Surface‐To‐Ocean Exchange by the Sinking of Impact Generated Melt Chambers on Europa

Impacts into icy bodies often generate near‐surface melt chambers and thermal perturbations that soften the ice. We explore the post‐impact evolution of non‐penetrating impacts into Europa's ice shell. Simulations of viscous ice deformation show that dense impact melts founder before refreezing. If the transient cavity depth exceeds half the ice shell thickness, over 40% of the impact melt drains into the underlying ocean. Drainage of impact melts from the near‐surface to the ocean occurs on timescales of 103–104 years. The drainage of melts to the ocean occurs for all plausible ice shell thicknesses and ice viscosities, suggesting that melt foundering is a natural consequence of impacts on icy worlds. Post‐impact viscous deformation is an important process on icy worlds that affects cryovolcanism, likely modifies crater morphology, creates porous columns through the ice for surface‐to‐ocean exchange, and may supply the oxidants required for habitability to subsurface oceans. Plain Language Summary Europa is an ocean world with an outer ice shell in our Solar System. Outer ice shells on ocean worlds serve as both a barrier and facilitator for internal ocean habitability and the detectability of its potential inhabitants. A prominent feature we observe on the surface of ice shells is highly variable craters from impacts that indent but do not penetrate the ice shell. Here, we find that many of the impacts into Europa's ice shell would have generated large near‐surface melt chambers, which rapidly drain into the underlying ocean and form a continuous surface‐to‐ocean melt column. This melt drainage occurs with any entrained surface materials and provides a consistent means of exchange between the surface and ocean, which likely increases the habitability of internal oceans. Furthermore, this drainage displaces large volumes of water from below impact craters, on the order of 10's of cubic kilometers. This large scale drainage may help to explain the wide range of collapsed, enigmatic crater morphologies observed on Europa, and other ocean worlds. Key Points Impacts into ice shells generate melt chambers that viciously deform and sink through the ice shell, likely modifying crater morphologies If transient cavity depth exceeds half the ice thickness, impact melts drain to the ocean and may deliver oxidants needed for habitability Draining impact melts form a stable porous channel that connects the ocean to near‐surface and may allow for the escape of ocean fl