The 3D Structure of Saturn Magnetospheric Neutral Tori Produced by the Enceladus Plumes

Abstract

This research provides updated and validated spatial distributions of Enceladus generated H₂O, OH, and O neutral tori. These tori are produced by the primary neutral source, Enceladus, and consist of populations of coorbiting neutral particles that provide the bulk of heavy molecules to Saturn's (neutral particle dominant) magnetosphere. We conducted self consistent neutral particle and plasma modeling that is constrained and validated by all relevant Cassini and Hubble Space Telescope observations. Our results include a three dimensional (3D) spatial distribution of all three neutral tori. Significant findings include (1) short term plume variability combines to produce an average H₂O source rate of ∼280 kg/s; (2) Enceladus plume variability does not impact the neutral tori distribution because it occurs on time scales less than the orbital periodicity (<17 h) (3) H₂O source torus particles quickly dissociate in <65 days while only ∼22% are directly ionized; (4) the resulting OH torus dissociates in <40 days and only ∼11% are directly ionized; (5) ∼59% of the significantly dispersed O torus is directly ionized; and (6) the near plume environment is very important and relatively small changes (<0.5 eV) in the core electron population within the plume region dramatically change the H₃O⁺ abundance.