Production of Tunguska-sized bodies by Earth's tidal forces

Tidal disruption of rubble-pile bodies (stony or icy aggregates held together by self-gravity) during close Earth encounters may produce significant numbers of Tunguska-sized (50 m) fragments. Using an N-body simulation to model encounters between strengthless, elongated, rotating, particulate bodies and the Earth, two disruption categories were found which produce small bodies: (a) "Shoemaker-Levy-9 type" catastrophic disruptions, where the progenitor is pulled into a line of similarly sized bodies, and (b) rotational disruptions, where the progenitor is distorted and spun-up by tidal torque such that particles are ejected along the equator. These events occur frequently at low encounter velocities (i.e. low e and i);it is predicted that Earth's tidal forces should be effective at disrupting larger bodies into Tunguska-sized fragments in this region of phase space. By creating a map of tidal disruption outcomes for the progenitor's encounter parameters and integrating over all possible values of those parameters, it is found that the tidal production rate of Tunguska-sized bodies (upper limit) was; comparable with the main-belt injection rate of Tunguska-sized bodies into resonant orbits. It is concluded that tidal disruption plays an important role in maintaining the steady-state fraction of small Earth-crossing asteroids. (C) 1998 Elsevier Science Ltd. All rights reserved.