FORMING RIDGE-AND-TROUGH SYSTEMS ON ICY SATELLITES: INSIGHTS FROM PHYSICAL ANALOGUE MODELING (Invited Presentation)

Analogue models have led to valuable insights into Earth tectonics, but have been underemployed for icy worlds. As such, we create a two-layer analogue model for icy satellite surface deformation, in order to explore how the brittle surface and the ductile subsurface interact on these bodies to form the surface structures that we observe. This interaction has implications for the resurfacing history of such bodies and could potentially reveal current or past ice shell thicknesses when the surface structures formed. Additionally, we will be able to constrain the rheology and mechanisms controlling the formation of surface structures on icy bodies such as Europa.

Our analogue model consists of a ductile, low viscosity layer underlying a cohesive brittle layer. We initially use therapeutic putty with a measured viscosity of about 10⁴ P×s for our ductile layer and fine-grained sand for our brittle layer. We chose these materials for our initial experiments because they will scale up properly to conditions on Europa. For example, if we scale with the cohesive strength of our sand (~60 Pa) and use well accepted values for Europa, we get a scale where about 2 km on Europa corresponds to 1 cm in our model, or 10^-5 scale factor. We run each experiment for 24 hours, corresponding to 10⁵-10⁶ years on the icy satellite of interest. Each experiment experiences the same amount of bulk strain (~33%) at the same strain rate (~10^-6/s), to allow for direct comparison between the experiments and investigate the effect of varying the thickness of the sand layer (corresponding to brittle ice shell thickness). In the compression experiments, we observe the formation of curvilinear ridges on the surface with varying wavelength depending on the thickness of the sand layer. When the sand is brushed off the surface to reveal the putty underneath, we observe that thrusts have formed in the sand layer and penetrated to the ductile layer. These results have been found for Earth analogues in prior studies, but this is the first study to pick materials with proper scaling and run at proper strain rates to relate these structures to icy worlds. In addition to running the extensional experiments, we will also run experiments with multiple episodes of deformation to explore the possibility of tectonic resurfacing on icy satellites.