Strange Sand Ripples on Mars Explained

The nature of strange ripples of sand on the Martian surface is clearer now thanks to pole-to-pole images returned by a NASA spacecraft. But even with this new information, scientists still are unsure just how the features, which are unlike anything on Earth, came to be.  The ripples are found over large swaths of Mars. They are smaller than the red planet's gigantic dunes but larger than sand ripple fields found on Earth.  Called Transverse Aeolian Ridges (TARs), these unusual features are formed by wind-driven particles (phenomena involving air movement are known as "Aeolian processes"). The winds blow the ridges into many shapes: simple ripples, forked ripples, snake-like sinuous waves, crescent shapes and complex, over-lapping networks.

http://www.livescience.com/space/081104-st-martian-landforms.html