Thermochemistry and vertical mixing in the tropospheres of Uranus and Neptune: How convection inhibition can affect the derivation of deep oxygen abundances

Abstract

Thermochemical models have been used in the past to constrain the deep oxygen abundance in the gas and ice giant planets from tropospheric CO spectroscopic measurements. Knowing the oxygen abundance of these planets is a key to better understand their formation. These models have widely used dry and/or moist adiabats to extrapolate temperatures from the measured values in the upper troposphere down to the level where the thermochemical equilibrium between H${}_2$O and CO is established. The mean molecular mass gradient produced by the condensation of H${}_2$O stabilizes the atmosphere against convection and results in a vertical thermal profile and H${}_2$O distribution that departs significantly from previous estimates. We revisit O/H estimates using an atmospheric structure that accounts for the inhibition of the convection by condensation. We use a thermochemical network and the latest observations of CO in Uranus and Neptune to calculate the internal oxygen enrichment required to satisfy both these new estimates of the thermal profile and the observations. We also present the current limitations of such modeling.

33 pages, 11 figures, accepted for publication in Icarus (2017)

References in corpus (15)

• Ab initio Equation of State data for hydrogen, helium, and water and the internal structure of Jupiter
• A chemical model for the atmosphere of hot Jupiters
• Pseudo 2D chemical model of hot Jupiter atmospheres: application to HD 209458b and HD 189733b
• Condensation-inhibited convection in hydrogen-rich atmospheres: Stability against double-diffusive processes and thermal profiles for Jupiter, Saturn, Uranus, and Neptune
• Methane on Uranus: The case for a compact CH4 cloud layer at low latitudes and a severe CH4 depletion at high-latitudes based on re-analysis of Voyager occultation measurements and STIS spectroscopy
• New chemical scheme for studying carbon-rich exoplanet atmospheres
• Neptune's Atmospheric Composition from AKARI Infrared Spectroscopy
• Mid-Infrared Spectroscopy of Uranus from the Spitzer Infrared Spectrometer: 1. Determination of the Mean Temperature Structure of the Upper Troposphere and Stratosphere
• Methane depletion in both polar regions of Uranus inferred from HST/STIS and Keck/NIRC2 observations
• Convection and Mixing in Giant Planet Evolution
• Constraining the Origins of Neptune's Carbon Monoxide Abundance with CARMA Millimeter-wave Observations
• Scientific rationale of Saturn's in situ exploration
• Measuring Jupiter's water abundance by Juno: the link between interior and formation models
• The measured compositions of Uranus and Neptune from their formation on the CO iceline
• New Insights on Jupiter's Deep Water Abundance from Disequilibrium Species

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