Mars plays host to a huge number of dune fields -- regions where fine wind-blown material gets deposited to form arguably some of the most beautiful dunes that can be found on any planetary body in the solar system. Using the powerful High-Resolution Imaging Science Experiment (HiRISE) camera on board NASA's Mars Reconnaissance Orbiter, planetary scientists have an orbital view on these features that aid our understanding of aeolian (wind-formed) processes and Martian geology. Here are some of our favorite Mars dunes as seen by HiRISE.
Pictured here are shell-like "barchan dunes" in the ancient Noachis Terra region of Mars.
Special thanks to Ari Espinoza of the HiRISE team at the University of Arizona for helping to compile this list.
Dunes of many shapes, sizes and formation processes can be found on the Red Planet. Shown here are elegant "linear dunes" with deposits of larger rocks and possibly ices in their troughs.
These slug-like dark dunes are striking examples of "dome dunes" -- elliptical accumulations of fine material with no-slip surfaces. These domes contrast greatly with the often jagged appearance of barchan dunes. Found at the bottom of Proctor Crater, they are darker than the surrounding crater floor as they are composed of dark basaltic sand that was transported by the wind.
Looking like a wind-blown silk sheet, this field of "star dunes" overlays a plain of small ripples, another aeolian feature. The ripples move more slowly across the bottom of Proctor Crater, so the large dune field will travel over the smaller ripples. Dunes are continuously evolving and moving with the wind, ensuring that the Martian surface is never static.
These "transverse dunes" are undergoing seasonal changes. Likely entering Mars summer, this region of dunes is stained with pockets of subliming ices -- likely carbon dioxide. As the ices turn from solid to vapor, dune material slumps, revealing dark, sandy material underneath.
Resembling the mouths of a shoal of feeding fish, this is a group of barchan dunes in Mars' North Polar region. Barchan dunes betray the prevailing wind direction. In this case, the prevailing wind is traveling from bottom right to top left; the steep slope of material (plus dune "horns") point to the downwind direction. The HiRISE camera monitors barchans to see if they move between observing opportunities, thereby revealing their speed of motion across the Martian plains.
This is the same barchan dune field, zoomed out, a "swarm" of dunes covering the plains.
Not all barchan dunes "behave" and form neat "horny" shapes. They can become muddled and overlapping, creating "barchanoid dunes," as shown here.
This very fluid-looking collection of barchans is accompanied by a wind-blown ridge in the Hellespontus region of Mars but...
...only when zoomed out does the true nature of this fascinating region become clear. The prevailing wind is eroding the mesas (small hills) to the right of the image, carrying fine material downwind (from right to left), creating a startling pattern of barchans and a viscous-looking trail of sandy ridges across the plains.
The band Train sang about the "Drops of Jupiter" -- what about the "Drops of Mars"? Sure, they're not made of any kind of fluid, but they do make for incredibly-shaped dunes. These raindrop-shaped dunes are found in Copernicus Crater and are known to be rich in the mineral olivine, a mineral that formed during the wet history of Mars' evolution.
These craggy-looking dunes are old barchanoids eroding away through seasonal processes (sublimation of sub-surface ices) and the persistent Martian wind.
These linking barchan dunes are at the leading edge of a dune field -- grains of dust have been blown across a plain, deposited and left to accumulate in elongated arrow shapes.
Dome-shaped dunes and barchans seem to "reach out" and touch their downwind partners with slumped material.
Barchan dunes inside Arkhangelsky Crater in the southern hemisphere of Mars reveal a wind direction from top left to bottom right. Note the tracks of Martian dust devils over the dune slopes.