Volatile Solubility Experiments on Planetary Melt Analogs and Implications for Rocky Exoplanet Interior-Atmosphere Connections

Magma worlds, due to their hot, extended atmospheres are readily characterized spectroscopically by ground- and space-based telescopes, such as JWST. As yet, the lack of direct observations means that the nature and composition of these planets’ atmospheres are poorly constrained.  Because the atmospheres of these planets are thought to be the result of chemical equilibrium with their interiors, their mass and composition are modulated by the solubilities of major gases in the magma. Therefore, we require a theoretical framework, informed by experimental data, to determine how volatile elements partition between the interior and atmosphere for diverse planetary compositions. Of the major gases, hydrogen is particularly important due to its cosmic abundance, significant presence during rocky planet formation if the planet forms before the nebular gas disk dissipates, and its role as an essential life-forming element. However, there is currently a lack of experimental data on hydrogen solubilities in diverse planetary magmas at the temperature, pressure and redox conditions relevant for magma worlds. To fill this gap, we performed new hydrogen solubility experiments on exoplanet melt analog materials at high temperatures (≥1400 ℃) using a 1-bar H₂-CO₂ gas-mixing furnace and an aerodynamic laser levitation furnace coupled to an FTIR spectrometer. Using FTIR spectroscopy, we determine the mechanism for hydrogen’s dissolution and its concentrations in these melts. We will present the findings of our experiments and how we can incorporate them into volatile partitioning models to determine the effect of hydrogen solubility on the atmospheric compositions of magma exoplanets. We will discuss the implications of volatile dissolution on the interior-atmosphere connection for magma planets including the early Earth.