On the abundance of non-cometary HCN on Jupiter

Moses, J. I.; Visscher, Channon; Keane, Thomas C.; Sperier, A. D.

doi:10.1039/c003954c

Cited by 40 publications

(87 citation statements)

References 165 publications

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“…Laboratory studies that investigate the kinetics of C 3 H 2 and C 3 H 3 reactions with other hydrocarbon radicals and molecules would aid exoplanet photochemistry studies. Other possible photochemically produced hazes include elemental sulfur (Zahnle et al 2016), elemental phosphorus or other refractory phosphorus species, and refractory products from coupled C 2 H 2 -NH 3 chemistry (e.g., Keane et al 1996;Ferris & Ishikawa 1988;Moses et al 2010).…”

Section: Discussionmentioning

confidence: 99%

“…Unlike on our own solar-system gas giants, hydrazine (N 2 H 4 ) is not a major product of the ammonia photochemistry in our young-Jupiter models because the NH 2 from ammonia photolysis preferentially reacts with the copious amounts of atomic H to produce NH, and eventually N and N 2 , or with CH 3 to form CH 3 NH 2 and eventually HCN. On Jupiter and Saturn, the coupled ammonia-methane photochemistry is less efficient due to the lack of CH 3 present in the tropospheric region where NH 3 is photolyzed (e.g., Kaye & Strobel 1983;Moses et al 2010). However, the hydrazine abundance is very sensitive to temperature and increases significantly as T eff decreases.…”

Section: Sensitivity Of Disequilibrium Chemistry To K Zzmentioning

confidence: 99%

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On the Composition of Young, Directly Imaged Giant Planets

Moses

Marley

Zahnle

et al. 2016

ApJ

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The past decade has seen significant progress on the direct detection and characterization of young, self-luminous giant planets at wide orbital separations from their host stars. Some of these planets show evidence for disequilibrium processes like transport-induced quenching in their atmospheres; photochemistry may also be important, despite the large orbital distances. These disequilibrium chemical processes can alter the expected composition, spectral behavior, thermal structure, and cooling history of the planets, and can potentially confuse determinations of bulk elemental ratios, which provide important insights into planet-formation mechanisms. Using a thermo/photochemical kinetics and transport model, we investigate the extent to which disequilibrium chemistry affects the composition and spectra of directly imaged giant exoplanets. Results for specific "young Jupiters" such as HR 8799 b and 51 Eri b are presented, as are general trends as a function of planetary effective temperature, surface gravity, incident ultraviolet flux, and strength of deep atmospheric convection. We find that quenching is very important on young Jupiters, leading to CO/CH 4 and N 2 /NH 3 ratios much greater than, and H 2 O mixing ratios a factor of a few less than, chemical-equilibrium predictions. Photochemistry can also be important on such planets, with CO 2 and HCN being key photochemical products. Carbon dioxide becomes a major constituent when stratospheric temperatures are low and recycling of water via the H 2 + OH reaction becomes kinetically stifled. Young Jupiters with effective temperatures 700 K are in a particularly interesting photochemical regime that differs from both transiting hot Jupiters and our own solar-system giant planets.

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Section: Discussionmentioning

confidence: 99%

Section: Sensitivity Of Disequilibrium Chemistry To K Zzmentioning

confidence: 99%

On the Composition of Young, Directly Imaged Giant Planets

Moses

Marley

Zahnle

et al. 2016

ApJ

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“…These molecules could also be supplied from external sources such as the rings, satellites or interplanetary dust particles. Alternatively, HCN could be produced in the lower atmosphere, provided a mechanism exists to couple the chemistry of methane and other hydrocarbons to tropospheric ammonia (Moses et al 2010). This could be due to vertical mixing of HCN thermochemically generated in the deep interior (Lewis & Fegley 1984), or shock chemistry under the extreme environmental conditions of lightning (e.g., Bar-Nun & Podolak 1985), sufficient to dissociate NH 3 , PH 3 and CH 4 for the generation of HCN and HCP (see below).…”

Section: Hydrogen Cyanide Hcnmentioning

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 equilibrium is achieved kinetically in the deepest, hottest regions of these models, but chemical reactions tend to be slower in the upper, cooler regions. When transport time scales drop below kinetic conversion time scales-at a pressure called the "quench pressure" or "quench level"-transport begins to dominate over chemical kinetics in controlling the species' vertical profiles (e.g., Prinn & Barshay 1977;Lewis & Fegley 1984;Moses et al 2010;. When this situation occurs, the species can be "quenched" at mole fractions that remain constant with altitude above the quench level (and thus diverge from chemical-equilibrium predictions), as long as transport times scales remain shorter than chemical-kinetics time scales.…”

Section: Chemical Modelsmentioning

confidence: 99%

“…also the K zz profiles inferred from Showman et al 2009, as shown in Moses et al 2011). In our kinetics and transport models, the K zz profile influences the quench behavior of molecules like CO, CH 4 , and NH 3 , and the observations themselves may ultimately provide the best means for defining both the K zz values at the quench levels and the pressures at which those quench levels occur (e.g., Bézard et al 2002;Visscher et al 2010b;Moses et al 2010;. However, the broadband photometric eclipse observations obtained to date for GJ 436b are not sufficient to constrain either the composition or thermal profile accurately enough to derive K zz values in such a manner at this time.…”

Section: Chemical Modelsmentioning

confidence: 99%

COMPOSITIONAL DIVERSITY IN THE ATMOSPHERES OF HOT NEPTUNES, WITH APPLICATION TO GJ 436b

Moses

Line

Visscher

et al. 2013

ApJ

289

375

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Neptune-sized extrasolar planets that orbit relatively close to their host stars-often called "hot Neptunes"-are common within the known population of exoplanets and planetary candidates. Similar to our own Uranus and Neptune, inefficient accretion of nebular gas is expected produce hot Neptunes whose masses are dominated by elements heavier than hydrogen and helium. At high atmospheric metallicities of 10-10,000 times solar, hot Neptunes will exhibit an interesting continuum of atmospheric compositions, ranging from more Neptune-like, H 2 -dominated atmospheres to more Venus-like, CO 2 -dominated atmospheres. We explore the predicted equilibrium and disequilibrium chemistry of generic hot Neptunes and find that the atmospheric composition varies strongly as a function of temperature and bulk atmospheric properties such as metallicity and the C/O ratio. Relatively exotic H 2 O, CO, CO 2 , and even O 2 -dominated atmospheres are possible for hot Neptunes. We apply our models to the case of GJ 436b, where we find that a CO-rich, CH 4 -poor atmosphere can be a natural consequence of a very high atmospheric metallicity. From comparisons of our results with Spitzer eclipse data for GJ 436b, we conclude that although the spectral fit from the high-metallicity forward models is not quite as good as the best fit obtained from pure retrieval methods, the atmospheric composition predicted by these forward models is more physically and chemically plausible in terms of the relative abundance of major constituents. High-metallicity atmospheres (orders of magnitude in excess of solar) should therefore be considered as a possibility for GJ 436b and other hot Neptunes.

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On the abundance of non-cometary HCN on Jupiter

Cited by 40 publications

References 165 publications

On the Composition of Young, Directly Imaged Giant Planets

On the Composition of Young, Directly Imaged Giant Planets

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

COMPOSITIONAL DIVERSITY IN THE ATMOSPHERES OF HOT NEPTUNES, WITH APPLICATION TO GJ 436b

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