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NASA NTRS2021

Martian subsurface cryosalt expansion and collapse as trigger for landslides

On Mars, seasonal martian flow features known as recurring slope lineae (RSL) are prevalent on sun-facing slopes and are associated with salts. On Earth, subsurface interactions of gypsum with chlorides and oxychlorine salts wreak havoc: instigating sinkholes, cave collapse, debris flows, and upheave. Here, we illustrate (i) the disruptive potential of sulfate-chloride reactions in laboratory soil crust experiments, (ii) the formation of thin films of mixed ice-liquid water “slush” at −40° to −20°C on salty Mars analog grains, (iii) how mixtures of sulfates and chlorine salts affect their solubilities in low-temperature environments, and (iv) how these salt brines could be contributing to RSL formation on Mars. Our results demonstrate that interactions of sulfates and chlorine salts in fine-grained soils on Mars could absorb water, expand, deliquesce, cause subsidence, form crusts, disrupt surfaces, and ultimately produce landslides after dust loading on these unstable surfaces.

J. L. Bishop↗
NASA NTRS2021

Kozai–Lidov Oscillations Triggered by a Tilt Instability of Detached Circumplanetary Discs

Circumplanetary discs can be linearly unstable to the growth of disc tilt in the tidal potential of the star–planet system. We use3D hydrodynamical simulations to characterize the disc conditions needed for instability, together with its long-term evolution.Tilt growth occurs for disc aspect ratios, evaluated near the disc outer edge, ofH/r0.05, with a weak dependence on viscosityin the wave-like regime of warp propagation. Lower mass giant planets are more likely to have circumplanetary discs thatsatisfy the conditions for instability. We show that the tilt instability can excite the inclination to above the threshold where thecircumplanetary disc becomes unstable to Kozai–Lidov (KL) oscillations. Dissipation in the KL unstable regime caps furthertilt growth, but the disc experiences large oscillations in both inclination and eccentricity. Planetary accretion occurs in episodicaccretion events. We discuss implications of the joint tilt–KL instability for the detectability of circumplanetary discs, for theobliquity evolution of forming giant planets, and for the formation of satellite systems.

Rebecca G Martin↗