Icy plumes on Enceladus

Abstract

This Master thesis consists in investigating the formation and behavior of vapor and ice plumes. These plumes can occur in icy moons of our solar system, such as Europa or Enceladus, which are widely believed to have a liquid water ocean beneath their crust. These plumes most likely consist of a sub- surface reservoir of liquid water fed by the ocean, a crevasse, and a vent at the ice surface. Under certain conditions, the liquid water starts evaporating and, due to the high reservoir pressure, the result- ing vapour starts flowing upwards through the crevasse. Due to the high pressure difference between the reservoir and the vent at near vacuum conditions, supersonic plumes are formed. This work stud- ies the reservoir conditions and plume physics, gathering different models available in literature and comparing them to available data, such as that from observations from Cassini spacecraft. First, a model capable of describing the condensation phenomenon is sought. The effects of the consequent release of latent heat to be absorbed back by the vapour flow are also studied. Grains will then start to nucleate and grow. These particles can either collide and stick to the walls or keep flowing mixed with the vapour. Some of the above mentioned latent heat can be absorbed back by the icy walls of the crevasse and generate more vapour by sublimation. Further, this project also aims to extend the model mentioned above so that it considers the effects of a fully multi-phase, multidimensional flow, checking for the effects of rarefaction and hence the limits of the continuum assumption. Finally, a similarity analysis is performed so that the influence of working with scales as different as the channels used in the laboratory at TU Delft or the real dimensions of the crevasses found in Enceladus can be fully tackled. Any progress on the ongoing investigations about the physical characteristics of these plumes could be crucial to deepen our knowledge on geological mechanisms in icy moons of our solar system. This, in turn, could trigger research on organic compounds present in these moons, perhaps even allowing for the existence of life. Further, the model used throughout this work can be applied to study power production devices where condensation might play an important role, such as steam turbines for light-water-cooled nuclear reactors or turbines proposed to be used in innovative organic Rankine cycle (ORC) configurations, natural gas supersonic separators, supercritical CO2 compressors for large-scale carbon capture and sequestration (CCS) and micro-nozzles.