From Dawn Till Dusk: How Light Might Reduce Martian Slope Angles

The dynamics of granular particles on Mars are influenced by environmental factors that are very different from those on Earth. While the low ambient pressure of 6 mbar makes movement by wind significantly more difficult, it is helpful and even necessary for another process that favors the slipping of particles on slopes.

In so-called thermal creep, gas flows from colder, deeper soil layers to layers near the surface, which are heated by solar insolation. This uncommon process does not occur on Earth at 1000 mbar, but it works efficient in the low mbar range of Mars (Bila et al. 2023). The gas flow creates an overpressure under the surface, which can loosen particles and if the whole process takes place on a slope, this leads to a reduction in the slope angle, way below the typical angle of repose (Bila et al. 2024).

By using a centrifuge in microgravity (on parabolic flights), we have experimentally simulated Martian slopes and observed the process described above under realistic conditions in terms of pressure, particle-properties, gravity and insolation. We have measured a pressure- and particle-size dependent reduction in the slope angle by several degrees, which can clearly be attributed to the irradiation.

This process could be relevant for the characteristics of Martian dunes, the formation of Recurring Slope Lineae, slope streaks as well as for the general dynamics of granular particles in the context of dust entrainment.

 

Tetyana Bila et al 2023 Planet. Sci. J. 4 16

Tetyana Bila et al 2024 Planet. Sci. J. 5 115