Size-Dependent Fallout of Icy Grains in Europa’s Water Vapor Eruptions

Jupiter's moon Europa is a primary target for astrobiological investigation, exhibiting a complex surface potentially linked to its internal ocean through tidal activity and plume outgassing. While some astronomical observations and Galileo plasma data suggest the presence of active plumes, their specific dynamics remain poorly understood. This study characterizes the transport of icy dust entrained within water vapor plumes to better understand the exchange between Europa's subsurface and surface.

We employ the Direct Simulation Monte Carlo (DSMC) method to model plume structures across a range of initial eruption velocities and gas production rates. By integrating these gas-phase results with dust trajectory modeling, we quantify the influence of gas drag on particle distribution. Our results demonstrate a clear size-sorting mechanism: fine particles (0.001–0.1 μm) undergo wide-scale dispersion, whereas coarser grains (0.1–10 μm) settle preferentially near the vent (Tseng et al., 2025). Notably, at a high outgassing rate (~10²⁹ molecules/s), gas drag becomes the primary driver of dust motion, effectively decoupling the final deposition pattern from initial ejection velocity. These findings provide a framework for interpreting surface morphology and offer predictive constraints for upcoming observations by the JUICE and Europa Clipper missions.