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.