Cometary nuclei internal structure from early aggregation simulations

A new model for the aggregation of cometesimals in the primordial solar nebula is proposed. The simulation of the aggregation takes into account disruptive and sticking effects of impacts on the aggregates properties together with the temporal evolution of cohesive strength during accretion due to sintering processes. Different regimes of aggregation are obtained depending on the value of the homogeneity exponent, μ, that indicates the fraction of kinetic energy available for cohesive energy dissipation during an impact. Porous fractal aggregates with different cohesive strength blocks are formed for 0 < μ < 0.4, while they are compact with a layered structure of different strengths for 0.4 < μ < 0.6 and weak ‘rubble piles’ for 0.6 < μ < 1. Cohesive strength estimations of the final cometary nuclei obtained give values generally lower than 10 kPa. The layered aggregates present the highest global cohesive strength, increasing their probability to survive collisions or moderate tidal stress. These results compare well with the structural and cohesive properties of comets deduced from observations and laboratory simulations.