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Overview of Martian Crater Degradation, including Simple Numerical Models

Overview. Motivation: Why study crater distributions?BackgroundCratering RatesMethods of Crater Degradation (Mars specific)ModelsDescriptionResults. Motivation. Craters investigated for?Dating/ Deducing geologic historyDeducing climate historyNumerical models allow predictions of observed c

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Overview of Martian Crater Degradation, including Simple Numerical Models

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    1. Overview of Martian Crater Degradation, including Simple Numerical Models Ge 151a 2004 Colette Salyk

    2. Overview Motivation: Why study crater distributions? Background Cratering Rates Methods of Crater Degradation (Mars specific) Models Description Results

    3. Motivation Craters investigated for Dating/ Deducing geologic history Deducing climate history Numerical models allow predictions of observed crater fields given age and climate

    4. Cratering Rates Determined by lunar crater counts N(D,t) =C (1+2*10-6) Exp[4.5 (4.5-t)] D-3 3.6 Ga surface on moon has 188 craters Martian production ~ 2 x lunar production

    5. Degradation Mechanisms: Dust Deposition/Erosion Dust trapped in depressions Sharp surface features eroded by wind Rates depend on Wind speed, direction, frequency Gravity Particle size Geometry of topography Linear deposition/erosion in time-averaged sense Estimates give ~ 18 ?m/yr deposition

    6. Degradation Mechanisms: Sublimation/Condensation Rates strongly dependent on surface temperature Sublimation estimates: 0.2 pr. mm/yr from polar regions in summer Similar winter condensation rates, if steady state Degradation of craters caused by preferential condensation/sublimation due to shadowing

    7. Degradation Mechanisms: Viscous Creep Viscous relaxation of material due to small stresses applied for a long time Craters relax under influence of gravity Relaxation time, ? = 4? ? /(? g D)

    8. Model Description Specify area, time of start, end, ?t, rates of erosion/infill Create craters using production equation Calculate depths, rim heights Allow craters to degrade, via creep, infill/erosion or both Erase shallow craters Increment time and repeat

    9. Result 1: Viscous Relaxation Relaxation rate depends on diameter Few in upper right Many in lower left

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