DPS Meeting, Madison, October 1998
Session 10. Asteroid Dynamics I
Contributed Oral Parallel Session, Monday, October 12, 1998, 2:15-3:35pm, Madison Ballroom D

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[10.08] Upper Bounds for the Earth-XF11 Collision Probability

K. Muinonen (Univ. Helsinki)

For a given time interval, upper bounds for the collision probability of two planetary bodies can be established using maximum likelihood collision orbits, i.e., orbital elements that minimize the observational residuals with the condition of collision some time within the given interval. The maximum likelihood collision orbit lies on a certain confidence boundary---assigning all the probability outside the boundary to collision provides a robust upper bound for the collision probability. Using the collision orbits and other newly-developed statistical methods, the asteroid 1997 XF11 close approach to the Earth (time interval 2028 October 24.0-31.0 TDT) is analyzed in detail starting from 1997 December 6. Three days after discovery, in December 9, the orbit is still highly indeterminate, the collision probability being smaller than 0.007. The December 19 and 21 observations bring the upper bound below ~10-42. In 1998 February 4, formally at ~10-966, the upper bound is negligibly small and, in March 4, the number further diminishes to ~10-1117. Archive observations from 1990 put the final upper bound at ~10-9772. In conclusion, the upper bound for the collision probability decreases steadily when more and more observations are incorporated into orbit determination. By 1998 December 21, the collision probability has decreased to a negligible level---assuming that all relevant factors affecting the orbit determination have been correctly accounted for.

The author(s) of this abstract have provided an email address for comments about the abstract: Karri.Muinonen@Helsinki.Fi

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