Delivery of asteroids and meteorites to the inner solar system

Critical observational constraints on the delivery of asteroids include orbital distributions, exposure ages and mineralogy. Orbital maturity in the inner solar system is indicated by the AM/PM distribution of meteorite falls and fireballs: Ordinary chondrites have short exposure ages, but their AM/PM fall statistics indicate significant orbital maturity. Hence, many may be collisional offspring of slightly larger parents that emigrated from the main belt. The required size distribution, extrapolated up to multi-km-size bodies, would also yield numbers of planet-crossing asteroids comparable to those astronomically observed. How multi-km Apollo-Amor-Atens are launched from the main belt is a major outstanding problem, as is identification of a parent population for the ordinary chondrites now that S-type asteroids once again are considered to be different from this most common kind of meteorite on the basis of reflectance spectroscopy. -from Authors