Mobility of icy sand packs, with application to Martian permafrost

Abstract

The physical state of water on Mars has fundamental ramifications for both climatology and astrobiology. The widespread presence of “softened” Martian landforms (such as impact craters) can be attributed to viscous creep of subsurface ground ice. We present laboratory experiments designed to determine the minimum amount of ice necessary to mobilize topography within Martian permafrost. Our results show that the jammed‐to‐mobile transition of icy sand packs neither occurs at fixed ice content nor is dependent on temperature or stress, but instead correlates strongly with the maximum dry packing density of the sand component. Viscosity also changes rapidly near the mobility transition. The results suggest a potentially lower minimum volatile inventory for the impact‐pulverized megaregolith of Mars. Furthermore, the long‐term preservation of partially relaxed craters implies that the ice content of Martian permafrost has remained close to that at the mobility transition throughout Martian history.

Rheological and Thermal Properties of Icy Materials

“…For mixtures of undeformable quartz sand + ice I (Fig. 9d), the strength of the weak phase dominates over much of the compositional range (Durham et al 1992), although an inflection point is introduced into the curve because at low concentrations of ice, <0.25 (Durham et al 2009), the aggregate remains nearly undeformable because quartz particles continue to form a rigid, load-bearing framework after a small amount of strain. Note the similar shape in one of the curves in Fig.…”

Planetary Ices Attenuation Properties

“…These authors considered a low content of silicate grains (<4 vol%). For a high content of silicates, jamming between silicate grains may become the main feature limiting creep, as demonstrated by the experimental work of Durham et al (2009). Silicate particles also act in preventing grain growth, which indirectly influences the mechanical properties of the material (Goodman et al 1977;Barr and Milkovich 2008).…”

Parallel numerical analysis on the rheology of the martian ice-rock mixture

“…The rheology of ice-rock mixtures has been studied under terrestrial conditions for engineering purposes at low pressure and stress near melting point (Yasui and Arakawa, 2008;Mangold, 2003). However, experimental data on the rheology of ice-rock mixture under Martian physical conditions are sparse, and the amount of ground ice that is needed to produce the viscous deformation observed in Martian ice-related landforms is still under investigation (Durham et al, 2009). Furthermore, it is time-consuming and also very expensive to perform these kinds of measurements in the laboratory.…”