Lecture #31: Planets with Air but no Jordan

I. Phases and atmospheres -- word "phase" means different things, so watch out -- liquid phase is the least common: examples? -- phase diagram and difficulty for life
II. Why are there atmospheres? -- difference between a gas and a solid: interparticle forces -- difference between gas pressure and solid-body forces (pressure always wants to expand) -- ideal gas law: PV = NkT (usually this equation tells you V, not P) -- particle speed, temperature, and molecular weight
III. Atmospheric scale height -- connection between isothermal scale height, bouyancy, and ideal gas law -- estimate this for Earth (6 km, about the height of Mt. Everest) -- atmosphere is very thin! ("walking distance" to space) (1/1000 radius) -- climbing Mt. Everest: don't try this at home (cold is the least problem) -- why do airplanes fly so high? Why not even higher?
IV. Atmospheric composition and escape -- how can chemistry of terrestrial planets be oxidizing, when most of the universe is hydrogen? -- thermal speed (decreases with mass) vs. escape speed (independent of mass) -- hydrogen gas is the fastest of all molecules -- formation of the gas giants
V. Primitive atmospheres -- solar nebula would have been about 2% of Earth's present atmosphere -- molecules moving slower than the escape speed will be trapped as the rest of the nebula blows off -- trapped particles slowly leak out unless much slower than the escape speed (like neon-- atomic number 10) -- gas giants retain primitive atmospheres, Earth, Venus, and Mars have "secondary" atmospheres -- our atmosphere has about 100 times more N and O relative to Ne -- role of "outgassing": H2O and CO2 are dominant outgassed agents, N2 a distant third -- role of life: O2 is released from CO2 by plant life, especially blue-green algae -- water can freeze or boil and get photodissociated -- CO2 on Mars can freeze or sublimate, and on Earth gets dissolved in ocean -- CO2 remains on Venus and some on Mars, N2 remains on Earth
VI. Weather and the effects of Earth's rotation -- air is heated, and warm air rises -- heating and air movements can lead to high and low pressure regions -- Earth's rotation produces the "coriolis effect" (like for Foucault pendulums in science museums) -- the combination of rising air, high and low pressure, and the coriolis effect is what causes weather -- one example is air circulates counter-clockwise around low pressure centers in the northern hemisphere -- worse case scenario: hurricane (see Katrina here)