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A model for the formation and distribution of sedimentary rocks on Mars isproposed. The rate-limiting step is supply of liquid water from seasonalmelting of snow or ice. The model is run for a O(10^2) mbar pure CO2atmosphere, dusty snow, and solar luminosity reduced by 23%. For theseconditions snow only melts near the equator, and only when obliquity >40degrees, eccentricity >0.12, and perihelion occurs near equinox. Theserequirements for melting are satisfied by 0.01-20% of the probabilitydistribution of Mars' past spin-orbit parameters. Total melt production issufficient to account for aqueous alteration of the sedimentary rocks. Thepattern of seasonal snowmelt is integrated over all spin-orbit parameters andcompared to the observed distribution of sedimentary rocks. The globaldistribution of snowmelt has maxima in Valles Marineris, Meridiani Planum andGale Crater. These correspond to maxima in the sedimentary-rock distribution.Higher pressures and especially higher temperatures lead to melting over abroader range of spin-orbit parameters. The pattern of sedimentary rocks onMars is most consistent with a Mars paleoclimate that only rarely producedenough meltwater to precipitate aqueous cements and indurate sediment. Theresults suggest intermittency of snowmelt and long globally-dry intervals,unfavorable for past life on Mars. This model makes testable predictions forthe Mars Science Laboratory rover at Gale Crater. Gale Crater is predicted tobe a hemispheric maximum for snowmelt on Mars.

Seasonal melting and the formation of sedimentary rocks on Mars, with predictions for the Gale Crater mound