Granular cohesion and fast rotators in the NEA population

Abstract

The relative strength of small rubble pile asteroids is scale dependent, with strength increasing as size decreases due to the ubiquitous but weak van der Waals cohesive forces that exist between materials. This counters classical theory that rubble pile asteroids should behave as scale-independent cohesionless collections of rocks. We propose a simple model for asteroid strength that is based on these weak forces, validate it through granular mechanics simulations and comparisons with properties of lunar regolith. Then show its implications and ability to explain and predict observed properties of small asteroids in the NEA and Main Belt populations. A conclusion is that the population of rapidly rotating asteroids consists of both distributions of smaller grains (i.e., rubble piles) and of monolithic boulders whose surfaces may still retain a size distribution of finer grains, potentially of size up to centimeters. © 2013 AIP Publishing LLC.