lec12_25oct2010

lec12_25oct2010 - How do planetesimals grow to form...

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Ge/Ay133 How do planetesimals grow to form ~terrestrial mass cores?
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For now, let’s ignore the gas. This means we can just worry about gravity. For the  pairwise interaction of two bodies, we have: b r=a 2 r=a 1  For collisions that are grazing, the velocity at “impact” can be shown to be  Plugging this into the equation above and setting  θ = π/2 allows us to solve for the  impact parameter  b . The cross section is not  geometric (true for any central force):
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planetesimal(s) is critical. You need SOME  V  to get collisions in the first place, just  not “too much”! This was first worked out by Safronov, and so now bears his name,  with the definitions: Safronov Number The next step in this analytical approach is to assume V characterizes the random velocity  distribution (w.r.t. the background Keplerian field) of a “swarm” of planetesimals. In this  gravitational focusing scenario: Note that for 
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lec12_25oct2010 - How do planetesimals grow to form...

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