2005 .

T. Encrenaz, B. Bézard, T. Owen, S. Lebonnois, F. Lefèvre, T. Greathouse, M. Richter, J. Lacy, S. Atreya, A. S. Wong, and F. Forget. Infrared imaging spectroscopy of Mars: H 2O mapping and determination of CO 2 isotopic ratios. Icarus, 179:43-54, 2005. [ bib | DOI | PDF version | ADS link ]

High-resolution infrared imaging spectroscopy of Mars has been achieved at the NASA Infrared Telescope Facility (IRTF) on June 19-21, 2003, using the Texas Echelon Cross Echelle Spectrograph (TEXES). The areocentric longitude was 206deg. Following the detection and mapping of hydrogen peroxide H 2O 2 [Encrenaz et al., 2004. Icarus 170, 424-429], we have derived, using the same data set, a map of the water vapor abundance. The results appear in good overall agreement with the TES results and with the predictions of the Global Circulation Model (GCM) developed at the Laboratory of Dynamical Meteorology (LMD), with a maximum abundance of water vapor of 31.5×10(179 pr-μm). We have searched for CH 4 over the martian disk, but were unable to detect it. Our upper limits are consistent with earlier reports on the methane abundance on Mars. Finally, we have obtained new measurements of CO 2 isotopic ratios in Mars. As compared to the terrestrial values, these values are: ( 18O/ 17O)[M/E] = 1.03 0.09; ( 13C/ 12C)[M/E] = 1.00 0.11. In conclusion, in contrast with the analysis of Krasnopolsky et al. [1996. Icarus 124, 553-568], we conclude that the derived martian isotopic ratios do not show evidence for a departure from their terrestrial values.

S. Lebonnois. Benzene and aerosol production in Titan and Jupiter's atmospheres: a sensitivity study. Planetary and Space Science, 53:486-497, 2005. [ bib | DOI | PDF version | ADS link ]

Benzene has recently been observed in the atmosphere of Jupiter, Saturn and also Titan. This compound is required as a precursor for larger aromatic species (PAHs) that may be part of aerosol particles. Several photochemical models have tried to reproduce the observed quantities of benzene in the atmospheres of Jupiter (both low- and high-latitudes regions), Saturn and Titan. In this present work, we have conducted a sensitivity study of benzene and PAHs formation, using similar photochemical schemes both for Titan and Jupiter (low-latitudes conditions). Two different photochemical schemes are used, for which the modeled composition fairly agrees with observational constraints, both for Jupiter and Titan. Some disagreements are specific to each atmospheric case, which may point to needed improvements, especially in kinetic data involved in the corresponding chemical cycles. The observed benzene mole fraction in Titan's stratosphere is reproduced by the model, but in the case of Jupiter, low-latitudes benzene abundance is only 3% of the observed column density, which may indicate a possible influence of latitudinal transport, since abundance of benzene is much higher in auroral regions. Though, the photochemical scheme of C6 compounds at temperature and pressure conditions of planetary atmospheres is still very uncertain. Several variations are therefore done on key reactions in benzene production. These variations show that benzene abundance is mainly sensitive to reactions that may affect the propargyl radical. The effect of aerosol production on hydrocarbons composition is also tested, as well as possible heterogenous recombination of atomic hydrogen in the case of Titan. PAHs are a major pathway for aerosol production in both models. The mass production profiles for aerosols are discussed for both Titan and Jupiter. Total production mass fluxes are roughly three times the one expected by observational constraints in both cases. Such comparative studies are useful to bring more constraints on photochemical models.

P. Rannou, S. Lebonnois, F. Hourdin, and D. Luz. Titan atmosphere database. Advances in Space Research, 36:2194-2198, 2005. [ bib | DOI | PDF version | ADS link ]

We have developed in the last decade a two-dimensional version of the Titan global circulation model LMDZ. This model accounts for multiple coupling occuring on Titan between dynamics, haze, chemistry and radiative transfer. It was successful at explaining many observed features related to atmosphere state (wind, temperature), haze structure and chemical species distributions, recently, an important step in our knowledge about Titan has been done with Cassini and Huygens visits to Titan. In this context, we want to make the results of our model available for the scientific community which is involved in the study of Titan. Such a tool should be useful to give a global frame (spatial and time behaviour of physical quantities) for interpreting ground based telescope observations.