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. Subject headings:

Very Slow Rotators from Tidally Synchronized Binaries

“…The cold population (also called the 'cold classical' population), with semimajor axes a = 42-47 au and i < 5 • , is thought to have formed in situ at > 40 au (e.g., Parker andKavelaars 2010, Batygin et al 2011). At least 30% (Noll et al 2008), and perhaps as much as 100% (Fraser et al 2017), of cold classicals formed as equal-size binaries (e.g., Goldreich et al 2002, Nesvorný et al 2010 Some wide equal-size binaries survived in the hot population suggesting that the initial binary fraction at ∼20-30 au was high (Nesvorný & Vokrouhlický 2019). The chances of survival are better for tight binaries that are more strongly bound together.…”

“…If the disk was long-lived (e.g., t disk ∼ 100 Myr), more binaries would become unbound by impacts. Binaries were also dissociated by dynamical perturbations during planetary encounters that occurred as bodies evolved from ∼20-30 au to 5.2 au (Nesvorný et al 2018, Nesvorný & Vokrouhlický 2019. 1 We ignore the effect of tides on binary semimajor axis.…”

“…This effect is small because there is not enough angular momentum contained, relative to the orbital momentum, in the initial spin (even if it is critical). et al (2018) and Nesvorný & Vokrouhlický (2019). Here we first consider the case with t disk = 10 Myr.…”

“…We tested this effect using the Boulder collisional code (Morbidelli et al 2009). We assumed that the slow rotators have P s = 100-500 h initially and adopted the outer disk parameters from Nesvorný & Vokrouhlický (2019). A large uncertainty in modeling the effect of impacts consists in coupling of the impactor's linear momentum to the angular momentum change of the target (e.g., Dobrovolskis & Burns 1984, Farinella et al 1992.…”

Colors of Trans-Neptunian Contact Binaries

“…These differences in dynamical history also likely account for the difference in the wide binary fraction seen for the Cold Classicals compared to the resonances and scattered disk objects (see Thirouin & Sheppard (2019)). That is, the more significant dynamical interactions likely experienced by the resonance and scattered objects caused most wide binaries to be unstable, with the wide secondary either being lost from the system or possibly collapsing down to form a closer or contact binary (see also Thirouin & Sheppard (2019) and Nesvorný, & Vokrouhlický (2019)).…”