Photo caption: Several sizes of waves in the sand created by the wind in the Namib Desert. You can see down the high dune small, straight waves formed in fine-grained sand and larger mega waves covered with grainy coarse sand. The coarse sand is grayish while the fine sand that builds the dunes is reddish.| Photo: Hezi Yizhaq (Ben Gurion University)
Scientists from Israel’s Ben-Gurion University of the Negev say they may have determined what causes sand ripples, a phenomenon that occurs on both Mars and the Earth.
Ben-Gurion University of the Negev physicists Prof. Hezi Yizhaq and Prof. Itzhak Katra and their colleagues from Denmark, Germany, Italy, China, and the US reported in a cover article published in Nature Geoscience that one unified theory could explain their formation on two different planets of our solar system.
Sand ripples are small ridges and furrows that form on the surface of loose sand. They are created by wind or water currents that flow over the sand. The wind or water current picks up sand grains and carries them along. As the grains are carried, they collide with other grains and come to rest. The way the grains come to rest determines the shape of the ripples.
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Sand ripples photographed on Mars by NASA’s Curiosity rover in 2015 showed two distinct patterns – large ripples (meter scale) and a shorter “impact” ripples pattern (decimeter scale). The prevailing theory proposed since then argues that the smaller scale ripples are produced by the impact mechanism of the particles transported by the wind like normal ripples on Earth and the larger ripples form due to hydrodynamic instability like subaqueous ripples. Furthermore, it was believed that the physical conditions that produced them on Mars could not produce them on Earth.
Prof. Yizhaq and Prof. Katra say that they have now proven experimentally, using Ben-Gurion University’s wind tunnel and Aarhus University’s Mars tunnel, that such a phenomenon could exist on Earth – we just haven’t noticed it yet because “we didn’t know we should be looking for it.”
The international research team has proposed a unified theoretical framework that would explain sand ripples on Mars and on Earth. At its most basic level, sand ripples on Mars caused by wind look like sand ripples on Earth caused by water.
However, there is still a great deal of work that needs to be done before the theory can be proven.
“There is much more research, both fieldwork and experimentally, needed to prove our theory,” says Prof. Yizhaq, “but it is amazing to propose something so radically new in a field I have been studying for over 20 years. It is exciting to go out and try to find on Earth what can clearly be seen on Mars.”
