Planet Four The South Pole of Mars is one of the most alien places in the Solar System. During the winter, under the cover of darkness, nearly a third of the Martian atmosphere freezes out to form a semi-translucent slab of carbon dioxide ice. With the arrival of spring at the Martian South Pole, the ice cap begins to thaw. Dark fans and blotches appear dotting the surface of the exposed ice. Their numbers increase as the days grow longer and longer, but once all the ice is gone in mid-Summer these dark fans and blotches simply vanish from sight. Unlike water ice, which turns from solid to liquid, carbon dioxide ice on the surface of Mars sublimates from solid straight to gas. Starting at the first sunrise in Southern Spring, the surface below the semi-transparent ice sheet is heated causing the ice at the base to sublimate. The carbon dioxide gas trapped between the ice sheet and the ground, finds cracks in the ice breaking out as jets. These jets carry dust and dirt from the ground below, depositing it onto the top of the ice sheet. It is thought that, if it is a windy day, then the blowing winds create the beautiful darks fans and streaks from the lofted material. If there is no wind, the particles settle around the vent to form the observed blotches. The size, shape, and direction of these dark fans and blotches provide important information on the conditions of the Martian climate and provide a wind map of the South Pole of Mars. This seasonal process is uniquely Martian. Nothing similar occurs on the entire Earth. NASA's Mars Reconnaissance Orbiter has been monitoring the thawing of the Pole of Mars observed from orbit by the HiRISE camera. Mars' South Pole for the past 4 Martian Left: Spider Morphology; Right: Starburst Spider years (8 Earth years). The spacecraft is ŠNASA/JPL/University of Arizona equipped with the High Resolution Imaging Science Experiment (HiRISE). From orbit, HiRISE can see features as small as a card table on the surface of Mars. Hundreds of thousands of these dark seasonal features have been captured in the HIRISE images. It has proven difficult for computers to spot the locations and map the shapes of the seasonal fans and blotches, but human beings are up to the task. Image Caption: Seasonal fans and blotches on the South
1/2