Abstract
Volcanic degassing of planetary interiors has important implications for their corresponding atmospheres. The oxidation state of rocky interiors affects the volatile partitioning during mantle melting and subsequent volatile speciation near the surface. Here we show that the mantle redox state is central to the chemical composition of atmospheres while factors such as planetary mass, thermal state, and age mainly affect the degassing rate. We further demonstrate that mantle oxygen fugacity has an effect on atmospheric thickness and that volcanic degassing is most efficient for planets between 2 and 4 Earth masses. We show that outgassing of reduced systems is dominated by strongly reduced gases such as text {H}_{2}, with only smaller fractions of moderately reduced/oxidised gases (text {CO}, text {H}_{2}text {O}). Overall, a reducing scenario leads to a lower atmospheric pressure at the surface and to a larger atmospheric thickness compared to an oxidised system. Atmosphere predictions based on interior redox scenarios can be compared to observations of atmospheres of rocky exoplanets, potentially broadening our knowledge on the diversity of exoplanetary redox states.
Highlights
Volcanic degassing of planetary interiors has important implications for their corresponding atmospheres
Rocky planets have suggested that the efficiency and the composition of volcanic outgassing depend on properties such as mass, thermal state, age, tectonic style and planetary bulk composition[14,15,16,17,18]
We employed as starting volatile contents of the mantle the H2O and CO2 stored after the magma ocean solidification (Table 1)
Summary
Volcanic degassing of planetary interiors has important implications for their corresponding atmospheres. Stored H2 O rocky planets have suggested that the efficiency and the composition of volcanic outgassing depend on properties such as mass, thermal state, age, tectonic style and planetary bulk composition[14,15,16,17,18]. We do not consider whether any lingering gases from the primary atmosphere would affect the compositions of the secondary atmospheres we model This assumes that the species degassed during a short magma ocean stage would be lost or replaced within billions of years of volcanic outgassing. We analyse how a planet’s mantle redox state affects its outgassed atmospheric composition through the double influences of mantle-melt volatile partitioning and gas chemical speciation. We consider the three main elements on Earth which together constitute the bulk of Earth’s volatile molecular inventory and which are central for determining surface habitability conditions, namely C, H and O
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