"Production of Tunguska-Sized Bodies by Earth's Tidal Forces"

W. F. Bottke, Jr., D. C. Richardson, S. G. Love

(1997) Planetary and Space Science, in press

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, we found two disruption categories 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); we predict that Earth's tidal forces should be effective at disrupting large bodies and producing Tunguska-sized bodies 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, we found the tidal production rate of Tunguska-sized bodies (upper limit) was comparable to the main-belt injection rate of Tunguska-sized bodies into resonant orbits. We conclude that tidal disruption, previously unaccounted for in asteroid evolution models, plays an important role in maintaining the steady-state fraction of small Earth-crossing asteroids.

For more information, contact Bill Bottke:bottke@astrosun.tn.cornell.edu