Astro NOtes

Astro NOtes - 10-8-09 Last Time Planetary atmospheres I...

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10-8-09 Last Time Planetary atmospheres I Escape speeds vs molecular speed Lifetime of an atmosphere Cross sections of terrestrials Earth molten Iron Outer Core Planetary Magnetic fields Requires: Follow Up questions Why Is earth so hot in middle? Why is iron in middle? Where did heat come from Why do moon, Mars have small/ no existant liquid core What does this tell us about the formation of solar system Heavy Balance of a planet chemical differentiation liquids (And gases) the “heavy stuff” is more dense material sinks. Known as atmosphereic differentiation This tells us that Earth, terrestrial planets started out as molten then it cooled The amount of seperation/ differentiation tells us how long the earth was molten Estimate Earth was molten for 1 x 10^9 years Comments 1. ON earth “Rare earth elements” tend to be denser, are depleted in crust compared to Earth on average Meteorites: fossil remnants of formation  same compositon of average of earths Iridum—Density 22.65 g/ cm^3 Iron 7.5 g/cm^3 Depleted in crust relative to meteorite composition Iridium: forensic signature of meteorite 2. Jovians 1. Helium tends to sink 2. Comes out as “mist” or rain. 3. On Saturn this is happening a lot “Quite marked” 4. Jupiter—not so much Where does internal planetary heat Come from
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1. Heat Retention Formation—planet was extremely hot and cools very slowly Major Factor in the formation Falling Matter colliding leads to HEAT Kelvin- Helmholtz heating 2. Rate of cooling  Size R= radius of planet Cooling/ amount of heat…. . Surface Area/ Volume = R^2/ R^3
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This note was uploaded on 12/01/2009 for the course ASTR 50800 at USC.

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Astro NOtes - 10-8-09 Last Time Planetary atmospheres I...

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