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 Incoming links: Binary planetesimal

Gas-driven contraction of a planetesimal binary 2026-10-05

For a weakly perturbed circular binary planetesimal, the constant differential headwind does zero work averaged over the unperturbed orbit. Orbit-averaged drag work gives

⟨ \overset{a}{˙} ⟩ = - 2 κa, τ = \frac{1}{2 κ} = \frac{m _{1} + m _{2}}{2 ( m _{1} / t _{2} + m _{2} / t _{1} )} .

With constant aerodynamic stopping times,

a (t) = a_{0} e^{- t / τ}

. This averaging assumes drag is slow compared with the orbital period and does not appreciably distort the circular orbit within one period.

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