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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2009.04.002 Byline: Sandrine Guerlet (a), Thierry Fouchet (a), Bruno Bezard (a), Amy A. Simon-Miller (b), F. Michael Flasar (b) Keywords: Saturn; Infrared observations; Atmospheres; Composition Abstract: Measuring the spatial distribution of chemical compounds in Saturn's stratosphere is critical to better understand the planet's photochemistry and dynamics. Here we present an analysis of infrared spectra in the range 600-1400cm.sup.-1 acquired in limb geometry by the Cassini spacecraft between March 2005 and January 2008. We first determine the vertical temperature profiles from 3 to 0.01hPa, at latitudes ranging from 70[degrees]N to 80[degrees]S. We infer a similar meridional temperature gradient at 1-2hPa as in recent previous studies [Fletcher, L.N., Irwin, P.G.J., Teanby, N.A., Orton, G.S., Parrish, P.D., de Kok, R., Howett, C., Calcutt, S.B., Bowles, N., Taylor, F.W., 2007. Icarus 189, 457-478; Howett, C.J.A., Irwin, P.G.J., Teanby, N.A., Simon-Miller, A., Calcutt, S.B., Fletcher, L.N., de Kok, R., 2007. Icarus 190, 556-572]. We then retrieve the vertical profiles of C.sub.2H.sub.6 and C.sub.2H.sub.2 from 3 to 0.01hPa and of C.sub.3H.sub.8 around 1hPa. At 1hPa, the meridional variation of C.sub.2H.sub.2 is found to follow the yearly averaged solar insolation, except for a strong equatorial mole fraction of 8x10.sup.-7, nearly two times higher than expected. This enhancement in abundance can be explained by the descent of hydrocarbon-rich air, with a vertical wind speed at the equator of 0.25[+ or -]0.1 mm/s at 1hPa and 0.4[+ or -]0.15 mm/s at 0.1hPa. The ethane distribution is relatively uniform at 1hPa, with only a moderate 25% increase from 35[degrees]S to 80[degrees]S. Propane is found to increase from north to south by a factor of 1.9, suggesting that its lifetime may be shorter than Saturn's year at 1hPa. At high altitudes (1Pa), C.sub.2H.sub.2 and C.sub.2H.sub.6 abundances depart significantly from the photochemical model predictions of Moses and Greathouse [Moses, J.I., Greathouse, T.K., 2005. J. Geophys. Res. 110, 9007], except at high southern latitudes (62, 70 and 80[degrees]S) and near the equator. The observed abundances are found strongly depleted in the 20-40[degrees]S region and enhanced in the 20-30[degrees]N region, the latter coinciding with the ring's shadow. We favor a dynamical explanation for these anomalies. Author Affiliation: (a) LESIA - Observatoire de Paris, 92195 Meudon, France (b) NASA/Goddard Space Flight Center, Code 693, Greenbelt, MD 20771, USA Article History: Received 18 December 2008; Revised 3 April 2009; Accepted 13 April 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.11.005 Byline: Renee Prange (a)(b), Thierry Fouchet (a)(c), Regis Courtin (a), J.E.P. Connerney (d), John C. McConnell (e) Keywords: Atmospheres; composition; Photochemistry; Saturn; atmosphere; Ultraviolet observations Abstract: We obtained spatially-resolved ultraviolet spectra of Saturn in 1994 with the Faint Object Spectrometer and Goddard High Resolution Spectrograph of the Hubble Space Telescope. We observed four areas on the planet at 15[degrees]aN, 33[degrees]aS, 41[degrees]aS, and 52[degrees]aS, with a field-of-view of less than 2x2 arcsec.sup.2, compared to the 16-arcsec planet diameter. The wavelength range, 1550-2300 A, encompasses absorption from major hydrocarbons (C.sub.2H.sub.6, C.sub.2H.sub.4, C.sub.2H.sub.2, CH.sub.3C.sub.2H, C.sub.4H.sub.2) and water. We find global hydrocarbon abundances and a C.sub.2H.sub.2 vertical distribution compatible with infrared observations, in contrast with previous analyses of ultraviolet spectra. The stratospheric haze opacity decreases from polar region to the equator. Saturn mid-latitudes are photochemically distinct from the rest of the planet. At 33[degrees]aS, the spectrum requires either (1) a distinctly different C.sub.2H.sub.2 vertical distribution or (2) a locally enhanced water abundance. At 41[degrees]aS, the hydrocarbon abundance exhibits a local minimum, within a global trend of increasing abundance from equator to pole. This global trend may result from an increased abundance of short-lived hydrocarbons such as C.sub.4H.sub.2. Photochemical models predict a depletion of hydrocarbon molecules in the presence of stratospheric water [Moses et al., 2000. Icarus 143, 166-202]. These results are consistent with a localized influx of water, in the form of high charge to mass ratio particles, flowing into Saturn's atmosphere at latitudes magnetically linked to the rings. Author Affiliation: (a) LESIA, Observatoire de Paris, 5 Place Jules Janssen, 92195 Meudon Cedex, France (b) Institut d'astrophysique spatiale, Universite Paris-Sud 11 and CNRS (UMR8617), BAcentstiment 121, F-91405 Orsay, France (c) AOPP, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK (d) Laboratory for Extraterrestrial Physics, Goddard Space Flight Center, Code 695, Greenbelt, MD 20771, USA (e) Department of Earth and Atmospheric Science, York University, Toronto, Canada M3J 1P3 Article History: Received 7 April 2005; Revised 31 October 2005

We have used the spectra obtained by the Composite Infrared Spectrometer (CIRS) onboard the Cassini spacecraft to search for latitudinal variation in the [sup.15]N/[sup.14]N ratio on Jupiter. We found no variations statistically significant given the observational and model uncertainties. The absence of latitudinal variations demonstrates that [sup.15]N[H.sub.3] is not fractionated in Jupiter's atmosphere, and that the measured [sup.15]N/[sup.14]N represents Jupiter's global value. Our mean value for the global jovian [sup.15]N/[sup.14]N ratio of (2.22 [+ or -] 0.52) x [10.sup.-3] agrees with previous measurements made by Fouchet et al. (2000, Icarus 143,223-243) and Owen et al. (2001, Astrophys. J. 553, L77-L79). We argue that the jovian isotopic [sup.15]N/[sup.14]N ratio must represent the solar nitrogen isotopic composition. The solar [sup.15]N/[sup.14]N ratio hence significantly differs from the terrestrial value: [([sup.15]N/[sup.14]N).sub.[direct sum]] = 3.68 x [10.sup.-3]. This supports the proposition that terrestrial nitrogen originates from a nitrogen reservoir isolated from the main nitrogen reservoir in the proto-solar nebula. The origin and carrier of this isolated reservoir are still unknown. Keywords: Abundances, atmospheres; Atmospheres, composition; Jupiter, atmosphere

We have determined the following upper limits for the mole fraction of hydrogen halides in Jupiter's atmosphere from Cassini/CIRS observations: [HF] < 2.7 x [10.sup.-11], [HCI] < 2.3 x [10.sup.-9], [HBr] < 1.0 x [10.sup.-9], [HI] < 7.6 x [10.sup.-9]. These limits are smaller than solar composition for HF and HC1, and support the halogens' condensation in ammonium salts predicted by thermochemical models for the upper jovian troposphere. Keywords: Jupiter, atmosphere; Atmospheres, composition; Abundances, atmospheres

The impact of the vapor pressure difference between deuterated and nondeuterated condensing molecules in planetary atmospheres is quantitatively assessed. This difference results in a loss of deuterium in the vapor phase above the condensation level. In Titan, Uranus, and Neptune, the effect on [CH.sub.3]D is too subtle to alter current D/H ratio determinations. In Mars, the effect can induce a large depletion of HDO, starting about one scale height above the condensation level. Although the current infrared measurements of the D/H ratio appear to be almost unaffected, the intensity of disk-averaged millimetric HDO lines can be modified by about 10%. The effect is much stronger in limb sounding and can be easily detected from orbiter observations. Key Words: atmospheres, composition; Mars, atmosphere; isotopes.

We present the results of the Infrared Space Observatory Short Wavelength Spectrometer (ISO-SWS) observations of Jupiter related to ammonia. We focus on two spectral regions; the first one (the 10-[micro]m region), ranging from 9.5 to 11.5 [micro]m, probes atmospheric levels between 1 and 0.2 bar, while the second one (the 5-[micro]m window), ranging from 4.8 to 5.5 [micro]m, sounds the atmosphere between 8 and 2 bar. The two spectral windows cannot be fitted with the same ammonia vertical distribution. From the 10-[micro]m region we infer an ammonia distribution of about half the saturation profile above the 1-bar level, where the N/H ratio is roughly solar. A totally different picture is derived from the 5-[micro]m window, where we determine an upper limit of 3.7 x [10.sup.-5] at 1 bar and find an increasing [NH.sub.3] abundance at least down to 4 bar. This profile is similar to that measured by the Galileo probe. The discrepancy between the two spectral regions most likely arises from the spatial heterogeneity of Jupiter, the 5-[micro]m window sounding dry areas unveiled by a locally thin cloud cover (the 5-[micro]m hot spots), and the 10-[micro]m region probing the mean jovian atmosphere above 1 bar. The [sup.15][NH.sub.3] mixing ratio is measured around 400 mbar from [v.sub.2] band absorptions in the 10-[micro]m region. We find the atmosphere of Jupiter highly depleted in [sup.15]N at this pressure level [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], while [([sup.15]N/[sup.14]N).sub.[direct sum]] = 3.68 x [10.sup.-3]]. It is not clear whether this depletion reveals the global jovian [sup.15]N/[sup.14]N ratio. Instead an isotopic fractionation process, taking place during the ammonia cloud condensation, is indicated as a possible mechanism. A fractionation coefficient [Alpha] higher than 1.08 would explain the observed isotopic ratio, but the lack of laboratory data does not allow us to decide unambiguously on the origin of the observed low [sup.15]N/[sup.14]N ratio. Key Words: atmospheres, composition; infrared observations; Jupiter, atmosphere.