Binary survival in the outer solar system

Abstract

As indicated by their special characteristics, the cold classical Kuiper belt objects (KBOs) formed and survived at ≃42–47 au. Notably, they show a large fraction of equal-size binaries whose formation is probably related to the accretion of KBOs themselves. These binaries are uncommon in other –hot, resonant, scattered– populations, which are thought to have been implanted from the massive disk below 30 au to >30 au during Neptune's migration. Here we highlight the possibility that equal-size binaries formed in the disk but were subsequently removed by impacts and/or dynamical effects (e.g., scattering encounters with Neptune). We determine the dependence of these processes on the size and separation of binary components. Our results indicate that tighter binaries, if they formed in the massive disk, have relatively good chances of survival (unless the disk was long-lived). In contrast, the widest binaries in the hot population, such as 2002 VF130, have a very low survival probability (<1%) even if the massive disk was short-lived. They may represent a trace of lucky survivors of a much larger population of the original disk binaries, or they formed at ∼30–40 au and dodged the impact- and encounter-related perturbations that we studied here. We find that all known satellites of the largest KBOs would survive during the dynamical implantation of these bodies in the Kuiper belt. The low orbital eccentricities of Pluto's small moons may have been excited by impacts and/or encounters of the Pluto system to Neptune.