On a Scattered-Disk Origin for the 2003 EL61 Collisional FAMILY—AN Example of the Importance of Collisions on the Dynamics of Small Bodies
The recent discovery of the 2003 EL61 collisional family in the Kuiper belt by M. Brown and collaborators is surprising because the formation of such a family is a highly improbable event in today's belt. Assuming Brown et al.'s estimate of the size of the progenitors, we find that the probability that a Kuiper belt object was involved in such a collision since primordial times is less than roughly 0.001. In addition, it is not possible for the collision to have occurred in a massive primordial Kuiper belt because the dynamical coherence of the family would not have survived whatever event produced the currently observed orbital excitation. Here, we suggest that the family is the result of a collision between two scattered-disk objects. We show that the probability that a collision occurred between two such objects with sizes similar to those advocated in Brown et al. and that the center of mass of the resulting family is on an orbit typical of the Kuiper belt can be as large as 47%. Given the large uncertainties involved in this estimate, this result is consistent with the existence of one such family. If true, this result has implications far beyond the origin of a single collisional family, because it shows that collisions played an important role in shaping the dynamical structure of the small body populations that we see today.