On the structure of the Enceladus plume

Abstract

ABSTRACT The detection of a water-rich plume erupting from ‘tiger stripes’ near the Enceladus south polar region is an important discovery of geologically active satellites within the Solar system. In this work, we apply an analytical approach to model the plume structure, using as a diagnostic the CO2 distribution extracted from the Cassini Ion and Neutral Mass Spectrometer measurements made during the E14, E17, and E18 flybys. Special focus is placed on the modelling of the spike-like structures by including only sources with substantial contributions to the plume densities. Such a procedure reduces greatly the model complexity and helps to better constrain the source parameters. Both the model source rate and Mach number are found to vary considerably among different sources during the same flyby and also among different flybys for the same source, revealing a complicated spatio-temporal variability in the plume structure. Our analysis suggests a total escape rate of (1.0–7.1) × 1026 s−1 for CO2 and (2.4–6.6) × 1028 s−1 for H2O, in broad agreement with previous estimates. Of particular interest is our identification of a tentative correlation between the Mach number and thermal brightness, of which the latter is a tracer of the geological activity of the emission source. Such a relation should be able to provide more insights into the nature of geyser emission along the ‘tiger stripes’.