UCLA

Sub-Neptune exoplanets are often modeled as rocky interiors surrounded by hydrogen-rich envelopes, but at the pressures and temperatures expected inside these planets, the boundary between rock and atmosphere may not remain sharp. Hydrogen can dissolve into silicate liquids and form supercritical silicate–hydrogen mixtures whose equations of state, conductivities, and phase behavior differ from those of pure end-member materials. This thesis uses first-principles molecular dynamics simulations to quantify the properties of hydrogen-bearing silicate liquids under conditions relevant to sub-Neptune interiors. I first develop a thermodynamically consistent equation of state for supercritical MgSiO3–H2 mixtures and use it to evaluate how these fluids affect planetary density structure and thermal profiles. I then calculate the electrical and thermal conductivities of these mixtures to assess whether hydrogen-bearing silicate liquids could influence magnetic field generation. Finally, I perform targeted simulations of ternary MgSiO3–H2–Fe mixtures to test whether silicate-rich and iron-rich liquids remain separated or dissolve into a single mixed phase. This thesis therefor links the atomic-scale behavior of hydrogen-bearing silicate liquids to the planetary-scale properties of sub-Neptunes.