Abstract DGP2026-49

Europa’s surface is geologically young and displays widespread tectonic and cryovolcanic modification, yet the mechanisms driving this activity are still debated. With an average surface age of ~40–90 Myr (Bierhaus et al., 2009), Europa likely experienced resurfacing in the recent past, and impacts are a plausible trigger because they impose strong, localized perturbations on the ice shell. In addition to crater formation, impacts generate transient heating and can emplace or redistribute dense, salt- and dust-bearing material, thereby modifying the dynamics and material mixing within the shell.

A major uncertainty is Europa’s ice-shell thickness, with published estimates ranging from <1 km (Billings et al., 2005) to ~90 km (Villela et al., 2020), while recent work favors ~23–47 km (Howell, 2021). Crater and basin morphologies provide key constraints on the background thermal structure and whether heat transport is predominantly conductive or convective. Crater-depth observations and numerical modeling indicate a transition in morphology for diameters ≳8 km, consistent with a mechanically weak layer at ~7–8 km depth (Schenk, 2002; Bray et al., 2014). This weak layer could reflect warm, deformable ice associated with convection or a shallow ocean interface (e.g., Silber and Johnson, 2017). Recent modeling of multiring basins similarly supports an ice shell thicker than 20 km, consisting of a ~6–8 km conductive lid over a warm convecting region (Wakita et al., 2024).

Here we quantify the post-impact thermo-chemical evolution using the geodynamic code GAIA (Hüttig et al., 2013). Impact-induced thermal and compositional anomalies are parameterized using scaling laws (Melosh, 1989). We assume that impact-generated meltwater refreezes rapidly, but leaves behind a residual thermal anomaly and a compositional anomaly within the shallow shell. The models include a composite creep rheology (Goldsby & Kohlstedt, 2001), pressure- and temperature-dependent thermal expansivity and thermal conductivity (Feistel & Wagner; Wolfenbarger et al., 2021), and tidal heating (Tobie et al., 2003). We test scenarios with different impactor sizes (radius 0.5–1.8 km), background thermal states at the time of impact (cold conductive vs. warm convective shells), and rheology (via grain size). Compositional density anomalies are modeled as mixtures of ice, salts, and dust; we explore salt concentrations from Earth-ocean values up to 2–4 times higher. We investigate the effects of impact-induced thermal and compositional anomalies on the dynamics and material transport within the ice shell.

Our simulations indicate that impacts can initiate convection beneath an otherwise conductive shell by locally reducing viscosity and increasing buoyancy stresses. In cold shells, impactor-derived material may remain trapped within the conductive upper layer if surface mobilization does not occur, prolonging near-surface anomalies. For sufficiently large impacts, the dense anomaly reaches the convecting layer, becomes entrained and mixed, and can be transported toward the ice–ocean interface.

In the future, we will replace scaling-law heating with shock-physics-based impact thermal anomalies and translate the resulting temperature- and salinity-driven density variations into predicted gravity-anomaly patterns relevant to Europa Clipper and JUICE.