Meteorite delivery via Yarkovsky orbital drift

We provide a unified discussion of the Yarkovsky effect in both the original, "diurnal" variant and also for the "seasonal" variant which has been recently shown by Rubincam (1995) to be important for meteorite-sized, regolith-free asteroid fragments. After computing the rate of the corresponding semimajor axis drift as a function of size and spin rate, and comparing the relevant time scales with those for collisional disruption and spin reorientation, we discuss some issues in meteorite science which are put in a new light by the relevance of the Yarkovsky effect. In particular, this mechanism provides a good explanation for the fact that meteorite cosmic ray exposure ages (in particular for irons) are much longer than the dynamical lifetimes of objects delivered to the Earth-crossing region through resonances. Thanks to the Yarkovsky effect, small asteroid fragments in the belt undergo a slow drift in semimajor axis (with a random-walk component related to their rotational state) and therefore have enough mobility to reach the resonances after comparatively long times spent in nonresonant main-belt orbits. Metal-rich fragments have slower Yarkovsky drift rates than stones, but their much longer collisional lifetimes may explain why iron meteorites appear to sample a larger number of asteroid parent bodies compared to ordinary chondrites. (C) 1998 Academic Press.