Rubin finds its first dwarf-planet candidate, 2026 ED138

NSF–DOE Vera C. Rubin Observatory found 2026 ED138 in early survey data, its first dwarf-planet candidate in our Solar System. A linking code searched billions of moving-object detections, and the team independently confirmed the target in more than a decade of archival DECam images. Its absolute magnitude is about 3.19; depending on reflectivity, its estimated diameter is roughly 612 to 1,530 kilometres, possibly large enough for gravity to make it round, but more measurement is required, so it remains a candidate. Its semimajor axis is about 43.09 astronomical units with an inclination near 24.4 degrees, at the edge of Neptune's 12:7 mean-motion resonance, and it is redder than the Haumea collision family. It remains bright enough for ground spectroscopy, light curves, Hubble and Webb follow-up. Modelling suggests around three similar bright objects may remain away from the Galactic plane and perhaps more within it. Size, shape, composition and classification are not final.