Download Venus and Mars

Natural Climate Change
When Good Planets go Bad
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Goals
• What are Venus and Mars like now?
• What happened to them?
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Atmosphere Origins
• Outgassing
• Volcanoes.
• CO2 and H2O main
gases.
• Mt. St. Helens
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Concept Test
•
For which terrestrial planets is the main
atmospheric gas one of the two main gases
produced by outgassing?
a.
b.
c.
d.
e.
Only Moon & Mercury
All five planets
Only Venus, Earth and Mars
Only Earth
Only Venus and Mars
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Atmosphere Loss
1. Thermal escape “boiling away” by temperature.
2. “Knocking away” by solar wind particles.
3. UV-rays break molecules into smaller atoms.
– Lighter atoms boil away.
4. Absorbed by surface
5. “Blasted away” by impacts
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Thermal Escape
• Atoms have mass.
• Attracted to planet by
gravity.
• Temperature is measure
of atoms motion.
• High temperature = high
velocity: escape velocity
if too light.
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Knocking away
• Sun blows off solar
wind:
– Protons
– Electrons
– Neutrons
• Billiards with
atmosphere (if no
magnetosphere).
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Dissociation
• Atoms held together in
molecules by
electromagnetic forces.
• UV-rays source of energy.
• Break molecular bonds.
• Light elements (H) can
boil away.
• Importance of protective
ozone layer.
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Absorption
• Chemical reactions.
– Rust for O2.
– Carbonate rocks for CO2 (when H20 is present)
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Concept Test
•
Under what circumstances is thermal escape
likely to be important?
a.
b.
c.
d.
e.
Light gases on big planets far from the Sun
Heavy gases on big planets far from the Sun
Light gases on small planets near the Sun
Light gases on small planets far from the Sun
Equally well on any kind of gas from any kind of
planet
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Mars Today
• Pressure just below triple point of water:
0.01 bar
• Temperature below freezing:
-50 C
• No rain, some clouds, dust, ice caps.
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P vs T for H2O
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Gusev
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Meridiani Planum
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What went wrong?
•
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Size.
Too small – core cools
Core cools – magnetic field stops (not magnetosphere).
Atmosphere CO2 stripped by solar winds.
UV-rays dissociate H2O
H boils away
O rusts rocks
No CO2 or H2O, no greenhouse effect.
Cold, dry Mars today.
Good scientific theory?
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Concept Test
•
All the following statements about Mars are true. Which
one might have led to a significant loss of atmospheric
gas to space?
a. The rock on Mars is probably red because of chemical reactions
with oxygen that had been released into the atmosphere through
the outgassing of water molecules.
b. Mars lost any global magnetic field that it may once have had.
c. The axis tilt of Mars is thought to change significantly with time.
d. Mars probably once had a much higher density of greenhouse
gases in its atmosphere than it does today.
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Venus Today
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Pressure = 90 bars.
Temperature = 880 F.
No pole/equator temperature difference.
No day/night temperature difference.
No seasonal temperature difference.
No rain hits surface.
No storms.
Little wind.
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Venera Landers
• Venera 13 and 14 color images from red, green
and blue filters.
Copyright: Don P. Mitchell – Mentallandscape.com
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What went wrong?
• Same size as Earth.
• Same outgassing as Earth.
– Same CO2 content.
– What happened to atmospheric H2O?
• Higher initial temperature.
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What went wrong?
•
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Higher initial temperature.
More water evaporates.
Atmosphere can hold more H2O before rains.
H2O is greenhouse gas – increases temp.
More water evaporates.
Feedback mechanism.
All H2O evaporates.
No oceans, seas or lakes.
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…it gets worse.
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No water for CO2 to react.
Increases greenhouse effect further.
UV-rays dissociate H2O.
H lost to space.
Result, 100% of CO2 in atmosphere.
Runaway greenhouse effect.
Hot, dry, Venus today.
Good scientific theory?
Venus once like Earth?
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Concept Test
•
Why do we think that Venus has so much more
atmospheric gas than Earth?
a. Earth has lost much more atmospheric gas than Venus, primarily
to condensation of water vapor into liquid water and to chemical
reactions that make carbonate rock.
b. Venus has gained much more gas through outgassing than has
Earth.
c. Because of its lack of magnetic field, Venus has been able to gain
gas through the process of bombardment, while Earth has not
gained gas in this way.
d. Earth has lost much more gas to thermal escape than has Venus.
e. None of the above.
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Concept Test
•
What would happen if Venus were moved to
Earth’s orbit today?
a.
b.
c.
d.
e.
Runaway greenhouse would reverse, pleasant climate
Some decrease in its temperature, but still too hot
CO2 would condense as on Mars, fall below freezing
No change at all
Slight increase in its temperature, way too hot
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Homework #17
• Due Wednesday 12-Nov:
• Read Bennett 10.6
• Do 20, 21, 40, 42
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