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Wind-blown deposits known as transverse aeolian ridges (TARs) are frequently visible in images of the Martian tropics. They are bright ripples with heights of 2.6 meters and spacing that averages 47 meters. The TARs generally appear inactive and eroded, sometimes cratered or littered with boulders from nearby impacts and avalanches.

In Syria Planum, unusual bright deposits might be accumulations of dust blown from higher to lower elevations by nighttime slope winds, reaching speeds of up to 50 meters per second. These dust deposits resemble TARs in height and spacing but with a distinct shape from other TARs. A close up view shows that the deposits form pyramidal features with steep faces on the upwind sides (wind is blowing from the top of the picture) and tapered slopes in the downwind direction. Ridges form where the "pyramids" line up together, and the spacing of the ridges appears to be controlled by the length of the "pyramids."

These observations suggest that TARs elsewhere on Mars may have formed in a similar fashion, perhaps millions of years ago when the atmosphere was more active. They also may be forming in Syria Planum today.

The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. (The original image scale is 25.6 centimeters [10.1 inches] per pixel [with 1 x 1 binning]; objects on the order of 77 centimeters [30.3 inches] across are resolved.) North is up.

The University of Arizona, in Tucson, operates HiRISE, which was built by Ball Aerospace & Technologies Corp., in Boulder, Colorado. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, California, manages the Mars Reconnaissance Orbiter Project for NASA's Science Mission Directorate, Washington.