PRELIMINARY RESULTS FROM SIMULATIONS MAPPING MOBILE LID CONVECTIVE REGIME IN ICY SHELLS: USE THE FORCE (TO AVOID STAGNANT LID)

Recent observational evidence points to the existence of plate tectonics on Europa. To date, this is only other body besides Earth to demonstrate active plate tectonics. We present initial work on the viability of plate tectonics occurring on Europa applying the criteria outlined in prior studies on Earth and other terrestrial bodies, but scaled to Europa conditions and the material properties of ice.

Plate tectonics is one mode of the surface manifestation of convection within a planet’s interior. In order for it to occur, the surface must be able to behave as a collection of coherent, rigid plates that can return into the interior along subduction zones. This behavior is dependent on the material properties of the surface as well as the strength of the convection. The criteria for plate tectonics has been explored in prior studies for terrestrial bodies, but has been limited for icy moons. Convection of a planetary body’s interior does not always lead to plate tectonics on the surface. Several modes of surface expression can occur including stagnant lid, episodic overturn or mobile-lid convection. Mobile-lid convection, akin to plate tectonics, has been in operation on the Earth for, at least, the past three billions years and now appears to be active and present on Europa. The transitions between these domains have been mapped out for terrestrial bodies and depend on the tradeoffs between multiple parameters such as the strength, thickness and buoyancy of the “plates” material, the strength of convection, as well as the size of the planetary body. Similar studies have been done for convection within icy moons, but they have focused on the trade-off only between yield stress and shell thickness or used velocity boundary conditions on the side walls that may geometrically impose deformation to occur.

We will present preliminary results from 2D simulations that couple ice convection with surface deformation. Given the uncertainty of the characteristics of the ice shell, we have mapped out the range of parameters that allow for plate tectonics to occur on Europa. The simulations also allow us to constrain the strength of the material of the shell required to localize deformation. These values will then be compared against other studies that have estimated the strength of the shell based on observed deformation.