Dunes on Mars, satellite image. These dunes are in an area of Mars called Olympia Undae, a large field of sand dunes surrounding Mars' North Polar ice cap. The dunes are covered with water and carbon dioxide frost in the winter. They are best viewed in the summer, when features such as ripples on the dune surfaces can be seen in detail. Here, the dunes are seen in early summer. The brighter areas are bedrock and patches of frost. This image, published in 2014, was obtained by the High Resolution Imaging Science Experiment (HiRISE) instrument on NASA's Mars Reconnaissance Orbiter (MRO) satellite.