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We have investigated the abundances of Titan's stratospheric oxygen compounds using 0.5 [cm.sup.-1] resolution spectra from the Composite Infrared Spectrometer on the Cassini orbiter. The CO abundance was derived for several observations of far-infrared nadir spectra, taken at a range of latitudes (75[degrees] S-35[degrees] N) and emission angles (0[degrees]-60[degrees]), using rotational lines that have not been analysed before the arrival of Cassini at Saturn. The derived volume mixing ratios for the different observations are mutually consistent regardless of latitude. The weighted mean CO volume mixing ratio is 47 [+ or -] 8 ppm if CO is assumed to be uniform with latitude. [H.sub.2]O could not be detected and an upper limit of 0.9 ppb was determined. C[O.sub.2] abundances derived from mid-infrared nadir spectra show no significant latitudinal variations, with typical values of 16 [+ or -] 2 ppb. Midinfrared limb spectra at 55[degrees] S were used to constrain the vertical profile of C[O.sub.2] for the first time. A vertical C[O.sub.2] profile that is constant above the condensation level at a volume mixing ratio of 15 ppb reproduces the limb spectra very well below 200 km. This is consistent with the long chemical lifetime of C[O.sub.2] in Titan's stratosphere. Above 200 km the C[O.sub.2] volume mixing ratio is not well constrained and an increase with altitude cannot be ruled out there. Keywords: Titan; Atmospheres, composition

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.05.018 Byline: E. Lellouch (a), B. Bezard (a), D.F. Strobel (b), G.L. Bjoraker (c), F.M. Flasar (c), P.N. Romani (c) Keywords: Jupiter; atmosphere; Atmospheres; dynamics; Atmospheres; composition Abstract: Observations of Jupiter by Cassini/CIRS, acquired during the December 2000 flyby, provide the latitudinal distribution of HCN and CO.sub.2 in Jupiter's stratosphere with unprecedented spatial resolution and coverage. Following up on a preliminary study by Kunde et al. [Kunde, V.G., and 41 colleagues, 2004. Science 305, 1582-1587], the analysis of these observations leads to two unexpected results (i) the total HCN mass in Jupiter's stratosphere in 2000 was (6.0[+ or -]1.5)x10.sup.13g, i.e., at least three times larger than measured immediately after the Shoemaker-Levy 9 (SL9) impacts in July 1994 and (ii) the latitudinal distributions of HCN and CO.sub.2 are strikingly different: while HCN exhibits a maximum at 45[degrees] S and a sharp decrease towards high Southern latitudes, the CO.sub.2 column densities peak over the South Pole. The total CO.sub.2 mass is (2.9[+ or -]1.2)x10.sup.13g. A possible cause for the HCN mass increase is its production from the photolysis of NH.sub.3, although a problem remains because, while millimeter-wave observations clearly indicate that HCN is currently restricted to submillibar ([approximately equal to]0.3mbar) levels, immediate post-impact infrared observations have suggested that most of the ammonia was present in the lower stratosphere near 20 mbar. HCN appears to be a good atmospheric tracer, with negligible chemical losses. Based on 1-dimensional (latitude) transport models, the HCN distribution is best interpreted as resulting from the combination of a sharp decrease (over an order of magnitude in K.sub.yy) of wave-induced eddy mixing poleward of 40[degrees] and an equatorward transport with [approximately equal to]7cms.sup.-1 velocity. The CO.sub.2 distribution was investigated by coupling the transport model with an elementary chemical model, in which CO.sub.2 is produced from the conversion of water originating either from SL9 or from auroral input. The auroral source does not appear adequate to reproduce the CO.sub.2 peak over the South Pole, as required fluxes are unrealistically high and the shape of the CO.sub.2 bulge is not properly matched. In contrast, the CO.sub.2 distribution can be fit by invoking poleward transport with a [approximately equal to]30cms.sup.-1 velocity and vigorous eddy mixing (K.sub.yy=2x10.sup.11cm.sup.2s.sup.-1). While the vertical distribution of CO.sub.2 is not measured, the combined HCN and CO.sub.2 results imply that the two species reside at different stratospheric levels. Comparing with the circulation regimes predicted by earlier radiative-dynamical models of Jupiter's stratosphere, and with inferences from the ethane and acetylene stratospheric latitudinal distribution, we suggest that CO.sub.2 lies in the middle stratosphere near or below the 5-mbar level. Author Affiliation: (a) Observatoire de Paris, F-92195 Meudon, France (b) The Johns Hopkins University, Baltimore, MD 21218, USA (c) NASA/GFSC, Code 693, Greenbelt, MD 20771, USA Article History: Received 14 November 2005; Revised 11 May 2006

We report on the discovery of emissions due to carbon monoxide from Titan's atmosphere, from mid-infrared observations with the ISAAC spectrometer at the Very Large Telescope and coveting the 4.50-4.85 [micro]m range. We detected about 45 emission lines coinciding with CO ro-vibrational lines, including CO (1-0) (P18 to R11) and CO(2-1) (P11 to R11). We show that these emissions cannot be generated thermally but occur in non-LTE conditions, due to radiative de-excitation from the v = 1 and v = 2 CO levels after excitation at 4.7 and 2.3 [micro]m by solar radiation. A complete fluorescence model is then developed, allowing to compute the state populations of the two most abundant CO isotopes and [N.sub.2](1). It includes absorption by CO and C[H.sub.4], and vibrational-thermal and vibrational--vibrational collisional exchanges with CO, [N.sub.2], C[H.sub.4], and [H.sub.2]. Emerging radiances at the top of the atmosphere are evaluated with a line-by-line code and compared to observations. Contribution functions show that the CO emissions sound Titan's stratosphere: while the (1-0) lines generally probe two layers, located respectively at 100-250 km and 300-550 km, the (2-1) lines are sensitive to the intermediate layer at 150-300 km. A sensitivity study is performed to establish the effect of the main model parameters (temperature profile, collisional scenario, and CO stratospheric abundance) on the results. Models reproduce the essential structure of the observed emissions. The (1-0) fundamental band is generally well fit with a nominal CO mixing ratio of 32 ppm--as inferred in the troposphere from observations at 4.80-5.10 [micro]m (Lellouch et al., 2003, Icarus 162, 126-143). However, this band is only weakly dependent on the CO abundance, and given temperature and collisional scenario uncertainties, it constrains the CO stratospheric mixing ratio only to within a factor of ~3. In addition, the nominal model with 32 ppm CO underestimates the first hot (2-1) transition by approximately a factor of 2. This discrepancy can be resolved by a combined adjustment of collisional rates and an increased CO stratospheric ratio of 60 ppm, consistent with the determination of Gurwell and Muhleman (2000, Icarus 145,653-656). In contrast, the CO vertical profile suggested by Hidayat et al. (1998, Icarus 133, 109-133), strongly depleted above 200 km, cannot match the data for any realistic collisional scenario, and is therefore not supported by our results. Keywords: Titan; Atmospheres, composition; Infrared observations; Radiative transfer; Spectroscopy; Aeronomy

We report on spectro-imaging infrared observations of Jupiter's auroral zones, acquired in October 1999 and October 2000 with the FTS/BEAR instrument at the Canada-France-Hawaii Telescope. The use of narrow-band filters at 2.09 and 2.12 [micro]m, combined with high spectral resolution (0.2 [cm.sup.-1]), allowed us to map emission from the [H.sub.2] [S.sub.1] (1) quadrupole line and from several [H.sub.3]+ lines. The [H.sub.2] and [H.sub.3]+ emission appears to be morphologically different, especially in the north, where the latter notably exhibits a 'hot spot' near 150[degrees]-170[degrees] System III longitude. This hot spot coincides in position with the region of increased and variable hydrocarbon, FUV and X-ray emission, but is not seen in the more uniform [H.sub.2] [S.sub.1] (1) emission. We also present the first images of the [H.sub.2] emission in the southern polar region. The spectra include a total of 14 [H.sub.3]+ lines, including two hot lines from the 3[v.sub.2]-[v.sub.2] band, detected on Jupiter for the first time. They can be used to determine [H.sub.3]+ column densities, rotational (Trot) and vibrational ([T.sub.vib]) temperatures. We find the mean [T.sub.vib] of the [v.sub.2] = 3 state to be lower (960 [+ or -] 50 K) than the mean [T.sub.rot] in [v.sub.2] = 2 (1170 [+ or -] 75 K), indicating an underpopulation of the [v.sub.2] = 3 level with respect to local thermodynamical equilibrium. Rotational temperatures and associated column densities are generally higher and lower, respectively, than inferred previously from [v.sub.2] observations. This is a likely consequence of a large positive temperature gradient in the sub-microbar auroral atmosphere. While the signal-to-noise is not sufficient to take full advantage of the 2-D capabilities of the observations, the search for correlations between line intensities, [T.sub.vib] and column densities, indicates that variations in line intensities are mostly due to correlated variations in the [H.sub.3]+ column densities. The thermostatic role played by [H.sub.3]+ at ionospheric levels may provide an explanation. The exception is the northern 'hot spot,' which exhibits a [T.sub.vib] about 250 K higher than other regions. A partial explanation might invoke a homopause elevation in this region, but a fully consistent scenario is not yet available. The different distributions of the [H.sub.2] and [H.sub.3]+ emission are equally difficult to explain. Keywords: Jupiter; Jupiter/atmosphere; Ionospheres infrared observations

We report on repeated mid-resolution (R ~ 2000) spectroscopic observations of Titan, acquired between November 2002 and January 2003 with ISAAC at the ESO/VLT and covering the 4.84-5.05 [mu]m range. These observations, which sample four different positions of Titan around Saturn, clearly indicate a variability of the 5-[mu]m continuum albedo, with Titan's geometric albedo decreasing by ~ 40% from Titan's leading side to the trailing side. This Titan 5-[mu]m 'lightcurve' appears to be in phase with the other near-infrared lightcurves. This can be understood in terms of a surface model in which water ice coexists in minor and variable proportions (13-25%, if pure) with a second, dark, component. Keywords: Surfaces, planets; Titan; Infrared observations

We report on mid-resolution (R~2000) spectroscopic observations of Titan, acquired in November 2000 with the Very Large Telescope and covering the range 4.75-5.07 [micro]m. These observations provide a detailed characterization of the CO (1-0) vibrational band, clearly separating for the first time individual CO lines (P10 to P19 lines of [sup.13]CO). They indicate that the CO/[N.sub.2] mixing ratio in Titan's troposphere is 32 [+ or -] 10 ppm. Comparison with photochemical models indicates that CO is not in a steady state in Titan's atmosphere. The observations confirm that Titan's 5-[micro]m continuum geometric albedo is ~0.06, and further indicates a ~20% albedo decrease over 4.98-5.07 [micro]m. Nonzero flux is detected at the 0.01 geometric albedo level in the saturated core of the [sup.12]CO (1-0) band, at 4.75-4.85 [micro]m, providing evidence for backscattering on the stratospheric haze. Finally, emission lines are detected at 4.75-4.835 [micro]m, coinciding in position with lines from the CO(1-0) and/or CO(2-1) bands. Matching them by thermal emission would require Titan's stratosphere to be much warmer (by ~ 25 K at 0.1 mbar) than indicated by the methane 7.7-[micro]m emission and the Voyager radio-occultation. We show instead that a nonthermal mechanism, namely solar-excited fluorescence, is a more plausible source for these emissions. Improved observations and laboratory measurements on the vibrational-translational relaxation of CO are needed for further interpretation of these emissions in terms of a CO stratospheric mixing ratio. Keywords: Infrared Observations; Atmospheres, Composition; Titan

We have analyzed Titan observations performed by the Infrared Space Observatory (ISO) in the range 7-30 [micro]m. The spectra obtained by three of the instruments on board the mission (the short wavelength spectrometer, the photometer, and the camera) were combined to provide new and more precise thermal and compositional knowledge of Titan's stratosphere. With the high spectral resolution achieved by the SWS (much higher than that of the Voyager 1 IRIS spectrometer), we were able to detect and separate the contributions of most of the atmospheric gases present on Titan and to determine disk-averaged mole fractions. We have also tested existing vertical distributions for [C.sub.2][H.sub.2], HCN, [C.sub.2][H.sub.6], and C[O.sub.2] and inferred some information on the abundance of the first species as a function of altitude. From the C[H.sub.3]D band at 1161 [cm.sup.-1] and for a C[H.sub.4] mole fraction assumed to be 1.9% in Titan's stratosphere, we have obtained the monodeuterated methane-averaged abundance and retrieved a D/H isotopic ratio of [8.7.sup.+3.2.sub.-1.9] x [10.sup.-5]. We discuss the implications of this value with respect to current evolutionary scenarios for Titan. The [[upsilon].sub.5] band of H[C.sub.3]N at 663 [cm.sup.-1] was observed for the first time in a disk-averaged spectrum. We have also obtained a first tentative detection of benzene at 674 [cm.sup.-1], where the fit of the ISO/SWS spectrum at R = 1980 is significantly improved when a constant mean mole fraction of 4 x [10.sup.-10] of [C.sub.6][H.sub.6] is incorporated into the atmospheric model. This corresponds to a column density of ~ 2 x [10.sup.15] molecules [cm.sup.-2] above the 30-mbar level. We have also tested available vertical profiles for H[C.sub.3]N and [C.sub.6][H.sub.6] and adjusted them to fit the data. Finally, we have inferred upper limits of a few [10.sup.-10] for a number of molecules proposed as likely candidates on Titan (such as allene, acetonitrile, propionitrile, and other more complex gases). Keywords: Titan; Satellites; Atmospheres; Infrared observations; ISO

Observations of [H.sub.2]O rotational lines from the Infrared Space Observatory (ISO) and the Submillimeter Wave Astronomy Satellite (SWAS) and of the C[O.sub.2] [v.sub.2] band by ISO are analyzed jointly to determine the origin of water vapor and carbon dioxide in Jupiter's stratosphere. Simultaneous modelling of ISO/LWS and ISO/SWS observations acquired in 1997 indicates that most of the stratospheric jovian water is restricted to pressures less than 0.5 [+ or -] 0.2 mbar, with a disk-averaged column density of (2.0 [+ or -] 0.5) x [10.sup.15] [cm.sup.-2]. Disk-resolved observations of C[O.sub.2] by ISO/SWS reveal latitudinal variations of the C[O.sub.2] abundance, with a decrease of at least a factor of 7 from mid-southern to mid-northern latitudes, and a disk-center column density of (3.4 [+ or -] 0.7) x [10.sup.14] [cm.sup.-2]. These results strongly suggest that the observed [H.sub.2]O and C[O.sub.2] primarily result from the production, at midsouthern latitudes, of oxygenated material in the form of CO and [H.sub.2]O by the Shoemaker-Levy 9 (SL9) impacts in July 1994 and subsequent chemical and transport evolution, rather than from a permanent interplanetary dust particle or satellite source. This conclusion is supported by quantitative evolution model calculations. Given the characteristic vertical mixing times in Jupiter's stratosphere, material deposited at ~0.1 mbar by the SL9 impacts is indeed expected to diffuse down to the ~0.5 mbar level after 3 years. A coupled chemical-horizontal transport model indicates that the stability of water vapor against photolysis and conversion to C[O.sub.2] is maintained over typically ~50 years by the decrease of the local CO mixing ratio associated with horizontal spreading. A model with an initial (i.e., SL9-produced) [H.sub.2]O/CO mass mixing ratio of 0.07, not inconsistent with immediate postimpact observations, matches the observed [H.sub.2]O abundance and C[O.sub.2] horizontal distribution 3 years after the impacts. In contrast, the production of C[O.sub.2] from SL9-produced CO and a water component deriving from an interplanetary dust component is insufficient to account for the observed C[O.sub.2] amounts. The observations can further be used to place a stringent upper limit (8 x [10.sup.4] [cm.sup.-2] [s.sup.-1]) on the permanent water influx into Jupiter. This may indicate that the much larger flux observed at Saturn derives dominantly from a ring source, or that the ablation of micrometeoroids leads dominantly to different species at Saturn ([H.sub.2]O) and Jupiter (CO). Finally, the SWAS [H.sub.2]O spectra do not appear fully consistent with the ISO data and should be confirmed by future ODIN and Herschel observations. Key Words: Jupiter's atmosphere; spectroscopy.

The Fourier transform spectrometer at the CFH Telescope in Hawaii was used to observe the near-infrared spectrum of Titan, Saturn's largest moon. The observations, which cover the planet's Greatest Western Elongation and opposite Conjunctions, revealed similar geometric albedos in Titan's 1.28- and 1.075-micrometer methane windows. All in all, they highlight the heterogeneous nature of Titan's surface and the presence of two distinct regions in the spectra of its surface albedo.

The mean level of H2O over the clouds of Venus' upper atmosphere is less than 12 ppm, low as compared to the day-side results obtained in earlier observations. The mesospheric temperature is found to be around 140 K at an altitude level z = 95 km. The water content varies throughout the year and temperature also is subject to temporal fluctuations. These results are obtained from the observations made on the spectral lines of H2O and HDO transitions in the Venus atmosphere.

A recent study shows that the temperature of Venus, at an altitude of 91 km is 10 K higher, and is lower by 3.6 K at an altitude between 74 and 83 km, as compared to the observations of the Pioneer Venus mission. The study, using a near infrared mapping spectrometer during Galileo-Venus encounter in Feb 1990, of Venusian atmosphere is done using high spatial resolution infrared spectra of night side.

The observation of the 183-gigahertz water vapor line on planet Mars, using IRAM 30-meter millimeter antenna reveals the abundance of water molecules in the atmosphere of Mars. The observations are performed under dry atmospheric conditions, and the measurements apply to the whole disk of the planet. The spectral line, though marginal, can be fitted into the existing model with a constant H2O mixing ratio of 1/100,000.

Wind velocities and vertical thermal profiles near 50 kilometers altitude are derived from the Doppler shift and line profiles at different points on planet Mars. This enables the study of warming at middle altitudes in the atmosphere of the planet. Infrared studies indicate that temperatures in these regions are not in radiative equilibrium. The deviation is more pronounced at the poles of the planet during solstice. Heterodyne measurements of CO transitions also reveal more information regarding the temperature variations on Mars, caused by atmospheric turbulence.

A CO hole was discovered over high altitude areas of Mars in an experiment to study seasonal variability of CO and H2O in the Martian atmosphere. Data was collected by the infrared imaging spectrometer ISM on the Phobos 2 spacecraft. Data analysis showed that the CO mixing ratio for low altitudes is between 5 and 9 x 10 raised to the fourth power. CO depletion can be measured over the high altitudes of the Great Martian Volcano. Orogenic studies could help in evaluating this CO hole.

We report on repeated bolometric observations of the Pluto-Charon system at 1.2 mm with the IRAM 30-m telescope. These observations indicate at most small (~1-2 mJy) variations of the millimeter-wave emission of Pluto with orbital longitude, suggesting that the dark regions of Pluto have a millimeter emissivity of ~0.6-0.7. [C] 2000 Academic Press Key Words: Pluto, surface; Charon; surface, planets; photometry.