Near-Earth and Mars-crosser asteroid 1997 XF11, was discovered in December 1997 by Jim Scotti in the course of the Spacewatch program at the University of Arizona. The object is estimated at 1.3—2.8 kilometres.
Shortly after 1997 XF11 discovery, an exceptionally close its approach to Earth in October 2028 was predicted. Prediscovery images of 1997 XF11 were next quickly identified on films taken at Palomar in 1990 during the Planet-Crossing Asteroid Survey by Eleanor Helin, Ken Lawrence and Brian Roman using the 0.46-m Schmidt telescope. Including this positional observations from 1990 it was found that on October 26, 2028 the asteroid will approach the Earth to within 0.006 AU (900 thousand kilometers) — this was the closest approaches predicted for any PHA up to that time.
The details about this prediction are given in the paper Motion of the Dangerous Asteroid 1997 XF11.
In this paper Sitarski found that only in 2042 the minimum distance between orbits of Earth and 1997 XF11 could be smaller than the Earth radius. However, the asteroid will pass through its descending node in July 2042 while a collision with the Earth could happen during the October encounter. After 2042 the minimum distance between orbits of both planets will be permanently growing up, and during the next several thousand years collision with the Earth will be impossible.
