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

• Published in: Nature (London) 2007-11, Vol.450 (7170), p.646-649
• Main Authors: Bertaux, Jean-Loup, Vandaele, Ann-Carine, Korablev, Oleg, Villard, E., Fedorova, A., Fussen, D., Quémerais, E., Belyaev, D., Mahieux, A., Montmessin, F., Muller, C., Neefs, E., Nevejans, D., Wilquet, V., Dubois, J. P., Hauchecorne, A., Stepanov, A., Vinogradov, I., Rodin, A.
• Format: Article
• Language: English
• Subjects: Aerosols; Astronomical research; Astrophysics; Atmosphere; Clouds; Cryosphere; Gases; Haze; Heating; Humanities and Social Sciences; letter; multidisciplinary; Ocean, Atmosphere; Probes; Science; Sciences of the Universe; Subsidence; Sulfur dioxide; Sulfuric acid; Temperature inversions; Upwelling; Venus; Vertical distribution
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/nature05974

Still delivering ESA's Venus Express probe has been in orbit since April 2006. Eight research papers in this issue present new results from the mission, covering the atmosphere, polar features, interactions with the solar wind and the controversial matter of venusian lightning. Håkan Svedham et al . open the section with a review of the similarities and (mostly) differences between Venus and its 'twin', the Earth. Andrew Ingersoll considers the latest results, and also how the project teams plan to make the most of the probe's remaining six years of life. Venus' mesosphere is a transition region between the retrograde super rotation at the top of the thick clouds and the solar-antisolar circulation in the thermosphere. The mesospheric distributions of HF, HCl, H 2 O and HDO are reported, and an unexpected extensive layer of warm air at altitudes 90–120 km on the nightside is found. Venus has thick clouds of H 2 SO 4 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 nightside 1 , 2 . The mesosphere has a light haze of variable optical thickness, with CO, SO 2 , HCl, HF, H 2 O 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, H 2 O and HDO. HCl is less abundant than reported 40 years ago 3 . HDO/H 2 O is enhanced by a factor of ∼2.5 with respect to the lower atmosphere, and there is a general depletion of H 2 O around 80–90 km for which we have no explanation.