Refined Orbit and Tidal Evolution of the Gonggong–Xiangliu System

Among the largest trans-Neptunian objects (TNOs), the majority of known satellite systems are now understood to possess satellites on nearly circular orbits. This emerging picture contrasts markedly with earlier interpretations, in which several systems appeared to retain significant orbital eccentricities. However, recent high-precision observations, together with careful re-analysis of archival data, have systematically shifted orbital solutions toward very low eccentricities, strengthening the case for efficient tidal dissipation and long-term tidal evolution in these distant binaries. Notably, this revision now includes the Quaoar–Weywot system, whose satellite orbit was originally reported to have an eccentricity of ~0.14, but which is now consistent with a substantially more circular configuration.

 

At present, the Gonggong–Xiangliu system remains the sole major outlier among the large TNO binaries, with Xiangliu’s orbit retaining a substantial eccentricity of e~0.29). Understanding whether this eccentricity reflects incomplete tidal evolution, recent dynamical excitation, or fundamentally different interior and tidal properties is therefore of considerable importance for constraining the formation and long-term evolution of outer Solar System satellite systems.

 

Here we present new measurements of Xiangliu obtained with the Hubble Space Telescope (HST), significantly extending the astrometric baseline available for orbital determination. By combining these new observations with previously published data, we derive an updated orbital solution and revised orbital elements for the Gonggong–Xiangliu system. We further carry out detailed tidal evolution calculations to investigate the dynamical history of the system and assess whether the currently observed orbit can be reconciled with plausible tidal evolution scenarios over the age of the Solar System.