Another Day, Another Water World in Our Own Solar System

The solar system just keeps getting wetter and wetter. According to a new study published in Geophysical Research Letters, Enceladus is not the only Saturnian moon harboring a global ocean beneath its frozen surface. Based on new modeling, Dione, the fourth largest moon in the system, can now be called a water world as well.

Abstract

Enceladus’ gravity and shape have been explained in terms of a thick isostatic ice shell floating on a global ocean, in contradiction of the thin shell implied by librations. Here we propose a new isostatic model minimizing crustal deviatoric stress, and demonstrate that gravity and shape data predict a 38 ± 4km-thick ocean beneath a 23 ± 4km-thick shell agreeing with – but independent from – libration data. Isostatic and tidal stresses are comparable in magnitude. South polar crust is only 7 ± 4km thick, facilitating the opening of water conduits and enhancing tidal dissipation through stress concentration. Enceladus’ resonant companion, Dione, is in a similar state of minimum stress isostasy. Its gravity and shape can be explained in terms of a 99 ± 23km-thick isostatic shell overlying a 65 ± 30km-thick global ocean, thus providing the first clear evidence for a present-day ocean within Dione.