The definitive fate and magnetospheric distribution of neutral torus particles originating from Enceladus

Abstract:

Saturn’s magnetosphere is unique in that the plumes from the small icy moon, Enceladus, provide the primary source for heavy particles in Saturn’s neutral particle dominated magnetosphere. The resulting co-orbiting neutral particles interact with ions, electrons, photons and other neutral particles to generate separate H₂O, OH and O populations (tori) that co-orbit around Saturn. Characterization of these toroidal distributions is essential for understanding Saturn magnetospheric sources, composition and dynamics. Unfortunately, limited direct observations of these features are available so modeling is required. Jurac and Richardson (2005) executed a self-consistent torus model to provide a detailed understanding of Saturnian neutral tori which is still used as input into current research. Unfortunately, these results are based on pre-Cassini observations while our knowledge of Enceladus and Saturn’s magnetosphere has evolved significantly over the last 15 years since the Jurac and Richardson (2005) results.

In a similar fashion, we have coupled a 3-D neutral particle model (Smith et al. 2004, 2005, 2006, 2007, 2009, 2010) with a plasma transport model (Richardson 1998; Richardson & Jurac 2004) to develop a self-consistent Saturn torus model that has been upgraded to incorporate the most current findings on Saturn’s magnetosphere and the Enceladus plume source. We have examined all possible Enceladus plume source rates and constrained our results with all available observations which were collected from the Cassini, Hubble Space Telescope, Voyager 1& 2 and Pioneer 11 missions. Our result is the most accurate and definitive distribution of Enceladus-generated neutral tori in Saturn’s magnetosphere which provides a clear picture of how particles from the Enceladus plumes interact with Saturn’s magnetosphere. For this presentation, we present the 3D distribution of Saturnian neutral tori as well as a map of how the originating H₂O neutral particles dissociate, ionize and/or disperse to create this neutral particle dominated magnetosphere.