US GEOLOGICAL SURVEY / SCIENCE PHOTO LIBRARY US GEOLOGICAL SURVEY / SCIENCE PHOTO LIBRARY
Mosaic showing the Martian south polar ice cap, made from 24 images obtained by the Viking 2 Orbiter. The images were acquired during the Martian southern summer when the ice cap was nearing its final stage of retreat. The cap is approximately 400 km across and the exposed surface is thought to consist dominantly of carbon dioxide ice ("dry ice"). Water ice is probably present in layers underlying the south polar cap and comprising the surrounding layered terrain whose scarps can be seen illuminated in this photo. The pits with sharp-rimmed cliffs near the top of the image were prbably etched by winds.
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