Implications of second-order resonance for the thermal and orbital evolution of Mimas

Abstract

ABSTRACT Mimas’s current eccentricity is not being excited by any present-day resonance. We investigate whether its eccentricity could have been excited by passage through the set of resonances associated with the Mimas:Enceladus 3:2 commensurability, which occurred roughly 0.3 Gyr ago. Both the 3:2 e-Mimas resonance and the 6:4 mixed resonance can explain the present-day eccentricity without violating heat flux constraints imposed by the absence of relaxation of the Herschel impact basin. We favour the 6:4 mixed resonance because it occurs first and often prevents capture into the subsequent 3:2. During passage through the 6:4 the k2/Q of Mimas was less than $\rm 2\times 10^{-5}$, while that of Enceladus was $\lt \rm \sim 5\times 10^{-5}$. Mimas’s lack of dissipation can be explained by a cold, rigid ice shell and no subsurface ocean, while Enceladus must have subsequently become more dissipative, probably as a result of its capture into the 2:1 resonance with Dione.