Mars HiRISE Image: Well-Speckled Polar Dunes “These barchan (crescent-shaped) sand dunes are found within the North Polar erg of Mars. This type of dune provides a great record of the wind environment when they formed and moved: barchan dunes’ horns point downwind. Although the question of present-day sand motion is still open, it appears possible that these dunes are active (when not covered in frost) as their crestlines are very […]