ORBITAL AND TEMPORAL DISTRIBUTIONS OF METEORITES ORIGINATING IN THE ASTEROID BELT

The recent discovery of the importance of Sun-grazing phenomena dramat ically changed our understanding of the dynamics of objects emerging f rom the asteroid belt via resonant phenomena. The typical lifetimes of such objects are now expected to be <10 Ma, thus demanding a reassess ment of our general picture of the meteorite delivery process. By anal ysing direct numerical integrations of similar to 2000 test particles beginning in the v(6), 3:1, and 5:2 resonances in the main belt, we ha ve reexamined the orbital and temporal distribution of meteoroids that journey to Earth. Comparing the results with fireball data, we find t hat the orbital distribution of Earth-impacting chondrites is consiste nt with a steady-state injection of meteoroids Into the 3:1 and vs res onances. Because this is the most complete and unbiased data set conce rning Earth-impacting meteoroids, the agreement leads us to believe th at our model is accurate. The simulations predict a P.M. fall ratio fo r chondrites similar to 14% lower than the observed value of similar t o 68%, which argues for a moderate bias being present in this statisti c. Most interestingly, the typical meteorite transfer times predicted by our models are several factors lower than the typical chondrite exp osure ages, which implies that these meteorites acquired most of their exposure in the main belt before entering the resonances. We discuss some processes that would allow such preexposure. The case of achondri tes and iron meteorites is also briefly discussed.