Impact breaching of Europa’s ice: Constraints from numerical modeling
Numerical simulations show that impactors can penetrate Europa's ice, creating conduits to the underlying ocean. Breaching becomes inevitable when transient cavity depth exceeds 90% of ice thickness. Results indicate that a 0.5 km comet would penetrate 5 km ice, and a 5 km comet could breach 40 km ice. Thinner ice would be breached more frequently, thicker ice less so, but even the 40 km upper estimates for ice thickness would be penetrated by comets with recurrence intervals less than 250 Ma. If actual ice thickness is 8–13 km (indicated by comparing Europan and simulated crater geometries), the ocean could be exposed by impactors in the range 0.7–1.5 km, which have recurrence intervals ≈3 to 7 Ma. Thus, it seems that Europa's ice has been penetrated often in the past and possibly in geologically recent time. The largest known impact sites, Callanish and Tyre, probably represent transition from craters to penetrating impacts. The geomorphic expression of full penetration must exist on the surface; chaos terrain is a candidate. Astrobiological materials could be transported to the ocean via these impact-created conduits.