Icy Tendrils from Enceladus

Abstract:

We extend our previous work (Mitchell et al., 2015) in simulating the
large-scale, sinuous structures, dubbed ‘tendrils’, observed in
Cassini ISS images of the E ring near Enceladus. We follow the
trajectories of particles launched from the geyser sources located
across the moon’s south polar terrain (Porco et al., 2014), assuming
the velocity distribution of Ingersoll and Ewald, (2011), and
including forces due to the gravity of Saturn and Enceladus, as well
as Saturn's magnetic and electric fields. Charging currents arising
from interactions with magnetospheric plasma and Solar UV radiation
are also included. The simulations are used to produce synthetic
images which we compare to Cassini ISS tendril images taken in 2006
and 2013. We found that specific subsets of geysers appear to be the
sources of identifiable tendril features present in the images.
However, there remained features not captured by our initial
simulations: a shift in longitude for the brightest part of the
tendrils and two features which only appear in some images.

In this initial work, we neglected Enceladus’ orbital eccentricity as
well as the periodicity and phase of the variability in geysering
activity recently discovered and attributed to a ~5-hour delay in the
diurnally variable tidal stresses at the surface (Nimmo et al. 2014).
And we made no attempt to do a photometric determination of the mass
lost from the moon into orbit around Saturn.

We will report on our progress in rectifying these inadequacies. We
will present the result of including Enceladus's orbital eccentricity,
as well as a diurnally variable particle flux out of each geyser, in
accord with the observed plume variability. Eventually, we will use
the absolute brightness of the tendrils, together with a photometric
model and information on the particle size distribution from our work,
and the work of other Cassini teams on E ring particles, to arrive at
the amount of mass leaving the moon and entering Saturn orbit.

Mitchell et al., 2015, AJ, 149, 156.
Nimmo et al., 2014, AJ, 148, 46.
Porco et al., 2014, AJ, 148, 45.
Ingersoll and Ewald, 2011, Icarus, 216, 492