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

17 A model for the formation and distribution of sedimentary rocks on Mars 18 is proposed. The rate–limiting step is supply of liquid water from seasonal 19 melting of snow or ice. The model is run for a O(10) mbar pure CO2 atmo20 sphere, dusty snow, and solar luminosity reduced by 23%. For these conditions 21 snow only melts near the equator, and only when obliquity &40◦, eccentricity 22 &0.12, and perihelion occurs near equinox. These requirements for melting are 23 satisfied by 0.01–20% of the probability distribution of Mars’ past spin-orbit 24 parameters. Total melt production is sufficient to account for aqueous alter25 ation of the sedimentary rocks. The pattern of seasonal snowmelt is integrated 26 over all spin-orbit parameters and compared to the observed distribution of 27 sedimentary rocks. The global distribution of snowmelt has maxima in Valles 28 Marineris, Meridiani Planum and Gale Crater. These correspond to maxima 29 in the sedimentary-rock distribution. Higher pressures and especially higher 30 temperatures lead to melting over a broader range of spin-orbit parameters. 31 The pattern of sedimentary rocks on Mars is most consistent with a Mars pa32 leoclimate that only rarely produced enough meltwater to precipitate aqueous 33 cements and indurate sediment. The results suggest intermittency of snowmelt 34 and long globally-dry intervals, unfavorable for past life on Mars. This model 35 makes testable predictions for the Mars Science Laboratory rover at Gale 36 Crater. Gale Crater is predicted to be a hemispheric maximum for snowmelt 37 on Mars. 38