What is this?

When I saw this image appearing in my RSS I couldn't tell what it was. It looked like a close up of the skin of some animal. Perhaps a detail of a bird or a reptile, I thought. Maybe a colorized microscopic view into some human body part. The answer couldn't possibly be more different than what I expected.

You are looking at Mars! A photograph taken by the HiRISE camera aboard NASA's Mars Reconnaissance Orbiter at the beginning of 2014. It's a "giant landform on Mars," according to the space agency. One with "steep faces or slip faces several hundreds of meters tall" what was "formed over thousands of Mars years, probably longer."

Sandy landforms formed by the wind, or aeolian bedforms, are classified by the wavelength—or length—between crests. On Mars, we can observe four classes of bedforms (in order of increasing wavelengths): ripples, transverse aeolian ridges (known as TARs), dunes, and what are called "draa." All of these are visible in this Juventae Chasma image.

Ripples are the smallest bedforms (less than 20 meters) and can only be observed in high-resolution images commonly superposed on many surfaces. TARs are slightly larger bedforms (wavelengths approximately 20 to 70 meters), which are often light in tone relative to their surroundings. Dark-toned dunes (wavelengths 100 meters to 1 kilometer) are a common landform and many are active today. What geologists call "draa" is the highest-order bedform with largest wavelengths (greater than 1 kilometer), and is relatively uncommon on Mars.

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