Early intrafamily collisions in newly formed asteroid families

Abstract

The dynamical and physical properties of asteroid family members are widely used to reconstruct the collisional evolution of the main belt and of individual objects. Families offer insights into the properties of the parent bodies and the fragmentation processes responsible for their formation. We investigate a poorly constrained phase of early collisional evolution among members of the same family. Our goal is to determine an intrinsic collision probability associated with intrafamily collisions and to assess their relevance compared to collisions with the background asteroid population. We performed numerical simulations of the early dynamical evolution of families, up to the randomization age of the true anomalies, recording mutual impacts between family members and converting them into an intrinsic collision probability. This probability was used to study intrafamily collisions for generic size distributions. We identified an intense phase of low-velocity intrafamily collisions occurring in the first few years after family formation. The collision probability can reach values up to $10^{-10}$ yr$^{-1}$km$^{-2}$ shortly after breakup and then decreases exponentially, following the same temporal trend predicted by previous statistical models. Variations among the orbital elements of the parent body and the properties of the ejection velocity field can change the collision probability by up to one or two orders of magnitude, without affecting its temporal evolution. Depending on the assumed size distribution, the number of impacts on the largest remnant ranges from fewer than ten to several million. Intrafamily collisions represent a physical mechanism whose importance must be assessed on a case-by-case basis. Although they are not expected to produce further fragmentation, they might contribute to early surface and structural evolution in some cases, while being negligible in others.