Climatic variations on Mars: 2. Evolution of carbon dioxide atmosphere and polar caps

Abstract

The long-term variations in the atmospheric pressure and the polar cap temperature of Mars resulting from the obliquity oscillations (presented by W. R. Ward, 1974) are discussed. In performing these calculations, the assumption is made that the atmosphere is in equilibrium with perennial CO_2 ice deposits at the north pole, as is proposed by R. B. Leighton and B. C. Murray (1966). If heat transport by the atmosphere is neglected, the temperature of CO_2 ice at the poles ranges from ∼130°K to ∼160°K, the corresponding atmospheric pressure rising from a few tenths of a millibar to ∼30 mbar, respectively. The neglect of atmospheric heat transport probably underestimates the peak pressure. Because the altitude of the south cap is ∼2 km higher than that of the north cap, CO_2 ice is unstable there and will migrate to the north cap at a rate ∼10 g/cm^2 yr, the implication being that the south residual cap is water ice. A simplified model of the annual polar caps and pressure fluctuations is also presented. This indicates that when the obliquity is at its maximum, the annual caps may be greatly enlarged in both mass and maximum coverage. The modifications introduced by including significant atmospheric heat transport are then discussed. Finally, the implications of different past climatic conditions on the mechanism of eolian erosion are briefly considered.

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