Long transit time from the Seafloor to the Ice Shell on Enceladus.

(Zhang. Y., Bire, S., Wang, S., Nath, A., Ramadhan, A., Kang, W., and Marshall, J.), Monthly Notices of the Royal Astronomical Society, vol. 541, no. 2, pp. pages, 2025.

Abstract

Tidal heating within the rocky core of Enceladus can drive convection in the ocean, inducing material transfer between the sea floor and the ice shell. This heating may be focused into narrow stripes, enhancing local heating rates that could trigger convection. Here, we use high-resolution numerical simulations to investigate the transport of tracers from the seafloor to the ocean top due to convection initiated by bottom heating patterns. For parameters typical of Enceladus, we find that horizontal temperature gradients induced by uneven bottom heating patterns generate turbulent vortices due to baroclinic instability. The resulting lateral mixing makes plumes spread horizontally quickly by entraining the cold ambient water, possibly mixing away lateral temperature gradients by the time the plume reaches the ocean top. The natural Rossby number, a non-dimensional number that characterizes the importance of rotation, is identified as a controlling parameter. Small natural Rossby numbers correspond to rotationally dominated plumes, vigorous lateral mixing, and slow vertical transport. Large natural Rossby numbers correspond to non-rotating plumes that rapidly bring tracers to the ocean top with limited lateral spreading. We establish a scaling between the vertical transit time and the natural Rossby number, which predicts a transit time of tens of years or more across the ocean of Enceladus. This long transit time is inconsistent with an association between silicon-rich particles in the E ring of Saturn and hydrothermal activity on Enceladus transporting silica particles from the core to the surface. Finally, a detailed regime diagram is presented to summarize our results.

doi = 10.1093/mnras/staf1008