This image of dark dunes on Mars, looks like a secret Morse code message written into the sand.
The image was taken on Feb. 6, 2016, at 15:16 local Mars time by the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter.
These dunes are influenced by local topography. The shape and orientation of dunes can usually tell us about wind direction. But here, the dune-forms are very complex, so it’s difficult to know the wind direction.
However, a circular depression has limited the amount of sand available for dune formation and influenced local winds.
According to The University of Arizona, Tucson, that operates HiRISE:
As a result, the dunes here form distinct dots and dashes. The “dashes” are linear dunes formed by bi-directional winds, which are not traveling parallel to the dune. Instead, the combined effect of winds from two directions at right angles to the dunes, funnels material into a linear shape. The smaller “dots” (called “barchanoid dunes”) occur where there is some interruption to the process forming those linear dunes. This process is not well understood at present and is one motivation for HiRISE to image this area.
Image Credit: NASA/JPL/University of Arizona
Caption: HiRISE Targeting Specialists