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Cohesive properties of ice powders and mixtures as analogues of regoliths of icy worlds

Presentation #114.04D in the session Laboratory Investigations (Oral Presentation)

Published onOct 23, 2023
Cohesive properties of ice powders and mixtures as analogues of regoliths of icy worlds

Many planetary bodies in the Solar System are likely covered with a surface regolith of water ice powder, potentially mixed with a variety of other compounds. For example, on Enceladus jet activity results in the deposition of very fine ice grains (∼10-100µm) at low temperature (∼70K) suggesting the formation of relatively stable powdery deposits (Choukroun et al., 2020). Similar processes involving salts could also be active on Europa (Roth et al., 2014). Ceres also potentially has a mixture of ice and rocky powder materials at its surface (De Sanctis et al., 2015). The mechanical behavior of ice powders at low temperatures relevant to these bodies is poorly constrained and mixed ice powders could further change their behavior. Hence, characterizing the properties of these powders is essential for understanding the evolution of the surface and the technical aspects of future missions involving landing and/or sampling of surface materials.

In the laboratory, we synthesize pure ice powders, and salt-ice and rock-ice mixture powders to produce analogues of different icy regoliths. To analyze the mechanical behavior of our samples, we developed a 64mm diameter liquid-nitrogen cooled rotating drum to perform measurements under very low temperatures. The cohesion of the icy powders is quantified by analyzing the angle and irregularities of the flowing surface inside the drum over a wide range of temperatures (~85-180K). Each measurement consists in 5 rotation speeds for each temperature step, with 50 images acquired for each speed from which we compute the mean angle of the flowing surface.

Our measurements of pure water ice powder show that its cohesion greatly increases with temperature, an effect not observed in any other material. At around 90K the ice powder behaves similarly to weakly-cohesive glass beads, while at 140K it behaves more like a cohesive limestone powder. Our preliminary results for mixtures of ice and glass beads show contrasting trends with temperature depending on the proportion of ice in the mixture. Below 54%, the overall cohesion increases, but no temperature dependence is observed. Whereas with > 54% ice the trend of increasing cohesion with the temperature is again observed. The influence of temperature and ice fraction on the cohesiveness of such powders could lead to temporally (day/night temperature cycles) and spatially (compositional variations across the surface) changing the mechanical stability of icy regoliths, leading to easier destabilization of the icy material. This could explain the observation of downslope flow morphologies observed on a variety of icy surfaces.

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