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The First Billion Years: Warm and Wet Or Cold and Icy? Robert M

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The First Billion Years: Warm and Wet Or Cold and Icy? Robert M The First Billion Years: Warm and Wet or Cold and Icy? Robert M. Haberle Space Science and Astrobiology Division NASA/Ames Research Center July 15, 2014 Mars 8 Meeting Acknowledgements: Mike Carr, David Catling, and Kevin Zahnle Haberle, 8th Mars Conference Evidence for a Different Valley Networks Climate Isotopic Heavy Isotopes Aqueous Minerals 14N/15N 170±15 (Viking) 20Ne/22Ne ~10 (Meteorites) 36Ar/38Ar 4.2±0.2 (MSL) δ13C 46±4‰ (MSL) Elmann and Edwards (2014) 129Xe/132Xe ~ 2.5 (Viking) Haberle, 8th Mars Conference The First Billion Years Haberle, 8th Mars Conference Faint Young Sun Problem Noachian Haberle, 8th Mars Conference Atmospheric Redox and Outgassing The oxidation state of volcanic gases (principally H2/H2O) is governed by the oxidation state (fO2) of the upper mantle. During core(a) formation After core(b) formation Since core formation was fast (< 10 My), the mantle was likely weakly reducing and Outgassing products were mostly CO2, H2O, and N2 Haberle, 8th Mars Conference 1-D Calculations of Pollack et al. (1987) Main Conclusion: Early Mars was Continuously Warm and Wet - 5 bars of CO2 maintained against carbonate loss by impact recycling Haberle, 8th Mars Conference Problems With This Model Haberle, 8th Mars Conference 1. CO2 condenses in the atmosphere reducing the greenhouse effect. Latent heat release warms the upper atmosphere Kasting (1991) Haberle, 8th Mars Conference 2. Collision Induced Absorption Overestimated We now have more accurate absorption data based on theoretical and experimental data Old parameterizations overestimated induced-dipole absorption -1 in the 250-500 cm region Haberle, 8th Mars Conference Wordsworth et al. (2010) 3. Rapid Thermal Escape of Carbon Noachian Carbon escape Thick CO2 atmospheres Not possible Haberle, 8th Mars Conference Tian et al. (2009) How Thick Could the Atmosphere Be? Haberle, 8th Mars Conference Noachian CO2 Atmosphere Estimates Tharsis Volcanism 1.5 bars Phillips et al (2001) Outgassing Models ~0.25 bars Grott et al (2011) 40Ar/36Ar in ALH84001 0.4 bars Casatta et al (2012) Small Crater Statistics 1-2 bars (max) Kite et al (2013) Haberle, 8th Mars Conference GCM Simulations Dry CO2 Atmosphere Moist CO2 Atmosphere Wordsworth et al. (2013) H2 O Melting Point Forget et al. (2013) CO2 Frost Point Global Mean Annual Temperatures < 250 K Haberle, 8th Mars Conference What Are Some Alternatives? Haberle, 8th Mars Conference 1. Trace Gases Window Haberle, 8th Mars Conference A CO2-H2 Rich Atmosphere ? Ramirez et al. (2013) show that this can work. But it requires: • 1.3-4 bars of CO2 and 5-20% H2 • A reducing mantle • Earth-like outgassing rates (to balance escape) Note: If such an atmosphere existed, it implies the absence of life. Haberle, 8th Mars Conference Water Ice Cloud Greenhouse? Urata and Toon (2013) Temperatures near melting point can be achieved under optimal conditions. Result is model dependent. Haberle, 8th Mars Conference Transient Warming? Haberle, 8th Mars Conference 1. Impact generated climate change (Segura et al 2002, 2008, 2012) Rainfall vs Impactor Size Segura et al. (2008) 0.15 bar atmosphere No clouds Total Rainfall from all impacts = 650 m Haberle, 8th Mars Conference 2. Valley Networks formed from snowmelt not rainfall Icy Highlands Hypothesis (Wordsworth et al., 2013) Haberle, 8th Mars Conference 3. Trace Gas / Obliquity Interactions (Mischna et al., 2013) Haberle, 8th Mars Conference So Where Do We Stand? • A long-lived continuously warm wet early Mars is difficult to explain • Pure CO2/H2O atmosphere’s cannot raise mean annual surface temperatures to melting point • CO2-H2 atmospheres ?? Cloud greenhouse ?? • Transient warming on an otherwise cold planet more likely. Forcing due to • Impacts, volcanism, and/or orbital changes Haberle, 8th Mars Conference Future Research Directions • Geology community – Does it have to rain? If so, how long and how much? • Geophysics community – What is the redox state of the mantle and its outgassing history? • Atmosphere community – What is the climate response to impacts, volcanism, orbital changes? Haberle, 8th Mars Conference .
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