The effect of the giant planets on the dynamical evolution of the mutual orbits of trans-Neptunian binaries

The action of tidal friction, coupled with the Kozai cycles, drastically changed the original orbits of trans-Neptunian binaries (TNBs). The dynamics of the Kozai mechanism is driven by the solar torque on the mutual orbit, so that the orientation of the latter relative to the heliocentric orbital plane plays a fundamental role in this process, both in the magnitude and in the characteristic of the cycles. In this way, any effect that makes this relative orientation vary may be relevant in the dynamics of the process. In this paper, we will focus on the effect that the perturbations of the giant planets on the heliocentric orbit of TNBs have on the dynamics of the Kozai cycles and tidal friction. For this task, we have performed numerical simulations of the evolution of a synthetic population of TNBs subject to Kozai cycles and tidal friction adding planetary perturbation on their heliocentric orbits. We found that in a non-negligible fraction of cases (similar to 25 per cent), this additional perturbation produces substantial changes in the orbital evolution. The slow precession of the heliocentric orbit and the variation of its inclination can make the dynamical evolution of the mutual orbits very irregular, completely changing the morphology of the Kozai cycles. When these variations are coupled to tidal friction, the lifetime of the TNBs can change substantially.

Automated summary

The action of tidal friction and Kozai cycles significantly alters the original orbits of trans-Neptunian binaries (TNBs). The dynamics of the Kozai mechanism depends on the orientation of the mutual orbit relative to the heliocentric orbital plane, which affects the magnitude and characteristics of the cycles. This study focuses on the effect of giant planet perturbations on the heliocentric orbits of TNBs in relation to the dynamics of Kozai cycles and tidal friction. Numerical simulations show that in about 25% of cases, these perturbations cause substantial changes in the orbital evolution, leading to irregular dynamics and a morphological shift in the Kozai cycles. When coupled with tidal friction, these variations can significantly impact the lifetime of TNBs.