%0 PhD Thesis %D 2022 %T Investigating Planetary Core Formation with Geophysical Modeling and High-Pressure Mineralogy %A , %I Harvard University %U https://dash.harvard.edu/bitstream/handle/1/37371993/v3_with_DAC.pdf?sequence=1&isAllowed=y %K MINEOS %X Earth’s core is impossible to sample or directly observe and yet is fundamentally important to the properties of, and our continued existence on, this planet. Indeed, planetary cores literally underlie every other area of geoscientific inquiry, and core properties controlled the development of Earth, Mars, and likely every other terrestrial planet. As this importance has become evident over the last century, several methods of indirectly investigating planetary cores have been developed. These include the use of mineral physics experiments to measure materials at ultra-high pressures and temperatures, seismic observations to constrain bulk physical properties, and numerical simulations to turn such data into comprehensive models of planetary interiors. In this dissertation, I present results from several studies that combine these methods in various ways to advance our understanding of the formation and evolution of the cores of Earth and Mars. Chapter 1 (General Introduction) gives a brief synopsis of the study of the deep Earth (and Mars). This includes the history of the field, the major research methodologies that appear in subsequent chapters, and the current scientific consensus concerning planetary cores. Chapter 2 (Martian Core Formation and the Geophysical Properties of Deep Mars) presents a simulation of Mars’ growth and core-mantle differentiation, parameterized by metal-silicate partitioning experiments and geophysical data measured by spacecraft. The model was able to reproduce the canonical Martian mantle composition in scenarios where Mars was built from oxidized primordial material that was highly equilibrated in a magma ocean of intermediate depth, resulting in a sulfur-rich core. This model allowed us to evaluate various physical properties of the deep Martian interior and generate predictions of observable seismic properties. We determined that to maintain consistency with measured physical parameters, the core must constitute about half of Mars’ radius, a size later confirmed by the groundbreaking seismic measurements of the InSight mission. Chapter 3 (Timing of Martian Accretion and Core Formation) extends the model described in Chapter 2 by incorporating realistic Martian accretion histories from dynamical simulations of solar system formation and constraints from the hafnium–tungsten (Hf–W) radioisotopic system. The evolution of Mars’ Hf–W signature is sensitive to a variety of accretionary conditions, especially the oxidation of primordial material. With the right conditions, it is possible to match the Martian signature for a variety of accretion histories, including ones which continue for many times longer than the previously supposed maximum growth period. Additionally, there does not appear to be a relationship between the final orbits of Mars-like bodies and the material that formed them. This implies that Mars might have accreted from a single geochemical reservoir somewhere in the protoplanetary disk before being gravitationally scattered to its modern location. Chapter 4 (Deformation Properties of Earth’s Inner Core) presents the results of diamond anvil cell radial X-ray diffraction experiments that investigated the yield strength and deformation texture of alloys similar in composition to Earth’s core. These are the first such experiments on alloys containing a light element, which we found increased alloy strength by up to an order of magnitude. The texture produced upon plastic deformation was consistent with that found by previous studies and believed to exist in Earth’s inner core. However, the enhanced mechanical strength of the alloy may imply that this texture developed by a mechanism other than deformation.