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Paul R. Weissman (Jet Propulsion Laboratory)
The random motion of the Sun and other stars in the galaxy results in about 12 to 14 stellar encounters with the solar system, within one parsec per Myr (Garcia-Sanchez et al., {\it Astron. J.}, in press, 1998). At that rate, the closest stellar approach over the history of the solar system is statistically on the order of 800--900 AU. This is comparable to the largest semimajor axes suggested for orbits in the outer regions of the Kuiper belt, the belt of ecliptic comets beyond Neptune. The effect of such close stellar encounters is investigated by integrating the passage of hypothetical stars of various masses and determining the changes in the orbits of an assemblage of test particles, simulating the Kuiper belt between 30 and 1,000 AU. Because of the stellar luminosity function, the most likely encounter is with a red dwarf star with a typical mass of 0.5 solar masses. This work is supported by the NASA Planetary Geology and Geophysics Program.