Ingersoll, A. P., Porco, C. C., West, R. A., Mitchell, C., Turtle, E. P. (2006). "Cassini Imaging of the Enceladus Plumes: Measurements and Models." Eos Trans. AGU 87(52), Fall Meet. Suppl., Abstract P22B-04.


Images of the plumes are sensitive to particles, larger than a few tenths of a micron, that are in flight above the surface of Enceladus [C. C. Porco et al. (2006) Science 311, 1393-1401]. The images reveal locations of the sources and degree of collimation of the jets. The steep falloff of density with altitude suggests that most of the particles leave the surface with velocities that are less than the escape velocity, which itself is less than the thermal velocity of the gas. In other words, most of the particles are falling back to the surface. Observations at different times and phase angles give information about temporal variability and particle size. These properties will be studied in a numerical model of three-dimensional particle trajectories in the vicinity of Enceladus. Gas drag is included in the model. The goal is to match the data by varying the model parameters, including particle size, ejection velocity, mass flux, and degree of coupling to the gas. The escape flux is a derived parameter. These parameters, in turn, will be the subject of thermodynamic modeling that explores conditions in the sub-surface reservoirs from which the particles are ejected. In principle, the particles could condense from an expanding vapor, be entrained into the vapor from the walls of the conduit, or form by flash freezing of a liquid that is boiling into vacuum. Each of these possibilities has implications for particle properties and plume morphologies. The goal of this research is a comprehensive description of reservoir conditions and the depth to the zone of liquid water.