Transcript Evolution of Mars and Venus

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
Gases (% by volume)
Planet or Body
Distance from Sun Surface Temperature (range)
Surface Atmospheric Pressure (millibars)
Albedo
-40 to 75C
1000
30
228 million
-120 to 25C
6 to 10
22
108 million
475C (range small)
90,000
80
N2
O2
CO2
Earth
78.08
20.95
0.03
150 million
Mars
2.7
1.3
95.32
Venus
3.5
<0.01
96.5
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 CO2 Cap, Southern
Year-Round CO2 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 CO2 and H2O 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
Isotope Ratio
Measured Value
Amount Lost to Space (%)
D/H
5
60 - 74
Ar-38 / Ar-36
1.3
50 - 90
C-13 / C-12
1.05 - 1.07
50 - 90
N-15 / N-14
1.7
90
O-18 / O-16
1.025
25 - 50
• Ar Ratio 30% Greater Than Elsewhere
• 50 to 90% of Atmos Lost This Way
Other Losses for H2O, CO2
• Loss to Polar Caps
• Carbonate Deposits Within Crust
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
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 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
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