First multi-opposition recoveries of large-orbit LSST TNOs

Abstract

We report 2026 CFHT second-opposition recovery observations of three large-orbit Trans-Neptunian Objects (TNOs) discovered by the Vera C. Rubin Telescope's Legacy Survey of Space and Time (LSST) during preliminary observations in 2025. Due to their potential scientific interest, we selected three TNOs whose nominal semimajor axis could be larger than 100~au according to their short-arc ($\leq0.2$-yr) LSST observations. These three targets (2025 LS2, 2025 ME278, 2025 MX348) had discovery opposition orbits of varying observation quality (in terms of the duration and distribution of observations). In two cases, the 2026 CFHT recoveries showed that the semimajor axis dropped by a factor of $\simeq$3-10, and that the object appears to be a (common) plutino in the 3:2 mean-motion resonance with Neptune. We discuss how and why the estimated orbital elements evolved, and re-caution the community to be skeptical of unusual TNO orbits until they have multi-opposition recoveries.