Sodium chloride as a geophysical probe of a subsurface ocean on Enceladus

Abstract

Recent data from the Cassini spacecraft suggest that an ocean exists inside Saturn's satellite Enceladus. Here, we show that the size of an ocean can be estimated if the NaCl concentration of the ocean is known. We find that concentrations of aqueous NaCl reported by Postberg et al. (2009) imply a relatively large ocean, comprising at least 17% by mass of volatiles on Enceladus. Structural calculations indicate that this ocean would underlie more of Enceladus' surface than just the geologically active south polar region, consistent with modeling of localized tidal dissipation. Conduction calculations suggest that a half-global ocean can be maintained by steady-state tidal heating, provided that clathrate hydrate dominates Enceladus' ice shell. We also find that rapid freezing of oceanic water could release large fluxes of stored tidal heat, perhaps partly explaining the anomalous energy output of Enceladus. An alternative, saltier ocean model is also examined.