Planetary Atmospheres Greenhouse Effect Greenhouse Effect 90 atmospheres!

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


Energy In Energy Out

100 energy units 100 energy units

100% gate 50% gate

200 energy unitsstored

in equilibrium


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


• 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


• Comparative Planetology - Earth and MarsComparative Planetology - Earth and Mars

MarsMars EarthEarth

Dormant volcanos Active volcanosDormant volcanos Active volcanos


• 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


• 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


• 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?


• Comparative Planetology - Earth and VenusComparative Planetology - Earth and Venus

VenusVenus EarthEarth

Active volcanos Active volcanosActive volcanos Active volcanos




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)





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


• 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”


• Runaway Greenhouse EffectRunaway Greenhouse Effect

• once RGE begins …once RGE begins …

RGERGEHH220 in0 in

atmosatmos

UVUVfromfromSunSun

HH22

OO22

EscapeEscape

SurfaceSurfaceCompoundsCompounds

++

Irreversible!!Irreversible!!


• 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

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Planetary Atmospheres Greenhouse Effect Greenhouse Effect 90 atmospheres!