‘In spite of the strength of gravitational forces between celestial bodies, gravitational capture is not a simple concept. The principles of conservation of linear momentum, and of conservation of angular momentum, always impose severe constraints, while conservation of energy and the vital distinction between dissipative and non-dissipative systems allows one to rule out capture in a wide variety of cases. In complex systems, especially those without dissipation, long dwell time is a more significant concept than permanent capture’.