NASAのインスタグラム(nasa) - 9月19日 09時55分

What appears to be an ocean on Earth are desolate dunes on Mars.
In this image acquired on Jan. 2, 2014, our Mars Reconnaissance Orbiter spotted a relatively rare class of dune fields located among canyon wall slopes.
Known as “wall dune fields,” these dunes are further identified as either climbing or falling. Falling dunes are defined as large bedforms with lee faces on the downhill side—indicating that this is the direction of their migration—and on moderate slopes greater than 10 to 12 degrees.
On Earth and Mars, these types of dunes are largely controlled by what is called “microtopography.” Physical obstacles can accelerate and decelerate airflow, create turbulence, potentially enhancing erosion, deposition, and/or transport of dune sediment.

Since launching in 2005, our Mars Reconnaissance Orbiter spacecraft beams high-resolution imagery to help us better understand the Red Planet.
Credit: NASA/JPL-Caltech/Univ. of Arizona

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