Tidal Evolution of the Eccentric Moon around Dwarf Planet (225088) Gonggong

Recent astronomical observations revealed that (225088) Gonggong, a 1000-km-sized trans-Neptunian dwarf planet, hosts an eccentric satellite, Xiangliu, with an eccentricity of approximately 0.3. As the majority of known satellite systems around trans-Neptunian dwarf planets have circular orbits, the observed eccentricity of Gonggong--Xiangliu system may reflect the singular properties of the system. In this study, we assumed that Gonggong--Xiangliu system formed via a giant impact and investigated the following secular tidal evolution of Gonggong--Xiangliu system under the simplifying assumption of homogeneous bodies and of zero orbital inclination. We conducted coupled thermal--orbital evolution simulations using the Andrade viscoelastic model and included higher-order eccentricity functions. The distribution of the final eccentricity from a large number of simulations with different initial conditions revealed that the radius of Xiangliu is not larger than 100 km. We also derived the analytical solution of the semilatus rectum evolution, a function of the radius of Xiangliu. From the point of view of the final semilatus rectum, the radius of Xiangliu was estimated to be close to 100 km. Together with the results of the Hubble Space Telescope observations, our findings suggest Gonggong and Xiangliu have similar albedos.