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Cool image time! The image on the right, cropped and reduced in resolution to fit here, shows an area of inexplicable dark dunes located in Mars’ high northern latitudes. Located in a circular depression (whose outline can be seen across the top and left side of the image), geologists only partly understand the processes producing these dunes. As the noted on the release webpage:
However, a circular depression (probably an old and infilled impact crater) has limited the amount of sand available for dune formation and influenced local winds. 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.
Be sure to look at the full image, as it covers a wider area and shows dunes that travel in all directions, forming mazelike patterns that no theory presently explains.