TIDAL DISRUPTION OF VISCOUS BODIES

We examine the tidal disruption of homogeneous, incompressible bodies ("planetesimals") of viscous fluid, passing by a planet on a parabolic orbit. If the planetesimal radius is small compared to the distance of closest approach, the surface of the planetesimal is always ellipsoidal, and we can therefore reduce the equations of fluid mechanics and Poisson's equation to a set of coupled ordinary differential equations that can be solved with high accuracy. We find that inviscid planetesimals are disrupted if their pericenter distance Q < 1.05(Mp/ρ{variant}0) 1 3, where Mp is the mass of the planet and ρ{variant}0 is the density of the planetesimal. Disrupted planetesimals evolve into needle-like ellipsoids but their density does not decrease. The viscous fluid treatment is approximately valid for solid planetesimals if tidal stresses exceed the strength while the planetesimal is still held together by self-gravity; this condition requires radii exceeding 100-200 km for ice or rock planetesimals. © 1992.