Planetary Atmospheres

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3 Greenhouse Effect Planetary Atmospheres 90 atmospheres!

4 Greenhouse Effect Planetary Atmospheres 240 watts/m 2 in 50% reflected by clouds and surface Small fraction escapes into space 240 watts/m 2 out CO 2 H 2 0

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

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

7 Greenhouse Effect Planetary Atmospheres

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

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

10 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 Lifetime of geological activity = Residual thermal energy Rate of energy loss 4 3 πr 3 planet 4πR planet 2 R planet Small planets go dormant sooner

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

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

13 Planetary Evolution Comparative Planetology - Earth and Mars Mars Earth Dormant volcanos Active volcanos Water in past Water at present Thin CO 2 atmosphere N 2 /O 2 atmosphere (0.01 atmos) ) (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

14 Planetary Evolution Comparative Planetology - Earth Ozone O 3 washed out with H 2 0 rain Plate tectonics is critical to Earth atmosphere

15 Planetary Evolution Comparative Planetology - Earth Ozone O 3 washed out with H 2 0 rain Life is critical to oxygen in Earth atmosphere

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

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

18 Planetary Evolution Comparative Planetology - Mars at 4.5 billion yr Recent liquid water?

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

20 Planetary Evolution Comparative Planetology - Earth and Venus Venus Earth Active volcanos Active volcanos V esc = 10.3 km/sec V esc = 11.2 km/sec

21 Planetary Evolution Comparative Planetology - Earth and Venus Venus Earth Active volcanos Active volcanos V esc = 10.3 km/sec V esc = 11.2 km/sec CO 2 atmosphere N 2 /O 2 atmosphere (90 atmos) (1 atmos)

22 Planetary Evolution Comparative Planetology - Earth and Venus Venus Earth Active volcanos Active volcanos V esc = 10.3 km/sec V esc = 11.2 km/sec CO 2 atmosphere N 2 /O 2 atmosphere (90 atmos) (1 atmos) Dry (10-4 Earth H 2 0) 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

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

24 Irreversible!! Planetary Atmospheres Runaway Greenhouse Effect once RGE begins Escape RGE H 2 0 in atmos + UV from Sun H 2 O 2 Surface Compounds

25 Planetary Atmospheres Comparative Planetology - Venus at 4.5 billion yr

26 Planetary Evolution - Summary Earth 77% N 2, 21% O 2 15 o C 1 atmosphere Mercury Trace of He, Na, O Venus 96% CO o C 90 atmospheres Mars 95% CO 2-50 o C 0.01 atmospheres Moon Trace of He, Na, Ar

27 Planetary Evolution - Summary Geological Evolution Mercury, Moon - smallest radii => dormant, cratered Mars - active for 10 9 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 N 2, O 2 Mars Runaway Icehouse, thin CO 2 atmos