The astronomical theory of climatic change on Mars

We examine the response of Martian climate to changes in solar energy deposition caused by variations of the Martian orbit and obliquity. We systematically investigate the seasonal cycles of carbon dioxide, water, and dust to provide a complete picture of the climate for various orbital configurations. We find that at low obliquity (15°) the atmospheric pressure will fall below 1 mbar; dust storms will cease; thick permanent CO ₂ caps will form; the regolith will release CO ₂; and H ₂O polar ice sheets will develop as the permafrost boundaries move poleward. At high obliquity (35°) the annual average polar temperature will increase by about 10°K, slightly desorbing the polar regolith and causing the atmospheric pressure to increase by not more than 10 to 20 mbar. Summer polar ground temperatures as high as 273°K will occur. Water ice caps will be unstable and may disappear as the equilibrium permafrost boundary moves equatorward. However, at high eccentricity, polar ice sheets will be favored at one pole over the other. At high obliquity dust storms may occur during summers in both hemispheres, independent of the eccentricity cycle. Eccentricity and longitude of perihelion are most significant at modest obliquity (25°). At high eccentricity and when the longitude of perihelion is close to the location of solstice hemispherical asymmetry in dust-storm generation and in polar ice extent and albedo will occur. The systematic examination of the relation of climate and planetary orbit provides a new theory for the formation of the polar laminae. The terraced structure of the polar laminae originates when eccentricity and/or obliquity variations begin to drive water ice off the dusty permanent H ₂O polar caps. Then a thin (meters) layer of consolidated dust forms on top of a dirty, slightly thicker (tens of meters) ice sheet and the composite is preserved as a layer of laminae composed predominately of water ice. Because of insolation variation on slopes, a series of poleward- and equatorward-facing scarps are formed where the edges of the laminae are exposed. Independently of orbital variations, these scarps propagate poleward both by erosion of the equatorward slopes and by deposition on the poleward slopes. Scarp propagation resurfaces and recycles the laminae forming the distinctive spiral bands of terraces observed and provides a supply of water to form new permanent ice caps. The polar laminae boundary marks the furthest eqautorward extension of the permanent H ₂O caps as the orbit varies. The polar debris boundary marks the furthest equatorward extension of the annual CO ₂ caps as the orbit varies. The Martian regolith is now a significant geochemical sink for carbon dioxide. CO ₂ has been irreversibly removed from the atmosphere by carbonate formation. CO ₂ has also benn removed by regolith adsorption. Polar temperature increases caused by orbital variations are not great enough