Planet-disk Torques

Planet-disk torques are the mediators of interaction between still-forming planets carving their way in the disk and the disk material. The complete physics of these torques is not yet fully understood and non-trivial. Often 2D and two-body approximations under several further constraints are used to

A body of mass passes by a second body with an impact parameter (i.e. a distance of closest approach) and a relative velocity . In the regime of a weak encounter the deflection angle is small and the impulse can be calculated assuming that the trajectory is unperturbed.