This image shows a traverse across a section of the North Polar erg, a vast sea of sand that surrounds the polar cap.
The source of the dunes may be from the eroding north polar layered deposits. Wind, acting on this mixture of sand, dust, and ice, has formed several dune types on top of bright megaripples and polygons. A dark mantle of sand lies beyond the dunes.
The central part of the field contains transverse dunes with the dominant wind direction coming from the northwest-west. The outer edges of the dune field transition into star dunes (with multiple arms) and barchanoid dunes (crescent-like shape). The star dunes indicate a multidirectional wind regime or a change in wind direction over the dune field’s evolution. The dunes are somewhat confined to their location and may have taken hundreds of years to form.
Written by: Circe Verba (12 September 2008)
More info and image formats at http://hirise.lpl.arizona.edu/PSP_009396_2590
Image: NASA/JPL/University of Arizona