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. EarthVenus Surface P, bar190 Surface T, °C+15+460 Composition, % N 2 O 2 Atmospheric H 2 O Total H 2 O, cm CO 2 SO 2 Clouds 0.78 0.21 < 0.03 ~3×10 5 0.0003 ~10 -9 H 2 O 0.035 ~ 0 0.00005 ~3 0.965 ~10 -4 H 2 SO 4 + ? (S x, FeCl 3 …) Different Twins

4. DeMore and Yung, Science, 1982 Upper Atmosphere

5. Outline Why Venus Venus Express Mesosphere Troposphere Unsolved Problems

6. Titov et al., 2009 Venus Express Payloads

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, H 2 O at ~35 km and H 2 O 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 O 2, 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 O 2 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. Atmospheric composition results SO 2 CO H 2 SO 4 H2OH2O H2OH2O SO 2 SOIR/ SPICAV VIRTIS VIRTIS

10. Outline Why Venus Venus Express Mesosphere Troposphere Unsolved Problems

11. Belyaev et al., Icarus, 2011 SO & SO 2

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

13. Volcanism? Glaze et al., 2010, LPSCSmrekar et al., Science, 2010

14. Latitudinal Transport?

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

16. Global Circulation Regimes Troposphere Zonal superrotation (>100 m/s) Poleward winds v ~ 10 m/s Thermosphere Zonal superrotation (~100 m/s) Solar-antisolar circulation (~200 m/s) Titov et al., 2009

17. Aerosol Profiles Wilquet et al., JGR, 2009

18. H 2 SO 4 Photolysis?

20. Sulfur Chemistry above 80 km Or…

21. Zhang et al., Icarus, 2011 H 2 SO 4 Case

22. H 2 SO 4 V.S. S x

24. A sulfur source is required to explain the SO 2 inversion layer above 80 km. The evaporation of the aerosols composed of sulfuric acid or polysulfur above 90 km could provide the sulfur source. Measurements of SO 3 and SO (a 1 ∆→X 3 ∑) emission at 1.7 μm may be the key to distinguish between the two models. Summary

27. Conclusions (1) Recent observations of enhanced amounts of SO 2 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 H 2 SO 4 vapor derived from evaporation of H 2 SO 4 aerosols provides a source of SO 3, which upon photolysis yields SO 2. The predicted concentrations of SO and SO 3 could be detected by future measurements.

28. Conclusions (2) More experimental work is needed to investigate the molecular dynamics of the photolysis of H 2 SO 4 and its hydrates, as well as the saturation vapor pressure of H 2 SO 4 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 H 2 SO 4 in the terrestrial stratosphere, where the Junge layer (composed of H 2 SO 4 aerosols) is a regulator of climate and the abundance of O 3.

29. Outline Why Venus Venus Express Mesosphere Troposphere Unsolved Problems

30. Atmospheric composition results SO 2 CO H 2 SO 4 H2OH2O H2OH2O SO 2 SOIR/ SPICAV VIRTIS VIRTIS

32. Novel Chemistry SO 3 + CO → CO 2 + SO 2 SO 3 + OCS → CO 2 + (SO) 2 (SO) 2 + OCS → CO + S 2 + SO 2 CO + (1/n)S n → OCS OCS + S → CO + S 2 Krasnopolsky, Pollack, Fegley, Yung

33. Polysulfur Chemistry S2S2 OCS S3S3 S4S4 S8S8 hv S S CO S4S4 S2S2 S S3S3 S4S4 hvS

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

36. Hadley Circulation Venus = 2000×10 9 kg/s ≈ 10×Earth Earth = 180×10 9 kg/s

39. OCS

44. 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 ~ 10 12 cm -2 s -1 Comparable production and flux for CO

45. Outline Why Venus Venus Express Mesosphere Troposphere Unsolved Problems

46. Atmospheric composition results SO 2 CO H 2 SO 4 H2OH2O H2OH2O SO 2 SOIR/ SPICAV VIRTIS VIRTIS

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

48. Liang and Yung (2009)

50. Long term evolution of SO 2 SPICAV UV (at 100 km) SO 2 abundance at level 40 mbar (~69 km), ppb upper limit YEAR SPICAV UV NADIR (~70 km)

51. 51 Li, …Yung 2009 Time 15 June 2009

52. 52

53. Co-authors: Liang, M. C., Mills, F. P., Belyaev, D. A., Arthur Zhang Marcq, E., Parkinson, C., Bougher, S., Brecht, A., Ingersoll, A., Yang, D., Zeng, R., Gerstell, M., Line, M. NASA Grant Venus Express Project Acknowledgement

54. Thanks