Statistics of encounters in the trans-Neptunian region

Abstract

The inventory of the populations of trans-Neptunian objects (TNO) has grown considerably over the last decade. As for other groups of small bodies in our solar system, TNOs are expected to have experienced a collisional evolution owing to their mutual impacts. The knowledge of the statistics of collisions, including determination of the rate of mutual collisions and the distribution of the impact velocity, is indeed a fundamental prerequisite for developing models of collisional evolution. We revised the evaluation of those statistical parameters for TNOs provided more than ten years ago on the basis of a much more limited sample of objects than currently available. We used the Canada-France Ecliptic Plane Survey (CFEPS) L7 model to extract an unbiased sample of orbits for TNOs, while the statistical parameters of impact are computed using a statistical tool. We investigated the statistics of impacts among TNOs for the whole population and for different dynamical subgroups. Moreover, we investigated the statistics of collisions between subgroups with crossing orbits. The peculiar dynamical behavior of objects in resonant orbits is taken into account. Our present computation of the probabilities of collision are 20% to 50% lower than previous estimates, while mean impact velocities turn out to be about 70% higher. For instance, the rate of collisions among Plutinos, expressed in terms of the so-called mean intrinsic probability of collision, results to be (3.90 ± 0.01) × 10-22 km-2 yr-1 and the mean impact velocity is 2.46 ± 0.01 km s-1. We also find that the distributions of impact velocities seem to be quite different from pure Maxwellian distributions. These results can be useful in developing models of the collisional evolution in the trans-Neptunian region.