How often does an NEA make a close approach?
A. That is an unanswerable question as NEAs don’t come around like clockwork, if they make a close approach at all! Some of the Amors (see the FAQ on classes) might not make an approach closer than 0.3 AU from Earth and others (even Apollos and Atens) might never make a close approach if their orbits aren’t lined up just right. That said, the most repeatable close approacher was (4179) Toutatis which was making close approaches to Earth every 4 years. It’s orbital period is about 3.98 years so it was repeating it’s encounter circumstances pretty closely at that interval, but those encounters slowly change until eventually it will avoid making any close approaches for awhile until the Earth and the object are in phase again sometime in the future. Other close approachers behave in a vastly different manner.
