A temporary or localized gravitational disturbance in the otherwise uniform motion of a body under a stable gravitational force. For example, the motion of a comet, which is largely determined by the gravitational force of the Sun, suffers perturbations if the comet passes close enough to a planet for its pull to be significant in comparison with that of the Sun. An encounter with the most massive planet, Jupiter, can alter very significantly the orbit of a comet, to the extent that a comet moving in a parabolic orbit may be captured into a short-period elliptical orbit.