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

Factors in Mars Evolution

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 CO 2 Cap, Southern Year-Round CO 2 Cap –Not enough CO2 for past greenhouse effect

History of Mars

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 CO 2 and H 2 O from volcanoes Substantial (Greenhouse) Atmosphere

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

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

Other Losses for H 2 O, CO 2 Loss to Polar Caps Carbonate Deposits Within Crust

Evidence of Recent Water Catastrophic Outflow Channels –Large quantities of H 2 0 released too quickly to instantly freeze –Other eroding agents explored, H 2 0 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

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

“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

Mars Recap Volcanism Releases H 2 O and CO 2 Impact Erosion Shutdown of Magnetic Field Solar Wind Stripping and Hydrodynamic Escape H 2 O and CO 2 Lost to Space, Polar Caps, and Crustal Carbonate Deposits Geological Features and Meteorites Suggest Grnd and Surf H 2 O

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