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Planetary Atmospheres

Planetary Atmospheres. Greenhouse Effect. 90 atmospheres!. Planetary Atmospheres. Greenhouse Effect. 240 watts/m 2 in. 240 watts/m 2 out. Small fraction escapes into space. 50% reflected by clouds and surface. CO 2 H 2 0. Planetary Atmospheres. Greenhouse Effect.

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Planetary Atmospheres

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  1. Planetary Atmospheres • Greenhouse Effect 90 atmospheres!

  2. Planetary Atmospheres • Greenhouse Effect • 240 • watts/m2 • in • 240 • watts/m2 • out Small fraction escapes into space • 50% reflected by • clouds and surface • CO2 • H20

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

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

  5. Planetary Atmospheres • Greenhouse Effect

  6. 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

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

  8. 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

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

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

  11. Planetary Evolution • Comparative Planetology - Earth and Mars • MarsEarth • Dormant volcanos Active volcanos • Water in past Water at present • Thin CO2 atmosphere N2/O2 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

  12. Plate tectonics is critical to Earth atmosphere Planetary Evolution • Comparative Planetology - Earth Ozone O3 washed out with H20 rain

  13. Planetary Evolution • Comparative Planetology - Earth Ozone O3 washed out with H20 rain Life is critical to oxygen in Earth atmosphere

  14. 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

  15. Planetary Evolution • Comparative Planetology - Mars at 1 billion yr • (end of geologic activity) UV O,C H2O rain washes CO2 into surface - permanently Greenhouse effect reduced Colder temperatures lead to enhanced rain, less gaseous CO2, less greenhouse (“Runaway Icehouse Effect”) Most CO2 in carbonate rocks, most H2O in permafrost UV sunlight breaks up molecules and provides energy of escape

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

  17. Planetary Evolution • Comparative Planetology - Earth and Venus • VenusEarth • Active volcanos Active volcanos

  18. Planetary Evolution • Comparative Planetology - Earth and Venus • VenusEarth • Active volcanos Active volcanos • Vesc = 10.3 km/sec Vesc = 11.2 km/sec

  19. Planetary Evolution • Comparative Planetology - Earth and Venus • VenusEarth • Active volcanos Active volcanos • Vesc = 10.3 km/sec Vesc = 11.2 km/sec • CO2 atmosphere N2/O2 atmosphere • (90 atmos) (1 atmos)

  20. Planetary Evolution • Comparative Planetology - Earth and Venus • VenusEarth • Active volcanos Active volcanos • Vesc = 10.3 km/sec Vesc = 11.2 km/sec • CO2 atmosphere N2/O2 atmosphere • (90 atmos) (1 atmos) • Dry (10-4 Earth H20) 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

  21. Temperature Light from Sun or CO2, H2O CO2, H2O from rocks from oceans Planetary Atmospheres • Comparative Planetology - Venus • Suppose Venus were “Earth-like” (liquid water) and … “Runaway Greenhouse Effect”

  22. Planetary Atmospheres • Runaway Greenhouse Effect • once RGE begins … Escape H2 UV from Sun H20 in atmos RGE + O2 Surface Compounds Irreversible!!

  23. Planetary Atmospheres • Comparative Planetology - Venus at 4.5 billion yr

  24. Planetary Evolution - Summary Earth 77% N2, 21% O2 15 oC 1 atmosphere Mars 95% CO2 -50 oC 0.01 atmospheres Venus 96% CO2 470 oC 90 atmospheres Mercury Trace of He, Na, O Moon Trace of He, Na, Ar

  25. Atmospheric Evolution • Moon, Mercury - low escape velocity, hot, atmos escapes • Venus RGE, massive CO2 atmos • Earth CO2, H2O , N2 N2, O2 • Mars Runaway Icehouse, • thin CO2 atmos 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

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