Numerical solution for Equation (7) for various eccentricities. Top: critical size of planetesimal as a function semimajor axis. Each curve corresponds to different orbital eccentricity e, and indicates the critical size ﹩{R}_{\star }(a)﹩ where both forces are equal. Aerodynamic drag dominates for smaller radii, while GDF dominates for larger radii. Note the log–log scale. Bottom: estimated Mach number as a function of semimajor axis for the same orbits. Note the logarithmic scale.