Kozai cycles, tidal friction, and the dynamical evolution of binary minor planets

Abstract

In recent years, many binary minor planets (BMPs) have been discovered in the solar system. Many models have been suggested for their formation, but these encounter difficulties explaining their observed characteristics. Here, we show that secular perturbations by the Sun (Kozai mechanism) fundamentally change the evolution and the initial distribution of BMPs predicted by such models and lead to unique observational signatures. The Kozai mechanism can lead to a large periodic oscillations in the eccentricity and inclination of highly inclined BMP orbits, where we predict such effects to be observable with current accuracy within a few years (e.g., for the binary asteroid Huenna). In addition, the combined effects of the Kozai mechanism and tidal friction (KCTF) drives BMPs into short-period circular orbits. We predict a specific inclination-dependent distribution of the separation and eccentricity of BMPs, due to these effects, including a zone of avoidance at the highest inclinations. Specifically, the Kozai evolution could explain the recently observed peculiar orbit of the Kuiper Belt binary 2001 QW322. Additionally, the KCTF process could lead to BMPs coalescence and serve as an important route for the formation of irregular shaped single minor planets with large axial tilts. © 2009. The American Astronomical Society.