answers.input_text: short
answers.span_text: CO ice ( dry ice )
questions: what is the snow on mars made of
name: Martian polar ice caps
contexts: The planet Mars has two permanent polar ice caps . During a pole 's winter , it lies in continuous darkness , chilling the surface and causing the deposition of 25 -- 30 % of the atmosphere into slabs of CO ice ( dry ice ) . When the poles are again exposed to sunlight , the frozen CO sublimes , creating enormous winds that sweep off the poles as fast as 400 km / h . These seasonal actions transport large amounts of dust and water vapor , giving rise to Earth - like frost and large cirrus clouds . Clouds of water - ice were photographed by the Opportunity rover in 2004 .