1. © 2005 Pearson Education Inc., publishing as Addison-Wesley Planetary Atmospheres The layer of gas surrounding the Earth and other Worlds Lecture 13 The Planets Lecture 13 The Planets

2. © 2005 Pearson Education Inc., publishing as Addison-Wesley Planetary Atmospheres The layer of gas surrounding the Earth and other Worlds Homework Read Chapter 10: Atmospheres of Planets MasteringAstronomy: Assignment Chapter 10 Due Friday, Oct 18

3. Observing Project due today!

4. © 2005 Pearson Education Inc., publishing as Addison-Wesley Planetary Atmospheres The layer of gas surrounding the Earth and other Worlds Subsection 1: Molecules and Light

5. © 2005 Pearson Education Inc., publishing as Addison-Wesley http://i.dailymail.co.uk/i/pix/2009/11/26/article-1231118-075FCB40000005DC-293_964x401.jpg

7. © 2005 Pearson Education Inc., publishing as Addison-Wesley Molecules Cycle: Water, CO 2 Protection against solar wind and Ultraviolet light Protection against meteorites Troposphere: Lower atmosphere Earth’s Atmosphere: Dynamic, Protective, Governing

8. © 2005 Pearson Education Inc., publishing as Addison-Wesley Roles of Atmospheres Breathe: N 2 O 2 CO 2 Oxygen: respiration for animal life Shields UV photons Protects us from meteorites Traps heat in: Greenhouse Effect Earth’s Atmosphere Unique in Solar System: Only one with oxygen ! Luck... ?

9. © 2005 Pearson Education Inc., publishing as Addison-Wesley Structure of the Atmosphere

10. © 2005 Pearson Education Inc., publishing as Addison-Wesley Molecules in the Earth’s Atmosphere 78% NITROGEN (N 2 ) 21% OXYGEN (O 2 ) ~1% ARGON (Ar) 0.04% CARBON DIOXIDE (CO 2 ) Produced by plants during photosynthesis Necessary for breathing by animals. Arrived 3.5 billion years ago: algae & bacteria Water vapor (H 2 O) Carbon monoxide (CO) Neon (Ne) Oxides of nitrogen Methane (CH 4 ) Krypton (Kr) Concentrations are a few parts per million (ppm) O O C O Water Methane

11. © 2005 Pearson Education Inc., publishing as Addison-Wesley Gases in the Earth’s Atmosphere CO 2 0.035% N 2 78% O 2 20.9% Ar 0.93%

12. © 2005 Pearson Education Inc., publishing as Addison-Wesley Carbon Dioxide in Our Atmosphere is Increasing Rapidly Added CO 2 causes The Greenhouse Effect: Next Lecture... Burning coal gasoline Natural gas CO 2 (ppm) Worldwide CO 2 1960 - 2012

13. © 2005 Pearson Education Inc., publishing as Addison-Wesley How Molecules Affect Visible Light Visible Light from Sun: Most light passes through atmosphere. Blue photons are scattered more than red photons

14. © 2005 Pearson Education Inc., publishing as Addison-Wesley Molecules Mostly Scatter Blue Light At Sunset: Blue scattered away Red photons survive.

15. © 2005 Pearson Education Inc., publishing as Addison-Wesley Quiz A certain city has street lights that are white light bulbs. The night sky appears: a)faintly blue b)faintly red c)faintly white with no color d)white, but missing the blue and red

16. © 2005 Pearson Education Inc., publishing as Addison-Wesley Section 2 The Origin of Atmospheres What holds them up against gravity? Section 2 The Origin of Atmospheres What holds them up against gravity?

17. © 2005 Pearson Education Inc., publishing as Addison-Wesley Origin of Atmospheres Venus, Earth, & Mars received their atmospheres through volcanic outgassing. H 2 O, CO 2, N 2, H 2 S, SO 2, NH 3 On Earth: N 2 was left as the dominant gas; CO 2 dissolves in oceans and goes into carbonate rocks like limestone (= calcium carbonate, Ca CO 3.) Most CO 2 is in the oceans as carbonates O 2 from photosynthesis by plants (cyanobacteria and blue-green algae) Mars and Venus: CO 2 is dominant gas Mars: lost much of its atmosphere through impacts less massive planet, lower escape velocity

18. © 2005 Pearson Education Inc., publishing as Addison-Wesley Origin of Earth’s Atmosphere Volcanic Outgassing: H 2 O, CO 2, N 2, H 2 S,...

19. © 2005 Pearson Education Inc., publishing as Addison-Wesley Origin of Atmospheric Gas: Volcanic Outgassing What about Oxygen? Where did it come from?

20. © 2005 Pearson Education Inc., publishing as Addison-Wesley Origin of Oxygen on Earth : Plants, Algae: Photosynthesis Fossilized remains of blue-green algae Appears 3 billion years ago. cyanobacteria Shark’s Bay (Western Australia): Colonies of microbes: Stramatolite (blue-green algae) Produced Oxygen (radioactive age dating) Banded-iron Formation Octopus spring (Yellowstone) Photosynthetic Blue-green algae mats

21. © 2005 Pearson Education Inc., publishing as Addison-Wesley Gain/Loss Processes of Atmospheric Gas Ways to Gain Gases Ways to Lose Gases

22. © 2005 Pearson Education Inc., publishing as Addison-Wesley Comparing Terrestrial Atmospheres Mercury: none Venus: CO 2 massive atmosphere Earth: modest Mars: CO 2 1% of Earth’s pressure Moon: None 90x Earth’s Mass: Mostly CO 2

23. © 2005 Pearson Education Inc., publishing as Addison-Wesley What is an Atmosphere ? A layer of gas held to a world by gravity. Very thin compared to planet radius Temperature: A measure of the average speed of molecules...

24. © 2005 Pearson Education Inc., publishing as Addison-Wesley Temperature: A Measure of the Speeds of Molecules Temperature: A Measure of the Speeds of Molecules 2 k T T is temp (K) m is mass of molecule k is Boltzmann’s constant = 1.38 x 10 -23 J-K

25. © 2005 Pearson Education Inc., publishing as Addison-Wesley Quiz Temperature: A Measure of the Speeds of Molecules Temperature: A Measure of the Speeds of Molecules 2 k T/m In a refrigerator, food is preserved longer because: a)Chemical reactions are slower b)Chemical reactions are faster c)Reaction rates stay the same d)Outside air doesn’t get in. T is temp (K) m is mass of molecule k is Boltzmann’s constant.

26. © 2005 Pearson Education Inc., publishing as Addison-Wesley What is Pressure? Pressure: Force per area caused by atoms & molecules colliding with walls or each other. heating a gas in a confined space increases pressure number of collisions increase unit of measure: 1 bar = 14.7 lbs/inch 2 Earth’s atmospheric pressure at sea level Upward Pressure balances Downward gravity. Pressure pushes balloon walls outward.

27. © 2005 Pearson Education Inc., publishing as Addison-Wesley Why doesn’t the atmosphere fall down due to gravity?

28. © 2005 Pearson Education Inc., publishing as Addison-Wesley Atmospheric Pressure: Balances Gravity Upward pressure supports air against weight of air above. Atmosphere

29. © 2005 Pearson Education Inc., publishing as Addison-Wesley Quiz Suppose the Earth’s atmosphere contained twice the number of molecules. Compared to our Earth, the pressure at the surface would be: a)2x as great b)4x as great c)1/2 as great d)1/4 as great

30. © 2005 Pearson Education Inc., publishing as Addison-Wesley Section 3 Layers in the Atmosphere Section 3 Layers in the Atmosphere

31. © 2005 Pearson Education Inc., publishing as Addison-Wesley Planetary Atmospheres Layers of the Atmosphere Global Wind Patterns Energy Balance

32. © 2005 Pearson Education Inc., publishing as Addison-Wesley Structure of Earth’s Atmosphere

33. © 2005 Pearson Education Inc., publishing as Addison-Wesley Structure of Earth’s Atmosphere Pressure & density of atmosphere decrease with altitude Temperature increases and decreases with altitude Temperature domains define the major atmospheric layers Exosphere Low density; fades into space Molecules can escape Thermosphere Xrays heat gas Temp begins to rise at the top Stratosphere UV from Sun absorbed by Ozone Rise (and fall) of temperature Troposphere Layer closest to surface Heating: Convection, IR trapping Temp drops with altitude Ozone Layer (absorbs UV) (mesosphere ) Troposphere Stratosphere

34. © 2005 Pearson Education Inc., publishing as Addison-Wesley Reasons for Atmospheric Structure Absorption of sunlight energyAbsorption of sunlight energy causes layering structure. Troposphere absorbs IR photons from the surface temperature drops with altitude hot air rises to warm upper region ( convection ) StratosphereStratosphere absorbs Solar UV photons by dissociating ozone (O 3 ) UV penetrates only top layer; hotter air is above colder air no convection or weather; the atmosphere is stratified ThermosphereThermosphere absorbs heat via Solar X-rays which ionizes all gases contains ionosphere, which reflects back human-made radio signals Exosphere hottest layer; gas extremely rarified; provides noticeable drag on satellites

35. © 2005 Pearson Education Inc., publishing as Addison-Wesley Structure of Terrestrial Planet Atmospheres Mars, Venus, Earth all have warm tropospheres (and greenhouse gases) have warm thermospheres which absorb Solar X rays Only Earth has a warm stratosphere an UV-absorbing gas (O 3 ) All three planets have warmer surface temps due to greenhouse effect

36. © 2005 Pearson Education Inc., publishing as Addison-Wesley CFCs Attack Ozone (O 3 ) The stratospheric ozone is an environmental success story. Scientists detected the declining ozone in the atmosphere, collecting the evidence that convinced governments around the world to take regulatory action.

37. © 2005 Pearson Education Inc., publishing as Addison-Wesley Earth’s Magnetic Field: Magnetospheres

38. © 2005 Pearson Education Inc., publishing as Addison-Wesley Magnetosphere: Diverts Solar Wind The Sun ejects a stream of charged particles, called the solar wind. It is mostly electrons, protons, and Helium nuclei Earth’s magnetic field diverts these particles to the magnetic poles. the particles spiral along magnetic field lines and emit light this causes the aurora (aka northern & southern lights) this protective “bubble” is called the magnetosphere Other terrestrial worlds have no strong magnetic fields solar wind particles impact the exospheres of Venus & Mars solar wind particles impact the surfaces of Mercury & Moon

39. © 2005 Pearson Education Inc., publishing as Addison-Wesley Earth’s Magnetosphere Solar Wind: Electrons, protons, helium nuclei

40. © 2005 Pearson Education Inc., publishing as Addison-Wesley Weather and Climate These are Earth’s global wind patterns or circulation local weather systems move along with them weather moves from W to E at mid- latitudes in N hemisphere Two factors cause these patterns atmospheric heating planetary rotation Weather – short-term changes in wind, clouds, temperature, and pressure in an atmosphere at a given location Climate – long-term average of the weather at a given location

41. © 2005 Pearson Education Inc., publishing as Addison-Wesley Global Wind Patterns Air heated more at equator Warm air rises at equator; Pressure pushes air to poles Cold air moves from poles to equator along the surface Two circulation cells are created in each hemisphere Cells of air do not go directly from pole to equator; air circulation is diverted by… Coriolis effect moving objects veer right on a surface rotating counterclockwise moving objects veer left on a surface rotating clockwise

42. © 2005 Pearson Education Inc., publishing as Addison-Wesley Global Wind Patterns On Earth, the Coriolis effect breaks each circulation cell into three separate cells winds move either W to E or E to W Coriolis effect not strong on Mars & Venus Mars is too small Venus rotates too slowly In thick Venusian atmosphere, the pole-to-equator circulation cells distribute heat efficiently surface temperature is uniform all over the planet

43. © 2005 Pearson Education Inc., publishing as Addison-Wesley Energy Balance: Heating = Cooling What if Earth gets too hot ? Can it correct its temperature back to normal? A planet absorbs light energy from the Sunlight Surface warms: Temperature increases. Planet emits light energy by thermal emission. Surface cools: Temperature decreases. Absorption of energy = Thermal emission of energy ===> stable temperature Heating: Cooling:

44. © 2005 Pearson Education Inc., publishing as Addison-Wesley What Determines a Planet’s Surface Temperature?

45. © 2005 Pearson Education Inc., publishing as Addison-Wesley Quiz Consider two moons around Jupiter (5.2 AU from the Sun). Moon #2 has twice the radius of Moon #1 (no atmospheres, volcanoes or tidal heating). The ratio of their temperatures (T 2 /T 1 ) is: a)1 b)2 c)4 d)8

46. © 2005 Pearson Education Inc., publishing as Addison-Wesley Effects of an Atmosphere on a Planet Scattering and absorption of light absorb high-energy radiation from the Sun scattering of optical light brightens the daytime sky Creates pressure can allow water to exist as a liquid (at the right temperature) Creates wind and weather promotes erosion of the planetary surface Protects surface from UV and solar wind Magnetic fields Auroras: Trap Solar wind particles Greenhouse effect makes the planetary surface warmer

47. © 2005 Pearson Education Inc., publishing as Addison-Wesley Planetary Atmospheres The layer of gas surrounding the Earth and other Worlds End of Lecture 13

48. The Greenhouse Effect & Global Warming Lecture 13: Atmospheres Section 4: Comparison of Atmospheres: Earth to Venus and Mars

49. 4.6 Billion Years Ago... (150 million km from Sun) 1 AU0.7 AU1.5 AUSUNVenusEarthMars

50. Temperature: Top of Atmosphere Temperature (Celsiu) 50 0 30 0 10 0 0 -100 decreases with distance from Sun 5500 o C Earth -18 o C (0 o F) Venus Distance From Sun Mars 0 0 0 300 500 200 100 -100 400 Temperature (C)

51. Climate History of Venus Suppose the Earth moved to Venus’Orbit Venus outgassed as much H 2 O as Earth (similar planets). Early on, when the Sun was dimmer, Venus probably had oceans. Venus’ proximity to the Sun caused H 2 O to vaporize. H 2 O vapor traps IR light from surface of planet H 2 O caused runaway greenhouse effect Surface heated to extreme temperature CO 2 released from rocks: Adds to greenhouse effect UV photons from Sun dissociate H 2 O; H 2 escapes. Water lost forever.

52. Clue: atm composition 500 300 10 0 0 -100 Temperature (Celsius) EARTH EARTH: Surface 15 o C (60 o F) Top of Atm: -18 o C (0 o F)  All three phases of water Surface warmer than top of atm  Greenhouse Effect Surface No Greenhouse

53. The Earth is Changing Rapidly Who oversees the health of the Earth?