These dunes are located around -72 degrees in latitude; if they were on Earth they'd be well south of the Antarctic Circle!
Because of their extreme southern positioning, they endure dramatic temperature changes over the course of the Martian year.
The HiRISE team attempts to monitor this area as these dunes get covered by seasonal frost in the fall and defrost in the spring, taking multiple images over the same locations in order to better understand the structure and evolution of these beautiful landforms.
This image was taken close to the Southern hemisphere autumnal equinox, the end of Southern hemisphere Summer and beginning of autumn.
Unlike that observed on Earth, the frost seen on the Richardson Crater dunes is composed of carbon dioxide, and sublimates (goes directly from a solid to a gas) rather than melts.
At the time of this image, the frost has likely disappeared to its greatest extent and will begin to re-acummulate soon.
Wide, dark streaks are visible extending from the crests of the dunes, likely due to movement of material as the dunes defrosted or to wind transportation of surface particles.
Numerous dust devil tracks are still visible as thin, dark, criss-crossing marks, although these will gradually be covered by carbon dioxide frost as Southern hemisphere winter sets in.
The subimage is approximately 1 kilometer (about 0.62 miles) across.
To see the previous image taken at this same location, taken in early Southern Hemisphere Spring as the dunes were thawing, see ESP_011785_1075.
To take a look at other impressive dunes from various locations within Richardson Crater, see ESP_012774_1080, PSP_004230_1080, and ESP_012985_1075.
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