There seems to be a never-ending flow of stunning images coming from the High Resolution Imaging Science Experiment (HiRISE) on board NASA’s Mars Reconnaissance Orbiter (MRO). In today’s high-resolution look at the Martian surface, large flat-topped hills (a.k.a. mesas) can be seen to be eroded by the Mars winds, stripping them of their material, creating sand dunes downwind. An incredible sight, it shows just how dynamic and powerful the Martian winds really are…
Imaged above the Hellespontus region of Mars, these fluid-like structures trailing across the surface are huge sand banks and sand dunes, built up after years of erosion from mesas upstream. The Mars winds have gradually stripped the large geological structures, allowing sand to build up as dunes in areas of calm. The curious crescent/droplet-shaped dune morphology indicates dominant winds blowing from west to east (left to right). As sand is carried from the mesa, it travels downstream. Where the winds begin to slack, possibly in large turbulent eddies; the suspended sand is dropped to allow dunes to grow.
The shapes of the Mars dunes bear a striking resemblance to barchan dunes, much like the ones found on Earth. The wind blows up the gentle slope of the dune, allowing sand to gradually build up. As the sand reaches a critical point, it collapses, forming a sharp slope on the downwind-facing side. Horn-like features are evident from above. In addition to the barchans, “seif”-like dunes are evident. Seifs are longitudinal stretches of sand parallel to wind direction. These are most obvious as they trail away from the mesas and stretch toward the clusters of barchan dunes.
These new images were captured on March 16th and resolve features to approximately 1.5 meters. At this level of resolution the small ripples in the wind blown sand can even be seen. To give an idea of scale, I’ve included a close up of one of the dunes. As annotated, the larger dunes are approximately 60 meters in length (from east to west) and around 40 meters in width.