Enceladus, one of Saturn’s icy moons, exhibits active geology and compelling evidence for a subsurface ocean. The detection of ammonia in its plumes indicates that ammonia–water ice mixtures likely play a critical role in shaping its internal evolution by lowering the melting point of ice. However, the distinct thermodynamic properties of both ammonia monohydrate (\ (NH₃ H₂ O\) ) and ammonia dihydrate (\ (NH₃ 2H₂ O\) ) have not been systematically evaluated in geophysical models. In this study, we present numerical geodynamic simulations that explore how each phase influences the thermal structure, onset of convection, and potential for thermodynamic conditions favorable for partial melting within Enceladus’s ice shell, under varying ice shell thicknesses, reference viscosity, and thermodynamic parameters. Our results show that both ammonia hydrates allow for the development of conditions conducive to localized melting and influence convective behavior under specific constraints. Additionally, the ammonia dihydrate system may sustain convective activity even at relatively high viscosities, allowing for the generation of localized partial melting. These findings highlight that ammonia hydrate phase composition might significantly influence geodynamic behavior and could contribute to conditions favorable for localized cryovolcanic resurfacing.
Villavicencio-Valero et al. (Thu,) studied this question.