Simulations of Enceladus’ Tendril Features

Abstract:

We simulate the large-scale, sinuous structures observed in Cassini
ISS images of the E ring near Enceladus, dubbed ‘tendrils’, by
numerically integrating the trajectories of particles launched from
the sources of geysers along the “tiger stripe” fractures crossing
Enceladus's South Polar Terrain (SPT) . In addition to gravitational
forces due to Saturn and Enceladus, we include electromagnetic forces
due to Saturn's magnetic and electric fields, and charging currents
arising from particle interactions with magnetospheric plasma and
Solar UV radiation. These simulations are used to produce synthetic
images which are then compared to Cassini ISS tendril images taken in
2006 and 2013.

For each image, we follow into the E ring the trajectories of
particles erupting from the 36 most active geysers, using the 3D
configuration and strength information reported in Porco et al., 2014
and the velocity distribution in Ingersoll and Ewald, 2011. This set
accounts for more than 50% of the total measured activity and also
provides a good sampling of geyser orientations. We find that specific
subsets of geysers appear to be the sources of identifiable tendril
features present in the images, and that none of the tendril features
can be reproduced by low eccentricity E ring particles, We conclude
that the tendrils are produced by geyser particles recently erupted
from Enceladus.

Finally, we find indications of the geysers’ time variability in the
changing appearance of the tendrils from one observation to the next.
We have been able to reproduce these changes in a crude way by varying
the number of particles ejected from the sources with time, according
to the brightness variation model presented in Nimmo et al. 2014.

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