The Abundances of Methane and Ortho/Para Hydrogen on Uranus and Neptune: Implications of New Laboratory 4-0 H2 Quadrupole Line Parameters

Baines, K. H.; Mickelson, Michael E.; Larson, L. E.; Ferguson, David W.

doi:10.1006/icar.1995.1065

Cited by 124 publications

(121 citation statements)

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“…The methane (CH 4 ) abundance follows Fletcher et al (2010) in the upper atmosphere and remains at a mole fraction of 0.022 in the troposphere below the condensation level (Baines et al 1995). The gas opacity at these wavelengths is dominated by H 2 collision-induced absorption (CIA) and CH 4 opacity; for CIA we use the coefficients for hydrogen, helium and methane from Borysow et al (1985Borysow et al ( , 1988 and Borysow (1991Borysow ( , 1992Borysow ( , 1993, assuming an equilibrium ortho/para ratio for H 2 .…”

Section: Cloud Feature Pressures From Radiative Transfer Modelingmentioning

confidence: 99%

Dispersion in Neptune’s zonal wind velocities from NIR Keck AO observations in July 2009

Fitzpatrick

Pater

Luszcz‐Cook

et al. 2013

Astrophys Space Sci

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We report observations of Neptune made in H-(1.4-1.8 µm) and K'-(2.0-2.4 µm) bands on 14 and 16 July 2009 from the 10-m W.M. Keck II Telescope using the near-infrared camera NIRC2 coupled to the Adaptive Optics (AO) system. We track the positions of 54 bright atmospheric features over a few hours to derive their zonal and latitudinal velocities, and perform radiative transfer modeling to measure the cloud-top pressures of 50 features seen simultaneously in both bands.We observe one South Polar Feature (SPF) on 14 July and three SPFs on 16 July at ∼65 • S. The SPFs observed on both nights are different features, consistent with the high variability of Neptune's storms.There is significant dispersion in Neptune's zonal wind velocities about the smooth Voyager wind profile fit of Sromovsky et al., Icarus 105, 140 (1993), much greater than the upper limit we expect from vertical wind shear, with the largest dispersion seen at equatorial and southern mid-latitudes. Comparison of feature pressures vs. residuals in zonal velocity from the smooth Voyager wind profile also directly reveals the dominance of mechanisms over vertical wind shear in causing dispersion in the zonal winds.Vertical wind shear is not the primary cause of the difference in dispersion and deviation in zonal veloc-

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Section: Cloud Feature Pressures From Radiative Transfer Modelingmentioning

confidence: 99%

Dispersion in Neptune’s zonal wind velocities from NIR Keck AO observations in July 2009

Fitzpatrick

Pater

Luszcz‐Cook

et al. 2013

Astrophys Space Sci

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“…The solar C/H number fraction is 0.000398 according to Grevesse and Anders (1991). Assuming H 2 + He = H 2 /0.81 and CH 4 /H 2 = 2C/H, then the solar benchmark for Neptune's CH 4 mole fraction is Baines et al (1995b) determined Neptune's deep tropospheric methane molar fraction to be in the range between 0.016 and 0.027, or 33 ± 9 times the solar value. However, the solar value itself is enough to saturate layers 8 and 7, and so fix layers 8 and upward in the model.…”

Section: Initial Methane Distributionmentioning

confidence: 99%

EPIC Simulations of Bright Companions to Neptune's Great Dark Spots

Stratman

Showman

Dowling

et al. 2001

Icarus

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“…We note that highmetallicity atmospheres are not unexpected for Neptune-mass planets (see Section 3.1 below). In fact, in our own solar system, Neptune's atmosphere is observed to have a C/H ratio of 40-120 times solar (Baines et al 1995;Karkoschka & Tomasko 2011) and is estimated to have an O/H ratio greater than 400 times solar Luszcz-Cook & de Pater 2013).…”

Section: Introductionmentioning

confidence: 99%

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

Moses

Line

Visscher

et al. 2013

ApJ

293

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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The Abundances of Methane and Ortho/Para Hydrogen on Uranus and Neptune: Implications of New Laboratory 4-0 H2 Quadrupole Line Parameters

Cited by 124 publications

References 0 publications

Dispersion in Neptune’s zonal wind velocities from NIR Keck AO observations in July 2009

Dispersion in Neptune’s zonal wind velocities from NIR Keck AO observations in July 2009

EPIC Simulations of Bright Companions to Neptune's Great Dark Spots

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

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