Modeling Planetary Interiors: From Microscopic to Global Scales

Published in Ph.D. Thesis, Department of Earth & Planetary Science, UC Berkeley, 2017

Committee: Burkhard Militzer (chair), Bruce Buffett, David Romps, Eugene Chiang

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Abstract

The inherent difficulty of making and interpreting measurements of the deep interior of the Earth and other planets necessitates constructing models of their structure and evolution. Properties of materials at actual planetary conditions are a key input to these models. For the Earth these conditions extend to the hundreds of GPa and thousands of Kelvin; for the energetic impact events and within the gas giants the range extends to several TPa and perhaps tens of thousands Kelvin. Despite tremendous advances in experimental techniques, much of this range of conditions remains out of reach, and thus, computer simulations of materials play an important role in characterizing materials within planetary interiors.

This thesis presents a variety of work using computational techniques to: 1) determine properties of planetary materials from first-principles simulations, and 2) apply these derived properties to models of large-scale planetary structure and processes. First-principles calculations are unique in their ability to simulate a nearly unbounded range of pressure-temperature conditions, including those beyond the capacity of any experimental techniques.

In this thesis, I discuss the physics and numerical techniques I have used and developed to simulate planetary materials at high pressures and temperatures, and to interpret and condense the results of these calculations. I also present results of studies applying the first-principles techniques to specific problems in planetary science. I test the stability of compact rocky cores in the metallic hydrogen-helium envelopes of gas giants, finding that such cores are likely to undergo dissolution and erosion. I then explore the miscibility of terrestrial cores and mantles at extreme temperatures. I predict that this mixed rock-metal state is of importance in catastrophic giant impacts that are now thought to be commonplace in the early history of the terrestrial planets, or deep inside ``super-Earth’’ exoplanets.

I continue by detailing studies applying material equations of state from simulation and experiment. I describe work towards developing a more comprehensive thermo-chemical model of liquid iron alloys integrated with models of Mercury’s thermal history and magnetic field energetics. I then describe the derivation and implementation of a new numerical, non-perturbative method for precise calculations of gravitational field strength for a rotating, liquid planet with tides. I then look at the consequences of this new method for the tidal responses of Jupiter and Saturn, finding a significant, previously uncharacterized contribution arising from the influence of rotation. Finally, I detail an ongoing effort using interior structure models of Jupiter to interpret the drastically improved measurements of Jupiter’s gravity by the \textit{Juno} spacecraft mission. I find evidence for the existence of a dilute core in spite of difficulties reconciling first-principles equations of state with observations of the planet’s atmosphere.