Dynamical implications of the recently detected feature around Quaoar and constraints on the presence of additional satellites

Abstract

A recently reported opaque feature in the Quaoar system, detected during the 25 June 2025 stellar occultation, has been interpreted as either a 15 km-radius satellite or a dense, sharp-edged arc orbiting at about 5600-5900 km. Here, we investigate both scenarios through numerical integrations that include Quaoar, its triaxial shape, and Weywot. If the feature is a satellite, stability maps show that it acquires a forced eccentricity of about 0.002 and has only a minor dynamical effect on the Q1R and Q2R rings. Its main effect is to clear a narrow region around its orbit, associated with the overlap of mean-motion resonances, preventing the long-term survival of kilometre-scale moons within approximately one Quaoar radius of the satellite. If instead the feature is an arc, we test confinement around the triangular equilibrium point of an unseen coorbital satellite. While azimuthal confinement is readily obtained for satellites with satellite-to-primary mass ratios up to 0.001, Weywot's secular perturbation induces large radial excursions in the arc particles, preventing reproduction of the observed radial extent. The required radial confinement is achieved only for confiners comparable to or more massive than Weywot, which would likely be detectable by direct imaging. We therefore disfavour triangular-point confinement as an explanation for a long-lived dense arc and argue that the feature is more dynamically consistent with a satellite. We identify broad stable zones where additional undetected moons could reside, including near the rings as possible shepherd moons. Furthermore, Quaoar's ellipticity alone is sufficient to induce non-resonant orbital excitation capable of preventing ring coagulation, an effect that may be enhanced by small moons near the rings.