Curtain-based Maps of Eruptive Activity in Enceladus’s South-polar Terrain at 15 Cassini Epochs

Abstract We map surface eruptive activity in Cassini images of Enceladus’s south-polar terrain (SPT) at 15 epochs spanning late 2009 to late 2015 using a refined curtain approach derived from that of J. N. Spitale et al. (S2015). This refined approach gives a better representation of the uncertainties in identifying source fractures by allowing for multiple candidate sources to be identified for an observed eruption. Our analysis includes the five epochs studied by S2015, which were independently reexamined here. The results in this work are intended to supersede those of S2015. About 80% of the currently active fracture system in the SPT (by length) was observed to be erupting at a level detectable in Cassini images during every epoch. On/off variability is observed almost exclusively at the fringes of the fracture system, possibly reflecting a thickening ice shell away from the pole. No definitive connection between surface activity and the roughly factor of 3 plume optical depth variation with mean anomaly is made here, but our results do not rule out a scenario where the pattern of eruptive activity on the surface is correlated with the mean anomaly, provided only the fractures at the fringe of the SPT ever turn completely off during the tidal cycle. Our results are best explained by eruptions sourced directly from the ocean.