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Jens Jacob Iversen

A lower-than-expected saltation threshold at Martian pressure and below

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Aeolian sediment transport is observed to occur on Mars as well as other extraterrestrial environments, generating ripples and dunes as on Earth. The search for terrestrial analogs of planetary bedforms, as well as environmental simulation experiments able to reproduce their formation in planetary conditions, are powerful ways to question our understanding of geomorphological processes toward unusual environmental conditions. Here, we perform sediment transport laboratory experiments in a closed-circuit wind tunnel placed in a vacuum chamber and operated at extremely low pressures to show that Martian conditions belong to a previously unexplored saltation regime. The threshold wind speed required to initiate saltation is only quantitatively predicted by state-of-the art models up to a density ratio between grain and air of 4 × 105 but unexpectedly falls to much lower values for higher density ratios. In contrast, impact ripples, whose emergence is continuously observed on the granular bed over the whole pressure range investigated, display a characteristic wavelength and propagation velocity essentially independent of pressure. A comparison of these findings with existing models suggests that sediment transport at low Reynolds number but high grain-to-fluid density ratio may be dominated by collective effects associated with grain inertia in the granular collisional layer.

TidsskriftProceedings of the National Academy of Sciences of the United States of America
Antal sider6
StatusUdgivet - feb. 2021

Bibliografisk note

Funding Information:
ACKNOWLEDGMENTS. This work has been funded by Europlanet grant 11376. Europlanet 2020 Research Infrastructure has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement 654208. We are grateful to R. C. Ewing for providing walnut shell samples for a new measurement of their bulk density.

Publisher Copyright:
© 2021 National Academy of Sciences. All rights reserved.

Copyright 2021 Elsevier B.V., All rights reserved.

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