The Strength and Shapes of Contact Binary Objects

Abstract While contact binary objects are common in the solar system, their formation mechanism is unclear. In this work we examine several contact binaries and calculate the necessary strength parameters that allow the two lobes to merge without the smaller of the two being gravitationally destroyed by the larger. We find a small but nonzero amount of cohesion or a large friction angle is required for the smaller lobe to survive the merging process, consistent with observations. This means it is possible for two previously separated rubble piles to experience a collapse of their mutual orbit and form a contact binary. The necessary strength required to survive this merger depends on the relative size, shape, and density of the body, with prolate shapes requiring more cohesion than oblate shapes.