Dry Ice and Dunes

Mars has a vast sea of sand dunes in the high latitude region encircling its North polar cap, known as the North polar erg. These dunes are made up of basalt and gypsum sand grains.

In some regions of the North polar erg where the sand supply is limited they take on an elongated crescent shape (see PSP_009324_2650). The icy ground that the dunes are on top of has irregular polygonal patterns. In other areas with an abundant supply of sand the dunes are continuous.

The entire North polar erg is covered in the winter with a seasonal polar cap composed of carbon dioxide (dry ice). In the springtime this seasonal polar cap evaporates. This image shows the dunes mostly still covered with dry ice, but the dark spots are places where the ice has evaporated and the dark sand of the dune is visible.

Photo credit: NASA/JPL/University of Arizona

Notes: While I am a big fan of Wikipedia, and frequently link to that website for my many posts, the information there is not always correct. For example, in looking for a link to "north polar erg," the only entry that used the term was for Olympia Undae, which is indeed an enormous north polar erg south of Planum Boreum. However, Olympia Undae is not the only enormous north polar erg, and that is the case with the location of this particular image. As a result, I have chosen to use the link for Vastitas Boreale for "north polar erg" as there is no other specific geographic feature I can use for this area.

The location of these sand dunes is northeast of Escorial Crater, which is the mid-sized crater that Chasma Boreale "points" to. The dunes may even be part of Hyperboreae Undae.