Surface Deposition of the Enceladus Plume and the Zenith Angle of Emissions

Abstract

Since the discovery of an ice particle plume erupting from the south polar terrain on Saturn's moon Enceladus, the geophysical mechanisms driving its activity have been the focus of substantial scientific research. The pattern and deposition rate of plume material on Enceladus' surface is of interest because it provides valuable information about the dynamics of the ice particle ejection as well as the surface erosion. Surface deposition maps derived from numerical plume simulations by Kempf et al. (2010) have been used by various researchers to interpret data obtained by various Cassini instruments. Here, an updated and detailed set of deposition maps is provided based on a deep-source plume model (Schmidt et al., 2008), for the eight ice-particle jets identified in Spitale and Porco (2007), the updated set of jets proposed in Porco et al. (2014), and a contrasting curtain-style plume proposed in Spitale et al. (2015). Methods for computing the surface deposition are detailed, and the structure of surface deposition patterns is shown to be consistent across changes in the production rate and size distribution of the plume. Maps are also provided of the surface deposition structure originating in each of the four Tiger Stripes. Finally, the differing approaches used in Porco et al. (2014) and Spitale et al. (2015) have given rise to a jets vs. curtains controversy regarding the emission structure of the Enceladus plume. Here we simulate each, leading to new insight that, over time, most emissions must be directed relatively orthogonal to the surface because jets "tilted" significantly away from orthogonal lead to surface deposition patterns inconsistent with surface images. Data for maps are available in HDF5 format for a variety of particle sizes at http://impact.colorado.edu/southworth_data.