Evidence of a New Arc or a Belt of Small Satellites around (50000) Quaoar

Abstract We report the results of an observation of a stellar occultation by the (50000) Quaoar system, observed on 2025 June 25. Observations were made from 10 sites in the USA in an attempt to detect Quaoar’s Q1R ring. Two telescopes at the Monterey Institute for Research in Astronomy station detected an unexpected event in Quaoar’s vicinity. Analysis of the light curves revealed simultaneous, sharp flux drops at both telescopes, consistent with the occultation of the star by an opaque object. Square-well modeling incorporating stellar diameter, diffraction, and instrumental effects yielded immersion and emersion times with high precision. From the chord geometry, we estimate a possible satellite with a minimum radius of 14.7 ± 0.6 km orbiting at a distance of 5676 ± 108 km from Quaoar. Alternatively, the detection can be interpreted as a dense arc orbiting Quaoar. If projected in Q1R’s orbital plane, it has a radial width of W r = 23 ± 2 km, while nearby negative chords limit its longitude interval to ≲28°. While the arc hypothesis is statistically favorable, it needs a complex dynamic system to be maintained. Therefore, we argue that we may have detected one component of a belt of tens of small satellites orbiting Quaoar. This new finding also supports the formation scenario in which the satellites and rings of the largest Trans-Neptunian Objects (TNOs) were formed from a giant collision in the early years of the solar system.