Temperatures, Winds, and Composition in the Saturnian System

Flasar, F. M.; Achterberg, R. K.; Conrath, B. J.; Pearl, J. C.; Bjoraker, G. L.; Jennings, Donald E.; Romani, P. N.; Simon-Miller, A. A.; Kunde, V. G.; Nixon, C. A.; Bézard, Bruno; Orton, Glenn S.; Spilker, L. J.; Spencer, J. R.; Irwin, Patrick; Teanby, N. A.; Owen, Tobias; Brasunas, J. C.; Segura, M.; Carlson, R.; Mamoutkine, A. A.; Gierasch, P. J.; Schinder, P. J.; Showalter, M. R.; Ferrari, C.; Barucci, A.; Courtin, R.; Coustenis, A.; Fouchet, Thierry; Gautier, D.; Lellouch, E.; Marten, A.; Prangé, Renée; Strobel, D. F.; Calcutt, S. B.; Read, P. L.; Taylor, F. W.; Bowles, N. E.; Samuelson, R. E.; Abbas, M. M.; Raulin, F.; Ade, Peter A. R.; Edgington, S. G.; Pilorz, S.; Wallis, B. D.; Wishnow, Ed

doi:10.1126/science.1105806

Cited by 183 publications

(103 citation statements)

References 25 publications

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“…Using two different sources for the rotational line intensities, SPIRE produced 1σ estimates of the mole fraction of (4.3 ± 0.3) × 10 −3 using the compilation of Brown et al (2003) with the dipole measurements of Wishnow et al (2007); and a mole fraction of (4.8 ± 0.3) × 10 −3 with the compilation of Boudon et al (2010). These results are broadly consistent with the results from Cassini far-infrared observations (Flasar et al 2005;Fletcher et al 2009b) and with the enrichment of carbon in Saturn compared to Jupiter. 5.…”

Section: Discussionsupporting

confidence: 76%

“…Nevertheless, this example demonstrates that we should be cautious about misinterpreting features in the data. These two SPIRE measurements are broadly consistent (to within one standard deviation) with the results from Cassini/CIRS -(4.7 ± 0.2) × 10 −3 (Fletcher et al 2009b) and (4.5 ± 0.9) × 10 −3 (Flasar et al 2005), which both used the compilation of Brown et al (2003) with the scaling factor from Wishnow et al (2007). Converting the two estimates into a C/H ratio for Saturn's bulk composition, we obtain carbon enrichments (relative to the solar chemical composition of Grevesse et al 2007) of 9.9 ± 0.7 and 11.1 ± 0.7 for the Wishnow et al (2007) and Boudon et al (2010) line intensities, respectively, consistent with the hypothesis that Saturn contains more carbon than Jupiter due to the increasing core-to-envelope ratio as we move away from the Sun (e.g., Owen & Encrenaz 2006).…”

Section: Methane Chsupporting

confidence: 86%

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Sub-millimetre spectroscopy of Saturn’s trace gases fromHerschel/SPIRE

Fletcher

Swinyard

Salji

et al. 2012

A&A

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Aims. We provide an extensive new sub-millimetre survey of the trace gas composition of Saturn's atmosphere using the broad spectral range (15-51 cm −1 ) and high spectral resolution (0.048 cm −1 ) offered by Fourier transform spectroscopy by the Herschel/SPIRE instrument (Spectral and Photometric Imaging REceiver). Observations were acquired in June 2010, shortly after equinox, with negligible contribution from Saturn's ring emission. Methods. Tropospheric temperatures and the vertical distributions of phosphine and ammonia are derived using an optimal estimation retrieval algorithm to reproduce the sub-millimetre data. The abundance of methane, water and upper limits on a range of different species are estimated using a line-by-line forward model. Results. Saturn's disc-averaged temperature profile is found to be quasi-isothermal between 60 and 300 mbar, with uncertainties of 7 K due to the absolute calibration of SPIRE. Modelling of PH 3 rotational lines confirms the vertical profile derived in previous studies and shows that negligible PH 3 is present above the 10-to 20-mbar level. The upper tropospheric abundance of NH 3 appears to follow a vapour pressure distribution throughout the region of sensitivity in the SPIRE data, but the degree of saturation is highly uncertain. The tropospheric CH 4 abundance and Saturn's bulk C/H ratio are consistent with Cassini studies. We improve the upper limits on several species (H 2 S, HCN, HCP and HI); provide the first observational constraints on others (SO 2 , CS, methanol, formaldehyde, CH 3 Cl); and confirm previous upper limits on HF, HCl and HBr. Stratospheric emission from H 2 O is suggested at 36.6 and 38.8 cm −1 with a 1σ significance level, and these lines are used to derive mole fractions and column abundances consistent with ISO and SWAS estimations a decade earlier.

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Section: Discussionsupporting

confidence: 76%

Section: Methane Chsupporting

confidence: 86%

Sub-millimetre spectroscopy of Saturn’s trace gases fromHerschel/SPIRE

Fletcher

Swinyard

Salji

et al. 2012

A&A

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“…A 3× enhancement in Jupiter is roughly consistent with observations by the Galileo Entry Probe (Wong et al 2004). An enhancement of 10× in Saturn is consistent with the CH 4 abundance deduced by Flasar et al (2005) via Cassini CIRS spectroscopy. An enhancement of 30-60× in Uranus and Neptune is consistent with the methane abundance in these atmospheres (e.g., Guillot & Gautier 2007).…”

Section: The Model Atmosphere Code and Validationsupporting

confidence: 82%

Self-Consistent Model Atmospheres and the Cooling of the Solar System's Giant Planets

Fortney¹,

Ikoma²,

Nettelmann³

et al. 2011

ApJ

142

149

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We compute grids of radiative-convective model atmospheres for Jupiter, Saturn, Uranus, and Neptune over a range of intrinsic fluxes and surface gravities. The atmosphere grids serve as an upper boundary condition for models of the thermal evolution of the planets. Unlike previous work, we customize these grids for the specific properties of each planet, including the appropriate chemical abundances and incident fluxes as a function of solar system age. Using these grids, we compute new models of the thermal evolution of the major planets in an attempt to match their measured luminosities at their known ages. Compared to previous work, we find longer cooling times, predominantly due to higher atmospheric opacity at young ages. For all planets, we employ simple "standard" cooling models that feature adiabatic temperature gradients in the interior H/He and water layers, and an initially hot starting point for the calculation of subsequent cooling. For Jupiter, we find a model cooling age ∼10% longer than previous work, a modest quantitative difference. This may indicate that the hydrogen equation of state used here overestimates the temperatures in the deep interior of the planet. For Saturn, we find a model cooling age ∼20% longer than previous work. However, an additional energy source, such as that due to helium phase separation, is still clearly needed. For Neptune, unlike in work from the 1980s and 1990s, we match the measured T eff of the planet with a model that also matches the planet's current gravity field constraints. This is predominantly due to advances in the high-pressure equation of state of water. This may indicate that the planet possesses no barriers to efficient convection in its deep interior. However, for Uranus, our models exacerbate the well-known problem that Uranus is far cooler than calculations predict, which could imply strong barriers to interior convective cooling. The atmosphere grids are published here as tables, so that they may be used by the wider community.

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“…Both are assumed to be homogeneously distributed in Saturn's stratosphere. The deep mixing ratio of CH 4 is set to 0.0045 (Flasar et al 2005) and then decreases with height following the Moses & Greathouse (2005) modelled vertical profile. The H 2 and He mole fractions are set to 0.86 and 0.1355, respectively, as obtained by Conrath & Gautier (2000).…”

Section: Discussionmentioning

confidence: 99%

Stratospheric benzene and hydrocarbon aerosols detected in Saturn’s auroral regions

Guerlet

Fouchet

Vinatier

et al. 2015

A&A

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Context. Saturn's polar upper atmosphere exhibits significant auroral activity; however, its impact on stratospheric chemistry (i.e. the production of benzene and heavier hydrocarbons) and thermal structure remains poorly documented. Aims. We aim to bring new constraints on the benzene distribution in Saturn's stratosphere, to characterize polar aerosols (their vertical distribution, composition, thermal infrared optical properties), and to quantify the aerosols' radiative impact on the thermal structure. Methods. Infrared spectra acquired by the Composite Infrared Spectrometer (CIRS) on board Cassini in limb viewing geometry are analysed to derive benzene column abundances and aerosol opacity profiles over the 3 to 0.1 mbar pressure range. The spectral dependency of the haze opacity is assessed in the ranges 680-900 and 1360-1440 cm −1 . Then, a radiative climate model is used to compute equilibrium temperature profiles, with and without haze, given the haze properties derived from CIRS measurements. Results. On Saturn's auroral region (80• S), benzene is found to be slightly enhanced compared to its equatorial and mid-latitude values. This contrasts with the Moses & Greathouse (2005, J. Geophys. Res., 110, 9007) photochemical model, which predicts a benzene abundance 50 times lower at 80• S than at the equator. This advocates for the inclusion of ion-related reactions in Saturn's chemical models. The polar stratosphere is also enriched in aerosols, with spectral signatures consistent with vibration modes assigned to aromatic and aliphatic hydrocarbons, and presenting similarities with the signatures observed in Titan's stratosphere. The aerosol mass loading at 80• S is estimated to be 1−4 × 10 −5 g cm −2 , an order of magnitude less than on Jupiter, which is consistent with the order of magnitude weaker auroral power at Saturn. We estimate that this polar haze warms the middle stratosphere by 6 K in summer and cools the upper stratosphere by 5 K in winter. Hence, aerosols linked with auroral activity can partly account for the warm polar hood observed in Saturn's summer stratosphere.

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Temperatures, Winds, and Composition in the Saturnian System

Cited by 183 publications

References 25 publications

Sub-millimetre spectroscopy of Saturn’s trace gases fromHerschel/SPIRE

Sub-millimetre spectroscopy of Saturn’s trace gases fromHerschel/SPIRE

Self-Consistent Model Atmospheres and the Cooling of the Solar System's Giant Planets

Stratospheric benzene and hydrocarbon aerosols detected in Saturn’s auroral regions

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