A Decrease in Slope Angles on Insolated Martian Slopes: Ground-based Experiments

Dry granular flow on Martian slopes can benefit from subsoil Knudsen compressors induced by thermal creep gas flow. The required temperature gradient for this natural compressor can be set by insolation. Here, we study the decrease of slope angles from the initial angles of repose on ambient pressure in ground-based laboratory experiments. At low pressure, we pour JSC Mars 1a particles with an average grain size of 75 μ m as a Martian simulant to form a pile. Typical angles of repose are about 30°, with some variation. One side of the pile is then illuminated. We find that up to 100 mbar, the illumination of the slope induces erosion and decreases the slope angle systematically. For continuous illumination at high light flux, necessary under Earth gravity, the angle decreases by about 10°. If the light source is turned off, amplified emission of material is triggered, which can further lower the slope angle. This study complements low-gravity work and suggests that the effects are important for granular flows of sand-sized particles on Martian slopes throughout the planet’s pressure range, i.e., independent of the specific location. A preliminary analysis shows that such a process could work for recurring slope lineae.