lec11_24oct2011

Lec11_24oct2011 - How do small dust grains grow in protoplanetary disks Ge/Ay133 /dustgraindisk Forsolids, mcmkmmoon/Mars(oligarchs)110MEarth

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Ge/Ay133 How do small dust grains grow in protoplanetary disks?
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How do we go from a well mixed gas/dust grain disk: To a mature planetary system? For solids, it is helpful to distinguish amongst several regimes:      μ  cm   km   moon/Mars (oligarchs)   1-10 M Earth
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Step #1: Growth from ~0.1  μ m to ~1 cm scales Need to think about how particles move in the sub-Keplerian field provided by  the gas. First let’s look at the radial component. Drag force on particles,  c  = sound speed. .. Stopping time (shed momentum). δ  = particle density,  Σ gas surface density. For small particles, well coupled to gas                         , radial velocity is Very slow for small particles.
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vertical  motion at a given R: The mean free path is >> the particle diameter, so in the Epstein not Stokes regime  (that is, the Brownian motion case). Thus… NO particle growth. Something like 1 M.Y. for 1  μ m grains, only 100 years  for  a  = 1 cm. Opposite extreme: Suppose ALL collisions are sticky. As the particle settles, how  large does is grow if it sweeps up all other grains that the falling particle  encounters?  ζ is the dust-to-gas ratio (not nec. 0.01). Fast if 
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This note was uploaded on 01/03/2012 for the course GEL 133 taught by Professor List during the Fall '10 term at Caltech.

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Lec11_24oct2011 - How do small dust grains grow in protoplanetary disks Ge/Ay133 /dustgraindisk Forsolids, mcmkmmoon/Mars(oligarchs)110MEarth

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