| Summary: | The Infrared Thermal Mappers aboard the two Viking orbiters obtained solar reflectance and infrared emission measurements of the Martian north and south polar regions during an entire Mars year. The observations were used to determine annual radiation budgets, infer annual carbon dioxide frost budgets, and constrain spring season surface and atmospheric properties with the aid of a polar radiative model. The results provide further confirmation of the presence of permanent CO_2 frost deposits near the south pole and show that the stability of these deposits can be explained by their high reflectivities. In the north, the observed absence of solid CO_2 during summer was primarily the result of enhanced CO_2 sublimation rates due to lower frost reflectivities during spring. The results suggest that the present asymmetric behavior of CO_2 frost at the Martian poles is caused by preferential contamination of the north seasonal polar cap by atmospheric dust. © 1985 American Association for the Advancement of Science. We thank all those who contributed to the great success of the Viking project, with special thanks to H. H. Kieffer, F. D. Palluconi, and R. W. Zurek for encouragement and assistance. Contribution 4148, Division of Geological and Planetary Sciences, California Institute of Technology.
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