3. Planetary Atmospheres Greenhouse Effect Greenhouse Effect 90 atmospheres!

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

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

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

7. Planetary Atmospheres Greenhouse Effect Greenhouse Effect

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

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

10. Planetary Evolution Essential Idea Essential Idea Recall Recall Amount of residual thermal energy stored in planet Amount 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 area Rate of energy loss depends on planet surface area Small planets go dormant sooner Small planets go dormant sooner

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

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

13. Planetary Evolution Comparative Planetology - Earth and Mars Comparative Planetology - Earth and Mars Mars Earth 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) (0.01 atmos) (1 atmos) 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 been So if liquid water in past, must also have been substantial atmosphere and greenhouse effect in past substantial atmosphere and greenhouse effect in past Active volcanoes could have provided such an atmosphere Active volcanoes could have provided such an atmosphere

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

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

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

17. Planetary Evolution Comparative Planetology - Mars at 1 billion yr Comparative Planetology - Mars at 1 billion yr (end of geologic activity) (end of geologic activity) 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”) (“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 UV O,C

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

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

20. Planetary Evolution Comparative Planetology - Earth and Venus Comparative Planetology - Earth and Venus Venus Earth 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 Comparative Planetology - Earth and Venus Venus Earth 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) (90 atmos) (1 atmos)

22. Planetary Evolution Comparative Planetology - Earth and Venus Comparative Planetology - Earth and Venus Venus Earth 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) (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 Venus had substantially more water in the past Consistent with outgassing from volcanos and large Consistent with outgassing from volcanos and large escape velocity escape velocity

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

24. Planetary Atmospheres Runaway Greenhouse Effect Runaway Greenhouse Effect once RGE begins … once RGE begins … RGE H 2 0 in atmos UVfromSun H2H2H2H2 O2O2O2O2 Escape SurfaceCompounds + Irreversible!!

25. Planetary Atmospheres Comparative Planetology - Venus at 4.5 billion yr Comparative Planetology - Venus at 4.5 billion yr

26. Planetary Evolution - Summary Mercury Trace of He, Na, O Venus 96% CO 2 470 o C 90 atmospheres Earth 77% N 2, 21% O 2 15 o C 1 atmosphere Moon Trace of He, Na, Ar Mars 95% CO 2 -50 o C 0.01 atmospheres

27. Planetary Evolution - Summary Geological Evolution Mercury, Moon - smallest radii => dormant, cratered Mercury, Moon - smallest radii => dormant, cratered Mars - active for 10 9 yr, now dormant (shield volcanoes) Mars - active for 10 9 yr, now dormant (shield volcanoes) Venus - current volcanos (shield volcanoes) Venus - current volcanos (shield volcanoes) Earth - convection => plate tectonics Earth - convection => plate tectonics Atmospheric Evolution Moon, Mercury - low escape velocity, hot, atmos escapes Moon, Mercury - low escape velocity, hot, atmos escapes Venus RGE, massive CO 2 atmos Venus RGE, massive CO 2 atmos Earth CO 2, H 2 O, N 2 N 2, O 2 Earth CO 2, H 2 O, N 2 N 2, O 2 Mars Runaway Icehouse, Mars Runaway Icehouse, thin CO 2 atmos thin CO 2 atmos