Chemical Models of the Deep Atmospheres of Jupiter and Saturn

Fegley, B.; Lodders, K.

doi:10.1006/icar.1994.1111

Cited by 277 publications

(348 citation statements)

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“…With this simplified composition we exclude all chemical reactions (except dissociation of H 2 O). This is not justified for T > ∼ 1000 K, and in addition, the presence of dust grains may actually increase the rate of chemical reactions (Fegley & Lodders 1994) throughout the envelope. Therefore, the absolute M crit values in Fig.…”

Section: Chemical Equilibrium Assumptionmentioning

confidence: 99%

Critical core mass for enriched envelopes: the role of H₂O condensation

Venturini

Alibert

Benz

et al. 2015

A&A

104

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Context. Within the core accretion scenario of planetary formation, most simulations performed so far always assume the accreting envelope to have a solar composition. From the study of meteorite showers on Earth and numerical simulations, we know that planetesimals must undergo thermal ablation and disruption when crossing a protoplanetary envelope. Thus, once the protoplanet has acquired an atmosphere, not all planetesimals reach the core intact, i.e. the primordial envelope (mainly H and He) gets enriched in volatiles and silicates from the planetesimals. This change of envelope composition during the formation can have a significant effect on the final atmospheric composition and on the formation timescale of giant planets. Aims. We investigate the physical implications of considering the envelope enrichment of protoplanets due to the disruption of icy planetesimals during their way to the core. Particular focus is placed on the effect on the critical core mass for envelopes where condensation of water can occur. Methods. Internal structure models are numerically solved with the implementation of updated opacities for all ranges of metallicities and the software Chemical Equilibrium with Applications to compute the equation of state. This package computes the chemical equilibrium for an arbitrary mixture of gases and allows the condensation of some species, including water. This means that the latent heat of phase transitions is consistently incorporated in the total energy budget. Results. The critical core mass is found to decrease significantly when an enriched envelope composition is considered in the internal structure equations. A particularly strong reduction of the critical core mass is obtained for planets whose envelope metallicity is larger than Z ≈ 0.45 when the outer boundary conditions are suitable for condensation of water to occur in the top layers of the atmosphere. We show that this effect is qualitatively preserved even when the atmosphere is out of chemical equilibrium. Conclusions. Our results indicate that the effect of water condensation in the envelope of protoplanets can severely affect the critical core mass, and should be considered in future studies.

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Section: Chemical Equilibrium Assumptionmentioning

confidence: 99%

Critical core mass for enriched envelopes: the role of H₂O condensation

Venturini

Alibert

Benz

et al. 2015

A&A

104

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“…Atmospheres of giant planets in the solar system and those of brown dwarfs have revealed the interplay between equilibrium and nonequilibrium chemical processes in hydrogen-rich atmospheres (Prinn & Bashay 1977;Fegley & Lodders 1994;Noll et al 1997;Saumon et al 2006). At high pressures deep in a planetary atmosphere, molecules react fast enough that all species are in thermochemical equilibrium.…”

Section: Chemistry Modelmentioning

confidence: 99%

HIGH METALLICITY AND NON-EQUILIBRIUM CHEMISTRY IN THE DAYSIDE ATMOSPHERE OF HOT-NEPTUNE GJ 436b

Madhusudhan

Seager

2011

ApJ

153

212

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We present a detailed analysis of the dayside atmosphere of the hot-Neptune GJ 436b, based on recent Spitzer observations. We report statistical constraints on the thermal and chemical properties of the planetary atmosphere, study correlations between the various molecular species, and discuss scenarios of equilibrium and non-equilibrium chemistry in GJ 436b. We model the atmosphere with a one-dimensional line-by-line radiative transfer code with parameterized molecular abundances and temperature structure. We explore the model parameter space with 10 6 models, using a Markov chain Monte Carlo scheme. Our results encompass previous findings, indicating a paucity of methane, an overabundance of CO and CO 2 , and a slight underabundance of H 2 O, as compared to equilibrium chemistry with solar metallicity. The concentrations of the species are highly correlated. Our best-fit, and most plausible, constraints require a CH 4 mixing ratio of 10 −7 to 10 −6 , with CO 10 −3 , CO 2 ∼ 10 −6 to 10 −4 , and H 2 O 10 −4 ; higher CH 4 would require much higher CO and CO 2 . Based on calculations of equilibrium and non-equilibrium chemistry, we find that the observed abundances can potentially be explained by a combination of high metallicity (∼10× solar) and vertical mixing with K zz ∼ 10 6 -10 7 cm 2 s −1 . The inferred metallicity is enhanced over that of the host star which is known to be consistent with solar metallicity. Our constraints rule out a dayside thermal inversion in GJ 436b. We emphasize that the constraints reported in this work depend crucially on the observations in the two Spitzer channels at 3.6 μm and 4.5 μm. Future observations with warm Spitzer and with the James Webb Space Telescope will be extremely important to improve upon the present constraints on the abundances of carbon species in the dayside atmosphere of GJ 436b.

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“…We conclude that SPIRE cannot provide useful upper limits on Saturn's CO. Teanby et al (2006) reported the best 3σ upper limits for the hydrogen halides to date using far-infrared Cassini/CIRS spectra. The halides are expected to react with NH 3 in the troposphere and condense as ammonium salts (e.g., Fegley & Lodders 1994), and so are not expected in the upper troposphere unless strong vertical mixing supplies halides as a disequlibrium species at a rate faster than they can react with NH 3 . Teanby et al (2006) estimated upper limits of 8.0 × 10 −12 , 6.7 × 10 −11 , 1.3 × 10 −10 and 1.4 × 10 −9 , respectively, for HF, HCl, HBr and HI.…”

Section: Carbon Monoxide Comentioning

confidence: 99%

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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Chemical Models of the Deep Atmospheres of Jupiter and Saturn

Cited by 277 publications

References 0 publications

Critical core mass for enriched envelopes: the role of H₂O condensation

Critical core mass for enriched envelopes: the role of H₂O condensation

HIGH METALLICITY AND NON-EQUILIBRIUM CHEMISTRY IN THE DAYSIDE ATMOSPHERE OF HOT-NEPTUNE GJ 436b

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

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Chemical Models of the Deep Atmospheres of Jupiter and Saturn

Cited by 277 publications

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Critical core mass for enriched envelopes: the role of H2O condensation

Critical core mass for enriched envelopes: the role of H2O condensation

HIGH METALLICITY AND NON-EQUILIBRIUM CHEMISTRY IN THE DAYSIDE ATMOSPHERE OF HOT-NEPTUNE GJ 436b

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

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Critical core mass for enriched envelopes: the role of H₂O condensation

Critical core mass for enriched envelopes: the role of H₂O condensation