Shifting Sands on Mars
As dust storms darkened the Martian sky, driving down solar power levels, NASA's Mars Exploration Rover Spirit captured images of wind-blown material moving across the Martian surface. As on Earth, winds that loft dust into the atmosphere can also move materials on the ground.
While waiting for the dust to clear, Spirit captured images of small ripples of sand beneath the rover's robotic arm that moved slightly closer to the rover over a period of five sols (Martian days). The ripples moved a distance of 1 to 2 centimeters, or about an inch, driven by Martian winds between July 20 and July 25, 2007.