PhD Thesis Defense: Tara Tomlinson

"The Influence of Composition On Porosity And Strength in Planetary Analog Saline Ices"

Abstract

This thesis investigates how composition influences the physical structure and mechanical behavior of saline ice, with implications for both terrestrial sea ice and the ice shells of ocean worlds such as Europa and Enceladus. This is done through a multi-pronged approach of both numerical modeling and laboratory experiments. Modeling results reveal that small-scale parameter variations in porosity, permeability, and permeability factor may produce large discrepancies when extrapolated to planetary scales, underscoring the need for improved experimental constraints on pore connectivity and thermochemical conditions. Laboratory analyses show that while total porosity is relatively uniform with depth, it varies strongly with composition and salinity. Terrestrial sea ice exhibits higher porosity and more connected pore networks, whereas Europa and Enceladus analogs display more isolated pore structures. These differences in pore morphology likely influence transport processes and contribute to variations in mechanical behavior. Mechanical testing further highlights compositional effects. Shear experiments indicate a transition from grain-size-controlled strength to brine-dominated weakening with increasing salinity. Flexural strength decreases on average with salinity but shows no consistent depth dependence due to competing structural factors. Compression tests reveal that frozen brine at grain boundaries can enhance strength in some cases. Findings demonstrate that empirical relationships derived from sea ice are not applicable to chemically distinct systems found on other planets. Overall, this work shows that the properties of saline ice emerge from coupled interactions among composition, microstructure, and thermodynamic conditions. These results have direct implications for modeling ice shell dynamics, interpreting geophysical observations, and assessing habitability on icy worlds, emphasizing the necessity of incorporating microscale constraints into planetary-scale models. 

Thesis Committee

• Colin Meyer (chair)
• Jacob Buffo
• Don Perovich
• Marisa Palucis
• Kathleen Craft (Johns Hopkins University Applied Physics Lab)

Contact

For more information, contact Thayer Registrar at thayer.registrar@dartmouth.edu .