial stratosphere, where the Junge layer (composed of H2SO4 aerosols) is a regulator of climate and the abundance of O3.

  25. Outline • Why Venus • Venus Express • Mesosphere • Troposphere • Unsolved Problems

  26. SO2 SOIR/ SPICAV VIRTIS SO2 H2O CO H2SO4 VIRTIS H2O Atmospheric composition results

  27. Novel Chemistry • SO3 + CO→CO2 + SO2 • SO3 + OCS→CO2 + (SO)2 • (SO)2 + OCS→CO + S2 + SO2 • CO + (1/n)Sn→OCS • OCS + S→CO + S2 • Krasnopolsky, Pollack, Fegley, Yung

  28. S hv S2 S S3 OCS S4 CO hv hv S hv hv S2 S3 hv S4 S8 S4 S Polysulfur Chemistry

  29. Carlson, R. W. Venus' Ultraviolet Absorber and Sulfuric Acid Droplets. International Venus Conference, Aussois, France, 44 (2010).

  30. Hadley Circulation • Venus = 2000×109 kg/s ≈ 10×Earth • Earth = 180×109 kg/s

  31. OCS OCS

  32. OCS

  33. Conclusions Novel Chemistry of OCS and CO via polysulfur photochemistry for converting CO to OCS Integrated destruction rate of OCS is 23,000 Tg-S/yr [Earth Pinatubo = 10 Tg-S/yr] Flux ~ 1012 cm-2s-1 Comparable production and flux for CO

  34. Outline • Why Venus • Venus Express • Mesosphere • Troposphere • Unsolved Problems

  35. SO2 SOIR/ SPICAV VIRTIS SO2 H2O CO H2SO4 VIRTIS H2O Atmospheric composition results

  36. Conclusion: Julie Moses is the greatest science fiction writer since Paul Asimov!

  37. Liang and Yung (2009)

  38. Liang and Yung (2009)

  39. SPICAV UV (at 100 km) SO2 abundance at level 40 mbar (~69 km), ppb upper limit YEAR Long term evolution of SO2 SPICAV UV NADIR (~70 km)

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