Fig.6. Clay-like dunes on the Mars(source: NASA/JPL/UA) (a) Clay-like dunes in the north of Herschel Crater;(b) Barchan dune of the black box in (a) (HiRISE ESP_036880_1760_RED, center point: 14.8°S, 127.9°E);Arrows represent the winddirection of dune development