The implications of tides on the Mimas ocean hypothesis

Abstract

We investigate whether a present‐day global ocean within Mimas is compatible with the lack of tectonic activity on its surface by computing tidal stresses for ocean‐bearing interior structure models derived from observed librations. We find that, for the suite of compatible rheological models, peak surface tidal stresses caused by Mimas' high eccentricity would range from a factor of 2 smaller to an order of magnitude larger than those on tidally active Europa. Thermal stresses from a freezing ocean, or a past higher eccentricity, would enhance present‐day tidal stresses, exceeding the magnitudes associated with Europa's ubiquitous tidally driven fractures and, in some cases, the failure strength of ice in laboratory studies. Therefore, in order for Mimas to have an ocean, its ice shell cannot fail at the stress values implied for Europa. Furthermore, if Mimas' ocean is freezing out, the ice shell must also be able to withstand thermal stresses that could be an order of magnitude higher than the failure strength of laboratory ice samples. In light of these challenges, we consider an ocean‐free Mimas to be the most straightforward model, best supported by our tidal stress analysis.

Charon: A Brief History of Tides

“…The equations were derived for a five‐layer body in which the core and ocean layers are assumed to be fluid. As in our previous work (Rhoden et al, 2015; Rhoden et al, 2017), we find that reducing the thickness of the innermost layer (i.e., the liquid core) to a radius of 10 km, and assigning it the same density as the overlying silicate layer, is equivalent to using a four‐layer model with a solid silicate innermost layer. Additional details as to the formulation, validation, and assumptions can be found in Rhoden et al (2015) and Rhoden et al (2017).…”

What Confines the Rings of Saturn?

“…= 42.1 km/Myr; thus, Tethys may be decelerating Mimas' orbital migration, and if the latter has been caught in the resonance since its formation, the migration time-scale would then be slightly larger. However, recent studies of Mimas suggest that it may possess a global subsurface ocean (Tajeddine et al 2014, Noyelles et al 2016, Noyelles 2017, Caudal 2017, although such a claim is difficult to reconcile with the absence of surface fracturing (Rhoden et al 2017). If this is true, orbital migration could have been delayed recently by tidal dissipation in the satellite, thus increasing the estimated age.…”

Evolution of Saturn’s mid-sized moons

“…On Mimas’ closer-in, more eccentric orbit, saturnian tides should be 30 times stronger 20 . Yet, Mimas shows no geological activity 1;21 . This dichotomy must arise from their differing propensity to deform due to tides, as previously postulated 22–24 but not elucidated.…”