Analytic formulae for estimating planetary accretion rates have long
been available for
conditions where random motion of planetesimals controls velocities relative
to a growing
planet. Recent Monte-Carlo studies have explored a wider range of
conditions, but gave impact
rates only for the specific conditions under which those
numerical experiments were
performed. Now analytical formulae, which are valid even when
keplerian shear controls the approach velocity, and which accurately
reproduce the Monte-Carlo results, give accretion
rates over a wide range of conditions relevant to the problem of
planet formation.