03.05

Look Out Below: from the Asteroid Belt to Meteorites

B. Gladman, A. Morbidelli (Observatoire de Nice)

Having achieved a considerably more advanced understanding of the dynamical pathways followed by objects emerging from the asteroid belt (see Morbidelli et al, this meeting), we have applied this knowledge to re-examine the flux of Earth-impacting objects coming out of the asteroid belt. This is of course important in terms of the flux of large impactors onto the Earth, but in that case the cometary component must be factored in; the pure dynamics we have simply indicates the dynamical pathways and time scales of NEAs are dominated by a relatively short residence in Earth-crossing space (median residence time about 10 Myr). In the case of the meteorites (the vast majority of which are known to come from the main belt) we are able to use cosmic-ray exposure age data, and orbital data from camera networks, to constrain some elements of the meteorite delivery process. In particular, we find that the neither the 3:1 mean-motion resonance with Jupiter nor the secular resonance can be dominating the injection of objects into Earth-crossing space, but that contributions from each are required. We also conclude that meteorites are not being injected into resonance in steady-state in either case, because then the spectrum of observed cosmic-ray exposure ages of the ordinary chondrites cannot be reproduced. This would imply the collisional events that liberated the meteorites as exposable fragments were large ancient events which do not have contemporary analogues in the last few Myr, or that the liberation events were simply not responsible for injecting the fragments into resonance.