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PHYSICAL SCIENCES / APPLIED PHYSICAL SCIENCES
Giant saltation on Mars
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Departamento de Física, Universidade Federal do Ceará, 60455-900, Fortaleza, CE, Brazil; and Computational Physics, Institut für Baustoffe, Eidgenössische Technische Hochschule Zürich, Schafmattstrasse 6, 8093 Zurich, Switzerland
Edited by H. Eugene Stanley, Boston University, Boston, MA, and approved March 11, 2008 (received for review January 9, 2008)
Saltation, the motion of sand grains in a sequence of ballistic trajectories close to the ground, is a major factor for surface erosion, dune formation, and triggering of dust storms on Mars. Although this mode of sand transport has been matter of research for decades through both simulations and wind tunnel experiments under Earth and Mars conditions, it has not been possible to provide accurate measurements of particle trajectories in fully developed turbulent flow. Here we calculate the motion of saltating grains by directly solving the turbulent wind field and its interaction with the particles. Our calculations show that the minimal wind velocity required to sustain saltation on Mars may be surprisingly lower than the aerodynamic minimal threshold measurable in wind tunnels. Indeed, Mars grains saltate in 100 times higher and longer trajectories and reach 5-10 times higher velocities than Earth grains do. On the basis of our results, we arrive at general expressions that can be applied to calculate the length and height of saltation trajectories and the flux of grains in saltation under various physical conditions, when the wind velocity is close to the minimal threshold for saltation.
aeolian transport | critical phenomena | turbulent flows | granular flows | particle-laden flows
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
¶ Marshall JR, Borucki J, Bratton C, Aeolian sand transport in the planetary context: Respective roles of aerodynamic and bed-dilatancy thresholds. 29th Lunar and Planetary Science Conference, March 16–20, 1998, Houston, TX, abstr 1131.
To whom correspondence should be addressed. E-mail: soares{at}fisica.ufc.br
© 2008 by The National Academy of Sciences of the USA
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