Example of a coplanar configuration where a passing star (in red) stabilizes a wide unstable planet orbit. Before the fly-by, the planet orbit still has a very low periastron, and after it gets much wider, thanks to the interaction with the passing star. We recall that according to Kepler’s laws, the planet spends most of its time near apoastron, so that any fly-by is likely to occur when the planet is at or near this point.