J.-L. Bertaux, A.-C. Vandaele, O. Korablev, E. Villard, A. Fedorova, D. Fussen, E. Quémerais, D. Belyaev, A. Mahieux, F. Montmessin, C. Muller, E. Neefs, D. Nevejans, V. Wilquet, J. P. Dubois, A. Hauchecorne, A. Stepanov, I. Vinogradov, A. Rodin, J.-L. Bertaux, D. Nevejans, O. Korablev, F. Montmessin, A.-C. Vandaele, A. Fedorova, M. Cabane, E. Chassefière, J. Y. Chaufray, E. Dimarellis, J. P. Dubois, A. Hauchecorne, F. Leblanc, F. Lefèvre, P. Rannou, E. Quémerais, E. Villard, D. Fussen, C. Muller, E. Neefs, E. van Ransbeeck, V. Wilquet, A. Rodin, A. Stepanov, I. Vinogradov, L. Zasova, F. Forget, S. Lebonnois, D. Titov, S. Rafkin, G. Durry, J. C. Gérard, and B. Sandel. A warm layer in Venus' cryosphere and high-altitude measurements of HF, HCl, H2O and HDO. Nature, 450:646-649, 2007. [ bib | DOI | PDF version | ADS link ]
Venus has thick clouds of H2SO4 aerosol particles extending from altitudes of 40 to 60km. The 60-100km region (the mesosphere) is a transition region between the 4day retrograde superrotation at the top of the thick clouds and the solar-antisolar circulation in the thermosphere (above 100km), which has upwelling over the subsolar point and transport to the nightside. 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 60km. Here we report the detection of an extensive layer of warm air at altitudes 90-120km 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 100km. We also measured the mesospheric distributions of HF, HCl, H2O and HDO. HCl is less abundant than reported 40years ago. 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 80-90km for which we have no explanation.
P. Drossart, G. Piccioni, J. C. Gérard, M. A. Lopez-Valverde, A. Sanchez-Lavega, L. Zasova, R. Hueso, F. W. Taylor, B. Bézard, A. Adriani, F. Angrilli, G. Arnold, K. H. Baines, G. Bellucci, J. Benkhoff, J. P. Bibring, A. Blanco, M. I. Blecka, R. W. Carlson, A. Coradini, A. di Lellis, T. Encrenaz, S. Erard, S. Fonti, V. Formisano, T. Fouchet, R. Garcia, R. Haus, J. Helbert, N. I. Ignatiev, P. Irwin, Y. Langevin, S. Lebonnois, D. Luz, L. Marinangeli, V. Orofino, A. V. Rodin, M. C. Roos-Serote, B. Saggin, D. M. Stam, D. Titov, G. Visconti, M. Zambelli, C. Tsang, E. Ammannito, A. Barbis, R. Berlin, C. Bettanini, A. Boccaccini, G. Bonnello, M. Bouyé, F. Capaccioni, A. Cardesin, F. Carraro, G. Cherubini, M. Cosi, M. Dami, M. de Nino, D. Del Vento, M. di Giampietro, A. Donati, O. Dupuis, S. Espinasse, A. Fabbri, A. Fave, I. Ficai Veltroni, G. Filacchione, K. Garceran, Y. Ghomchi, M. Giustizi, B. Gondet, Y. Hello, F. Henry, S. Hofer, G. Huntzinger, J. Kachlicki, R. Knoll, D. Kouach, A. Mazzoni, R. Melchiorri, G. Mondello, F. Monti, C. Neumann, F. Nuccilli, J. Parisot, C. Pasqui, S. Perferi, G. Peter, A. Piacentino, C. Pompei, J.-M. Réess, J.-P. Rivet, A. Romano, N. Russ, M. Santoni, A. Scarpelli, A. Sémery, A. Soufflot, D. Stefanovitch, E. Suetta, F. Tarchi, N. Tonetti, F. Tosi, and B. Ulmer. A dynamic upper atmosphere of Venus as revealed by VIRTIS on Venus Express. Nature, 450:641-645, 2007. [ bib | DOI | PDF version | ADS link ]
The upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space. Molecular emissions from the upper atmosphere (90-120km altitude) of Venus can be used to investigate the energetics and to trace the circulation of this hitherto little-studied region. Previous spacecraft and ground-based observations of infrared emission from CO2, O2 and NO have established that photochemical and dynamic activity controls the structure of the upper atmosphere of Venus. These data, however, have left unresolved the precise altitude of the emission owing to a lack of data and of an adequate observing geometry. Here we report measurements of day-side CO2 non-local thermodynamic equilibrium emission at 4.3m, extending from 90 to 120km altitude, and of night-side O2 emission extending from 95 to 100km. The CO2 emission peak occurs at ˜115km and varies with solar zenith angle over a range of ˜10km. This confirms previous modelling, and permits the beginning of a systematic study of the variability of the emission. The O2 peak emission happens at 96km+/-1km, which is consistent with three-body recombination of oxygen atoms transported from the day side by a global thermospheric sub-solar to anti-solar circulation, as previously predicted.
G. Piccioni, P. Drossart, A. Sanchez-Lavega, R. Hueso, F. W. Taylor, C. F. Wilson, D. Grassi, L. Zasova, M. Moriconi, A. Adriani, S. Lebonnois, A. Coradini, B. Bézard, F. Angrilli, G. Arnold, K. H. Baines, G. Bellucci, J. Benkhoff, J. P. Bibring, A. Blanco, M. I. Blecka, R. W. Carlson, A. di Lellis, T. Encrenaz, S. Erard, S. Fonti, V. Formisano, T. Fouchet, R. Garcia, R. Haus, J. Helbert, N. I. Ignatiev, P. G. J. Irwin, Y. Langevin, M. A. Lopez-Valverde, D. Luz, L. Marinangeli, V. Orofino, A. V. Rodin, M. C. Roos-Serote, B. Saggin, D. M. Stam, D. Titov, G. Visconti, M. Zambelli, E. Ammannito, A. Barbis, R. Berlin, C. Bettanini, A. Boccaccini, G. Bonnello, M. Bouye, F. Capaccioni, A. Cardesin Moinelo, F. Carraro, G. Cherubini, M. Cosi, M. Dami, M. de Nino, D. Del Vento, M. di Giampietro, A. Donati, O. Dupuis, S. Espinasse, A. Fabbri, A. Fave, I. F. Veltroni, G. Filacchione, K. Garceran, Y. Ghomchi, M. Giustini, B. Gondet, Y. Hello, F. Henry, S. Hofer, G. Huntzinger, J. Kachlicki, R. Knoll, K. Driss, A. Mazzoni, R. Melchiorri, G. Mondello, F. Monti, C. Neumann, F. Nuccilli, J. Parisot, C. Pasqui, S. Perferi, G. Peter, A. Piacentino, C. Pompei, J.-M. Reess, J.-P. Rivet, A. Romano, N. Russ, M. Santoni, A. Scarpelli, A. Semery, A. Soufflot, D. Stefanovitch, E. Suetta, F. Tarchi, N. Tonetti, F. Tosi, and B. Ulmer. South-polar features on Venus similar to those near the north pole. Nature, 450:637-640, 2007. [ bib | DOI | PDF version | ADS link ]
Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright `dipole' feature surrounded by a cold `collar' at its north pole. The polar dipole is a `double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition.
V. De La Haye, J. H. Waite, T. E. Cravens, A. F. Nagy, R. E. Johnson, S. Lebonnois, and I. P. Robertson. Titan's corona: The contribution of exothermic chemistry. Icarus, 191:236-250, 2007. [ bib | DOI | PDF version | ADS link ]
The contribution of exothermic ion and neutral chemistry to Titan's corona is studied. The production rates for fast neutrals N 2, CH 4, H, H 2, 3CH 2, CH 3, C 2H 4, C 2H 5, C 2H 6, N( 4S), NH, and HCN are determined using a coupled ion and neutral model of Titan's upper atmosphere. After production, the formation of the suprathermal particles is modeled using a two-stream simulation, as they travel simultaneously through a thermal mixture of N 2, CH 4, and H 2. The resulting suprathermal fluxes, hot density profiles, and energy distributions are compared to the N 2 and CH 4 INMS exospheric data presented in [De La Haye, V., Waite Jr., J.H., Johnson, R.E., Yelle, R.V., Cravens, T.E., Luhmann, J.G., Kasprzak, W.T., Gell, D.A., Magee, B., Leblanc, F., Michael, M., Jurac, S., Robertson, I.P., 2007. J. Geophys. Res., doi:10.1029/2006JA012222, in press], and are found insufficient for producing the suprathermal populations measured. Global losses of nitrogen atoms and carbon atoms in all forms due to exothermic chemistry are estimated to be 8.3×10 Ns and 7.2×10 Cs.
P. Drossart, G. Piccioni, A. Adriani, F. Angrilli, G. Arnold, K. H. Baines, G. Bellucci, J. Benkhoff, B. Bézard, J.-P. Bibring, A. Blanco, M. I. Blecka, R. W. Carlson, A. Coradini, A. Di Lellis, T. Encrenaz, S. Erard, S. Fonti, V. Formisano, T. Fouchet, R. Garcia, R. Haus, J. Helbert, N. I. Ignatiev, P. G. J. Irwin, Y. Langevin, S. Lebonnois, M. A. Lopez-Valverde, D. Luz, L. Marinangeli, V. Orofino, A. V. Rodin, M. C. Roos-Serote, B. Saggin, A. Sanchez-Lavega, D. M. Stam, F. W. Taylor, D. Titov, G. Visconti, M. Zambelli, R. Hueso, C. C. C. Tsang, C. F. Wilson, and T. Z. Afanasenko. Scientific goals for the observation of Venus by VIRTIS on ESA/Venus express mission. Planetary and Space Science, 55:1653-1672, 2007. [ bib | DOI | PDF version | ADS link ]
The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) on board the ESA/Venus Express mission has technical specifications well suited for many science objectives of Venus exploration. VIRTIS will both comprehensively explore a plethora of atmospheric properties and processes and map optical properties of the surface through its three channels, VIRTIS-M-vis (imaging spectrometer in the 0.3-1 μm range), VIRTIS-M-IR (imaging spectrometer in the 1-5 μm range) and VIRTIS-H (aperture high-resolution spectrometer in the 2-5 μm range). The atmospheric composition below the clouds will be repeatedly measured in the night side infrared windows over a wide range of latitudes and longitudes, thereby providing information on Venus's chemical cycles. In particular, CO, H 2O, OCS and SO 2 can be studied. The cloud structure will be repeatedly mapped from the brightness contrasts in the near-infrared night side windows, providing new insights into Venusian meteorology. The global circulation and local dynamics of Venus will be extensively studied from infrared and visible spectral images. The thermal structure above the clouds will be retrieved in the night side using the 4.3 μm fundamental band of CO 2. The surface of Venus is detectable in the short-wave infrared windows on the night side at 1.01, 1.10 and 1.18 μm, providing constraints on surface properties and the extent of active volcanism. Many more tentative studies are also possible, such as lightning detection, the composition of volcanic emissions, and mesospheric wave propagation.