Martian Spiders Launch Dark Jets

New images give clues to the reasons for the "spiders" and "dark fans" that appear on Mars' south pole every spring. Sunlight filters through the layer of dry ice covering the pole and turns the bottom layer to gas. The gas forms spider-shaped channels trying to escape the ice, and then erupts in fan-shaped jets of white carbon dioxide and black dust. Images by HiRISE. [National Geographic]