2026 Theses Doctoral

Experimental Constraints on Frictional and Poroviscous Processes on Icy Moons

Zaman, Maheenuz

Potentially habitable ice-covered ocean worlds appear to be widespread in the outer solar system and beyond, with purported global subsurface oceans on moons of the giant planets, dwarf planets, and exoplanets. Many of the icy shells on these worlds that encase subsurface oceans have been found to be geologically active, with ongoing ice-ocean exchange processes that leave clues about the ocean chemistry. However, characterizing the dynamics of the ice shell requires understanding of the mechanical behavior of ice at these conditions. The purpose of this thesis is to constrain frictional and poroviscous processes in the ice shell through laboratory experiments on the mechanical behavior of ice at conditions relevant to ocean worlds.

The first two chapters explore the frictional strength and stability of faults on icy satellites. The first chapter presents the results of steady-state ice-on-ice friction experiments with pure water ice and ice doped with ammonia at a range of temperatures appropriate to depths within an ice shell. I identify a homologous-temperature dependence on the frictional strength of binary ice mixtures and, using a rate-and-state frictional framework, identify a temperature-dependent seismogenic zone with depth in an ice shell. The second chapter considers the effects of oscillatory loading on the frictional behavior of ice, analogous to tidal forcing on icy-satellite faults. Here, I show that oscillatory loading alters the frictional stability of ice, implying generally more unstable sliding on icy faults relative to the steady-state loading case. I also show through forward modeling of our laboratory experiments at tidal forcing frequencies that oscillating friction may lead to weaker faults with overall lower frictional heating rates than previously assumed, implying less potential for shallow, frictionally generated partial melt in the ice shell.

The last two chapters explore the mobility of brine in the ice shell through observations of the dynamics of partially molten saline ice. The third chapter presents the results of axial compaction experiments on partially molten saline ice, where melt is extracted as the ice compacts. Here, I quantify the dependence on axial stress and melt fraction of the compaction viscosity of partially molten saline ice and derive a constitutive porosity-evolution equation that is broadly applicable to partially molten geologic materials at low melt fractions. I make the first experimentally derived estimates for the compaction length of partially molten ice, the length scale over which pressure changes from melt flow and ice compaction are transferred in a partially molten system and which controls melt drainage rates and astrobiologically relevant tracer transport. I find that the compaction length is likely to be orders of magnitude smaller than the range of estimated thicknesses of an ice shell, implying that brine migration rates are highly susceptible to local-scale thermodynamic heterogeneities and, as a result, may be less efficient than previously assumed.

In the fourth chapter, I present the results of surface-tension-driven melt migration experiments on a partially molten saline ice aggregate under confining pressure. Here, the melt migrates from a partially molten saline ice source to a fully dense, initially melt-free pure water ice sink. Adapting a two-phase-flow theoretical framework developed for terrestrial magma dynamics, I simulate the results of these experiments using a force-balance framework in which melt is driven by capillary forces and resisted by viscous compaction. By fitting the simulation results to the experimental melt-migration profiles, I make estimates for the permeability of texturally equilibrated, partially molten, granular saline ice and find that the permeability may independently depend on both temperature and solute composition at equivalent melt fractions. This is in contrast to the permeability of texturally disequilibrated columnar ice, which is predominantly controlled by melt fraction and exhibits a percolation threshold. I suggest, based on these results, that the permeability in the ice shell will depend on the local formation conditions of the ice in specific geodynamic settings.

This dissertation as a whole explores the “story” of melt in the ice shell of ocean worlds from the perspective of the mechanical behavior of ice, from frictional melt generation to melt migration under two-phase flow.