Beautiful views of sand dune formations on Mars via the HiRISE camera on the Mars Reconnaissance Orbiter (MRO):

** The Splitting of the Dunes

The mound in the center of this image appears to have blocked the path of the dunes as they marched south (north is to the left in this image) across the scene. Many of these transverse dunes have slipfaces that face south, although in some cases, it’s hard to tell for certain. Smaller dunes run perpendicular to some of the larger-scale dunes, probably indicating a shift in wind directions in this area.

Although it might be hard to tell, this group of dunes is very near the central pit of a 35-kilometer-wide impact crater. Data from other instruments indicate the presence of clay-like materials in the rock exposed in the central pit.

This is a stereo pair with ESP_013319_1685.

** Dunes of the Southern Highlands 

Sand dunes are scattered across Mars and one of the larger populations exists in the Southern hemisphere, just west of the Hellas impact basin. The Hellespontus region features numerous collections of dark, dune formations that collect both within depressions such as craters, and among “extra-crater” plains areas.

This image displays the middle portion of a large dune field composed primarily of crescent-shaped “barchan” dunes. Here, the steep, sunlit side of the dune, called a slip face, indicates the down-wind side of the dune and direction of its migration. Other long, narrow linear dunes known as “seif” dunes are also here and in other locales to the east.

NB: “Seif” comes from the Arabic word meaning “sword.”

** Layers and Dark Dunes

Much of Mars’ surface is covered by fine-grained materials that hide the bedrock, but elsewhere, such as in this scene, the bedrock is well exposed (except where covered by sand dunes).

Colors are enhanced in the cutout of a pit exposing reddish layers. This is part of a stereo pair, so check out the stereo anaglyph for a 3D view.

This is a stereo pair with ESP_039581_1520.