Dynamical spreading of asteroid families by the Yarkovsky effect

The orbital distributions of prominent asteroid families are thought to be direct by-products of catastrophic disruption events among diameter D great er than or similar to 100 kilometer bodies. Ejection velocities derived fro m studying observed families, however, are surprisingly high compared with results from impact experiments and simulations. One way to resolve this ap parent contradiction is by assuming that D less than or similar to 20 kilom eter family members, since their formation, have undergone semimajor axis d rift by the thermal force called the Yarkovsky effect. interactions between drifting family members and resonances can also produce unique eccentricit y and/or inclination changes. Together, these outcomes help explain (i) why families are sharply bounded by nearby Kirkwood gaps, (ii) why some famili es have asymmetric shapes, and (iii) the curious presence of family members on short-lived orbits.