Wednesday, Mar. 20

1. Wednesday, Mar. 20 QUIZ #3 IN CLASS Assignments: Article Outline #1 (due today) Mini-Project #1 - Part 2 (due Wed. Mar. 26)

2. Venus from the Ground:

3. Thought Question: Suppose a terrestrial planet the same age as Earth is discovered orbiting another star, and it is your job to predict what it is like. If the planet is known to have a mass and size smaller than Venus but larger than Mars, what would be the best prediction? • It should have no volcanoes. • It should have volcanoes, but they may or may not be active. • It should have a moderate number of active volcanoes spread evenly over the surface. • It should have a large number of active volcanoes found only in small areas of the surface.

4. Terrestrial Planet Interiors • thermal energy added by radioactivity: • radioactive atoms release heat when they decay LEAKY BUCKET ANALOGY: Temperature of interior depends on balance between: SOURCE OF HEAT HEAT NOW IN PLANET • thermal energy lost to space: • heat can only escape from planet’s surface HEAT LOST FROM SURFACE

5. Terrestrial Planet Interiors • thermal energy lost to space: • heat can only escape from planet’s surface • thermal energy added by radioactivity: every bit of mass contains a small fraction of radioactive atoms: energy lost per second energy added per second planet area planet mass is related to is related to average density

6. Thought Question: Based on the rates of energy being added and lost, which terrestrial planet should cool off most slowly? (Hint: compare rates of adding and losing thermal energy by doing a ratio.) • Mercury • Venus • Earth • Moon • Mars

7. Loss of Internal Heat The ratio of energy input to energy loss is: • For a large planet: • ratio is large • energy addition is larger compared to loss • planet’s interior cools slower

8. The Heat Inside: • As planets formed, collisions and radioactivity melted them into sphere shape: • large planets take longer to cool off and solidify inside: Mars: active volcanoes once, but not many Mercury, Moon: dead for a long time Earth, Venus: still active today

9. Atmosphere Conditions Average Temperature: 850 F 60 F -60 F 737 K 288 K 210 K Atmospheric Pressure: 90x Earth 0.007x Earth Chemicals: 96% CO278% N2 95% CO2

10. Terrestrial Planet Atmospheres Addition of Gases • Outgassing by volcanoes • Bombardment Loss of Gases: • Gas escape into space • Condensation • Chemical reactions

11. Where Did It Come From? Comet impacts bring “ices”: water vapor (H2O) carbon monoxide (CO) ammonia (NH3) methane (CH4) Volcanoes release gas from molten rock: carbon dioxide (CO2) nitrogen (N2) water vapor (H2O)

12. Escape Speeds • Larger planet mass gas molecules have to move faster to escape escape speed: • Higher temperature faster gas molecules move  easier to escape

13. Temperature Temperature relates to average speed of motions of atoms absolute zero (0 K) is when thermal motion stops box increases the average particle speed Gas animation

14. Speeds of Gas Molecules Average particle kinetic energy in a gas only depends on temperature: (Boltzmann’s constant) Gas of a particular chemical has a chance to escape over the history of the solar system if:

15. Thought Question: What combination of factors makes it more likely to lose a gas from a planet’s atmosphere? (Enter a three letter answer.) • High mass planet • Low mass planet • High temperature planet • Low temperature planet • High-mass gas molecules • Low-mass gas molecules