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Important Physical Factors for Liquid Water Forming at the Martian Surface

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. Water Ice in the Near-Surface: High Latitudes.

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Important Physical Factors for Liquid Water Forming at the Martian Surface

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  1. Important Physical Factors for Liquid Water Forming at the Martian Surface

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

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

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

  5. 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 CO2 (~150 K) or H2O (~200 K) Conduction from below (probably important to near-surface only in geothermally anomalous environments: hydrothermal, volcanic)

  6. From Hecht, HEND2003 Presentation 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.

  7. 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°).

  8. Phase Diagram

  9. 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 CO2 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)

  10. HiRISE view of gullies PSP_002932_1445

  11. 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? • Malin and Edgett, 2000 (Mars)

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