Mars: Northern Summer Ice Cap—Water Vapor Observations from Viking 2

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Science  17 Dec 1976:
Vol. 194, Issue 4271, pp. 1339-1341
DOI: 10.1126/science.194.4271.1339


Observations of the latitude dependence of water vapor made from the Viking 2 orbiter show peak abundances in the latitude band 70° to 80° north in the northern midsummer season (planetocentric longitude ∼ 108°). Total column abundances in the polar regions require near-surface atmospheric temperatures in excess of 200°K, and are incompatible with the survival of a frozen carbon dioxide cap at martian pressures. The remnant (or residual) north polar cap, and the outlying patches of ice at lower latitudes, are thus predominantly water ice, whose thickness can be estimated to be between 1 meter and 1 kilometer.