Keyhole deflection
Keyholes are small regions in space near Earth through which a passing Near Earth Object (NEO) orbit may be perturbed due to gravitational effects, possibly placing it onto a path that would impact earth. An asteriod, which is called 2011 AG5, is about 140 meters wide. It may come close enough to Earth in 2040 that some researchers are calling for a discussion about how to deflect it. 2011 AG5 may zip through such a keyhole on its close approach to Earth in February 2023 (Space News, March 5, 2012).