Evolution of Mars Burton Gray Introduction Comparison of

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 CO 2 for past greenhouse effect

History of Mars

Early Volcanism Evidence • Global Warping of Surface – Formation of Tharsis rise – Encircling trough at 5000 km 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 20 released too quickly to instantly freeze – Other eroding agents explored, H 20 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 CO 2 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 • Mc. Kinnon, “Impacts Giveth and Impacts Taketh Away”, Nature Vol 338, Apr 1989