Solubility of Rock in Steam Atmospheres of Planets

Abstract

Extensive experimental studies show all major rocky elements (Si, Mg, Fe, Ni, Ca, Al, Na, K) dissolve in steam to a greater or lesser extent. We use these results to compute chemical equilibrium abundances of rocky element-bearing gases in steam atmospheres equilibrated with silicate magma oceans. Rocky elements partition into steam atmospheres as volatile hydroxide gases and via reaction with HF or HCl as volatile halide gases in much larger amounts than expected from their vapor pressures over volatile-free solid or molten rock at the same temperature. We compute the extent of fractional vaporization by defining gas to magma partition coefficients and show Earth's sub-solar Si to Mg bulk elemental ratio may be due to loss of a primordial steam atmosphere. We conclude hot rocky exoplanets that are undergoing or have undergone escape of steam atmospheres may experience fractional vaporization and loss of Si, Mg, Fe, Ni, Ca, Al, Na, and K. This loss may modify their bulk composition, density, heat balance, and internal structure.

arXiv commentIn press in The Astrophysical Journal, 83 pages text and references, 6 tables, 30 figures

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• Laboratory spectra of hot molecules: data needs for hot super-Earth exoplanets
• Solubility of water in peridotite liquids and the prevalence of steam atmospheres on rocky planets
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• Potassium Isotope Compositions of Carbonaceous and Ordinary Chondrites: Implications on the Origin of Volatile Depletion in the Early Solar System
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• The effect of a small amount of hydrogen in the atmosphere of ultrahot magma-ocean planets: atmospheric composition and escape
• Chemical Equilibrium Calculations for Bulk Silicate Earth Material at High Temperatures
• The Exosphere as a Boundary: Origin and Evolution of Airless Bodies in the Inner Solar System and Beyond Including Planets with Silicate Atmospheres
• Modification of the radioactive heat budget of Earth-like exoplanets by the loss of primordial atmospheres
• MARVEL analysis of the measured high-resolution rovibronic spectra of the calcium monohydroxide radical (CaOH)
• The sulphur species in hot rocky exoplanet atmospheres
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• Theoretical rovibronic spectroscopy of the calcium monohydroxide radical (CaOH)
• Physicochemical Controls on the Compositions of the Earth and Planets