LABORATORY STUDIES ON THE RHEOLOGY OF CRYOGENIC SLURRIES WITH IMPLICATIONS FOR ICY SATELLITES

Interpretation of Cassini RADAR and VIMS data has suggested some landforms on Titan may be due to effusive cryovolcanic processes that created cones, craters and flows [1]. High-resolution Voyager 2 images of Triton also show strong evidence of cryovolcanic features [2]. Fundamental to modeling of cryovolcanic features is the understanding of the rheological properties of cryogenic icy slurries in a thermodynamic and fluid mechanical context, i.e., how they deform and flow or stall under an applied stress. We performed a series of experiments on a 40 wt% methanol-water mixtures and 29 wt% ammonia-water mixtures, aimed at measuring the rheology of the slurries as a function of temperature and strain rate. These experiments revealed development of yield stress-like behaviors, shear-rate dependence, and thixotropic behavior, even at relatively low crystal fractions. Most importantly, we found that rheological properties of methanol-water slurries are strongly history dependent [3]. Visualization of icy slurries suggest that crystallization and the resulting 3-D arrangement of ice crystals dominate rheological properties. Viscosity measurements of methanol-water and ammonia-water slurries leads to constraining yield strength parameters to better inform dome formation models for locations in the solar system, such as Titan, where cyrovolcanism is a suspected formation mechanism of some geomorphological features. We will discuss our laboratory results and their implications for cryovolcanism on icy satellites.

[1] Lopes, R. M. C., et al., 2013. Cryovolcanism on Titan: New results from Cassini RADAR and VIMS. J. Geo. Res. 118, 416-435.

[2] Smith, B. A., et al., 1989. Voyager 2 at Neptune: Imaging science results. Science 246, 1422-1450.

[3] Zhong, F., et al., 2009. The rheology of cryovolcanic slurries: Motivation and phenomenology of methanol-water slurries with implications for Titan. Icarus 202, 607-619.