Regions of slow apparent motion of close approaching asteroids: The case of 2019 OK

Close approaching (or impacting) asteroids can have slow apparent motion in some directions in the sky as they approach Earth. For some objects that approach Earth from east of opposition, the induced topocentric motion coming from Earth’s rotation cancels the natural eastward motion in the sky, making the object appear to be almost stationary, This makes discovery difficult. Near-Earth asteroid 2019 OK passed within about 70000 km of Earth on 2019 July 25.06. It evaded discovery inbound, and despite its ∼100 m size and approaching from the nighttime side of Earth, was first seen only about 24 h before closest approach. The reasons why various surveys did not detect it are analyzed. It is compared to a range of synthetic impactors and the appearance of impactors coming from various directions in the nighttime sky is discussed. 2019 OK appeared to be almost stationary, and as a result was not detected as a moving object. Some impacting objects approaching from east of opposition will likely have similar slow motion to 2019 OK. Detection of slow moving nearby objects is a new, unrecognized challenge for Near-Earth Object surveys.