Planetary Atmospheres Greenhouse Effect 90 atmospheres Planetary Atmospheres

Planetary Atmospheres • Greenhouse Effect 90 atmospheres!

Planetary Atmospheres • Greenhouse Effect 240 watts/m 2 in Small fraction escapes into space 240 watts/m 2 out 50% reflected by clouds and surface CO 2 H 20

Planetary Atmospheres • Greenhouse Effect Energy In 100 energy units 100% gate Energy Out 200 energy units stored in equilibrium 100 energy units 50% gate

Planetary Atmospheres • Greenhouse Effect Energy In 100 energy units 100% gate Energy Out 10, 000 energy units stored in equilibrium 100 energy units 1% gate

Planetary Atmospheres • Greenhouse Effect

Concep. Test! Frosts are most likely to happen on clear nights rather than cloudy nights. This is because A) B) C) D) Cloudy nights lead to falling snow Clouds are not transparent to optical light More infrared light can be radiated through clear skies Snow and frost reflect rather than absorb visible light

Planetary Evolution • Essential Idea • Evolution of both geology and atmospheres driven by energy flow from planetary cores

Planetary Evolution • Essential Idea • Recall • Amount of residual thermal energy stored in planet depends on planet volume (amount of material) • Rate of energy loss depends on planet surface area • Small planets go dormant sooner

Planetary Evolution • Comparative Planetology - Earth and Mars Dormant volcanos Earth Active volcanos

Planetary Evolution • Comparative Planetology - Earth and Mars Dormant volcanos Water in past Earth Active volcanos Water at present

Planetary Evolution • Comparative Planetology - Earth and Mars Dormant volcanos Water in past Thin CO 2 atmosphere (0. 01 atmos) Earth Active volcanos Water at present N 2/O 2 atmosphere (1 atmos) Note: Liquid water would not survive on Mars today it would boil due to low atmospheric pressure. So if liquid water in past, must also have been substantial atmosphere and greenhouse effect in past Active volcanoes could have provided such an atmosphere

Planetary Evolution • Comparative Planetology - Earth Ozone O 3 washed out with H 20 rain Plate tectonics is critical to Earth atmosphere

Planetary Evolution • Comparative Planetology - Earth Ozone O 3 washed out with H 20 rain Life is critical to oxygen in Earth atmosphere

Concep. Test! If plate tectonics on the Earth were to end, you would expect the temperature of the Earth’s surface to A) B) C) Increase Change little or not at all Decrease

Planetary Evolution • Comparative Planetology - Mars at 1 billion yr (end of geologic activity) UV O, C 1. 2. 3. 4. 4. 5. H 2 O rain washes CO 2 into surface - permanently Greenhouse effect reduced Colder temperatures lead to enhanced rain, less gaseous CO 2, less greenhouse (“Runaway Icehouse Effect”) Most CO 2 in carbonate rocks, most H 2 O in permafrost UV sunlight breaks up molecules and provides energy of escape

Planetary Evolution • Comparative Planetology - Mars at 4. 5 billion yr Recent liquid water?

Planetary Evolution • Comparative Planetology - Earth and Venus Active volcanos Earth Active volcanos

Planetary Evolution • Comparative Planetology - Earth and Venus Active volcanos Vesc = 10. 3 km/sec Earth Active volcanos Vesc = 11. 2 km/sec

Planetary Evolution • Comparative Planetology - Earth and Venus Active volcanos Vesc = 10. 3 km/sec CO 2 atmosphere (90 atmos) Earth Active volcanos Vesc = 11. 2 km/sec N 2/O 2 atmosphere (1 atmos)

Planetary Evolution • Comparative Planetology - Earth and Venus Active volcanos Vesc = 10. 3 km/sec CO 2 atmosphere (90 atmos) Dry (10 -4 Earth H 20) Earth Active volcanos Vesc = 11. 2 km/sec N 2/O 2 atmosphere (1 atmos) Water at present Note: Based on measurements of deuterium (“heavy water”) Venus had substantially more water in the past Consistent with outgassing from volcanos and large escape velocity

Planetary Atmospheres • Comparative Planetology - Venus • Suppose Venus were “Earth-like” (liquid water) and … Temperature Light from Sun or CO 2, H 2 O from rocks from oceans “Runaway Greenhouse Effect”

Planetary Atmospheres • Runaway Greenhouse Effect • once RGE begins … Escape RGE UV H 20 in + from atmos Sun Irreversible!! H 2 O 2 Surface Compounds

Planetary Atmospheres • Comparative Planetology - Venus at 4. 5 billion yr

Planetary Evolution - Summary Earth 77% N 2, 21% O 2 15 o. C 1 atmosphere Mars Venus Mercury Trace of He, Na, O 95% CO 2 -50 o. C 0. 01 atmospheres 96% CO 2 470 o. C 90 atmospheres Moon Trace of He, Na, Ar

Planetary Evolution - Summary • Geological Evolution • Mercury, Moon - smallest radii => dormant, cratered • Mars - active for 109 yr, now dormant (shield volcanoes) • Venus - current volcanos (shield volcanoes) • Earth - convection => plate tectonics • Atmospheric Evolution • Moon, Mercury - low escape velocity, hot, atmos escapes • Venus RGE, massive CO 2 atmos • Earth CO 2, H 2 O , N 2, O 2 • Mars Runaway Icehouse, thin CO 2 atmos