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

A model for the formation and distribution of sedimentary rocks on Mars is proposed. The rate-limiting step is supply of liquid water from seasonal melting of snow or ice. The model is run for a O(10^2) mbar pure CO2 atmosphere, dusty snow, and solar luminosity reduced by 23%. For these conditions snow only melts near the equator, and only when obliquity >40 degrees, eccentricity >0.12, and perihelion occurs near equinox. These requirements for melting are satisfied by 0.01-20% of the probability distribution of Mars' past spin-orbit parameters. Total melt production is sufficient to account for aqueous alteration of the sedimentary rocks. The pattern of seasonal snowmelt is integrated over all spin-orbit parameters and compared to the observed distribution of sedimentary rocks. The global distribution of snowmelt has maxima in Valles Marineris, Meridiani Planum and Gale Crater. These correspond to maxima in the sedimentary-rock distribution. Higher pressures and especially higher temperatures lead to melting over a broader range of spin-orbit parameters. The pattern of sedimentary rocks on Mars is most consistent with a Mars paleoclimate that only rarely produced enough meltwater to precipitate aqueous cements and indurate sediment. The results suggest intermittency of snowmelt and long globally-dry intervals, unfavorable for past life on Mars. This model makes testable predictions for the Mars Science Laboratory rover at Gale Crater. Gale Crater is predicted to be a hemispheric maximum for snowmelt on Mars.Comment: Submitted to Icarus. Minor changes from submitted versio

Valleys, Paleolakes and Possible Shorelines at the Libya Montes/Isidis Boundary: Implications for the Hydrologic Evolution of Mars

We describe the results of our morphologic, stratigraphic and mineralogic investigations of fluvial landforms, paleolakes and possible shoreline morphologies at the Libya Montes / Isidis Planitia boundary between 85°/86.5°E and 1.8°/5°N [1]. The landforms are indicative of aqueous activity and standing bodies of water, that are attributed to a complex hydrologic cycle that may have once existed on Mars in the Noachian (>3.7 Ga) and perhaps also in the Hesperian (>3.1 Ga). At the Libya Montes / Isidis Planitia boundary, we identified series of morphologic landforms at three different elevation levels (Fig. 1). The morphologies have been associated with intense fluvial activity, standing bodies of water, hydrous alteration, wave-cut action, distinct still stands as well as freezing and sublimation of a cold ocean [e.g., 1-10]. We can distinguish between (1) local occurences of fluvial and lacustrine landforms of the Libya / Isidis contact between -2500 and -2800 m, (2) a series of cliffs of the Arabia shoreline at -3600 and -3700 m, and (3) the Deuteronilus contact that occurs as an onlap morphology at the boundary between the Isidis interior plains and the Isidis exterior plains