Asteroid 1997 XF11 received much notoriety in March 1998 when for a time, orbit solutions indicated that it would make a remarkably close approach to the Earth on October 26, 2028. The miss distance calculated for the orbital solution ssing the observations available on March 11, 1998 (an 8-day data arc), was less than one quarter of a lunar distance, and possibly even smaller, making it easily the closest-ever predicted approach of a minor planet to the Earth. The fairly large size of the asteroid, probably over a kilometer across, also made the object notable. Interest in this object spread rapidly when initial reports to the press suggested that a collision in 2028 could not be ruled out. A complete analysis of the 88-day orbital solution, however, shows that the probability of impact in 2028 was very tiny, essentially zero. A linear analysis of the uncertainties mapped to the target plane in 2028 produces an extremely elongated uncertainty ellipse which does not intersect the Earth. The minimum possible miss distance in 2028 is about 28,000 km. Nonlinear analyses of the uncertainties confirm this result. On March 12, pre-discovery images of the asteroid were found, which greatly strengthened the orbital solution and moved the predicted close approach out to a less remarkable 980,000 km. These observations were not needed to rule out the possibility of a collision in 2028. But using only the 88-day-arc solution, was it possible to rule out collisions after 2028? Linear analyses are inadequate to investigate this question, but nonlinear analyses show that there was indeed a non-neglible probability of impact on the order of 10(-5) for the year 2040, using the 88-day-arc solution.
AAS/Division of Dynamical Astronomy Meeting
- Pub Date:
- September 1999