Asteroid 1997XF11 is among the near-Earth objects (NEOs) with the smallest known minimum orbital intersection distance (MOID); that is, its orbit approaches that of the Earth very closely in three-dimensional space. As such it will repeatedly come close to the Earth and may well eventually strike our planet. It is therefore of great interest, both scientifically and as a long-term threat. For NEOs like this that make such close planetary encounters, we cannot reliably calculate detailed orbits for more than a century in the future. XF11 will undoubtedly be closely tracked over the next decades and centuries, as well as being an excellent target for scientific studies such as radar imaging.
Asteroid 1997XF11 never presented a significant hazard to the Earth at its close passage in 2028. Initially any calculated orbit is of course uncertain, but once a few weeks of observations were available it would have been clear, had anyone done the calculations, that XF11 could not strike the Earth in 2028. While there was considerable uncertainty in the miss distance, ranging from about 25,000 km up to more than 700,000 km, all the calculated points of closest approach, projected into the plane of intersection, missed the Earth by a substantial margin. Later, as new observations were made in March and then pre-discovery observations were located extending the observed arc to several years, the uncertainty in the position quickly shrank. However, these observations did not significantly change the probability of impact in 2028, which was (and is) essentially zero.
Part of the initial confusion associated with public and media comments on XF11 resulted from the fact that the Minor Planet Center (MPC) did not calculate the impact probability, so their statement that "the chance of an actual collision [in 2028] is small, but one is not entirely out of the question" was largely subjective. When JPL scientists made the first formal calculation of the impact probability, they realized within an hour of addressing the issue that the probability of impact by XF11 in 2028 was essentially zero, a conclusion since verified by several further calculations using different approaches, and confirmed in IAU Circular 6879.
Because asteroid 1997XF11 has an unusually small MOID, even among the one-hundred-odd known Potentially Hazardous Asteroids (PHAs), it warrants continued attention from a hazard perspective. XF11 will make several close passes by the Earth in the next century; however, none of these appears to represent a hazard, and the risk of impact in 2037, which is the only post-2028 close approach so far investigated in quantitative detail, is effectively zero. Further near-term improvements in the orbit of XF11 (the asteroid is easily radar detectable in 2002) will lead to even more certain results concerning future impact risks.
Any discussion of impact hazard from a known NEO should be placed in the context of the background hazard we all live with due to undiscovered NEOs. In any year there is a probability of roughly one in 100,000 of the Earth being hit, with little or no warning, by an unknown object 1 km or greater in diameter. In any year the chances may be as high as one in 100 of being hit by an undiscovered object similar in magnitude to the Tunguska event of 1908. As a larger and larger fraction of the NEOs are discovered, this risk from unknown NEOs declines; that is in part the purpose of searching for these objects. No known NEO, including XF11, poses a threat of striking the Earth within the next century that is nearly as high as this background risk due to unknown objects.