Laboratory Research on Ice Rheology in support of Ocean World Exploration

Understanding the rheology of ice in the outer shells of ocean worlds is important for a variety of reasons. The mechanical behavior has long been studied to make sense of intriguing surface morphologies, some of which bear striking resemblance to rocky features on Earth and other bodies, some of which are totally unique. The mechanical behavior of planetary ice also is used to provide possible answers to questions related to transport and conveyance of melt and/or chemical species, which in turn addresses potential habitability. Finally, in the era of ocean world exploration, knowledge of the mechanical behavior of very cold and moderately impure ice provides critical information needed to manage expectations and inform protocols for future missions. In this presentation I will share results from experiments conducted in our lab on ice and ice-mixtures that are designed to measure the mechanical behavior at planetary conditions. In particular we use a custom cryogenic, servo-controlled biaxial apparatus to measure frictional response of ice sliding on ice to explore faulting behavior in the upper, brittle portion of an icy shell. Moving beyond simple Coulomb analysis, we measure fault stability as a function of temperature and velocity, which point to a predicted source region for icequakes at depth, a so-called “seismogenic zone” for icy worlds. We employ rate- and state- dependent frictional properties determined from experiments in numerical models to describe a variety of fault and boundary types, including thrust, subduction, and strike-slip faulting. We explore the nature of unstable frictional behavior by analyzing laboratory stick-slip events for frequency-magnitude, or recurrence, relations. Such information can inform expected seismic activity and be useful for planning instrument sensitivity and can be used ultimately to interpret results from a lander-based seismometer. Additionally we will present results from performance testing of communications hardware that may be deployed in the vicinity of such active faults. We will share mechanical and optical results from a series of shear-testing experiments on fiber optic communication tethers embedded in ice and will articulate the feasibility of their use in future probe missions that will descend into an icy shell. The experimental work coming out of our lab seeks to unravel the dynamic properties of ice on icy moons, identify challenges that may arise when spacecraft interact with it, and develop the technology required for assessing the habitability of ocean worlds.