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A warm layer in Venus' cryosphere and high-altitude measurements of HF, HCl, H2O and HDO


Venus has thick clouds of H2SO4 aerosol particles extending from altitudes of 40 to 60 km. The 60–100 km region (the mesosphere) is a transition region between the 4 day retrograde superrotation at the top of the thick clouds and the solar–antisolar circulation in the thermosphere (above 100 km), which has upwelling over the subsolar point and transport to the nightside1,2. The mesosphere has a light haze of variable optical thickness, with CO, SO2, HCl, HF, H2O and HDO as the most important minor gaseous constituents, but the vertical distribution of the haze and molecules is poorly known because previous descent probes began their measurements at or below 60 km. Here we report the detection of an extensive layer of warm air at altitudes 90–120 km on the night side that we interpret as the result of adiabatic heating during air subsidence. Such a strong temperature inversion was not expected, because the night side of Venus was otherwise so cold that it was named the ‘cryosphere’ above 100 km. We also measured the mesospheric distributions of HF, HCl, H2O and HDO. HCl is less abundant than reported 40 years ago3. HDO/H2O is enhanced by a factor of 2.5 with respect to the lower atmosphere, and there is a general depletion of H2O around 80–90 km for which we have no explanation.

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Figure 1: Night-side temperature of Venus atmosphere.
Figure 2: Typical evolution of atmospheric spectral transmittances through one solar occultation observed by SOIR spectrometer.
Figure 3: HF and HCl mixing ratio vertical profiles retrieved from SOIR occultations.
Figure 4: HDO and H 2 O mixing ratio, HDO/ H 2 O vertical profiles.

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Venus Express is a space mission from the European Space Agency (ESA). We wish to thank all ESA members who participated in this successful mission, and in particular H. Svedhem, D. McCoy, O. Witasse, A. Accomazzo and J. Louet. We also thank Astrium for the design and construction of the spacecraft, and in particular A. Clochet, responsible for the payload. We thank D. Hinson for communication of the Magellan radio-occultation atmospheric profile, and Y. Yung and T. Clancy for discussions. We thank our collaborators at Service d’Aéronomie/France, BIRA/Belgium and IKI/Moscow for the design and fabrication of the instrument. We thank CNRS and CNES for financing SPICAV/SOIR in France, the Belgian government, Roskosmos and the Russian Academy of Sciences. The Russian team acknowledges support from the Russian Foundation for Basic Research, and from the Russian Science Support Foundation.

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Correspondence to Jean-Loup Bertaux.

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Supplementary Information

The file contains Supplementary Notes and Supplementary Figure 1 with Legend. The Supplementary Notes discuss the retrieval of CO2 density and temperature for stellar occultations in the UV, about the concept of the new SOIR spectrometer, and retrieval of atmospheric minor constituents from SOIR. The Supplementary Figure 1 is composed of four panels, showing for a typical stellar occultation: a) the atmospheric spectral transmission at various altitudes and their best fit model; b) the derived line densities vertical profile; c) the derived densities vertical profile; d) the temperature vertical profile. (PDF 155 kb)

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Bertaux, JL., Vandaele, AC., Korablev, O. et al. A warm layer in Venus' cryosphere and high-altitude measurements of HF, HCl, H2O and HDO. Nature 450, 646–649 (2007).

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