A new method for identifying dynamical transitions in rubble-pile asteroid scenarios

Context. Evidence supports the idea that asteroids are rubble piles, that is, gravitational aggregates of loosely consolidated material. This makes their dynamics subject not only to the complex N-body gravitational interactions between its constituents, but also to the laws of granular mechanics, which is one of the main unsolved problems in physics. Aims. We aim to develop a new method to identify dynamical transitions and predict qualitative behavior in the granular N-body problem, in which the dynamics of individual bodies are driven both by mutual gravity, contact and collision interactions. Methods. The method has its foundation in the combination of two elements: a granular N-body simulation code that can resolve the dynamics of granular fragments to particle-scale precision, and a theoretical framework that can decode the nature of particle-scale dynamics and their transitions by means of ad hoc indicators. Results. We present here a proof-of-concept of the method, with application to the spinning rubble-pile asteroid problem. We investigate the density-spin parameter space and demonstrate that the approach can identify the breakup limit and reshape region for spinning rubble-pile aggregates. Conclusions. We provide the performance of several ad hoc indicators and discuss whether they are suitable for identifying and predicting the features of the dynamical problem.