Impact Crater Morphology and the Structure of Europa's Ice Shell

We performed numerical simulations of impact crater formation on Europa to infer the thickness and structure of its ice shell. The simulations were performed using iSALE to test both the conductive ice shell over ocean and the conductive lid over warm convective ice scenarios for a variety of conditions. The modeled crater depth-diameter is strongly dependent on the thermal gradient and temperature of the warm convective ice. Our results indicate that both a fully conductive (thin) shell and a conductive-convective (thick) shell can reproduce the observed crater depth-diameter and morphologies. For the conductive ice shell over ocean, the best fit is an approximately 8 km thick conductive ice shell. Depending on the temperature (255–265 K) and therefore strength of warm convective ice, the thickness of the conductive ice lid is estimated at 5–7 km. If central features within the crater, such as pits and domes, form during crater collapse, our simulations are in better agreement with the fully conductive shell (thin shell). If central features form well after the impact, however, our simulations suggest that a conductive-convective shell (thick shell) is more likely. Although our study does not provide a firm conclusion regarding the thickness of Europa’s ice shell, our work indicates that Valhalla class multiring basins on Europa may provide robust constraints on the thickness of Europa’s ice shell. Plain Language Summary Jupiter’s moon Europa has an ocean beneath its ice shell and is one of the targets for a search for life in the solar system. Impact craters on Europa exhibit unusually shallow depths at larger diameters and show interesting features such as central pits and domes. These characteristics are intrinsic indicators of conditions at depth, such as the thickness and structure of the ice shell. Despite recent developments in observational and theoretical techniques, the question whether the ice shell covering Europa’s ocean is thin or thick remains open. The implications of thin versus thick ice shell are extremely pertinent to the search for life on Europa and future space mission planning. We performed computer simulations to model the formation of impact craters on Europa to probe the thickness and structure of its ice shell. Our study explored whether Europa’s ice shell is thin or thick by simultaneously matching our simulation results to the observed crater dimensions and features. Our results suggest that both thin and thick ice shell scenarios can reproduce the observed crater depths, diameters, and morphologies. In future work, modeling even larger impact craters known as multiring basins might better constrain Europa’s ice shell thickness and structure.