Planetary AtmospheresPlanetary Atmospheres
• Greenhouse EffectGreenhouse Effect
90 atmospheres!90 atmospheres!
Planetary AtmospheresPlanetary Atmospheres• Greenhouse EffectGreenhouse Effect
COCO22
HH2200
240 240 watts/mwatts/m22
inin
240 240 watts/mwatts/m22
outout50% reflected by50% reflected by
clouds and surfaceclouds and surface
Small fractionSmall fractionescapes intoescapes into
spacespace
Planetary AtmospheresPlanetary Atmospheres• Greenhouse EffectGreenhouse Effect
Energy In Energy Out
100 energy units 100 energy units
100% gate 50% gate
200 energy unitsstored
in equilibrium
Planetary AtmospheresPlanetary Atmospheres• Greenhouse EffectGreenhouse Effect
Energy In Energy Out
100 energy units 100 energy units
100% gate 1% gate
10, 000 energy unitsstored
in equilibrium
Frosts are most likely to happen on clear nights rather than Frosts are most likely to happen on clear nights rather than cloudy nights. This is because cloudy nights. This is because
A) Cloudy nights lead to falling snowA) Cloudy nights lead to falling snow B) Clouds are not transparent to optical lightB) Clouds are not transparent to optical light C) More infrared light can be radiated through clear skiesC) More infrared light can be radiated through clear skies D) Snow and frost reflect rather than absorb visible lightD) Snow and frost reflect rather than absorb visible light
ConcepTest!ConcepTest!
Planetary EvolutionPlanetary Evolution
• Essential IdeaEssential Idea
• Evolution of both geology and atmospheresEvolution of both geology and atmospheres driven by energy flow from planetary coresdriven by energy flow from planetary cores
Planetary EvolutionPlanetary Evolution
• Essential IdeaEssential Idea
• RecallRecall• Amount of residual thermal energy stored in planetAmount of residual thermal energy stored in planet depends on planet volume (amount of material)depends on planet volume (amount of material)
• Rate of energy loss depends on planet surface areaRate of energy loss depends on planet surface area
• Small planets go dormant soonerSmall planets go dormant sooner€
Lifetime of geological activity = Residual thermal energy
Rate of energy loss ∝
4
3πRplanet
3
4πRplanet2
∝ Rplanet
Planetary EvolutionPlanetary Evolution
• Comparative Planetology - Earth and MarsComparative Planetology - Earth and Mars
MarsMars EarthEarth
Dormant volcanos Active volcanosDormant volcanos Active volcanos
Planetary EvolutionPlanetary Evolution
• Comparative Planetology - Earth and MarsComparative Planetology - Earth and Mars
MarsMars EarthEarth
Dormant volcanos Active volcanosDormant volcanos Active volcanosWater in past Water at presentWater in past Water at present
Planetary EvolutionPlanetary Evolution• Comparative Planetology - Earth and MarsComparative Planetology - Earth and Mars
MarsMars EarthEarth
Dormant volcanos Active volcanosDormant volcanos Active volcanosWater in past Water at presentWater in past Water at presentThin COThin CO22 atmosphere N atmosphere N22/O/O22 atmosphere atmosphere
(0.01 atmos) (1 atmos)(0.01 atmos) (1 atmos)
Note: Liquid water would not survive on Mars today -Note: Liquid water would not survive on Mars today - it would boil due to low atmospheric pressure. it would boil due to low atmospheric pressure. So if liquid water in past, must also have beenSo if liquid water in past, must also have been substantial atmosphere and greenhouse effect in pastsubstantial atmosphere and greenhouse effect in past Active volcanoes could have provided such an atmosphereActive volcanoes could have provided such an atmosphere
Planetary EvolutionPlanetary Evolution
• Comparative Planetology - EarthComparative Planetology - Earth
Plate tectonics is critical to Earth atmospherePlate tectonics is critical to Earth atmosphere
washed out with H20 rain
Ozone O3
Planetary EvolutionPlanetary Evolution
• Comparative Planetology - EarthComparative Planetology - Earth
Life is critical to oxygen in Earth atmosphereLife is critical to oxygen in Earth atmosphere
washed out with H20 rain
Ozone O3
If plate tectonics on the Earth were to end, you would expect the If plate tectonics on the Earth were to end, you would expect the temperature of the Earth’s surface totemperature of the Earth’s surface to
A) IncreaseA) Increase B) Change little or not at allB) Change little or not at all C) DecreaseC) Decrease
ConcepTest!ConcepTest!
Planetary EvolutionPlanetary Evolution• Comparative Planetology - Mars at 1 billion yrComparative Planetology - Mars at 1 billion yr (end of geologic activity)(end of geologic activity)
1.1. HH22O rain washes COO rain washes CO22 into surface - into surface - permanentlypermanently
2.2. Greenhouse effect reducedGreenhouse effect reduced3.3. Colder temperatures lead to enhanced rain, less gaseous COColder temperatures lead to enhanced rain, less gaseous CO22, less greenhouse, less greenhouse
(“Runaway Icehouse Effect”)(“Runaway Icehouse Effect”)4.4. Most COMost CO22 in carbonate rocks, most H in carbonate rocks, most H22O in permafrostO in permafrost
5.5. UV sunlight breaks up molecules and provides energy of escapeUV sunlight breaks up molecules and provides energy of escape
UV
O,C
Planetary EvolutionPlanetary Evolution• Comparative Planetology - Mars at 4.5 billion yrComparative Planetology - Mars at 4.5 billion yr
Recent liquid water?Recent liquid water?
Planetary EvolutionPlanetary Evolution
• Comparative Planetology - Earth and VenusComparative Planetology - Earth and Venus
VenusVenus EarthEarth
Active volcanos Active volcanosActive volcanos Active volcanos
Planetary EvolutionPlanetary Evolution
• Comparative Planetology - Earth and VenusComparative Planetology - Earth and Venus
VenusVenus EarthEarth
Active volcanos Active volcanosActive volcanos Active volcanosVVescesc = 10.3 km/sec V = 10.3 km/sec Vescesc = 11.2 km/sec = 11.2 km/sec
Planetary EvolutionPlanetary Evolution
• Comparative Planetology - Earth and VenusComparative Planetology - Earth and Venus
VenusVenus EarthEarth
Active volcanos Active volcanosActive volcanos Active volcanosVVescesc = 10.3 km/sec V = 10.3 km/sec Vescesc = 11.2 km/sec = 11.2 km/sec
COCO22 atmosphere atmosphere N N22/O/O22 atmosphere atmosphere
(90 atmos) (1 atmos)(90 atmos) (1 atmos)
Planetary EvolutionPlanetary Evolution
• Comparative Planetology - Earth and VenusComparative Planetology - Earth and Venus
VenusVenus EarthEarth
Active volcanos Active volcanosActive volcanos Active volcanosVVescesc = 10.3 km/sec V = 10.3 km/sec Vescesc = 11.2 km/sec = 11.2 km/sec
COCO22 atmosphere atmosphere N N22/O/O22 atmosphere atmosphere
(90 atmos) (1 atmos)(90 atmos) (1 atmos)Dry (10Dry (10-4-4 Earth H Earth H220) Water at present0) Water at present
Note: Based on measurements of deuterium (“heavy water”)Note: Based on measurements of deuterium (“heavy water”) Venus had substantially more water in the pastVenus had substantially more water in the past Consistent with outgassing from volcanos and largeConsistent with outgassing from volcanos and large escape velocityescape velocity
Planetary AtmospheresPlanetary Atmospheres
• Comparative Planetology - VenusComparative Planetology - Venus• Suppose Venus were “Earth-like” (liquid water) and …Suppose Venus were “Earth-like” (liquid water) and …
Light from Sun Light from Sun or COor CO22, H, H22O O
Temperature Temperature
COCO22, H, H22O O
from oceansfrom oceansfrom rocksfrom rocks
““Runaway Greenhouse Effect”Runaway Greenhouse Effect”
Planetary AtmospheresPlanetary Atmospheres
• Runaway Greenhouse EffectRunaway Greenhouse Effect
• once RGE begins …once RGE begins …
RGERGEHH220 in0 in
atmosatmos
UVUVfromfromSunSun
HH22
OO22
EscapeEscape
SurfaceSurfaceCompoundsCompounds
++
Irreversible!!Irreversible!!
Planetary AtmospheresPlanetary Atmospheres
• Comparative Planetology - Venus at 4.5 billion yrComparative Planetology - Venus at 4.5 billion yr
Planetary Evolution - SummaryPlanetary Evolution - Summary
MercuryMercury
Trace ofTrace ofHe, Na, OHe, Na, O
VenusVenus
96% CO96% CO22
470 470 ooCC90 atmospheres90 atmospheres
EarthEarth
77% N77% N22, 21% O, 21% O22
15 15 ooCC1 atmosphere1 atmosphere
Moon Trace of He, Na, ArMoon Trace of He, Na, Ar
MarsMars
95% CO95% CO22
-50 -50 ooCC0.01 atmospheres0.01 atmospheres
Planetary Evolution - SummaryPlanetary Evolution - Summary
• Geological EvolutionGeological Evolution• Mercury, Moon - smallest radii => dormant, crateredMercury, Moon - smallest radii => dormant, cratered• Mars - active for 10Mars - active for 1099 yr, now dormant (shield volcanoes) yr, now dormant (shield volcanoes)• Venus - current volcanos (shield volcanoes)Venus - current volcanos (shield volcanoes)• Earth - convection => plate tectonicsEarth - convection => plate tectonics
• Atmospheric EvolutionAtmospheric Evolution• Moon, Mercury - low escape velocity, hot, atmos escapesMoon, Mercury - low escape velocity, hot, atmos escapes• Venus RGE, massive COVenus RGE, massive CO22 atmos atmos• Earth COEarth CO22, H, H22O , NO , N22 N N22, O, O22
• Mars Runaway Icehouse,Mars Runaway Icehouse, thin COthin CO22 atmos atmos