This HiRISE observation shows the northwest quadrant of a fracture-filled crater on Mars.

NASA/JPL/University of Arizona

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A lacy web of bright frost-filled fractures fills a crater near the north pole of Mars in this image, acquired Sept. 20, 2015 with the HiRISE camera aboard NASA’s Mars Reconnaissance Orbiter (MRO).
PHOTOS: Weirdest Mars Craters Spotted by HiRISE
The entire crater is around 3 miles (5 km) across and its ancient interior has undergone countless millennia of freeze/thaw cycles that have broken the surface into polygonal shapes. This process is common on Mars and can even be found on Earth, but this particular image depicts it exceptionally nicely.
The fractured surface polygons can be seen to get more compressed nearer to the crater’s rim. The image description by the HiRISE team explains:

The crater rim constrains the polygon formation within the crater close to the rim, creating a spoke and ring pattern of cracks. This leads to more rectangular polygons than those near the center of the crater. The polygons close to the center of the crater display a more typical pattern. A closer look shows some of these central polygons, which have smaller polygons within them, and smaller polygons within those smaller polygons, which makes for a natural fractal!

PHOTOS: NASA Spacecraft’s Epic 10 Years of Mars
A full map-projected scan of the area is below:

Polygonal terrain within and around a polar crater on Mars (monochrome red-filter HiRISE image.)

NASA/JPL-Caltech/University of Arizona

Launched Aug. 12, 2005, the MRO spacecraft has been studying the surface of Mars from orbit since March 2006. Its High-Resolution Imaging Science Experiment (HiRISE) camera, run by researchers at the University of Arizona’s Lunar and Planetary Laboratory, provides incredibly detailed images of Mars’ varied terrain in visible and near-infrared wavelengths.
PHOTOS: Mind-Blowing Beauty of Mars’ Dunes
HiRISE is capable of resolving structures on Mars’ surface down to about a meter in size from its location in orbit. The image above was acquired from a distance of 196 miles (314 km). You can see many more images from HiRISE here.

: HiRISE Photos

Jan 14, 2014 01:40 PM ET // by Ian O'Neill

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.
PHOTOS: The Weirdest Craters on Mars

NASA/JPL-Caltech/University of Arizona

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.
READ MORE: Sand Dunes Could Reveal Weather on Alien Worlds

NASA/JPL-Caltech/University of Arizona

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.
READ MORE: Slug-Like Dunes on Mars

NASA/JPL-Caltech/University of Arizona

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.
READ MORE: Bouncing Sands of Mars Blow in the Wind

NASA/JPL-Caltech/University of Arizona

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.

NASA/JPL-Caltech/University of Arizona

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.

NASA/JPL-Caltech/University of Arizona

This is the same barchan dune field, zoomed out, a "swarm" of dunes covering the plains.

NASA/JPL-Caltech/University of Arizona

Not all barchan dunes "behave" and form neat "horny" shapes. They can become muddled and overlapping, creating "barchanoid dunes," as shown here.

NASA/JPL-Caltech/University of Arizona

This very fluid-looking collection of barchans is accompanied by a wind-blown ridge in the Hellespontus region of Mars but...

NASA/JPL-Caltech/University of Arizona

...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.

NASA/JPL-Caltech/University of Arizona

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.
READ MORE: Mars' 'Raindrop' Sand Dunes Swarm

NASA/JPL-Caltech/University of Arizona

These craggy-looking dunes are old barchanoids eroding away through seasonal processes (sublimation of sub-surface ices) and the persistent Martian wind.

NASA/JPL-Caltech/University of Arizona

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.

NASA/JPL-Caltech/University of Arizona

Dome-shaped dunes and barchans seem to "reach out" and touch their downwind partners with slumped material.

NASA/JPL-Caltech/University of Arizona

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.
For more on the HiRISE camera, see the HiRISE website and regularly updated Tumblr page. For more on Mars dune definitions, check out the USGS Mars Dunes site.

NASA/JPL-Caltech/University of Arizona

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