We investigate the pre-compaction structural properties of dust rims (porosity, grain alignment, monomer size distribution) accreted on a chondrule surface as the chondrule sweeps up dust in the nebular gas. The collision process is simulated using an N-body code, taking into account the morphology of dust rims, trajectory and orientation of the incoming particle, and the electrostatic interactions. Energetic collisions result in the restructuring/fragmentation of the dust rim. To speed up the computation, machine learning techniques are used to develop a regression model for the impact outcome (either restructuring or fragmentation) and impact range (the distance from the contact point of the dust particle to the farthest monomer participating in the restructuring/fragmentation) as a function of rim porosity, relative velocity, incidence angle, as well as the size and orientation of the incoming particle. Only the constituent monomers within the impact range are set to be mobile in the N-body code, and the remaining monomers in the rim are fixed. Machine learning techniques are also used to determine the thickness and porosity of the resulting rim after collision, based on the properties of the original rim and the characteristics of the incoming dust particle. This regression model is used to build dust rims under different turbulence conditions; these rims are then compared with the rims built by the detailed N-body simulation and will be compared to experimental simulations produced at Baylor. Preliminary results show that rims comprised of ellipsoidal monomers are more porous and show a greater difference in rim porosity between the neutral and charged cases than rims comprised of spherical monomers. The range of restructuring in dust rims increases with the rim porosity and the kinetic energy of the incoming particles. The incidence angle of the incoming dust also affects the range, with a maximum restructuring range occurring for incidence angle of ~27°. Although rimmed chondrules in strong turbulence collide with dust frequently and their rims grow quickly, the regression model shows that dust rims experience significant restructuring and fragmentation, which pose a barrier for further growth. These results for the initial rim structure can be used to infer their formation environments and establish the foundation for the onset of the next stage where the collision between rimmed-chondrule agglomerates and their incorporation into the parent bodies take place.
Acknowledgments: Support from the National Science Foundation (PHY-2008493) and NASA (EW20_2-0053) is gratefully acknowledged.