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

Abstract

Fractures and vents in the ice crust of Europa, exposing the sub-surface ocean or liquid-water inclusions to the vacuum, might be responsible for the generation of water-vapor plumes. During its passage through the ice, the plume vapor is expected to partially condense on the cold ice walls. Together with other effects (water spillage, compression forces, etc.) this mechanism likely contributes to sealing the vent. In this work, we develop a simple lumped-parameter model that can quantify how quickly a hypothetical vent of prescribed width would be sealed via water-vapor deposition. As an example, we apply our model to the vent size and density conditions inferred from the 2012 Hubble Space Telescope plume detection, predicting a sealing time of about 30 minutes. This suggests that the actual ice fracture might have been larger than originally proposed and/or the plume density at the vent might have been lower. While many other effects could have been present and responsible for sealing the vent, our estimates indicate that vapor deposition might have played a major role in eventually shutting off the observed plume. 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 vapor deposition and are thus incompatible with observations.