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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

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.

Abstract: Limb and nadir spectra acquired by Cassini/CIRS (Composite InfraRed Spectrometer) are analyzed in order to derive, for the first time, the meridional variations of diacetylene (C4H2) and methylacetylene (CH3C2H) mixing ratios in Saturn’s stratosphere, from 5hPa up to 0.05hPa and 80°S to 45°N. We find that the C4H2 and CH3C2H meridional distributions mimic that of acetylene (C2H2), exhibiting small-scale variations that are not present in photochemical model predictions. The most striking feature of the meridional distribution of both molecules is an asymmetry between mid-southern and mid-northern latitudes. The mid-southern latitudes are found depleted in hydrocarbons relative to their northern counterparts. In contrast, photochemical models predict similar abundances at north and south mid-latitudes. We favor a dynamical explanation for this asymmetry, with upwelling in the south and downwelling in the north, the latter coinciding with the region undergoing ring shadowing. The depletion in hydrocarbons at mid-southern latitudes could also result from chemical reactions with oxygen-bearing molecules. Poleward of 60°S, at 0.1 and 0.05hPa, we find that the CH3C2H and C4H2 abundances increase dramatically. This behavior is in sharp contradiction with photochemical model predictions, which exhibit a strong decrease towards the south pole. Several processes could explain our observations, such as subsidence, a large vertical eddy diffusion coefficient at high altitudes, auroral chemistry that enhances CH3C2H and C4H2 production, or shielding from photolysis by aerosols or molecules produced from auroral chemistry. However, problems remain with all these hypotheses, including the lack of similar behavior at lower altitudes. Our derived mean mixing ratios at 0.5hPa of (2.4±0.3)×10−10 for C4H2 and of (1.1±0.3)×10−9 for CH3C2H are compatible with the analysis of global-average ISO observations performed by Moses et al. (Moses, J.I., Bézard, B., Lellouch, E., Gladstone, G.R., Feuchtgruber, H., Allen, M. [2000a]. Icarus 143, 244–298). Finally, we provide values for the ratios [CH3C2H]/[C2H2] and [C4H2]/[C2H2] that can constrain the coupled chemistry of these hydrocarbons. [Copyright &y& Elsevier]

We have used the spectra obtained by the Composite Infrared Spectrometer (CIRS) onboard the Cassini spacecraft to search for latitudinal variation in the 15N/14N ratio on Jupiter. We found no variations statistically significant given the observational and model uncertainties. The absence of latitudinal variations demonstrates that 15NH3 is not fractionated in Jupiter''s atmosphere, and that the measured 15N/14N represents Jupiter''s global value. Our mean value for the global jovian 15N/14N ratio of (2.22±0.52)×10-3 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 15N/14N ratio must represent the solar nitrogen isotopic composition. The solar 15N/14N ratio hence significantly differs from the terrestrial value: (15N/14N)⊕=3.68×10-3. 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. [Copyright &y& Elsevier]

Abstract: Limb spectra recorded by the Composite InfraRed Spectrometer (CIRS) on Cassini provide information on abundance vertical profiles of C2H2, C2H4, C2H6, CH3C2H, C3H8, C4H2, C6H6 and HCN, along with the temperature profiles in Titan''s atmosphere. We analyzed two sets of spectra, one at 15° S (Tb flyby) and the other one at 80° N (T3 flyby). The spectral range 600–1400 cm−1, recorded at a resolution of 0.5 cm−1, was used to determine molecular abundances and temperatures in the stratosphere in the altitude range 100–460 km for Tb and 170–495 km for T3. Both temperature profiles show a well defined stratopause, at around 310 km (0.07 mbar) and 183 K at 13° S, and 380 km (0.01 mbar) with 207 K at 80° N. Near the north pole, stratospheric temperatures are colder and mesospheric temperatures are warmer than near the equator. C2H2, C2H6, C3H8 and HCN display vertical mixing ratio profiles that increase with height at 15° S and 80° N, consistent with their formation in the upper atmosphere, diffusion downwards and condensation in the lower stratosphere, as expected from photochemical models. The CH3C2H and C4H2 mixing ratios also increase with height at 15° S. But near the north pole, their profiles present an unexpected minimum around 300 km, observed for the first time thanks to the high vertical resolution of the CIRS limb data. C2H4 is the only molecule having a vertical abundance profile that decreases with height at 15° S. At 80° N, it also displays a minimum of its mixing ratio around the 0.1-mbar level. For C6H6, an upper limit of 1.1 ppb (in the 0.3–10 mbar range) is derived at 15° S, whereas a constant mixing ratio profile of is inferred near the north pole. At 15° S, the vertical profile of HCN exhibits a steeper gradient than other molecules, which suggests that a sink for this molecule exists in the stratosphere, possibly due to haze formation. All molecules display a more or less pronounced enrichment towards the north pole, probably due, in part, to subsidence of air at the north (winter) pole that brings air enriched in photochemical compounds from the upper atmosphere to lower levels. [Copyright &y& Elsevier]