Title: 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.