OSSOS. XXI. Collision Probabilities in the Edgeworth–Kuiper Belt

Abstract

Here, we present results on the intrinsic collision probabilities, P I , and range of collision speeds, V I , as a function of the heliocentric distance, r, in the trans-Neptunian region. The collision speed is one of the parameters, that serves as a proxy to a collisional outcome e.g., complete disruption and scattering of fragments, or formation of crater, where both processes are directly related to the impact energy. We utilize an improved and de-biased model of the trans-Neptunian object (TNO) region from the "Outer Solar System Origins Survey" (OSSOS). It provides a well-defined orbital distribution model of TNOs, based on multiple opposition observations of more than 1000 bodies. In this work we compute collisional probabilities for the OSSOS models of the main classical, resonant, detached+outer and scattering TNO populations. The intrinsic collision probabilities and collision speeds are computed using theÖpik's approach, as revised and modified by Wetherill for non-circular and inclined orbits. The calculations are carried out for each of the dynamical TNO groups, allowing for inter-population collisions as well as collisions within each TNO population, resulting in 28 combinations in total. Our results indicate that collisions in the trans-Neptunian region are possible over a wide range in (r, V I ) phase space. Although collisions are calculated to happen within r ∼ 20−200 AU and V I ∼ 0.1 km/s to as high as V I ∼ 9 km/s, most of the collisions are likely to happen at low relative velocities V I < 1 km/s and are dominated by the main classical belt.

OSSOS Finds an Exponential Cutoff in the Size Distribution of the Cold Classical Kuiper Belt

“…This appears unlikely as any process that removed significant mass would very likely have disrupted the binary KBO population we see today. The cratering record seen on Arrokoth is fully consistent with the low total populations reported here (see Greenstreet et al 2019;Singer et al 2019b;Abedin et al 2021) indicating that any period of high number density would have been very rapidly removed which would have implications for the orbit distribution in the cold belt (Gladman & Volk 2021). Thus, it appears unlikely that the surface density at ∼ 43 au was significantly higher than today.…”

“…Recently, observations of the cold classical KBO 486958 Arrokoth by the New Horizons mission have provided direct evidence of the low collision rate in this region (McKinnon et al 2020). Arrokoth impactors are dominantly cold classical KBOs and the observed low crater density, well below the crater saturation threshold, is consistent with the ancient number density of material being within a factor of a few of that currently observed in this region (Greenstreet et al 2019;Abedin et al 2021). In addition, the photometric properties of the cold belt members appear distinct from the rest of the KBOs (e.g., Tegler et al 2003;Pike et al 2017;Schwamb et al 2019).…”

“…Cold main classical Kuiper belt objects (KBOs) appear to be unevolved products of the initial planetesimal formation process in this region of the Solar System. The current number density of cold objects is such that collisions between these planetesimals are infrequent (e.g., Greenstreet et al 2019;Abedin et al 2021). The cold KBOs are known to contain a large number of loosely bound binary pairs (Noll et al 2008); such pairs are very likely to be destroyed if collisions among KBOs are common (Petit & Mousis 2004) implying that the number density at the epoch of formation was similar to that we see today.…”

Collisions of Small Kuiper Belt Objects With (486958) Arrokoth: Implications for Its Spin Evolution and Bulk Density

“…In terms of their impact velocity characteristics, these four subgroups can be divided into two categories based on velocity: the majority of impacts (76%) are due to the cold classicals, whose low orbital eccentricities and inclinations guarantee relatively slow collisions, while hot classicals represent the high velocity subpopulations (i.e., hot, outer, and 3:2 resonant subpopulations) reasonably well (cf. Abedin et al, 2021). We thus assume the remaining 24% are represented by the hot classical KBO velocity distribution.…”

Peculiar orbits and asymmetries in extreme trans-Neptunian space

“…Close encounters and collisions in the trans-Neptunian or Kuiper belt are relatively well understood (see e.g. Dell'Oro et al 2013;Abedin et al 2021). Collisional families are known to populate regular TNO space that is also affected by orbital resonances with small integer ratios and secular resonances like the so-called von Zeipel- Lidov-Kozai oscillation (von Zeipel 1910;Lidov 1962;Kozai 1962;Ito & Ohtsuka 2019).…”