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L16GH09Gas_Giants

L16GH09Gas_Giants - The Gas Giants Lecture topics...

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March 10, 2009 gas giants The Gas Giants •Lecture topics: atmospheres, internal heating •Text reading: Chapter 11 – esp pp 335-343
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March 10, 2009 gas giants The Gas Giants Jupiter Saturn Uranus Neptune Mass (M Earth ) 317.8 95.2 14.4 17.2 Distance from Sun (AU) 5.20 9.54 19.2 30.1 Equatorial Radius (R Earth ) 11.2 9.46 3.98 3.81 Average Density (kg/m 3 ) 1330 710 1240 1670 Together they account for 99.5% of our planetary system
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March 10, 2009 gas giants Size-Mass Relationship • As with terrestrials, composition can be guessed from mean density. But the high compressibility of volatiles must be accounted for because the Jovian planets are mostly atmosphere ¾ Initially, as they accrete mass they grow in radius ¾ But at a mass of ~300 earth masses, further accretion causes the radius to decrease. Why?
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March 10, 2009 Composition • Jupiter and Saturn are well matched by H+He models ¾ Require some ice/rock as well • Uranus and Neptune are much better represented by an icy composition. T=0 K models T>0K 1
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March 10, 2009 gas giants Recall: Moment of Inertia • The moment of inertia is a measure of degree of concentration ¾ Related to the “inertia” (resistance) of a spinning body to external torques ¾ Shows giant planets are centrally concentrated: cores? Body I/MR 2 Sun 0.06 Mercury 0.33 Venus 0.33 Earth 0.33 Moon 0.393 Mars 0.366 Jupiter 0.254 Saturn 0.210 Uranus 0.23 Neptune 0.23 = mass point a for 0 shell hollow a for 67 0 sphere s homogeneou a for 4 . 0 2 . MR I
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