Thermal Creep On Mars: Visualizing A Soil Layer Under Tension

By Keith Cowing
Status Report
February 26, 2023
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Thermal Creep On Mars: Visualizing A Soil Layer Under Tension
Strength of the motion of grains with depth y over time at 5.2 mbar ambient pressure. Dark color marks little motion (reversed color from correlation plot fig. 5). — astro-ph.EP

At low ambient pressure, temperature gradients in porous soil lead to a gas flow, called thermal creep. With this regard, Mars is a unique as the conditions for thermal creep to occur in natural soil only exist on this planet in the solar system.

Known as Knudsen compressor, thermal creep induces pressure variations. In the case of Mars, there might be a pressure maximum below the very top dust particle layers of the soil, which would support particle lift and might decrease threshold wind velocities necessary to trigger saltation or reduce angles of repose on certain slopes. In laboratory experiments, we applied diffusing wave spectroscopy (DWS) to trace minute motions of grains on the nm-scale in an illuminated simulated soil.

This way, DWS visualizes pressure variations. We observe a minimum of motion which we attribute to the pressure maximum ~ 2 mm below the surface. The motion above but especially below that depth characteristically depends on the ambient pressure with a peak at an ambient pressure of about 3 mbar for our sample. This is consistent with earlier work on ejection of particle layers and is in agreement to a thermal creep origin. It underlines the supporting nature of thermal creep for particle lift which might be especially important on Mars.

Tetyana Bila, Jonathan Kollmer, Jens Teiser, Gerhard Wurm

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2302.06882 [astro-ph.EP] (or arXiv:2302.06882v1 [astro-ph.EP] for this version)
Journal reference: Planet. Sci. J. 4 16 (2023)
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Submission history
From: Tetyana Bila
[v1] Tue, 14 Feb 2023 08:10:26 UTC (2,794 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻