In one stage of classic accretion, the mass growth rate with time (dm/dt) for individual planetesimals is proportional to $m^{2/3}$ and in another stage it is proportional to $m^{4/3}$. My question is why are the exponents different? Which stage is a runaway and which stage comes first?

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    $\begingroup$ There are different theories of planetesimal formation - can you clarify where you are finding these relations, and more about what that source says about what the different stages are? $\endgroup$ Jun 12 '20 at 17:51
  • $\begingroup$ Some superficial knowledge of differentiation is sufficient to conclude that solutions blow up in finite time for m in the 4/3 power and grow indefinitely as time cubed for m in the 2/3 power. $\endgroup$ Dec 22 '20 at 18:50

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