Secondary gravitational keyholes are searched for by importance sampling: Virtual asteroid trajectories (or rather their ‘initial’ values at the time of the first encounter) are sampled according to their likelihood given the observations of the asteroid.
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There are even more but smaller secondary keyholes, with trajectories including a less close intermediate encounter (bank shots).
Through the Keyhole | Gravitational collapse | Keyhole Kate | Keyhole | Gravitational lens | Gravitational constant | Gravitational acceleration | European Gravitational Observatory |