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Evolution of Mars

Evolution of Mars. Burton Gray. Introduction. Comparison of Current Earth, Mars, and Venus Atmospheres Physical and Atmospheric Evolution of Mars. Goldilocks. Venus is Too Hot Greenhouse effect = 400 K Mars is Too Cold Greenhouse effect = 5 K Earth is Just Right Greenhouse effect = 40 K.

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Evolution of Mars

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  1. Evolution of Mars Burton Gray

  2. Introduction • Comparison of Current Earth, Mars, and Venus Atmospheres • Physical and Atmospheric Evolution of Mars

  3. Goldilocks • Venus is Too Hot • Greenhouse effect = 400 K • Mars is Too Cold • Greenhouse effect = 5 K • Earth is Just Right • Greenhouse effect = 40 K

  4. Factors in Mars Evolution

  5. Present-Day Mars • Atmospheric Pressure = 6 mbar • Earth: 1000 mbar • Water Vapor Partial Press = 10^-3 mbar • Earth is 10^4 times greater • Average Surf Temp = 220 K • Equatorial noontime temp exceeds 273 K • Press too low for water • Northern Seasonal CO2 Cap, Southern Year-Round CO2 Cap • Not enough CO2 for past greenhouse effect

  6. History of Mars

  7. Early Volcanism Evidence • Global Warping of Surface • Formation of Tharsis rise • Encircling trough at 5000km radius • Flood channels beginning at Valles Marineris and extending to Chryse basin • Geochemical Analysis of M. Meteorites • Water content ~1.8% by weight • Lots of CO2 and H2O from volcanoes • Substantial (Greenhouse) Atmosphere

  8. Atmospheric Losses • Comet and Asteroid Impact • Capable of removing an entire atmosphere • Likely to have ejected 50 to 90% of atmos • All isotopes removed equally efficiently • Shutdown of Global Magnetic Field • Solar Wind Stripping • Lighter isotopes enriched at top of atmos • Net result: Atmos features heavier isotopes

  9. Solar Wind, Hydrodynamic Loss • Ar Ratio 30% Greater Than Elsewhere • 50 to 90% of Atmos Lost This Way

  10. Other Losses for H2O, CO2 • Loss to Polar Caps • Carbonate Deposits Within Crust

  11. Evidence of Recent Water • Catastrophic Outflow Channels • Large quantities of H20 released too quickly to instantly freeze • Other eroding agents explored, H20 most plausible • Martian Meteorites w/ Heavy Isotopes • Settling of gases from atmos to surface • Groundwater circulation from surface to crust • Young meteorites suggest recent grnd water

  12. Evidence of Surface Water • Pristine Gullies on Exposed Walls of Impact Craters • Potential Crater Lakes with Channels Flowing In and Out • “Delta” Deposits Near Craters • Catastrophic Outflow Channels All “Drain” Into Northern Lowlands • Smoothness of Lowland

  13. “Outrageous Hypothesis” • No Surface Water and No Thick Atmosphere Ever • Liquid CO2 in Crust • Turns to gas when exposed at fissures • Explosion and debris flow results • Nature of gullies explained “better” • Theory Doesn’t Explain Deuterium-Heavy Atmosphere

  14. Mars Recap • Volcanism Releases H2O and CO2 • Impact Erosion • Shutdown of Magnetic Field • Solar Wind Stripping and Hydrodynamic Escape • H2O and CO2 Lost to Space, Polar Caps, and Crustal Carbonate Deposits • Geological Features and Meteorites Suggest Grnd and Surf H2O

  15. Mars Information Sources • Jakosky and Phillips, “Mars’ Volatile and Climate History”, Nature Vol 412, Jul 2001 • Titus, “Water, Water Everywhere”, Nature Vol 428, Apr 2004 • O’Hanlon, “The Outrageous Hypothesis”, Nature Vol 413, Oct 2001 • McKinnon, “Impacts Giveth and Impacts Taketh Away”, Nature Vol 338, Apr 1989

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