Riddle of Mars's Mysterious "Spiders" Solved

Features on Mars, called "spiders," form at Mars' (carbon dioxide ice) polar caps. As sunlight warms the lower layers of the CO2 ice, gas is produced, which builds pressure and creates channels beneath the ice. These channels eventually find holes in the ice, erupting any dust particles they have picked up along the way. What is interesting is that these channels deepen as they go uphill (opposite to the type of erosional feature that a river would create), supporting the fact that gas is causing the erosion. When these fans originate from one heat source, they create the spider-like formations.