Rheological properties of ammonia-water liquids and crystal-liquid slurries - Planetological applications

Abstract The viscosities of aqueous mixtures plausibly representing a range of cryovolcanic substances seen on the icy satellites have been measured in the laboratory or obtained from literature sources. These viscosities range from 10−2 poise (pure water) to 102 poises (ammonia-water peritectic) to about 105 poises (ammonia-water-methanol peritectic). The viscosities of the liquid mixtures examined in this work are much greater than would be expected based on the assumption that the end member molecules are noninteractive. This observation supports others based on molar volumes and vapor pressure relations indicating that strong molecular interactive forces exist and have an important bearing on the physical properties of the mixtures. With supercooling and/or partial crystallization, these substances may attain viscosities several orders of magnitude greater than those given above. The rheological effects of partial crystallization parallel the same effects in silicate lavas, so it is reasonable to interpret cryovolcanic morphologies on the icy satellites in the same ways that we interpret remotely observed silicate volcanic morphologies on the Earth and terrestrial planets, after accounting for differences in surface gravities and lava densities, and allowing for uncertainties in surface slopes and extrusion rates. Given the wide range of viscosities for simple aqueous mixtures, and the rheological effects of realistic thermal states, the characteristics of observed cryovolcanic flows and resurfaced plains on the icy satellites can be understood within the framework of conventional magmatic processes working on exotic icy substances.