Charles Hakes Fort Lewis College 1

Atmospheres/ Greenhouse Effect/ Spectroscopy Charles Hakes Fort Lewis College 2

Logistics Midterm grades will be posted by Monday (faculty.fortlewis.edu/hakes_c) Review Atmospheres Planet Temperatures Spectroscopy Green House Effect Charles Hakes Fort Lewis College 3

Distance to Mercury Look up distance from Sun (A.U.) in appendix… Need eccentricity of Mercury. (Then check page 32.) Charles Hakes Fort Lewis College 4

Seti@home Notes Credit is available if you join! link is on my home page download the software install and run - you will have to “connect” to the SETI project after you install after completing a work unit, join the FLC group email me for credit (Keep running it if you want to keep the credit.) Charles Hakes Fort Lewis College 5

Review What was the most important thing you learned? Albedo is how much light gets reflected. Earth has an albedo of 0.3 Albedo is not related to libido. For any given temperature, the lighter stuff moves faster. Wien’s law: Charles Hakes Fort Lewis College 6

Blackbody Radiation (Review!) Higher temperature bodies radiate energy in shorter wavelength radiation. The Sun radiates at visible wavelengths The Earth (and other planets) radiate at much longer wavelengths. Charles Hakes Fort Lewis College 7

Figure 2.10 Blackbody Curves Note the logarithmic temperature scale. For linear scale, go look at the “blackbody” section of: http://solarsystem.colorado.edu/ Charles Hakes Fort Lewis College 8

Wien’s Law The “peak” frequency of the radiation “curve” is directly proportional to the temperature of the radiator. Charles Hakes Fort Lewis College 9

You observe E-M radiation emitted from a warm dense object You observe E-M radiation emitted from a warm dense object. The most radiation appears to be emitted at 5.8x10-4 cm. What temperature is the object? A) 400 K B) 500 K C) 600 K D) 700 K Charles Hakes Fort Lewis College 10

You observe E-M radiation emitted from a warm dense object You observe E-M radiation emitted from a warm dense object. The most radiation appears to be emitted at 5.8x10-4 cm. What temperature is the object? A) 400 K B) 500 K C) 600 K D) 700 K Charles Hakes Fort Lewis College 11

Planet Temperature Go to Solar System Collaboratory on EVM “physics” page. A planet must balance absorbed light and radiated light to get a temperature. Light intensity decreases with distance. (another 1/r2 law) Farther from the sun, the absorbed light is less. Charles Hakes Fort Lewis College 12

Planet Temperature Go to Solar System Collaboratory on EVM “physics” page. A planet must balance absorbed light and radiated light to get a temperature. Light intensity decreases with distance. (another 1/r2 law) Farther from the sun, the absorbed light is less. Go to Solar System Collaboratory on planet temperature page. Charles Hakes Fort Lewis College 13

Figure 5.7 About 30% of the sunlight hitting the Earth is reflected Charles Hakes Fort Lewis College 14

To Atmosphere or Not Once you know a planet’s temperature you can see if it will have an atmosphere, and how that atmosphere can affect a planet’s temperature. Compare kinetic energy of molecules with “escape velocity” from the planet. Light molecules (of a given temperature T) move faster than heavy molecules of the same temperature. A small fraction will always escape. Charles Hakes Fort Lewis College 15

To Atmosphere or Not Primary atmosphere Secondary atmosphere What a planet had after formation Mostly H, He - almost all gone from the terrestrial planets (never really was here) Secondary atmosphere Heavier molecules N2, CO2 From rock outgassing H2O from outgassing and comet impacts. O2 from Life Charles Hakes Fort Lewis College 16

Earth’s Atmosphere 78% nitrogen 21% oxygen - this is from living organisms Plus Ar, CO2, H2O. Note layers Charles Hakes Fort Lewis College 17

Which will have the greatest effect on a planet’s temperature? A) doubling a planet’s distance to the sun B) doubling a planet’s albedo C) doubling a planet’s mass D) doubling a planet’s rotation rate Charles Hakes Fort Lewis College 18

Which will have the greatest effect on a planet’s temperature? A) doubling a planet’s distance to the sun B) doubling a planet’s albedo C) doubling a planet’s mass D) doubling a planet’s rotation rate Charles Hakes Fort Lewis College 19

Compared to Earth, the Moon undergoes temperature extremes because? A) It orbits the Earth, and therefore gets both closer and farther from the Sun than Earth B) It has no atmosphere C) It rotates very slowly D) Both B and C Charles Hakes Fort Lewis College 20

Compared to Earth, the Moon undergoes temperature extremes because? A) It orbits the Earth, and therefore gets both closer and farther from the Sun than Earth B) It has no atmosphere C) It rotates very slowly D) Both B and C Charles Hakes Fort Lewis College 21

Planet Temperatures Go to Solar System Collaboratory to see planet temperatures page. Look at fact sheet Earth - (albedo 0.3) 288 K Moon - (albedo 0.07) 280 K Mars - (albedo 0.2) 218 K Venus - (albedo 0.8) 730 K Compare model to fact sheet. Review model - distance and albedo. Charles Hakes Fort Lewis College 22

Planet Temperatures Compare the model to the fact sheet. Earth - (albedo 0.3) 288 K (model 255 K) Moon - (albedo 0.07) 280 K (model 273 K) Mars - (albedo 0.2) 218 K (model 214 K) Venus - (albedo 0.8) 730 K (model 219 K) Model with fast-rotating planet with variable albedo predicted temperatures that were too low. Something is missing from the model… Charles Hakes Fort Lewis College 23

What is Missing from the model? A) Realistic rotation rates for the planets B) Geothermal Energy C) Distance from the Sun D) Something else important Charles Hakes Fort Lewis College 24

What is Missing from the model? A) Realistic rotation rates for the planets B) Geothermal Energy C) Distance from the Sun D) Something else important Charles Hakes Fort Lewis College 25

Greenhouse Effect Exhale Charles Hakes Fort Lewis College 26

Removing all greenhouse gasses from the Earth’s atmosphere would be good A) True B) False Charles Hakes Fort Lewis College 27

Greenhouse Effect Visible light comes in though the atmosphere and heats the ground. Re-radiating infrared light can’t get out because the atmosphere is partially opaque. Greenhouse gasses must have at least 3 atoms in each molecule to absorb effectively in the IR. Note - “real” greenhouses merely stop convection from carrying away heat. Charles Hakes Fort Lewis College 28

Figure 2.8 Electromagnetic Spectrum Charles Hakes Fort Lewis College 29

Figure 5.7 About 30% of the sunlight hitting the Earth is reflected Charles Hakes Fort Lewis College 30

Greenhouse “Strength” Contributors Total atmospheric pressure Greenhouse gas percent Greenhouse gas effectiveness Charles Hakes Fort Lewis College 31

Add Greenhouse “Strength” to Model Earth - 0.65 Mars - 0.077 Venus - 121.0 Charles Hakes Fort Lewis College 32

Planet Temperatures Compare the model to the fact sheet. Earth - (A 0.3, GH 0.65) 288 K (model 289 K) Moon - (albedo 0.07) 280 K (model 274 K) Mars - (albedo 0.2) 218 K (model 218 K) Venus - (albedo 0.8) 730 K (model 730 K) Charles Hakes Fort Lewis College 33

Planet Temperatures Much better agreement! Compare the model to the fact sheet. Earth - (A 0.3, GH 0.65) 288 K (model 289 K) Moon - (albedo 0.07) 280 K (model 274 K) Mars - (albedo 0.2) 218 K (model 218 K) Venus - (albedo 0.8) 730 K (model 730 K) Much better agreement! Charles Hakes Fort Lewis College 34

Greenhouse Runaway On Venus, the temperature was just high enough to keep most of the water in the atmosphere. CO2 could not be absorbed into the water, and eventually trapped in the surface rocks. If all Earth’s CO2 were released into the atmosphere, it would be ~98% CO2, 2% N2 and the pressure would be ~70x current. Charles Hakes Fort Lewis College 35

Figure 6.8 Venus, Up Close Charles Hakes Fort Lewis College 36

Figure 6.30 Venus’s Atmosphere Charles Hakes Fort Lewis College 37

Discovery 5-2a The Greenhouse Effect and Global Warming Charles Hakes Fort Lewis College 38

Discovery 5-2b The Greenhouse Effect and Global Warming Charles Hakes Fort Lewis College 39

What gas is the most significant contributor to Earth’s greenhouse effect? A) Methane B) Water vapor C) Carbon monoxide D) Carbon dioxide Charles Hakes Fort Lewis College 40

What gas is the most significant contributor to Earth’s greenhouse effect? A) Methane B) Water vapor C) Carbon monoxide D) Carbon dioxide Charles Hakes Fort Lewis College 41

Three Minute Paper Write 1-3 sentences. What was the most important thing you learned today? What questions do you still have about today’s topics? Charles Hakes Fort Lewis College 42