North polar dunes on Mars

The CaSSIS camera from the ESA / Roscosmos ExoMars Trace Gas Orbiter took this captivating picture in the North Polar Region of Mars.

The dunes come in different characteristic forms on Mars as well as on Earth, providing clues as to the direction of the prevailing winds. Their monitoring over time also provides us with a natural laboratory for studying the evolution of dunes and how sediments are transported around the planet.

In winter, in the polar regions, a thin layer of carbon dioxide ice covers the surface and then sublimates – turns directly into ice-steam – in the first light of spring. In the dune fields, this spring, defrosting occurs from bottom to top, trapping gas between ice and sand. When the ice cracks, this gas is released violently and causes sand, thus forming the dark spots and trails observed on this CaSSIS image.

The image also captures the dunes "barchan" – the crescent-shaped or U-shaped dunes visible to the right of the image – when they meet and merge into barchanoid ridges. The curved peaks of the Barchan dunes point to the wind. The transition from barchanoid to barchanoid dunes indicates that secondary winds also play a role in the formation of the dune field.

The image is centered at 74.46ºN / 348.3ºE. The picture was taken on May 25, 2019.