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Pristine Dust Deposits in Syria Planum. Science Theme: Aeolian Processes. Acquisition date 11 August 2019. > Audio clip: https://www.uahirise.org/media/audio2/ESP_061126_1680.mp3 NASA Text: 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. Written by: Paul Geissler (narration: Tre Gibbs) (14 October 2019)