Frictional Strength, Stability, and Potential Shear Heating on Icy Satellite Faults.

We determined the frictional strength and stability of polycrystalline ice and ice‐ammonia to constrain fault behavior on icy satellites such as Enceladus and Europa. Friction experiments including velocity steps and slide‐hold‐slide tests were conducted to measure the steady‐state coefficient of friction, velocity dependence and healing between temperatures of 98 and 248 K at a normal stress of 100 kPa. Rate‐state friction parameters determined from velocity steps provide stability values. The friction results are used to infer fault strength and frictional heating of an icy crust with depth for both a pure ice crust and one containing ammonia. We find a reduced coefficient of friction for an ammonia‐bearing crust and stronger velocity dependence in the presence of partial melt. The temperature dependence of fault stability maps a seismogenic zone with depth analogous to the synoptic model for terrestrial fault stability, where we find instability between 0.7 and 3.9 km with a return to stability from 4.6 km if we assume a 6 km ice shell. We consider the role of sliding velocity and fault thickness on localized frictional heating in both systems and estimate the depth of melt generation in an ammonia‐bearing crust. Our results imply that faults at conditions similar to icy satellites can be seismogenic. Plain Language Summary: We performed laboratory friction experiments with ice at conditions (e.g., temperature, composition, stresses) analogous to tidally driven faults on icy satellites in the outer solar system. We observed a temperature dependence on the coefficient of friction of ice under these conditions, which may help improve shear heating models on icy faults. We use the velocity dependence of friction observed in the experiments to constrain the depths (based on temperature) in a 6 km ice shell where seismic activity may occur. We find instability between 0.7 and 3.9 km with a return to stability from 4.6 km. We explored the effect of partial melt on ice friction and fault stability using ice‐ammonia mixtures and found that the presence of ammonia decreases the coefficient of friction while the presence of partial melt increases the velocity dependence. Key Points: Velocity weakening friction behavior is observed below 220 K, indicating a potential seismogenic zone with depth on icy moonsWe establish temperature dependence of the coefficient of friction for water ice that can be used to improve shear heating modelsThe effect of solid‐state impurities on friction is constrained using homologous temperature and melt fraction with ice + ammonia mixtures [ABSTRACT FROM AUTHOR]