Sealing Europa's vents by vapor deposition: An order of magnitude study

Fractures and vents in the ice crust of Europa, exposing the sub-surface ocean to the vacuum, might be responsible for the generation of planetary-scale water-vapor plumes. During its passage through the ice, the plume vapor is expected to partially condense on the walls, depositing until the vent is sealed. We develop a lumped-parameter model to analyze the sealing time scales. Neglecting all other possible mechanisms (water spillage, compression forces, etc.), we find shutting-off times compatible with the 7-hour plume observed in 2012 by the Hubble Space Telescope, suggesting that vapor deposition alone could have been responsible for sealing the vent. A map of sealing times vs. plume density, mass flow rate and aperture areas is given. Plume quantities from the literature are analyzed and compared to our results. For a given plume density/mass flow rate, small apertures would be sealed quickly by molecular deposition and are thus incompatible with observations.