Important Physical Factors for Liquid Water Forming at the Martian Surface

Atmospheric-Surface Exchange of Water Vapor (Is this the Amazonian Hydrological Cycle) Seasonal cycle of atmospheric water vapor, measured by TES on MGS

Ground Ice beneath till, Antarctic Dry Valleys (from Mellon et al, 2004) Water Ice in the Near-Surface: High Latitudes

Water Ice in the Near-Surface: Patterned Ground Earth (Antarctic Dry Valleys)Mars (Phoenix Box D) HiRISECAMBOT

Near-Surface Temperature Controls: Radiative Forcing - Insolation [strong function of latitude, season, time of day, surface topography, and orbit] - Albedo [material property] - Thermal Inertia [material property] - Trapped Radiation [fairly minor on Mars] Cooling - Visibility of the sky (radiative loss) [topography] - Atmospheric Convection [almost negligible on Mars] Phase changes (very important in some places to thermal balance) - Commonly pin surface temperatures at frost point of CO 2 (~150 K) or H 2 O (~200 K) Conduction from below (probably important to near-surface only in geothermally anomalous environments: hydrothermal, volcanic)

Apparent Emissivity (% of visible sky) is important. (X-AXIS IS POSITION, Y-AXIS IS RADIATIVE LOSS RATE) ‘Sun’-facing (eq) topography slopes have both more direct insolation and less radiative cooling than a flat surface at the same latitude. From Hecht, HEND2003 Presentation

Preservation potential for Water Ice at various locations on Mars Estimated survival times of possible water ice reservoirs under current and recent Mars conditions: Myr+ – Polar Caps; Near-surface ground ice at high latitudes Buried ice at all latitudes (**Constraint seems to be if you could get surface the first place**) Kyrs – Surface ice in the low-to-mid-latitudes at high- obliquity (preserved to present obliq. only where buried) Seasons – Surface frost in winter season presently at latitudes down to ~25° (in optimal locations); could be preferred at lower latitudes at high obliquity (~45°).

Phase Diagram

Many places where liquid water has affected the surface presently have surface pressures less than the pure water triple point. - Possible ‘solutions’: - Higher pressure in earlier times when water altered surface e.g., liberation of CO 2 ice from S Polar Cap or from regolith; (as discussed in Head et al PNAS) - Minor (or major) contribution from salts to drop melting point (noted in Hecht) - Protection from atmosphere by ice (Hecht)

HiRISE view of gullies PSP_002932_1445

Malin and Edgett, 2000 (Mars) Gullies How can we connect our understanding of gullies with the presumed recent water cycle on Mars? What does metastability have to do with it? Are gullies formed at equilibrium conditions? Disequilibrium conditions?