New Insights into the Atmospheric Chemistry of Venus

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

Surface P, bar Surface T, °C N 2 O 2 Atmospheric H 2 O Total H 2 O, cm CO 2 SO 2 Earth Venus 1 90 +15 +460 Composition , % 0. 78 0. 21 < 0. 03 ~3× 105 0. 0003 ~10 -9 Clouds H 2 O 0. 035 ~0 0. 00005 ~3 0. 965 ~10 -4 H 2 SO 4 + ? (Sx, Fe. Cl 3…)

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

Venus Express Payloads Titov et al. , 2009

“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, SO 2, 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 thermal wind field in 50 -80 km 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

“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 3 D 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

Atmospheric composition results SO 2 SOIR/ SPICAV VIRTIS SO 2 H 2 O CO H 2 SO 4 VIRTIS H 2 O

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

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

Why there is a problem Yung and De. More, Icarus, 1982 Mills, 1998

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

Latitudinal Transport?

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

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

Sulfur Chemistry above 80 km Or…

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

H 2 SO 4 V. S. Sx

Aerosol Profiles Wilquet et al. , JGR, 2009

Gao et al. 2012

H 2 SO 4 Photolysis?

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.

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.

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

Atmospheric composition results SO 2 SOIR/ SPICAV VIRTIS SO 2 H 2 O CO H 2 SO 4 VIRTIS H 2 O

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

Polysulfur Chemistry S hv S 3 S 2 S 4 OCS S CO hv hv S 2 hv S 3 S 4 S S 8

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

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

OCS

OCS

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-2 s-1 Comparable production and flux for CO

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

Atmospheric composition results SO 2 SOIR/ SPICAV VIRTIS SO 2 H 2 O CO H 2 SO 4 VIRTIS H 2 O

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

Liang and Yung (2009)

Liang and Yung (2009)

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

Li, …Yung 2009 Time 15 June 2009 51

Ultimate Fate of the Earth is Venus! 52

Thanks

Acknowledgement • 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

Upper Atmosphere De. More and Yung, Science, 1982