Today's Mars Photo is of a feature called starburst spiders, which develop when carbon dioxide frost accumulates at high latitudes (near the pole) during the winter. In the spring the carbon dioxide frost begins to sublimate, and the gas that rises from the bottom of the frost moves the dust and can even create channels like those seen below.
These channels are called starburst because they seem to emanate from a center point and explode outward. They form what look like many legged spiders, thus the name starburst spider.
This image will link to the captioned photo from HiRISE.