HiRISE: Dunes and ripples in Olympia Undae

Olympia Undae is a large field of sand dunes surrounding Mars’ North Polar ice cap. Because of the high latitude of the dunes, they are covered with water and carbon dioxide frost in the winter and are poorly illuminated. They are best viewed in the summer, when features such as ripples on the dunes’ surface can be seen in detail… [More at link]