NASA's Mars Reconnaissance Orbiter (MRO) satellite has photographed strange polygonal structures covering the Martian landscape.
The image was captured by the MRO using the HiRISE (High Resolution Imaging Science Experiment) camera, and high resolution versions up to 10K are available on the HiRISE website. The Martian surface pictured is divided into numerous polygonal sections by water that freezes into ice in the ground, splitting the soil. Dry ice (frozen carbon dioxide) sublimates into a gaseous form in the springtime, further fracturing the boundaries of the polygons.
Dry ice covers the visible ground, and various vents form across the surface as the temperature rises, allowing gas to escape while eroding other particles that are then carried along with the gas. These particles are carried a short distance, creating dark, fan-shaped deposits. The vents occasionally close and reopen, though a change in wind direction produces a second fan-shaped deposit extending in another direction.
You can see more updates from fascinating features of the Martian landscape photographed by HiRISE here.