Discovery of araneiforms outside of the South Polar Layered Deposits

Mars' south polar region is sculpted by the seasonal cycle of freezing and thawing of exposed carbon dioxide (CO 2) ice. In the Southern Spring, CO 2 jets loft dust and dirt through cracks in the sublimating CO 2 ice sheet to the surface where winds blow the material into the hundreds of thousands of dark fans observed from orbit. During this seasonal process, it is thought that the CO 2 gas also exploits weaknesses in the surface below the ice sheet to carve dendritic channels known as araneiforms. Planet Four: Terrains (http://terrains. planetfour. org) is a citizen science project enlisting the general public to review~ 6 m/pixel resolution Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) subimages to identify:(1) araneiforms (including features with a central pit and radiating channels known asspiders')(2) erosional depressions, troughs, mesas, ridges, and quasi-circular pits characteristic of the South Polar …