Evolution of Mars

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 104 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 Doesnt 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
• OHanlon, The Outrageous Hypothesis, Nature Vol
  413, Oct 2001
• McKinnon, Impacts Giveth and Impacts Taketh
  Away, Nature Vol 338, Apr 1989